@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990-1995, 1998-1999, 2001-2018 Free Software @c Foundation, Inc. @c See the file elisp.texi for copying conditions. @node Processes @chapter Processes @cindex child process @cindex parent process @cindex subprocess @cindex process In the terminology of operating systems, a @dfn{process} is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called @dfn{subprocesses} or @dfn{child processes} of the Emacs process, which is their @dfn{parent process}. A subprocess of Emacs may be @dfn{synchronous} or @dfn{asynchronous}, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a ``process''. Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it. In addition to processes that run programs, Lisp programs can open connections of several types to devices or processes running on the same machine or on other machines. The supported connection types are: TCP and UDP network connections, serial port connections, and pipe connections. Each such connection is also represented by a process object. @defun processp object This function returns @code{t} if @var{object} represents an Emacs process object, @code{nil} otherwise. The process object can represent a subprocess running a program or a connection of any supported type. @end defun In addition to subprocesses of the current Emacs session, you can also access other processes running on your machine. @xref{System Processes}. @menu * Subprocess Creation:: Functions that start subprocesses. * Shell Arguments:: Quoting an argument to pass it to a shell. * Synchronous Processes:: Details of using synchronous subprocesses. * Asynchronous Processes:: Starting up an asynchronous subprocess. * Deleting Processes:: Eliminating an asynchronous subprocess. * Process Information:: Accessing run-status and other attributes. * Input to Processes:: Sending input to an asynchronous subprocess. * Signals to Processes:: Stopping, continuing or interrupting an asynchronous subprocess. * Output from Processes:: Collecting output from an asynchronous subprocess. * Sentinels:: Sentinels run when process run-status changes. * Query Before Exit:: Whether to query if exiting will kill a process. * System Processes:: Accessing other processes running on your system. * Transaction Queues:: Transaction-based communication with subprocesses. * Network:: Opening network connections. * Network Servers:: Network servers let Emacs accept net connections. * Datagrams:: UDP network connections. * Low-Level Network:: Lower-level but more general function to create connections and servers. * Misc Network:: Additional relevant functions for net connections. * Serial Ports:: Communicating with serial ports. * Byte Packing:: Using bindat to pack and unpack binary data. @end menu @node Subprocess Creation @section Functions that Create Subprocesses @cindex create subprocess @cindex process creation There are three primitives that create a new subprocess in which to run a program. One of them, @code{make-process}, creates an asynchronous process and returns a process object (@pxref{Asynchronous Processes}). The other two, @code{call-process} and @code{call-process-region}, create a synchronous process and do not return a process object (@pxref{Synchronous Processes}). There are various higher-level functions that make use of these primitives to run particular types of process. Synchronous and asynchronous processes are explained in the following sections. Since the three functions are all called in a similar fashion, their common arguments are described here. @cindex execute program @cindex @env{PATH} environment variable @cindex @env{HOME} environment variable In all cases, the functions specify the program to be run. An error is signaled if the file is not found or cannot be executed. If the file name is relative, the variable @code{exec-path} contains a list of directories to search. Emacs initializes @code{exec-path} when it starts up, based on the value of the environment variable @env{PATH}. The standard file name constructs, @samp{~}, @samp{.}, and @samp{..}, are interpreted as usual in @code{exec-path}, but environment variable substitutions (@samp{$HOME}, etc.)@: are not recognized; use @code{substitute-in-file-name} to perform them (@pxref{File Name Expansion}). @code{nil} in this list refers to @code{default-directory}. Executing a program can also try adding suffixes to the specified name: @defopt exec-suffixes This variable is a list of suffixes (strings) to try adding to the specified program file name. The list should include @code{""} if you want the name to be tried exactly as specified. The default value is system-dependent. @end defopt @strong{Please note:} The argument @var{program} contains only the name of the program file; it may not contain any command-line arguments. You must use a separate argument, @var{args}, to provide those, as described below. Each of the subprocess-creating functions has a @var{buffer-or-name} argument that specifies where the output from the program will go. It should be a buffer or a buffer name; if it is a buffer name, that will create the buffer if it does not already exist. It can also be @code{nil}, which says to discard the output, unless a custom filter function handles it. (@xref{Filter Functions}, and @ref{Read and Print}.) Normally, you should avoid having multiple processes send output to the same buffer because their output would be intermixed randomly. For synchronous processes, you can send the output to a file instead of a buffer (and the corresponding argument is therefore more appropriately called @var{destination}). By default, both standard output and standard error streams go to the same destination, but all the 3 primitives allow optionally to direct the standard error stream to a different destination. @cindex program arguments All three of the subprocess-creating functions allow to specify command-line arguments for the process to run. For @code{call-process} and @code{call-process-region}, these come in the form of a @code{&rest} argument, @var{args}. For @code{make-process}, both the program to run and its command-line arguments are specified as a list of strings. The command-line arguments must all be strings, and they are supplied to the program as separate argument strings. Wildcard characters and other shell constructs have no special meanings in these strings, since the strings are passed directly to the specified program. @cindex environment variables, subprocesses The subprocess inherits its environment from Emacs, but you can specify overrides for it with @code{process-environment}. @xref{System Environment}. The subprocess gets its current directory from the value of @code{default-directory}. @defvar exec-directory @pindex movemail The value of this variable is a string, the name of a directory that contains programs that come with GNU Emacs and are intended for Emacs to invoke. The program @code{movemail} is an example of such a program; Rmail uses it to fetch new mail from an inbox. @end defvar @defopt exec-path The value of this variable is a list of directories to search for programs to run in subprocesses. Each element is either the name of a directory (i.e., a string), or @code{nil}, which stands for the default directory (which is the value of @code{default-directory}). @xref{Locating Files, executable-find}, for the details of this search. @cindex program directories The value of @code{exec-path} is used by @code{call-process} and @code{start-process} when the @var{program} argument is not an absolute file name. Generally, you should not modify @code{exec-path} directly. Instead, ensure that your @env{PATH} environment variable is set appropriately before starting Emacs. Trying to modify @code{exec-path} independently of @env{PATH} can lead to confusing results. @end defopt @defun exec-path This function is an extension of the variable @code{exec-path}. If @code{default-directory} indicates a remote directory, this function returns a list of directories used for searching programs on the respective remote host. In case of a local @code{default-directory}, the function returns just the value of the variable @code{exec-path}. @end defun @node Shell Arguments @section Shell Arguments @cindex arguments for shell commands @cindex shell command arguments Lisp programs sometimes need to run a shell and give it a command that contains file names that were specified by the user. These programs ought to be able to support any valid file name. But the shell gives special treatment to certain characters, and if these characters occur in the file name, they will confuse the shell. To handle these characters, use the function @code{shell-quote-argument}: @defun shell-quote-argument argument This function returns a string that represents, in shell syntax, an argument whose actual contents are @var{argument}. It should work reliably to concatenate the return value into a shell command and then pass it to a shell for execution. Precisely what this function does depends on your operating system. The function is designed to work with the syntax of your system's standard shell; if you use an unusual shell, you will need to redefine this function. @xref{Security Considerations}. @example ;; @r{This example shows the behavior on GNU and Unix systems.} (shell-quote-argument "foo > bar") @result{} "foo\\ \\>\\ bar" ;; @r{This example shows the behavior on MS-DOS and MS-Windows.} (shell-quote-argument "foo > bar") @result{} "\"foo > bar\"" @end example Here's an example of using @code{shell-quote-argument} to construct a shell command: @example (concat "diff -u " (shell-quote-argument oldfile) " " (shell-quote-argument newfile)) @end example @end defun @cindex quoting and unquoting command-line arguments @cindex minibuffer input, and command-line arguments @cindex @code{call-process}, command-line arguments from minibuffer @cindex @code{start-process}, command-line arguments from minibuffer The following two functions are useful for combining a list of individual command-line argument strings into a single string, and taking a string apart into a list of individual command-line arguments. These functions are mainly intended for converting user input in the minibuffer, a Lisp string, into a list of string arguments to be passed to @code{make-process}, @code{call-process} or @code{start-process}, or for converting such lists of arguments into a single Lisp string to be presented in the minibuffer or echo area. Note that if a shell is involved (e.g., if using @code{call-process-shell-command}), arguments should still be protected by @code{shell-quote-argument}; @code{combine-and-quote-strings} is @emph{not} intended to protect special characters from shell evaluation. @defun split-string-and-unquote string &optional separators This function splits @var{string} into substrings at matches for the regular expression @var{separators}, like @code{split-string} does (@pxref{Creating Strings}); in addition, it removes quoting from the substrings. It then makes a list of the substrings and returns it. If @var{separators} is omitted or @code{nil}, it defaults to @code{"\\s-+"}, which is a regular expression that matches one or more characters with whitespace syntax (@pxref{Syntax Class Table}). This function supports two types of quoting: enclosing a whole string in double quotes @code{"@dots{}"}, and quoting individual characters with a backslash escape @samp{\}. The latter is also used in Lisp strings, so this function can handle those as well. @end defun @defun combine-and-quote-strings list-of-strings &optional separator This function concatenates @var{list-of-strings} into a single string, quoting each string as necessary. It also sticks the @var{separator} string between each pair of strings; if @var{separator} is omitted or @code{nil}, it defaults to @code{" "}. The return value is the resulting string. The strings in @var{list-of-strings} that need quoting are those that include @var{separator} as their substring. Quoting a string encloses it in double quotes @code{"@dots{}"}. In the simplest case, if you are consing a command from the individual command-line arguments, every argument that includes embedded blanks will be quoted. @end defun @node Synchronous Processes @section Creating a Synchronous Process @cindex synchronous subprocess After a @dfn{synchronous process} is created, Emacs waits for the process to terminate before continuing. Starting Dired on GNU or Unix@footnote{On other systems, Emacs uses a Lisp emulation of @code{ls}; see @ref{Contents of Directories}.} is an example of this: it runs @code{ls} in a synchronous process, then modifies the output slightly. Because the process is synchronous, the entire directory listing arrives in the buffer before Emacs tries to do anything with it. While Emacs waits for the synchronous subprocess to terminate, the user can quit by typing @kbd{C-g}. The first @kbd{C-g} tries to kill the subprocess with a @code{SIGINT} signal; but it waits until the subprocess actually terminates before quitting. If during that time the user types another @kbd{C-g}, that kills the subprocess instantly with @code{SIGKILL} and quits immediately (except on MS-DOS, where killing other processes doesn't work). @xref{Quitting}. The synchronous subprocess functions return an indication of how the process terminated. The output from a synchronous subprocess is generally decoded using a coding system, much like text read from a file. The input sent to a subprocess by @code{call-process-region} is encoded using a coding system, much like text written into a file. @xref{Coding Systems}. @defun call-process program &optional infile destination display &rest args This function calls @var{program} and waits for it to finish. The current working directory of the subprocess is set to the current buffer's value of @code{default-directory} if that is local (as determined by @code{unhandled-file-name-directory}), or "~" otherwise. If you want to run a process in a remote directory use @code{process-file}. The standard input for the new process comes from file @var{infile} if @var{infile} is not @code{nil}, and from the null device otherwise. The argument @var{destination} says where to put the process output. Here are the possibilities: @table @asis @item a buffer Insert the output in that buffer, before point. This includes both the standard output stream and the standard error stream of the process. @item a buffer name (a string) Insert the output in a buffer with that name, before point. @item @code{t} Insert the output in the current buffer, before point. @item @code{nil} Discard the output. @item 0 Discard the output, and return @code{nil} immediately without waiting for the subprocess to finish. In this case, the process is not truly synchronous, since it can run in parallel with Emacs; but you can think of it as synchronous in that Emacs is essentially finished with the subprocess as soon as this function returns. MS-DOS doesn't support asynchronous subprocesses, so this option doesn't work there. @item @code{(:file @var{file-name})} Send the output to the file name specified, overwriting it if it already exists. @item @code{(@var{real-destination} @var{error-destination})} Keep the standard output stream separate from the standard error stream; deal with the ordinary output as specified by @var{real-destination}, and dispose of the error output according to @var{error-destination}. If @var{error-destination} is @code{nil}, that means to discard the error output, @code{t} means mix it with the ordinary output, and a string specifies a file name to redirect error output into. You can't directly specify a buffer to put the error output in; that is too difficult to implement. But you can achieve this result by sending the error output to a temporary file and then inserting the file into a buffer when the subprocess finishes. @end table If @var{display} is non-@code{nil}, then @code{call-process} redisplays the buffer as output is inserted. (However, if the coding system chosen for decoding output is @code{undecided}, meaning deduce the encoding from the actual data, then redisplay sometimes cannot continue once non-@acronym{ASCII} characters are encountered. There are fundamental reasons why it is hard to fix this; see @ref{Output from Processes}.) Otherwise the function @code{call-process} does no redisplay, and the results become visible on the screen only when Emacs redisplays that buffer in the normal course of events. The remaining arguments, @var{args}, are strings that specify command line arguments for the program. Each string is passed to @var{program} as a separate argument. The value returned by @code{call-process} (unless you told it not to wait) indicates the reason for process termination. A number gives the exit status of the subprocess; 0 means success, and any other value means failure. If the process terminated with a signal, @code{call-process} returns a string describing the signal. If you told @code{call-process} not to wait, it returns @code{nil}. In the examples below, the buffer @samp{foo} is current. @smallexample @group (call-process "pwd" nil t) @result{} 0 ---------- Buffer: foo ---------- /home/lewis/manual ---------- Buffer: foo ---------- @end group @group (call-process "grep" nil "bar" nil "lewis" "/etc/passwd") @result{} 0 ---------- Buffer: bar ---------- lewis:x:1001:1001:Bil Lewis,,,,:/home/lewis:/bin/bash ---------- Buffer: bar ---------- @end group @end smallexample Here is an example of the use of @code{call-process}, as used to be found in the definition of the @code{insert-directory} function: @smallexample @group (call-process insert-directory-program nil t nil switches (if full-directory-p (concat (file-name-as-directory file) ".") file)) @end group @end smallexample @end defun @defun process-file program &optional infile buffer display &rest args This function processes files synchronously in a separate process. It is similar to @code{call-process}, but may invoke a file handler based on the value of the variable @code{default-directory}, which specifies the current working directory of the subprocess. The arguments are handled in almost the same way as for @code{call-process}, with the following differences: Some file handlers may not support all combinations and forms of the arguments @var{infile}, @var{buffer}, and @var{display}. For example, some file handlers might behave as if @var{display} were @code{nil}, regardless of the value actually passed. As another example, some file handlers might not support separating standard output and error output by way of the @var{buffer} argument. If a file handler is invoked, it determines the program to run based on the first argument @var{program}. For instance, suppose that a handler for remote files is invoked. Then the path that is used for searching for the program might be different from @code{exec-path}. The second argument @var{infile} may invoke a file handler. The file handler could be different from the handler chosen for the @code{process-file} function itself. (For example, @code{default-directory} could be on one remote host, and @var{infile} on a different remote host. Or @code{default-directory} could be non-special, whereas @var{infile} is on a remote host.) If @var{buffer} is a list of the form @code{(@var{real-destination} @var{error-destination})}, and @var{error-destination} names a file, then the same remarks as for @var{infile} apply. The remaining arguments (@var{args}) will be passed to the process verbatim. Emacs is not involved in processing file names that are present in @var{args}. To avoid confusion, it may be best to avoid absolute file names in @var{args}, but rather to specify all file names as relative to @code{default-directory}. The function @code{file-relative-name} is useful for constructing such relative file names. @end defun @defvar process-file-side-effects This variable indicates whether a call of @code{process-file} changes remote files. By default, this variable is always set to @code{t}, meaning that a call of @code{process-file} could potentially change any file on a remote host. When set to @code{nil}, a file handler could optimize its behavior with respect to remote file attribute caching. You should only ever change this variable with a let-binding; never with @code{setq}. @end defvar @defun call-process-region start end program &optional delete destination display &rest args This function sends the text from @var{start} to @var{end} as standard input to a process running @var{program}. It deletes the text sent if @var{delete} is non-@code{nil}; this is useful when @var{destination} is @code{t}, to insert the output in the current buffer in place of the input. The arguments @var{destination} and @var{display} control what to do with the output from the subprocess, and whether to update the display as it comes in. For details, see the description of @code{call-process}, above. If @var{destination} is the integer 0, @code{call-process-region} discards the output and returns @code{nil} immediately, without waiting for the subprocess to finish (this only works if asynchronous subprocesses are supported; i.e., not on MS-DOS). The remaining arguments, @var{args}, are strings that specify command line arguments for the program. The return value of @code{call-process-region} is just like that of @code{call-process}: @code{nil} if you told it to return without waiting; otherwise, a number or string which indicates how the subprocess terminated. In the following example, we use @code{call-process-region} to run the @code{cat} utility, with standard input being the first five characters in buffer @samp{foo} (the word @samp{input}). @code{cat} copies its standard input into its standard output. Since the argument @var{destination} is @code{t}, this output is inserted in the current buffer. @smallexample @group ---------- Buffer: foo ---------- input@point{} ---------- Buffer: foo ---------- @end group @group (call-process-region 1 6 "cat" nil t) @result{} 0 ---------- Buffer: foo ---------- inputinput@point{} ---------- Buffer: foo ---------- @end group @end smallexample For example, the @code{shell-command-on-region} command uses @code{call-shell-region} in a manner similar to this: @smallexample @group (call-shell-region start end command ; @r{shell command} nil ; @r{do not delete region} buffer) ; @r{send output to @code{buffer}} @end group @end smallexample @end defun @defun call-process-shell-command command &optional infile destination display This function executes the shell command @var{command} synchronously. The other arguments are handled as in @code{call-process}. An old calling convention allowed passing any number of additional arguments after @var{display}, which were concatenated to @var{command}; this is still supported, but strongly discouraged. @end defun @defun process-file-shell-command command &optional infile destination display This function is like @code{call-process-shell-command}, but uses @code{process-file} internally. Depending on @code{default-directory}, @var{command} can be executed also on remote hosts. An old calling convention allowed passing any number of additional arguments after @var{display}, which were concatenated to @var{command}; this is still supported, but strongly discouraged. @end defun @defun call-shell-region start end command &optional delete destination This function sends the text from @var{start} to @var{end} as standard input to an inferior shell running @var{command}. This function is similar than @code{call-process-region}, with process being a shell. The arguments @code{delete}, @code{destination} and the return value are like in @code{call-process-region}. Note that this function doesn't accept additional arguments. @end defun @defun shell-command-to-string command This function executes @var{command} (a string) as a shell command, then returns the command's output as a string. @end defun @c There is also shell-command-on-region, but that is more of a user @c command, not something to use in programs. @defun process-lines program &rest args This function runs @var{program}, waits for it to finish, and returns its output as a list of strings. Each string in the list holds a single line of text output by the program; the end-of-line characters are stripped from each line. The arguments beyond @var{program}, @var{args}, are strings that specify command-line arguments with which to run the program. If @var{program} exits with a non-zero exit status, this function signals an error. This function works by calling @code{call-process}, so program output is decoded in the same way as for @code{call-process}. @end defun @node Asynchronous Processes @section Creating an Asynchronous Process @cindex asynchronous subprocess In this section, we describe how to create an @dfn{asynchronous process}. After an asynchronous process is created, it runs in parallel with Emacs, and Emacs can communicate with it using the functions described in the following sections (@pxref{Input to Processes}, and @pxref{Output from Processes}). Note that process communication is only partially asynchronous: Emacs sends data to the process only when certain functions are called, and Emacs accepts data from the process only while waiting for input or for a time delay. @cindex pty @cindex pipe An asynchronous process is controlled either via a @dfn{pty} (pseudo-terminal) or a @dfn{pipe}. The choice of pty or pipe is made when creating the process, by default based on the value of the variable @code{process-connection-type} (see below). If available, ptys are usually preferable for processes visible to the user, as in Shell mode, because they allow for job control (@kbd{C-c}, @kbd{C-z}, etc.)@: between the process and its children, and because interactive programs treat ptys as terminal devices, whereas pipes don't support these features. However, for subprocesses used by Lisp programs for internal purposes, it is often better to use a pipe, because pipes are more efficient, and because they are immune to stray character injections that ptys introduce for large (around 500 byte) messages. Also, the total number of ptys is limited on many systems and it is good not to waste them. @defun make-process &rest args This function is the basic low-level primitive for starting asynchronous subprocesses. It returns a process object representing the subprocess. Compared to the more high-level @code{start-process}, described below, it takes keyword arguments, is more flexible, and allows to specify process filters and sentinels in a single call. The arguments @var{args} are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value @code{nil}. Here are the meaningful keywords: @table @asis @item :name @var{name} Use the string @var{name} as the process name; if a process with this name already exists, then @var{name} is modified (by appending @samp{<1>}, etc.)@: to be unique. @item :buffer @var{buffer} Use @var{buffer} as the process buffer. If the value is @code{nil}, the subprocess is not associated with any buffer. @item :command @var{command} Use @var{command} as the command line of the process. The value should be a list starting with the program's executable file name, followed by strings to give to the program as its arguments. If the first element of the list is @code{nil}, Emacs opens a new pseudoterminal (pty) and associates its input and output with @var{buffer}, without actually running any program; the rest of the list elements are ignored in that case. @item :coding @var{coding} If @var{coding} is a symbol, it specifies the coding system to be used for both reading and writing of data from and to the connection. If @var{coding} is a cons cell @w{@code{(@var{decoding} . @var{encoding})}}, then @var{decoding} will be used for reading and @var{encoding} for writing. The coding system used for encoding the data written to the program is also used for encoding the command-line arguments (but not the program itself, whose file name is encoded as any other file name; @pxref{Encoding and I/O, file-name-coding-system}). If @var{coding} is @code{nil}, the default rules for finding the coding system will apply. @xref{Default Coding Systems}. @item :connection-type @var{type} Initialize the type of device used to communicate with the subprocess. Possible values are @code{pty} to use a pty, @code{pipe} to use a pipe, or @code{nil} to use the default derived from the value of the @code{process-connection-type} variable. This parameter and the value of @code{process-connection-type} are ignored if a non-@code{nil} value is specified for the @code{:stderr} parameter; in that case, the type will always be @code{pipe}. @item :noquery @var{query-flag} Initialize the process query flag to @var{query-flag}. @xref{Query Before Exit}. @item :stop @var{stopped} If @var{stopped} is non-@code{nil}, start the process in the stopped state. @item :filter @var{filter} Initialize the process filter to @var{filter}. If not specified, a default filter will be provided, which can be overridden later. @xref{Filter Functions}. @item :sentinel @var{sentinel} Initialize the process sentinel to @var{sentinel}. If not specified, a default sentinel will be used, which can be overridden later. @xref{Sentinels}. @item :stderr @var{stderr} Associate @var{stderr} with the standard error of the process. A non-@code{nil} value should be either a buffer or a pipe process created with @code{make-pipe-process}, described below. If @var{stderr} is @code{nil}, standard error is mixed with standard output, and both are sent to @var{buffer} or @var{filter}. @end table The original argument list, modified with the actual connection information, is available via the @code{process-contact} function. The current working directory of the subprocess is set to the current buffer's value of @code{default-directory} if that is local (as determined by `unhandled-file-name-directory'), or "~" otherwise. If you want to run a process in a remote directory use @code{start-file-process}. @end defun @defun make-pipe-process &rest args This function creates a bidirectional pipe which can be attached to a child process. This is useful with the @code{:stderr} keyword of @code{make-process}. The function returns a process object. The arguments @var{args} are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value @code{nil}. Here are the meaningful keywords: @table @asis @item :name @var{name} Use the string @var{name} as the process name. As with @code{make-process}, it is modified if necessary to make it unique. @item :buffer @var{buffer} Use @var{buffer} as the process buffer. @item :coding @var{coding} If @var{coding} is a symbol, it specifies the coding system to be used for both reading and writing of data from and to the connection. If @var{coding} is a cons cell @w{@code{(@var{decoding} . @var{encoding})}}, then @var{decoding} will be used for reading and @var{encoding} for writing. If @var{coding} is @code{nil}, the default rules for finding the coding system will apply. @xref{Default Coding Systems}. @item :noquery @var{query-flag} Initialize the process query flag to @var{query-flag}. @xref{Query Before Exit}. @item :stop @var{stopped} If @var{stopped} is non-@code{nil}, start the process in the stopped state. In the stopped state, a pipe process does not accept incoming data, but you can send outgoing data. The stopped state is set by @code{stop-process} and cleared by @code{continue-process} (@pxref{Signals to Processes}). @item :filter @var{filter} Initialize the process filter to @var{filter}. If not specified, a default filter will be provided, which can be changed later. @xref{Filter Functions}. @item :sentinel @var{sentinel} Initialize the process sentinel to @var{sentinel}. If not specified, a default sentinel will be used, which can be changed later. @xref{Sentinels}. @end table The original argument list, modified with the actual connection information, is available via the @code{process-contact} function. @end defun @defun start-process name buffer-or-name program &rest args This function is a higher-level wrapper around @code{make-process}, exposing an interface that is similar to @code{call-process}. It creates a new asynchronous subprocess and starts the specified @var{program} running in it. It returns a process object that stands for the new subprocess in Lisp. The argument @var{name} specifies the name for the process object; as with @code{make-process}, it is modified if necessary to make it unique. The buffer @var{buffer-or-name} is the buffer to associate with the process. If @var{program} is @code{nil}, Emacs opens a new pseudoterminal (pty) and associates its input and output with @var{buffer-or-name}, without creating a subprocess. In that case, the remaining arguments @var{args} are ignored. The rest of @var{args} are strings that specify command line arguments for the subprocess. In the example below, the first process is started and runs (rather, sleeps) for 100 seconds (the output buffer @samp{foo} is created immediately). Meanwhile, the second process is started, and given the name @samp{my-process<1>} for the sake of uniqueness. It inserts the directory listing at the end of the buffer @samp{foo}, before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it. @smallexample @group (start-process "my-process" "foo" "sleep" "100") @result{} # @end group @group (start-process "my-process" "foo" "ls" "-l" "/bin") @result{} #> ---------- Buffer: foo ---------- total 8336 -rwxr-xr-x 1 root root 971384 Mar 30 10:14 bash -rwxr-xr-x 1 root root 146920 Jul 5 2011 bsd-csh @dots{} -rwxr-xr-x 1 root root 696880 Feb 28 15:55 zsh4 Process my-process<1> finished Process my-process finished ---------- Buffer: foo ---------- @end group @end smallexample @end defun @defun start-file-process name buffer-or-name program &rest args Like @code{start-process}, this function starts a new asynchronous subprocess running @var{program} in it, and returns its process object. The difference from @code{start-process} is that this function may invoke a file handler based on the value of @code{default-directory}. This handler ought to run @var{program}, perhaps on the local host, perhaps on a remote host that corresponds to @code{default-directory}. In the latter case, the local part of @code{default-directory} becomes the working directory of the process. This function does not try to invoke file name handlers for @var{program} or for the rest of @var{args}. Depending on the implementation of the file handler, it might not be possible to apply @code{process-filter} or @code{process-sentinel} to the resulting process object. @xref{Filter Functions}, and @ref{Sentinels}. @c FIXME Can we find a better example (i.e., a more modern function @c that is actually documented). Some file handlers may not support @code{start-file-process} (for example the function @code{ange-ftp-hook-function}). In such cases, this function does nothing and returns @code{nil}. @end defun @defun start-process-shell-command name buffer-or-name command This function is like @code{start-process}, except that it uses a shell to execute the specified @var{command}. The argument @var{command} is a shell command string. The variable @code{shell-file-name} specifies which shell to use. The point of running a program through the shell, rather than directly with @code{make-process} or @code{start-process}, is so that you can employ shell features such as wildcards in the arguments. It follows that if you include any arbitrary user-specified arguments in the command, you should quote them with @code{shell-quote-argument} first, so that any special shell characters do @emph{not} have their special shell meanings. @xref{Shell Arguments}. Of course, when executing commands based on user input you should also consider the security implications. @end defun @defun start-file-process-shell-command name buffer-or-name command This function is like @code{start-process-shell-command}, but uses @code{start-file-process} internally. Because of this, @var{command} can also be executed on remote hosts, depending on @code{default-directory}. @end defun @defvar process-connection-type This variable controls the type of device used to communicate with asynchronous subprocesses. If it is non-@code{nil}, then ptys are used, when available. Otherwise, pipes are used. The value of @code{process-connection-type} takes effect when @code{make-process} or @code{start-process} is called. So you can specify how to communicate with one subprocess by binding the variable around the call to these functions. Note that the value of this variable is ignored when @code{make-process} is called with a non-@code{nil} value of the @code{:stderr} parameter; in that case, Emacs will communicate with the process using pipes. @smallexample @group (let ((process-connection-type nil)) ; @r{use a pipe} (start-process @dots{})) @end group @end smallexample To determine whether a given subprocess actually got a pipe or a pty, use the function @code{process-tty-name} (@pxref{Process Information}). @end defvar @node Deleting Processes @section Deleting Processes @cindex deleting processes @dfn{Deleting a process} disconnects Emacs immediately from the subprocess. Processes are deleted automatically after they terminate, but not necessarily right away. You can delete a process explicitly at any time. If you explicitly delete a terminated process before it is deleted automatically, no harm results. Deleting a running process sends a signal to terminate it (and its child processes, if any), and calls the process sentinel. @xref{Sentinels}. When a process is deleted, the process object itself continues to exist as long as other Lisp objects point to it. All the Lisp primitives that work on process objects accept deleted processes, but those that do I/O or send signals will report an error. The process mark continues to point to the same place as before, usually into a buffer where output from the process was being inserted. @defopt delete-exited-processes This variable controls automatic deletion of processes that have terminated (due to calling @code{exit} or to a signal). If it is @code{nil}, then they continue to exist until the user runs @code{list-processes}. Otherwise, they are deleted immediately after they exit. @end defopt @defun delete-process process This function deletes a process, killing it with a @code{SIGKILL} signal if the process was running a program. The argument may be a process, the name of a process, a buffer, or the name of a buffer. (A buffer or buffer-name stands for the process that @code{get-buffer-process} returns.) Calling @code{delete-process} on a running process terminates it, updates the process status, and runs the sentinel immediately. If the process has already terminated, calling @code{delete-process} has no effect on its status, or on the running of its sentinel (which will happen sooner or later). If the process object represents a network, serial, or pipe connection, its status changes to @code{closed}; otherwise, it changes to @code{signal}, unless the process already exited. @xref{Process Information, process-status}. @smallexample @group (delete-process "*shell*") @result{} nil @end group @end smallexample @end defun @node Process Information @section Process Information @cindex process information Several functions return information about processes. @deffn Command list-processes &optional query-only buffer This command displays a listing of all living processes. In addition, it finally deletes any process whose status was @samp{Exited} or @samp{Signaled}. It returns @code{nil}. The processes are shown in a buffer named @file{*Process List*} (unless you specify otherwise using the optional argument @var{buffer}), whose major mode is Process Menu mode. If @var{query-only} is non-@code{nil}, it only lists processes whose query flag is non-@code{nil}. @xref{Query Before Exit}. @end deffn @defun process-list This function returns a list of all processes that have not been deleted. @smallexample @group (process-list) @result{} (# #) @end group @end smallexample @end defun @defun get-process name This function returns the process named @var{name} (a string), or @code{nil} if there is none. The argument @var{name} can also be a process object, in which case it is returned. @smallexample @group (get-process "shell") @result{} # @end group @end smallexample @end defun @defun process-command process This function returns the command that was executed to start @var{process}. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program. For a network, serial, or pipe connection, this is either @code{nil}, which means the process is running or @code{t} (process is stopped). @smallexample @group (process-command (get-process "shell")) @result{} ("bash" "-i") @end group @end smallexample @end defun @defun process-contact process &optional key This function returns information about how a network, a serial, or a pipe connection was set up. When @var{key} is @code{nil}, it returns @code{(@var{hostname} @var{service})} for a network connection, @code{(@var{port} @var{speed})} for a serial connection, and @code{t} for a pipe connection. For an ordinary child process, this function always returns @code{t} when called with a @code{nil} @var{key}. If @var{key} is @code{t}, the value is the complete status information for the connection, server, serial port, or pipe; that is, the list of keywords and values specified in @code{make-network-process}, @code{make-serial-process}, or @code{make-pipe-process}, except that some of the values represent the current status instead of what you specified. For a network process, the values include (see @code{make-network-process} for a complete list): @table @code @item :buffer The associated value is the process buffer. @item :filter The associated value is the process filter function. @xref{Filter Functions}. @item :sentinel The associated value is the process sentinel function. @xref{Sentinels}. @item :remote In a connection, the address in internal format of the remote peer. @item :local The local address, in internal format. @item :service In a server, if you specified @code{t} for @var{service}, this value is the actual port number. @end table @code{:local} and @code{:remote} are included even if they were not specified explicitly in @code{make-network-process}. For a serial connection, see @code{make-serial-process} and @code{serial-process-configure} for the list of keys. For a pipe connection, see @code{make-pipe-process} for the list of keys. If @var{key} is a keyword, the function returns the value corresponding to that keyword. @end defun @defun process-id process This function returns the @acronym{PID} of @var{process}. This is an integral number that distinguishes the process @var{process} from all other processes running on the same computer at the current time. The @acronym{PID} of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists. For network, serial, and pipe connections, this function returns @code{nil}. @end defun @defun process-name process This function returns the name of @var{process}, as a string. @end defun @defun process-status process-name This function returns the status of @var{process-name} as a symbol. The argument @var{process-name} must be a process, a buffer, or a process name (a string). The possible values for an actual subprocess are: @table @code @item run for a process that is running. @item stop for a process that is stopped but continuable. @item exit for a process that has exited. @item signal for a process that has received a fatal signal. @item open for a network, serial, or pipe connection that is open. @item closed for a network, serial, or pipe connection that is closed. Once a connection is closed, you cannot reopen it, though you might be able to open a new connection to the same place. @item connect for a non-blocking connection that is waiting to complete. @item failed for a non-blocking connection that has failed to complete. @item listen for a network server that is listening. @item nil if @var{process-name} is not the name of an existing process. @end table @smallexample @group (process-status (get-buffer "*shell*")) @result{} run @end group @end smallexample For a network, serial, or pipe connection, @code{process-status} returns one of the symbols @code{open}, @code{stop}, or @code{closed}. The latter means that the other side closed the connection, or Emacs did @code{delete-process}. The value @code{stop} means that @code{stop-process} was called on the connection. @end defun @defun process-live-p process This function returns non-@code{nil} if @var{process} is alive. A process is considered alive if its status is @code{run}, @code{open}, @code{listen}, @code{connect} or @code{stop}. @end defun @defun process-type process This function returns the symbol @code{network} for a network connection or server, @code{serial} for a serial port connection, @code{pipe} for a pipe connection, or @code{real} for a subprocess created for running a program. @end defun @defun process-exit-status process This function returns the exit status of @var{process} or the signal number that killed it. (Use the result of @code{process-status} to determine which of those it is.) If @var{process} has not yet terminated, the value is 0. For network, serial, and pipe connections that are already closed, the value is either 0 or 256, depending on whether the connection was closed normally or abnormally. @end defun @defun process-tty-name process This function returns the terminal name that @var{process} is using for its communication with Emacs---or @code{nil} if it is using pipes instead of a pty (see @code{process-connection-type} in @ref{Asynchronous Processes}). If @var{process} represents a program running on a remote host, the terminal name used by that program on the remote host is provided as process property @code{remote-tty}. If @var{process} represents a network, serial, or pipe connection, the value is @code{nil}. @end defun @defun process-coding-system process @anchor{Coding systems for a subprocess} This function returns a cons cell @code{(@var{decode} . @var{encode})}, describing the coding systems in use for decoding output from, and encoding input to, @var{process} (@pxref{Coding Systems}). @end defun @defun set-process-coding-system process &optional decoding-system encoding-system This function specifies the coding systems to use for subsequent output from and input to @var{process}. It will use @var{decoding-system} to decode subprocess output, and @var{encoding-system} to encode subprocess input. @end defun Every process also has a property list that you can use to store miscellaneous values associated with the process. @defun process-get process propname This function returns the value of the @var{propname} property of @var{process}. @end defun @defun process-put process propname value This function sets the value of the @var{propname} property of @var{process} to @var{value}. @end defun @defun process-plist process This function returns the process plist of @var{process}. @end defun @defun set-process-plist process plist This function sets the process plist of @var{process} to @var{plist}. @end defun @node Input to Processes @section Sending Input to Processes @cindex process input Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. If the subprocess runs a program, the data appears on the standard input of that program; for connections, the data is sent to the connected device or program. @c FIXME which? Some operating systems have limited space for buffered input in a pty. On these systems, Emacs sends an @acronym{EOF} periodically amidst the other characters, to force them through. For most programs, these @acronym{EOF}s do no harm. Subprocess input is normally encoded using a coding system before the subprocess receives it, much like text written into a file. You can use @code{set-process-coding-system} to specify which coding system to use (@pxref{Process Information}). Otherwise, the coding system comes from @code{coding-system-for-write}, if that is non-@code{nil}; or else from the defaulting mechanism (@pxref{Default Coding Systems}). Sometimes the system is unable to accept input for that process, because the input buffer is full. When this happens, the send functions wait a short while, accepting output from subprocesses, and then try again. This gives the subprocess a chance to read more of its pending input and make space in the buffer. It also allows filters, sentinels and timers to run---so take account of that in writing your code. In these functions, the @var{process} argument can be a process or the name of a process, or a buffer or buffer name (which stands for a process via @code{get-buffer-process}). @code{nil} means the current buffer's process. @defun process-send-string process string This function sends @var{process} the contents of @var{string} as standard input. It returns @code{nil}. For example, to make a Shell buffer list files: @smallexample @group (process-send-string "shell<1>" "ls\n") @result{} nil @end group @end smallexample @end defun @defun process-send-region process start end This function sends the text in the region defined by @var{start} and @var{end} as standard input to @var{process}. An error is signaled unless both @var{start} and @var{end} are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.) @end defun @defun process-send-eof &optional process This function makes @var{process} see an end-of-file in its input. The @acronym{EOF} comes after any text already sent to it. The function returns @var{process}. @smallexample @group (process-send-eof "shell") @result{} "shell" @end group @end smallexample @end defun @defun process-running-child-p &optional process This function will tell you whether a @var{process}, which must not be a connection but a real subprocess, has given control of its terminal to a child process of its own. If this is true, the function returns the numeric ID of the foreground process group of @var{process}; it returns @code{nil} if Emacs can be certain that this is not so. The value is @code{t} if Emacs cannot tell whether this is true. This function signals an error if @var{process} is a network, serial, or pipe connection, or is the subprocess is not active. @end defun @node Signals to Processes @section Sending Signals to Processes @cindex process signals @cindex sending signals @cindex signals @dfn{Sending a signal} to a subprocess is a way of interrupting its activities. There are several different signals, each with its own meaning. The set of signals and their names is defined by the operating system. For example, the signal @code{SIGINT} means that the user has typed @kbd{C-c}, or that some analogous thing has happened. Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop (or resume) execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects. You can send signals explicitly by calling the functions in this section. Emacs also sends signals automatically at certain times: killing a buffer sends a @code{SIGHUP} signal to all its associated processes; killing Emacs sends a @code{SIGHUP} signal to all remaining processes. (@code{SIGHUP} is a signal that usually indicates that the user ``hung up the phone'', i.e., disconnected.) Each of the signal-sending functions takes two optional arguments: @var{process} and @var{current-group}. The argument @var{process} must be either a process, a process name, a buffer, a buffer name, or @code{nil}. A buffer or buffer name stands for a process through @code{get-buffer-process}. @code{nil} stands for the process associated with the current buffer. Except with @code{stop-process} and @code{continue-process}, an error is signaled if @var{process} does not identify an active process, or if it represents a network, serial, or pipe connection. The argument @var{current-group} is a flag that makes a difference when you are running a job-control shell as an Emacs subprocess. If it is non-@code{nil}, then the signal is sent to the current process-group of the terminal that Emacs uses to communicate with the subprocess. If the process is a job-control shell, this means the shell's current subjob. If @var{current-group} is @code{nil}, the signal is sent to the process group of the immediate subprocess of Emacs. If the subprocess is a job-control shell, this is the shell itself. If @var{current-group} is @code{lambda}, the signal is sent to the process-group that owns the terminal, but only if it is not the shell itself. The flag @var{current-group} has no effect when a pipe is used to communicate with the subprocess, because the operating system does not support the distinction in the case of pipes. For the same reason, job-control shells won't work when a pipe is used. See @code{process-connection-type} in @ref{Asynchronous Processes}. @defun interrupt-process &optional process current-group This function interrupts the process @var{process} by sending the signal @code{SIGINT}. Outside of Emacs, typing the interrupt character (normally @kbd{C-c} on some systems, and @key{DEL} on others) sends this signal. When the argument @var{current-group} is non-@code{nil}, you can think of this function as typing @kbd{C-c} on the terminal by which Emacs talks to the subprocess. @end defun @defun kill-process &optional process current-group This function kills the process @var{process} by sending the signal @code{SIGKILL}. This signal kills the subprocess immediately, and cannot be handled by the subprocess. @end defun @defun quit-process &optional process current-group This function sends the signal @code{SIGQUIT} to the process @var{process}. This signal is the one sent by the quit character (usually @kbd{C-\}) when you are not inside Emacs. @end defun @defun stop-process &optional process current-group This function stops the specified @var{process}. If it is a real subprocess running a program, it sends the signal @code{SIGTSTP} to that subprocess. If @var{process} represents a network, serial, or pipe connection, this function inhibits handling of the incoming data from the connection; for a network server, this means not accepting new connections. Use @code{continue-process} to resume normal execution. Outside of Emacs, on systems with job control, the stop character (usually @kbd{C-z}) normally sends the @code{SIGTSTP} signal to a subprocess. When @var{current-group} is non-@code{nil}, you can think of this function as typing @kbd{C-z} on the terminal Emacs uses to communicate with the subprocess. @end defun @defun continue-process &optional process current-group This function resumes execution of the process @var{process}. If it is a real subprocess running a program, it sends the signal @code{SIGCONT} to that subprocess; this presumes that @var{process} was stopped previously. If @var{process} represents a network, serial, or pipe connection, this function resumes handling of the incoming data from the connection. For serial connections, data that arrived during the time the process was stopped might be lost. @end defun @deffn Command signal-process process signal This function sends a signal to process @var{process}. The argument @var{signal} specifies which signal to send; it should be an integer, or a symbol whose name is a signal. The @var{process} argument can be a system process @acronym{ID} (an integer); that allows you to send signals to processes that are not children of Emacs. @xref{System Processes}. @end deffn Sometimes, it is necessary to send a signal to a non-local asynchronous process. This is possible by writing an own @code{interrupt-process} implementation. This function must be added then to @code{interrupt-process-functions}. @defvar interrupt-process-functions This variable is a list of functions to be called for @code{interrupt-process}. The arguments of the functions are the same as for @code{interrupt-process}. These functions are called in the order of the list, until one of them returns non-@code{nil}. The default function, which shall always be the last in this list, is @code{internal-default-interrupt-process}. This is the mechanism, how Tramp implements @code{interrupt-process}. @end defvar @node Output from Processes @section Receiving Output from Processes @cindex process output @cindex output from processes The output that an asynchronous subprocess writes to its standard output stream is passed to a function called the @dfn{filter function}. The default filter function simply inserts the output into a buffer, which is called the associated buffer of the process (@pxref{Process Buffers}). If the process has no buffer then the default filter discards the output. If the subprocess writes to its standard error stream, by default the error output is also passed to the process filter function. If Emacs uses a pseudo-TTY (pty) for communication with the subprocess, then it is impossible to separate the standard output and standard error streams of the subprocess, because a pseudo-TTY has only one output channel. In that case, if you want to keep the output to those streams separate, you should redirect one of them to a file---for example, by using an appropriate shell command via @code{start-process-shell-command} or a similar function. Alternatively, you could use the @code{:stderr} parameter with a non-@code{nil} value in a call to @code{make-process} (@pxref{Asynchronous Processes, make-process}) to make the destination of the error output separate from the standard output; in that case, Emacs will use pipes for communicating with the subprocess. When a subprocess terminates, Emacs reads any pending output, then stops reading output from that subprocess. Therefore, if the subprocess has children that are still live and still producing output, Emacs won't receive that output. Output from a subprocess can arrive only while Emacs is waiting: when reading terminal input (see the function @code{waiting-for-user-input-p}), in @code{sit-for} and @code{sleep-for} (@pxref{Waiting}), and in @code{accept-process-output} (@pxref{Accepting Output}). This minimizes the problem of timing errors that usually plague parallel programming. For example, you can safely create a process and only then specify its buffer or filter function; no output can arrive before you finish, if the code in between does not call any primitive that waits. @defvar process-adaptive-read-buffering On some systems, when Emacs reads the output from a subprocess, the output data is read in very small blocks, potentially resulting in very poor performance. This behavior can be remedied to some extent by setting the variable @code{process-adaptive-read-buffering} to a non-@code{nil} value (the default), as it will automatically delay reading from such processes, thus allowing them to produce more output before Emacs tries to read it. @end defvar @menu * Process Buffers:: By default, output is put in a buffer. * Filter Functions:: Filter functions accept output from the process. * Decoding Output:: Filters can get unibyte or multibyte strings. * Accepting Output:: How to wait until process output arrives. * Processes and Threads:: How processes and threads interact. @end menu @node Process Buffers @subsection Process Buffers A process can (and usually does) have an @dfn{associated buffer}, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp. By default, process output is inserted in the associated buffer. (You can change this by defining a custom filter function, @pxref{Filter Functions}.) The position to insert the output is determined by the @code{process-mark}, which is then updated to point to the end of the text just inserted. Usually, but not always, the @code{process-mark} is at the end of the buffer. @findex process-kill-buffer-query-function Killing the associated buffer of a process also kills the process. Emacs asks for confirmation first, if the process's @code{process-query-on-exit-flag} is non-@code{nil} (@pxref{Query Before Exit}). This confirmation is done by the function @code{process-kill-buffer-query-function}, which is run from @code{kill-buffer-query-functions} (@pxref{Killing Buffers}). @defun process-buffer process This function returns the associated buffer of the specified @var{process}. @smallexample @group (process-buffer (get-process "shell")) @result{} # @end group @end smallexample @end defun @defun process-mark process This function returns the process marker for @var{process}, which is the marker that says where to insert output from the process. If @var{process} does not have a buffer, @code{process-mark} returns a marker that points nowhere. The default filter function uses this marker to decide where to insert process output, and updates it to point after the inserted text. That is why successive batches of output are inserted consecutively. Custom filter functions normally should use this marker in the same fashion. For an example of a filter function that uses @code{process-mark}, @pxref{Process Filter Example}. When the user is expected to enter input in the process buffer for transmission to the process, the process marker separates the new input from previous output. @end defun @defun set-process-buffer process buffer This function sets the buffer associated with @var{process} to @var{buffer}. If @var{buffer} is @code{nil}, the process becomes associated with no buffer. @end defun @defun get-buffer-process buffer-or-name This function returns a nondeleted process associated with the buffer specified by @var{buffer-or-name}. If there are several processes associated with it, this function chooses one (currently, the one most recently created, but don't count on that). Deletion of a process (see @code{delete-process}) makes it ineligible for this function to return. It is usually a bad idea to have more than one process associated with the same buffer. @smallexample @group (get-buffer-process "*shell*") @result{} # @end group @end smallexample Killing the process's buffer deletes the process, which kills the subprocess with a @code{SIGHUP} signal (@pxref{Signals to Processes}). @end defun If the process's buffer is displayed in a window, your Lisp program may wish to tell the process the dimensions of that window, so that the process could adapt its output to those dimensions, much as it adapts to the screen dimensions. The following functions allow communicating this kind of information to processes; however, not all systems support the underlying functionality, so it is best to provide fallbacks, e.g., via command-line arguments or environment variables. @defun set-process-window-size process height width Tell @var{process} that its logical window size has dimensions @var{width} by @var{height}, in character units. If this function succeeds in communicating this information to the process, it returns @code{t}; otherwise it returns @code{nil}. @end defun When windows that display buffers associated with process change their dimensions, the affected processes should be told about these changes. By default, when the window configuration changes, Emacs will automatically call @code{set-process-window-size} on behalf of every process whose buffer is displayed in a window, passing it the smallest dimensions of all the windows displaying the process's buffer. This works via @code{window-configuration-change-hook} (@pxref{Window Hooks}), which is told to invoke the function that is the value of the variable @code{window-adjust-process-window-size-function} for each process whose buffer is displayed in at least one window. You can customize this behavior by setting the value of that variable. @defopt window-adjust-process-window-size-function The value of this variable should be a function of two arguments: a process and the list of windows displaying the process's buffer. When the function is called, the process's buffer is the current buffer. The function should return a cons cell @w{@code{(@var{width} . @var{height})}} that describes the dimensions of the logical process window to be passed via a call to @code{set-process-window-size}. The function can also return @code{nil}, in which case Emacs will not call @code{set-process-window-size} for this process. Emacs supplies two predefined values for this variable: @code{window-adjust-process-window-size-smallest}, which returns the smallest of all the dimensions of the windows that display a process's buffer; and @code{window-adjust-process-window-size-largest}, which returns the largest dimensions. For more complex strategies, write your own function. This variable can be buffer-local. @end defopt If the process has the @code{adjust-window-size-function} property (@pxref{Process Information}), its value overrides the global and buffer-local values of @code{window-adjust-process-window-size-function}. @node Filter Functions @subsection Process Filter Functions @cindex filter function @cindex process filter @cindex default filter function of a process A process @dfn{filter function} is a function that receives the standard output from the associated process. @emph{All} output from that process is passed to the filter. The default filter simply outputs directly to the process buffer. By default, the error output from the process, if any, is also passed to the filter function, unless the destination for the standard error stream of the process was separated from the standard output when the process was created (@pxref{Output from Processes}). The filter function can only be called when Emacs is waiting for something, because process output arrives only at such times. Emacs waits when reading terminal input (see the function @code{waiting-for-user-input-p}), in @code{sit-for} and @code{sleep-for} (@pxref{Waiting}), and in @code{accept-process-output} (@pxref{Accepting Output}). A filter function must accept two arguments: the associated process and a string, which is output just received from it. The function is then free to do whatever it chooses with the output. @c Note this text is duplicated in the sentinels section. Quitting is normally inhibited within a filter function---otherwise, the effect of typing @kbd{C-g} at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a filter function, bind @code{inhibit-quit} to @code{nil}. In most cases, the right way to do this is with the macro @code{with-local-quit}. @xref{Quitting}. If an error happens during execution of a filter function, it is caught automatically, so that it doesn't stop the execution of whatever program was running when the filter function was started. However, if @code{debug-on-error} is non-@code{nil}, errors are not caught. This makes it possible to use the Lisp debugger to debug filter functions. @xref{Debugger}. Many filter functions sometimes (or always) insert the output in the process's buffer, mimicking the actions of the default filter. Such filter functions need to make sure that they save the current buffer, select the correct buffer (if different) before inserting output, and then restore the original buffer. They should also check whether the buffer is still alive, update the process marker, and in some cases update the value of point. Here is how to do these things: @anchor{Process Filter Example} @smallexample @group (defun ordinary-insertion-filter (proc string) (when (buffer-live-p (process-buffer proc)) (with-current-buffer (process-buffer proc) (let ((moving (= (point) (process-mark proc)))) @end group @group (save-excursion ;; @r{Insert the text, advancing the process marker.} (goto-char (process-mark proc)) (insert string) (set-marker (process-mark proc) (point))) (if moving (goto-char (process-mark proc))))))) @end group @end smallexample To make the filter force the process buffer to be visible whenever new text arrives, you could insert a line like the following just before the @code{with-current-buffer} construct: @smallexample (display-buffer (process-buffer proc)) @end smallexample To force point to the end of the new output, no matter where it was previously, eliminate the variable @code{moving} from the example and call @code{goto-char} unconditionally. @ignore In earlier Emacs versions, every filter function that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for filter functions; they never need to do it explicitly. @end ignore Note that Emacs automatically saves and restores the match data while executing filter functions. @xref{Match Data}. The output to the filter may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next. If the filter looks for certain text strings in the subprocess output, make sure to handle the case where one of these strings is split across two or more batches of output; one way to do this is to insert the received text into a temporary buffer, which can then be searched. @defun set-process-filter process filter This function gives @var{process} the filter function @var{filter}. If @var{filter} is @code{nil}, it gives the process the default filter, which inserts the process output into the process buffer. @end defun @defun process-filter process This function returns the filter function of @var{process}. @end defun In case the process's output needs to be passed to several filters, you can use @code{add-function} to combine an existing filter with a new one. @xref{Advising Functions}. Here is an example of the use of a filter function: @smallexample @group (defun keep-output (process output) (setq kept (cons output kept))) @result{} keep-output @end group @group (setq kept nil) @result{} nil @end group @group (set-process-filter (get-process "shell") 'keep-output) @result{} keep-output @end group @group (process-send-string "shell" "ls ~/other\n") @result{} nil kept @result{} ("lewis@@slug:$ " @end group @group "FINAL-W87-SHORT.MSS backup.otl kolstad.mss~ address.txt backup.psf kolstad.psf backup.bib~ david.mss resume-Dec-86.mss~ backup.err david.psf resume-Dec.psf backup.mss dland syllabus.mss " "#backups.mss# backup.mss~ kolstad.mss ") @end group @end smallexample @ignore @c The code in this example doesn't show the right way to do things. Here is another, more realistic example, which demonstrates how to use the process mark to do insertion in the same fashion as the default filter: @smallexample @group ;; @r{Insert input in the buffer specified by @code{my-shell-buffer}} ;; @r{and make sure that buffer is shown in some window.} (defun my-process-filter (proc str) (let ((cur (selected-window)) (pop-up-windows t)) (pop-to-buffer my-shell-buffer) @end group @group (goto-char (point-max)) (insert str) (set-marker (process-mark proc) (point-max)) (select-window cur))) @end group @end smallexample @end ignore @node Decoding Output @subsection Decoding Process Output @cindex decode process output When Emacs writes process output directly into a multibyte buffer, it decodes the output according to the process output coding system. If the coding system is @code{raw-text} or @code{no-conversion}, Emacs converts the unibyte output to multibyte using @code{string-to-multibyte}, and inserts the resulting multibyte text. You can use @code{set-process-coding-system} to specify which coding system to use (@pxref{Process Information}). Otherwise, the coding system comes from @code{coding-system-for-read}, if that is non-@code{nil}; or else from the defaulting mechanism (@pxref{Default Coding Systems}). If the text output by a process contains null bytes, Emacs by default uses @code{no-conversion} for it; see @ref{Lisp and Coding Systems, inhibit-null-byte-detection}, for how to control this behavior. @strong{Warning:} Coding systems such as @code{undecided}, which determine the coding system from the data, do not work entirely reliably with asynchronous subprocess output. This is because Emacs has to process asynchronous subprocess output in batches, as it arrives. Emacs must try to detect the proper coding system from one batch at a time, and this does not always work. Therefore, if at all possible, specify a coding system that determines both the character code conversion and the end of line conversion---that is, one like @code{latin-1-unix}, rather than @code{undecided} or @code{latin-1}. @c Let's keep the index entries that were there for @c set-process-filter-multibyte and process-filter-multibyte-p, @cindex filter multibyte flag, of process @cindex process filter multibyte flag When Emacs calls a process filter function, it provides the process output as a multibyte string or as a unibyte string according to the process's filter coding system. Emacs decodes the output according to the process output coding system, which usually produces a multibyte string, except for coding systems such as @code{binary} and @code{raw-text}. @node Accepting Output @subsection Accepting Output from Processes @cindex accept input from processes Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process. @defun accept-process-output &optional process seconds millisec just-this-one This function allows Emacs to read pending output from processes. The output is given to their filter functions. If @var{process} is non-@code{nil} then this function does not return until some output has been received from @var{process}. The arguments @var{seconds} and @var{millisec} let you specify timeout periods. The former specifies a period measured in seconds and the latter specifies one measured in milliseconds. The two time periods thus specified are added together, and @code{accept-process-output} returns after that much time, even if there is no subprocess output. The argument @var{millisec} is obsolete (and should not be used), because @var{seconds} can be floating point to specify waiting a fractional number of seconds. If @var{seconds} is 0, the function accepts whatever output is pending but does not wait. @c Emacs 22.1 feature If @var{process} is a process, and the argument @var{just-this-one} is non-@code{nil}, only output from that process is handled, suspending output from other processes until some output has been received from that process or the timeout expires. If @var{just-this-one} is an integer, also inhibit running timers. This feature is generally not recommended, but may be necessary for specific applications, such as speech synthesis. The function @code{accept-process-output} returns non-@code{nil} if it got output from @var{process}, or from any process if @var{process} is @code{nil}. It returns @code{nil} if the timeout expired before output arrived. @end defun @node Processes and Threads @subsection Processes and Threads @cindex processes, threads Because threads were a relatively late addition to Emacs Lisp, and due to the way dynamic binding was sometimes used in conjunction with @code{accept-process-output}, by default a process is locked to the thread that created it. When a process is locked to a thread, output from the process can only be accepted by that thread. A Lisp program can specify to which thread a process is to be locked, or instruct Emacs to unlock a process, in which case its output can be processed by any thread. Only a single thread will wait for output from a given process at one time---once one thread begins waiting for output, the process is temporarily locked until @code{accept-process-output} or @code{sit-for} returns. If the thread exits, all the processes locked to it are unlocked. @defun process-thread process Return the thread to which @var{process} is locked. If @var{process} is unlocked, return @code{nil}. @end defun @defun set-process-thread process thread Set the locking thread of @var{process} to @var{thread}. @var{thread} may be @code{nil}, in which case the process is unlocked. @end defun @node Sentinels @section Sentinels: Detecting Process Status Changes @cindex process sentinel @cindex sentinel (of process) A @dfn{process sentinel} is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process's own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event. @cindex default sentinel function of a process If no sentinel function was specified for a process, it will use the default sentinel function, which inserts a message in the process's buffer with the process name and the string describing the event. The string describing the event looks like one of the following: @itemize @bullet @item @code{"finished\n"}. @item @code{"deleted\n"}. @item @code{"exited abnormally with code @var{exitcode} (core dumped)\n"}. The ``core dumped'' part is optional, and only appears if the process dumped core. @item @code{"failed with code @var{fail-code}\n"}. @item @code{"@var{signal-description} (core dumped)\n"}. The @var{signal-description} is a system-dependent textual description of a signal, e.g., @code{"killed"} for @code{SIGKILL}. The ``core dumped'' part is optional, and only appears if the process dumped core. @item @code{"open from @var{host-name}\n"}. @item @code{"open\n"}. @item @code{"connection broken by remote peer\n"}. @end itemize A sentinel runs only while Emacs is waiting (e.g., for terminal input, or for time to elapse, or for process output). This avoids the timing errors that could result from running sentinels at random places in the middle of other Lisp programs. A program can wait, so that sentinels will run, by calling @code{sit-for} or @code{sleep-for} (@pxref{Waiting}), or @code{accept-process-output} (@pxref{Accepting Output}). Emacs also allows sentinels to run when the command loop is reading input. @code{delete-process} calls the sentinel when it terminates a running process. Emacs does not keep a queue of multiple reasons to call the sentinel of one process; it records just the current status and the fact that there has been a change. Therefore two changes in status, coming in quick succession, can call the sentinel just once. However, process termination will always run the sentinel exactly once. This is because the process status can't change again after termination. Emacs explicitly checks for output from the process before running the process sentinel. Once the sentinel runs due to process termination, no further output can arrive from the process. A sentinel that writes the output into the buffer of the process should check whether the buffer is still alive. If it tries to insert into a dead buffer, it will get an error. If the buffer is dead, @code{(buffer-name (process-buffer @var{process}))} returns @code{nil}. @c Note this text is duplicated in the filter functions section. Quitting is normally inhibited within a sentinel---otherwise, the effect of typing @kbd{C-g} at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a sentinel, bind @code{inhibit-quit} to @code{nil}. In most cases, the right way to do this is with the macro @code{with-local-quit}. @xref{Quitting}. If an error happens during execution of a sentinel, it is caught automatically, so that it doesn't stop the execution of whatever programs was running when the sentinel was started. However, if @code{debug-on-error} is non-@code{nil}, errors are not caught. This makes it possible to use the Lisp debugger to debug the sentinel. @xref{Debugger}. While a sentinel is running, the process sentinel is temporarily set to @code{nil} so that the sentinel won't run recursively. For this reason it is not possible for a sentinel to specify a new sentinel. @ignore In earlier Emacs versions, every sentinel that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for sentinels; they never need to do it explicitly. @end ignore Note that Emacs automatically saves and restores the match data while executing sentinels. @xref{Match Data}. @defun set-process-sentinel process sentinel This function associates @var{sentinel} with @var{process}. If @var{sentinel} is @code{nil}, then the process will have the default sentinel, which inserts a message in the process's buffer when the process status changes. Changes in process sentinels take effect immediately---if the sentinel is slated to be run but has not been called yet, and you specify a new sentinel, the eventual call to the sentinel will use the new one. @smallexample @group (defun msg-me (process event) (princ (format "Process: %s had the event '%s'" process event))) (set-process-sentinel (get-process "shell") 'msg-me) @result{} msg-me @end group @group (kill-process (get-process "shell")) @print{} Process: # had the event 'killed' @result{} # @end group @end smallexample @end defun @defun process-sentinel process This function returns the sentinel of @var{process}. @end defun In case a process status changes need to be passed to several sentinels, you can use @code{add-function} to combine an existing sentinel with a new one. @xref{Advising Functions}. @defun waiting-for-user-input-p While a sentinel or filter function is running, this function returns non-@code{nil} if Emacs was waiting for keyboard input from the user at the time the sentinel or filter function was called, or @code{nil} if it was not. @end defun @node Query Before Exit @section Querying Before Exit When Emacs exits, it terminates all its subprocesses. For subprocesses that run a program, it sends them the @code{SIGHUP} signal; connections are simply closed. Because subprocesses may be doing valuable work, Emacs normally asks the user to confirm that it is ok to terminate them. Each process has a query flag, which, if non-@code{nil}, says that Emacs should ask for confirmation before exiting and thus killing that process. The default for the query flag is @code{t}, meaning @emph{do} query. @defun process-query-on-exit-flag process This returns the query flag of @var{process}. @end defun @defun set-process-query-on-exit-flag process flag This function sets the query flag of @var{process} to @var{flag}. It returns @var{flag}. Here is an example of using @code{set-process-query-on-exit-flag} on a shell process to avoid querying: @smallexample @group (set-process-query-on-exit-flag (get-process "shell") nil) @result{} nil @end group @end smallexample @end defun @defopt confirm-kill-processes If this user option is set to @code{t} (the default), then Emacs asks for confirmation before killing processes on exit. If it is @code{nil}, Emacs kills processes without confirmation, i.e., the query flag of all processes is ignored. @end defopt @node System Processes @section Accessing Other Processes @cindex system processes In addition to accessing and manipulating processes that are subprocesses of the current Emacs session, Emacs Lisp programs can also access other processes running on the same machine. We call these @dfn{system processes}, to distinguish them from Emacs subprocesses. Emacs provides several primitives for accessing system processes. Not all platforms support these primitives; on those which don't, these primitives return @code{nil}. @defun list-system-processes This function returns a list of all the processes running on the system. Each process is identified by its @acronym{PID}, a numerical process ID that is assigned by the OS and distinguishes the process from all the other processes running on the same machine at the same time. @end defun @defun process-attributes pid This function returns an alist of attributes for the process specified by its process ID @var{pid}. Each association in the alist is of the form @code{(@var{key} . @var{value})}, where @var{key} designates the attribute and @var{value} is the value of that attribute. The various attribute @var{key}s that this function can return are listed below. Not all platforms support all of these attributes; if an attribute is not supported, its association will not appear in the returned alist. Values that are numbers can be either integer or floating point, depending on the magnitude of the value. @table @code @item euid The effective user ID of the user who invoked the process. The corresponding @var{value} is a number. If the process was invoked by the same user who runs the current Emacs session, the value is identical to what @code{user-uid} returns (@pxref{User Identification}). @item user User name corresponding to the process's effective user ID, a string. @item egid The group ID of the effective user ID, a number. @item group Group name corresponding to the effective user's group ID, a string. @item comm The name of the command that runs in the process. This is a string that usually specifies the name of the executable file of the process, without the leading directories. However, some special system processes can report strings that do not correspond to an executable file of a program. @item state The state code of the process. This is a short string that encodes the scheduling state of the process. Here's a list of the most frequently seen codes: @table @code @item "D" uninterruptible sleep (usually I/O) @item "R" running @item "S" interruptible sleep (waiting for some event) @item "T" stopped, e.g., by a job control signal @item "Z" zombie: a process that terminated, but was not reaped by its parent @end table @noindent For the full list of the possible states, see the manual page of the @command{ps} command. @item ppid The process ID of the parent process, a number. @item pgrp The process group ID of the process, a number. @item sess The session ID of the process. This is a number that is the process ID of the process's @dfn{session leader}. @item ttname A string that is the name of the process's controlling terminal. On Unix and GNU systems, this is normally the file name of the corresponding terminal device, such as @file{/dev/pts65}. @item tpgid The numerical process group ID of the foreground process group that uses the process's terminal. @item minflt The number of minor page faults caused by the process since its beginning. (Minor page faults are those that don't involve reading from disk.) @item majflt The number of major page faults caused by the process since its beginning. (Major page faults require a disk to be read, and are thus more expensive than minor page faults.) @item cminflt @itemx cmajflt Like @code{minflt} and @code{majflt}, but include the number of page faults for all the child processes of the given process. @item utime Time spent by the process in the user context, for running the application's code. The corresponding @var{value} is in the @w{@code{(@var{high} @var{low} @var{microsec} @var{picosec})}} format, the same format used by functions @code{current-time} (@pxref{Time of Day, current-time}) and @code{file-attributes} (@pxref{File Attributes}). @item stime Time spent by the process in the system (kernel) context, for processing system calls. The corresponding @var{value} is in the same format as for @code{utime}. @item time The sum of @code{utime} and @code{stime}. The corresponding @var{value} is in the same format as for @code{utime}. @item cutime @itemx cstime @itemx ctime Like @code{utime}, @code{stime}, and @code{time}, but include the times of all the child processes of the given process. @item pri The numerical priority of the process. @item nice The @dfn{nice value} of the process, a number. (Processes with smaller nice values get scheduled more favorably.) @item thcount The number of threads in the process. @item start The time when the process was started, in the same @code{(@var{high} @var{low} @var{microsec} @var{picosec})} format used by @code{file-attributes} and @code{current-time}. @item etime The time elapsed since the process started, in the format @code{(@var{high} @var{low} @var{microsec} @var{picosec})}. @item vsize The virtual memory size of the process, measured in kilobytes. @item rss The size of the process's @dfn{resident set}, the number of kilobytes occupied by the process in the machine's physical memory. @item pcpu The percentage of the CPU time used by the process since it started. The corresponding @var{value} is a floating-point number between 0 and 100. @item pmem The percentage of the total physical memory installed on the machine used by the process's resident set. The value is a floating-point number between 0 and 100. @item args The command-line with which the process was invoked. This is a string in which individual command-line arguments are separated by blanks; whitespace characters that are embedded in the arguments are quoted as appropriate for the system's shell: escaped by backslash characters on GNU and Unix, and enclosed in double quote characters on Windows. Thus, this command-line string can be directly used in primitives such as @code{shell-command}. @end table @end defun @node Transaction Queues @section Transaction Queues @cindex transaction queue @c That's not very informative. What is a transaction, and when might @c I want to use one? You can use a @dfn{transaction queue} to communicate with a subprocess using transactions. First use @code{tq-create} to create a transaction queue communicating with a specified process. Then you can call @code{tq-enqueue} to send a transaction. @defun tq-create process This function creates and returns a transaction queue communicating with @var{process}. The argument @var{process} should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server, possibly on another machine. @end defun @defun tq-enqueue queue question regexp closure fn &optional delay-question This function sends a transaction to queue @var{queue}. Specifying the queue has the effect of specifying the subprocess to talk to. The argument @var{question} is the outgoing message that starts the transaction. The argument @var{fn} is the function to call when the corresponding answer comes back; it is called with two arguments: @var{closure}, and the answer received. The argument @var{regexp} is a regular expression that should match text at the end of the entire answer, but nothing before; that's how @code{tq-enqueue} determines where the answer ends. If the argument @var{delay-question} is non-@code{nil}, delay sending this question until the process has finished replying to any previous questions. This produces more reliable results with some processes. @ignore @c Let's not mention it then. The return value of @code{tq-enqueue} itself is not meaningful. @end ignore @end defun @defun tq-close queue Shut down transaction queue @var{queue}, waiting for all pending transactions to complete, and then terminate the connection or child process. @end defun Transaction queues are implemented by means of a filter function. @xref{Filter Functions}. @node Network @section Network Connections @cindex network connection @cindex TCP @cindex UDP Emacs Lisp programs can open stream (TCP) and datagram (UDP) network connections (@pxref{Datagrams}) to other processes on the same machine or other machines. A network connection is handled by Lisp much like a subprocess, and is represented by a process object. However, the process you are communicating with is not a child of the Emacs process, has no process @acronym{ID}, and you can't kill it or send it signals. All you can do is send and receive data. @code{delete-process} closes the connection, but does not kill the program at the other end; that program must decide what to do about closure of the connection. Lisp programs can listen for connections by creating network servers. A network server is also represented by a kind of process object, but unlike a network connection, the network server never transfers data itself. When it receives a connection request, it creates a new network connection to represent the connection just made. (The network connection inherits certain information, including the process plist, from the server.) The network server then goes back to listening for more connection requests. Network connections and servers are created by calling @code{make-network-process} with an argument list consisting of keyword/argument pairs, for example @code{:server t} to create a server process, or @code{:type 'datagram} to create a datagram connection. @xref{Low-Level Network}, for details. You can also use the @code{open-network-stream} function described below. To distinguish the different types of processes, the @code{process-type} function returns the symbol @code{network} for a network connection or server, @code{serial} for a serial port connection, @code{pipe} for a pipe connection, or @code{real} for a real subprocess. The @code{process-status} function returns @code{open}, @code{closed}, @code{connect}, @code{stop}, or @code{failed} for network connections. For a network server, the status is always @code{listen}. Except for @code{stop}, none of those values is possible for a real subprocess. @xref{Process Information}. You can stop and resume operation of a network process by calling @code{stop-process} and @code{continue-process}. For a server process, being stopped means not accepting new connections. (Up to 5 connection requests will be queued for when you resume the server; you can increase this limit, unless it is imposed by the operating system---see the @code{:server} keyword of @code{make-network-process}, @ref{Network Processes}.) For a network stream connection, being stopped means not processing input (any arriving input waits until you resume the connection). For a datagram connection, some number of packets may be queued but input may be lost. You can use the function @code{process-command} to determine whether a network connection or server is stopped; a non-@code{nil} value means yes. @cindex network connection, encrypted @cindex encrypted network connections @cindex @acronym{TLS} network connections @cindex @acronym{STARTTLS} network connections Emacs can create encrypted network connections, using either built-in or external support. The built-in support uses the GnuTLS Transport Layer Security Library; see @uref{https://www.gnu.org/software/gnutls/, the GnuTLS project page}. If your Emacs was compiled with GnuTLS support, the function @code{gnutls-available-p} is defined and returns non-@code{nil}. For more details, @pxref{Top,, Overview, emacs-gnutls, The Emacs-GnuTLS manual}. The external support uses the @file{starttls.el} library, which requires a helper utility such as @command{gnutls-cli} to be installed on the system. The @code{open-network-stream} function can transparently handle the details of creating encrypted connections for you, using whatever support is available. @defun open-network-stream name buffer host service &rest parameters This function opens a TCP connection, with optional encryption, and returns a process object that represents the connection. The @var{name} argument specifies the name for the process object. It is modified as necessary to make it unique. The @var{buffer} argument is the buffer to associate with the connection. Output from the connection is inserted in the buffer, unless you specify your own filter function to handle the output. If @var{buffer} is @code{nil}, it means that the connection is not associated with any buffer. The arguments @var{host} and @var{service} specify where to connect to; @var{host} is the host name (a string), and @var{service} is the name of a defined network service (a string) or a port number (an integer like @code{80} or an integer string like @code{"80"}). The remaining arguments @var{parameters} are keyword/argument pairs that are mainly relevant to encrypted connections: @table @code @item :nowait @var{boolean} If non-@code{nil}, try to make an asynchronous connection. @item :type @var{type} The type of connection. Options are: @table @code @item plain An ordinary, unencrypted connection. @item tls @itemx ssl A @acronym{TLS} (Transport Layer Security) connection. @item nil @itemx network Start with a plain connection, and if parameters @samp{:success} and @samp{:capability-command} are supplied, try to upgrade to an encrypted connection via @acronym{STARTTLS}. If that fails, retain the unencrypted connection. @item starttls As for @code{nil}, but if @acronym{STARTTLS} fails drop the connection. @item shell A shell connection. @end table @item :always-query-capabilities @var{boolean} If non-@code{nil}, always ask for the server's capabilities, even when doing a @samp{plain} connection. @item :capability-command @var{capability-command} Command string to query the host capabilities. @item :end-of-command @var{regexp} @itemx :end-of-capability @var{regexp} Regular expression matching the end of a command, or the end of the command @var{capability-command}. The latter defaults to the former. @item :starttls-function @var{function} Function of one argument (the response to @var{capability-command}), which returns either @code{nil}, or the command to activate @acronym{STARTTLS} if supported. @item :success @var{regexp} Regular expression matching a successful @acronym{STARTTLS} negotiation. @item :use-starttls-if-possible @var{boolean} If non-@code{nil}, do opportunistic @acronym{STARTTLS} upgrades even if Emacs doesn't have built-in @acronym{TLS} support. @item :warn-unless-encrypted @var{boolean} If non-@code{nil}, and @code{:return-value} is also non-@code{nil}, Emacs will warn if the connection isn't encrypted. This is useful for protocols like @acronym{IMAP} and the like, where most users would expect the network traffic to be encrypted. @item :client-certificate @var{list-or-t} Either a list of the form @code{(@var{key-file} @var{cert-file})}, naming the certificate key file and certificate file itself, or @code{t}, meaning to query @code{auth-source} for this information (@pxref{Top,,Overview, auth, The Auth-Source Manual}). Only used for @acronym{TLS} or @acronym{STARTTLS}. @item :return-list @var{cons-or-nil} The return value of this function. If omitted or @code{nil}, return a process object. Otherwise, a cons of the form @code{(@var{process-object} . @var{plist})}, where @var{plist} has keywords: @table @code @item :greeting @var{string-or-nil} If non-@code{nil}, the greeting string returned by the host. @item :capabilities @var{string-or-nil} If non-@code{nil}, the host's capability string. @item :type @var{symbol} The connection type: @samp{plain} or @samp{tls}. @end table @item :shell-command @var{string-or-nil} If the connection @code{type} is @code{shell}, this parameter will be interpreted as a format-spec string that will be executed to make the connection. The specs available are @samp{%s} for the host name and @samp{%p} for the port number. For instance, if you want to first ssh to @samp{gateway} before making a plain connection, then this parameter could be something like @samp{ssh gateway nc %s %p}. @end table @end defun @node Network Servers @section Network Servers @cindex network servers You create a server by calling @code{make-network-process} (@pxref{Network Processes}) with @code{:server t}. The server will listen for connection requests from clients. When it accepts a client connection request, that creates a new network connection, itself a process object, with the following parameters: @itemize @bullet @item The connection's process name is constructed by concatenating the server process's @var{name} with a client identification string. The @c FIXME? What about IPv6? Say briefly what the difference is? client identification string for an IPv4 connection looks like @samp{<@var{a}.@var{b}.@var{c}.@var{d}:@var{p}>}, which represents an address and port number. Otherwise, it is a unique number in brackets, as in @samp{<@var{nnn}>}. The number is unique for each connection in the Emacs session. @item If the server has a non-default filter, the connection process does not get a separate process buffer; otherwise, Emacs creates a new buffer for the purpose. The buffer name is the server's buffer name or process name, concatenated with the client identification string. The server's process buffer value is never used directly, but the log function can retrieve it and use it to log connections by inserting text there. @item The communication type and the process filter and sentinel are inherited from those of the server. The server never directly uses its filter and sentinel; their sole purpose is to initialize connections made to the server. @item The connection's process contact information is set according to the client's addressing information (typically an IP address and a port number). This information is associated with the @code{process-contact} keywords @code{:host}, @code{:service}, @code{:remote}. @item The connection's local address is set up according to the port number used for the connection. @item The client process's plist is initialized from the server's plist. @end itemize @node Datagrams @section Datagrams @cindex datagrams A @dfn{datagram} connection communicates with individual packets rather than streams of data. Each call to @code{process-send} sends one datagram packet (@pxref{Input to Processes}), and each datagram received results in one call to the filter function. The datagram connection doesn't have to talk with the same remote peer all the time. It has a @dfn{remote peer address} which specifies where to send datagrams to. Each time an incoming datagram is passed to the filter function, the peer address is set to the address that datagram came from; that way, if the filter function sends a datagram, it will go back to that place. You can specify the remote peer address when you create the datagram connection using the @code{:remote} keyword. You can change it later on by calling @code{set-process-datagram-address}. @defun process-datagram-address process If @var{process} is a datagram connection or server, this function returns its remote peer address. @end defun @defun set-process-datagram-address process address If @var{process} is a datagram connection or server, this function sets its remote peer address to @var{address}. @end defun @node Low-Level Network @section Low-Level Network Access You can also create network connections by operating at a lower level than that of @code{open-network-stream}, using @code{make-network-process}. @menu * Proc: Network Processes. Using @code{make-network-process}. * Options: Network Options. Further control over network connections. * Features: Network Feature Testing. Determining which network features work on the machine you are using. @end menu @node Network Processes @subsection @code{make-network-process} The basic function for creating network connections and network servers is @code{make-network-process}. It can do either of those jobs, depending on the arguments you give it. @defun make-network-process &rest args This function creates a network connection or server and returns the process object that represents it. The arguments @var{args} are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value @code{nil}, except for @code{:coding}, @code{:filter-multibyte}, and @code{:reuseaddr}. Here are the meaningful keywords (those corresponding to network options are listed in the following section): @table @asis @item :name @var{name} Use the string @var{name} as the process name. It is modified if necessary to make it unique. @item :type @var{type} Specify the communication type. A value of @code{nil} specifies a stream connection (the default); @code{datagram} specifies a datagram connection; @code{seqpacket} specifies a sequenced packet stream connection. Both connections and servers can be of these types. @item :server @var{server-flag} If @var{server-flag} is non-@code{nil}, create a server. Otherwise, create a connection. For a stream type server, @var{server-flag} may be an integer, which then specifies the length of the queue of pending connections to the server. The default queue length is 5. @item :host @var{host} Specify the host to connect to. @var{host} should be a host name or Internet address, as a string, or the symbol @code{local} to specify the local host. If you specify @var{host} for a server, it must specify a valid address for the local host, and only clients connecting to that address will be accepted. @item :service @var{service} @var{service} specifies a port number to connect to; or, for a server, the port number to listen on. It should be a service name like @samp{"http"} that translates to a port number, or an integer like @samp{80} or an integer string like @samp{"80"} that specifies the port number directly. For a server, it can also be @code{t}, which means to let the system select an unused port number. @item :family @var{family} @var{family} specifies the address (and protocol) family for communication. @code{nil} means determine the proper address family automatically for the given @var{host} and @var{service}. @code{local} specifies a Unix socket, in which case @var{host} is ignored. @code{ipv4} and @code{ipv6} specify to use IPv4 and IPv6, respectively. @item :use-external-socket @var{use-external-socket} If @var{use-external-socket} is non-@code{nil} use any sockets passed to Emacs on invocation instead of allocating one. This is used by the Emacs server code to allow on-demand socket activation. If Emacs wasn't passed a socket, this option is silently ignored. @item :local @var{local-address} For a server process, @var{local-address} is the address to listen on. It overrides @var{family}, @var{host} and @var{service}, so you might as well not specify them. @item :remote @var{remote-address} For a connection, @var{remote-address} is the address to connect to. It overrides @var{family}, @var{host} and @var{service}, so you might as well not specify them. For a datagram server, @var{remote-address} specifies the initial setting of the remote datagram address. The format of @var{local-address} or @var{remote-address} depends on the address family: @itemize - @item An IPv4 address is represented as a five-element vector of four 8-bit integers and one 16-bit integer @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]} corresponding to numeric IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port number @var{p}. @item An IPv6 address is represented as a nine-element vector of 16-bit integers @code{[@var{a} @var{b} @var{c} @var{d} @var{e} @var{f} @var{g} @var{h} @var{p}]} corresponding to numeric IPv6 address @var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h} and port number @var{p}. @item A local address is represented as a string, which specifies the address in the local address space. @item An unsupported-family address is represented by a cons @code{(@var{f} . @var{av})}, where @var{f} is the family number and @var{av} is a vector specifying the socket address using one element per address data byte. Do not rely on this format in portable code, as it may depend on implementation defined constants, data sizes, and data structure alignment. @end itemize @item :nowait @var{bool} If @var{bool} is non-@code{nil} for a stream connection, return without waiting for the connection to complete. When the connection succeeds or fails, Emacs will call the sentinel function, with a second argument matching @code{"open"} (if successful) or @code{"failed"}. The default is to block, so that @code{make-network-process} does not return until the connection has succeeded or failed. If you're setting up an asynchronous TLS connection, you have to also provide the @code{:tls-parameters} parameter (see below). Depending on the capabilities of Emacs, how asynchronous @code{:nowait} is may vary. The three elements that may (or may not) be done asynchronously are domain name resolution, socket setup, and (for TLS connections) TLS negotiation. Many functions that interact with process objects, (for instance, @code{process-datagram-address}) rely on them at least having a socket before they can return a useful value. These functions will block until the socket has achieved the desired status. The recommended way of interacting with asynchronous sockets is to place a sentinel on the process, and not try to interact with it before it has changed status to @samp{"run"}. That way, none of these functions will block. @item :tls-parameters When opening a TLS connection, this should be where the first element is the TLS type (which should either be @code{gnutls-x509pki} or @code{gnutls-anon}, and the remaining elements should form a keyword list acceptable for @code{gnutls-boot}. (This keyword list can be obtained from the @code{gnutls-boot-parameters} function.) The TLS connection will then be negotiated after completing the connection to the host. @item :stop @var{stopped} If @var{stopped} is non-@code{nil}, start the network connection or server in the stopped state. @item :buffer @var{buffer} Use @var{buffer} as the process buffer. @item :coding @var{coding} Use @var{coding} as the coding system for this process. To specify different coding systems for decoding data from the connection and for encoding data sent to it, specify @code{(@var{decoding} . @var{encoding})} for @var{coding}. If you don't specify this keyword at all, the default is to determine the coding systems from the data. @item :noquery @var{query-flag} Initialize the process query flag to @var{query-flag}. @xref{Query Before Exit}. @item :filter @var{filter} Initialize the process filter to @var{filter}. @item :filter-multibyte @var{multibyte} If @var{multibyte} is non-@code{nil}, strings given to the process filter are multibyte, otherwise they are unibyte. The default is @code{t}. @item :sentinel @var{sentinel} Initialize the process sentinel to @var{sentinel}. @item :log @var{log} Initialize the log function of a server process to @var{log}. The log function is called each time the server accepts a network connection from a client. The arguments passed to the log function are @var{server}, @var{connection}, and @var{message}; where @var{server} is the server process, @var{connection} is the new process for the connection, and @var{message} is a string describing what has happened. @item :plist @var{plist} Initialize the process plist to @var{plist}. @end table The original argument list, modified with the actual connection information, is available via the @code{process-contact} function. @end defun @node Network Options @subsection Network Options The following network options can be specified when you create a network process. Except for @code{:reuseaddr}, you can also set or modify these options later, using @code{set-network-process-option}. For a server process, the options specified with @code{make-network-process} are not inherited by the client connections, so you will need to set the necessary options for each child connection as it is created. @table @asis @item :bindtodevice @var{device-name} If @var{device-name} is a non-empty string identifying a network interface name (see @code{network-interface-list}), only handle packets received on that interface. If @var{device-name} is @code{nil} (the default), handle packets received on any interface. Using this option may require special privileges on some systems. @item :broadcast @var{broadcast-flag} If @var{broadcast-flag} is non-@code{nil} for a datagram process, the process will receive datagram packet sent to a broadcast address, and be able to send packets to a broadcast address. This is ignored for a stream connection. @item :dontroute @var{dontroute-flag} If @var{dontroute-flag} is non-@code{nil}, the process can only send to hosts on the same network as the local host. @item :keepalive @var{keepalive-flag} If @var{keepalive-flag} is non-@code{nil} for a stream connection, enable exchange of low-level keep-alive messages. @item :linger @var{linger-arg} If @var{linger-arg} is non-@code{nil}, wait for successful transmission of all queued packets on the connection before it is deleted (see @code{delete-process}). If @var{linger-arg} is an integer, it specifies the maximum time in seconds to wait for queued packets to be sent before closing the connection. The default is @code{nil}, which means to discard unsent queued packets when the process is deleted. @c FIXME Where out-of-band data is ...? @item :oobinline @var{oobinline-flag} If @var{oobinline-flag} is non-@code{nil} for a stream connection, receive out-of-band data in the normal data stream. Otherwise, ignore out-of-band data. @item :priority @var{priority} Set the priority for packets sent on this connection to the integer @var{priority}. The interpretation of this number is protocol specific; such as setting the TOS (type of service) field on IP packets sent on this connection. It may also have system dependent effects, such as selecting a specific output queue on the network interface. @item :reuseaddr @var{reuseaddr-flag} If @var{reuseaddr-flag} is non-@code{nil} (the default) for a stream server process, allow this server to reuse a specific port number (see @code{:service}), unless another process on this host is already listening on that port. If @var{reuseaddr-flag} is @code{nil}, there may be a period of time after the last use of that port (by any process on the host) where it is not possible to make a new server on that port. @end table @defun set-network-process-option process option value &optional no-error This function sets or modifies a network option for network process @var{process}. The accepted options and values are as for @code{make-network-process}. If @var{no-error} is non-@code{nil}, this function returns @code{nil} instead of signaling an error if @var{option} is not a supported option. If the function successfully completes, it returns @code{t}. The current setting of an option is available via the @code{process-contact} function. @end defun @node Network Feature Testing @subsection Testing Availability of Network Features To test for the availability of a given network feature, use @code{featurep} like this: @example (featurep 'make-network-process '(@var{keyword} @var{value})) @end example @noindent The result of this form is @code{t} if it works to specify @var{keyword} with value @var{value} in @code{make-network-process}. Here are some of the @var{keyword}---@var{value} pairs you can test in this way. @table @code @item (:nowait t) Non-@code{nil} if non-blocking connect is supported. @item (:type datagram) Non-@code{nil} if datagrams are supported. @item (:family local) Non-@code{nil} if local (a.k.a.@: ``UNIX domain'') sockets are supported. @item (:family ipv6) Non-@code{nil} if IPv6 is supported. @item (:service t) Non-@code{nil} if the system can select the port for a server. @end table To test for the availability of a given network option, use @code{featurep} like this: @example (featurep 'make-network-process '@var{keyword}) @end example @noindent The accepted @var{keyword} values are @code{:bindtodevice}, etc. For the complete list, @pxref{Network Options}. This form returns non-@code{nil} if that particular network option is supported by @code{make-network-process} (or @code{set-network-process-option}). @node Misc Network @section Misc Network Facilities These additional functions are useful for creating and operating on network connections. Note that they are supported only on some systems. @defun network-interface-list This function returns a list describing the network interfaces of the machine you are using. The value is an alist whose elements have the form @code{(@var{name} . @var{address})}. @var{address} has the same form as the @var{local-address} and @var{remote-address} arguments to @code{make-network-process}. @end defun @defun network-interface-info ifname This function returns information about the network interface named @var{ifname}. The value is a list of the form @code{(@var{addr} @var{bcast} @var{netmask} @var{hwaddr} @var{flags})}. @table @var @item addr The Internet protocol address. @item bcast The broadcast address. @item netmask The network mask. @item hwaddr The layer 2 address (Ethernet MAC address, for instance). @item flags The current flags of the interface. @end table @end defun @defun format-network-address address &optional omit-port This function converts the Lisp representation of a network address to a string. A five-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]} represents an IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port number @var{p}. @code{format-network-address} converts that to the string @code{"@var{a}.@var{b}.@var{c}.@var{d}:@var{p}"}. A nine-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{e} @var{f} @var{g} @var{h} @var{p}]} represents an IPv6 address along with a port number. @code{format-network-address} converts that to the string @code{"[@var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h}]:@var{p}"}. If the vector does not include the port number, @var{p}, or if @var{omit-port} is non-@code{nil}, the result does not include the @code{:@var{p}} suffix. @end defun @defun network-lookup-address-info name &optional family This function is used to perform hostname lookups on @var{name}, which is expected to be an ASCII-only string, otherwise an error is signaled. Call @code{puny-encode-domain} on @var{name} first if you wish to lookup internationalized hostnames. If successful it returns a list of Lisp representations of network addresses (without port numbers), otherwise it returns @code{nil}. By default both IPv4 and IPv6 lookups are attempted. The optional argument @var{family} controls this behavior, specifying the symbol @code{ipv4} or @code{ipv6} restricts lookups to IPv4 and IPv6 respectively. @end defun @node Serial Ports @section Communicating with Serial Ports @cindex @file{/dev/tty} @cindex @file{COM1} @cindex serial connections Emacs can communicate with serial ports. For interactive use, @kbd{M-x serial-term} opens a terminal window. In a Lisp program, @code{make-serial-process} creates a process object. The serial port can be configured at run-time, without having to close and re-open it. The function @code{serial-process-configure} lets you change the speed, bytesize, and other parameters. In a terminal window created by @code{serial-term}, you can click on the mode line for configuration. A serial connection is represented by a process object, which can be used in a similar way to a subprocess or network process. You can send and receive data, and configure the serial port. A serial process object has no process ID, however, and you can't send signals to it, and the status codes are different from other types of processes. @code{delete-process} on the process object or @code{kill-buffer} on the process buffer close the connection, but this does not affect the device connected to the serial port. The function @code{process-type} returns the symbol @code{serial} for a process object representing a serial port connection. Serial ports are available on GNU/Linux, Unix, and MS Windows systems. @deffn Command serial-term port speed Start a terminal-emulator for a serial port in a new buffer. @var{port} is the name of the serial port to connect to. For example, this could be @file{/dev/ttyS0} on Unix. On MS Windows, this could be @file{COM1}, or @file{\\.\COM10} (double the backslashes in Lisp strings). @c FIXME is 9600 still the most common value, or is it 115200 now? @c (Same value, 9600, appears below as well.) @var{speed} is the speed of the serial port in bits per second. 9600 is a common value. The buffer is in Term mode; see @ref{Term Mode,,, emacs, The GNU Emacs Manual}, for the commands to use in that buffer. You can change the speed and the configuration in the mode line menu. @end deffn @defun make-serial-process &rest args This function creates a process and a buffer. Arguments are specified as keyword/argument pairs. Here's the list of the meaningful keywords, with the first two (@var{port} and @var{speed}) being mandatory: @table @code @item :port @var{port} This is the name of the serial port. On Unix and GNU systems, this is a file name such as @file{/dev/ttyS0}. On Windows, this could be @file{COM1}, or @file{\\.\COM10} for ports higher than @file{COM9} (double the backslashes in Lisp strings). @item :speed @var{speed} The speed of the serial port in bits per second. This function calls @code{serial-process-configure} to handle the speed; see the following documentation of that function for more details. @item :name @var{name} The name of the process. If @var{name} is not given, @var{port} will serve as the process name as well. @item :buffer @var{buffer} The buffer to associate with the process. The value can be either a buffer or a string that names a buffer. Process output goes at the end of that buffer, unless you specify an output stream or filter function to handle the output. If @var{buffer} is not given, the process buffer's name is taken from the value of the @code{:name} keyword. @item :coding @var{coding} If @var{coding} is a symbol, it specifies the coding system used for both reading and writing for this process. If @var{coding} is a cons @code{(@var{decoding} . @var{encoding})}, @var{decoding} is used for reading, and @var{encoding} is used for writing. If not specified, the default is to determine the coding systems from the data itself. @item :noquery @var{query-flag} Initialize the process query flag to @var{query-flag}. @xref{Query Before Exit}. The flags defaults to @code{nil} if unspecified. @item :stop @var{bool} Start process in the stopped state if @var{bool} is non-@code{nil}. In the stopped state, a serial process does not accept incoming data, but you can send outgoing data. The stopped state is cleared by @code{continue-process} and set by @code{stop-process}. @item :filter @var{filter} Install @var{filter} as the process filter. @item :sentinel @var{sentinel} Install @var{sentinel} as the process sentinel. @item :plist @var{plist} Install @var{plist} as the initial plist of the process. @item :bytesize @itemx :parity @itemx :stopbits @itemx :flowcontrol These are handled by @code{serial-process-configure}, which is called by @code{make-serial-process}. @end table The original argument list, possibly modified by later configuration, is available via the function @code{process-contact}. Here is an example: @example (make-serial-process :port "/dev/ttyS0" :speed 9600) @end example @end defun @defun serial-process-configure &rest args @cindex baud, in serial connections @cindex bytesize, in serial connections @cindex parity, in serial connections @cindex stopbits, in serial connections @cindex flowcontrol, in serial connections This function configures a serial port connection. Arguments are specified as keyword/argument pairs. Attributes that are not given are re-initialized from the process's current configuration (available via the function @code{process-contact}), or set to reasonable default values. The following arguments are defined: @table @code @item :process @var{process} @itemx :name @var{name} @itemx :buffer @var{buffer} @itemx :port @var{port} Any of these arguments can be given to identify the process that is to be configured. If none of these arguments is given, the current buffer's process is used. @item :speed @var{speed} The speed of the serial port in bits per second, a.k.a.@: @dfn{baud rate}. The value can be any number, but most serial ports work only at a few defined values between 1200 and 115200, with 9600 being the most common value. If @var{speed} is @code{nil}, the function ignores all other arguments and does not configure the port. This may be useful for special serial ports such as Bluetooth-to-serial converters, which can only be configured through @samp{AT} commands sent through the connection. The value of @code{nil} for @var{speed} is valid only for connections that were already opened by a previous call to @code{make-serial-process} or @code{serial-term}. @item :bytesize @var{bytesize} The number of bits per byte, which can be 7 or 8. If @var{bytesize} is not given or @code{nil}, it defaults to 8. @item :parity @var{parity} The value can be @code{nil} (don't use parity), the symbol @code{odd} (use odd parity), or the symbol @code{even} (use even parity). If @var{parity} is not given, it defaults to no parity. @item :stopbits @var{stopbits} The number of stopbits used to terminate a transmission of each byte. @var{stopbits} can be 1 or 2. If @var{stopbits} is not given or @code{nil}, it defaults to 1. @item :flowcontrol @var{flowcontrol} The type of flow control to use for this connection, which is either @code{nil} (don't use flow control), the symbol @code{hw} (use RTS/CTS hardware flow control), or the symbol @code{sw} (use XON/XOFF software flow control). If @var{flowcontrol} is not given, it defaults to no flow control. @end table Internally, @code{make-serial-process} calls @code{serial-process-configure} for the initial configuration of the serial port. @end defun @node Byte Packing @section Packing and Unpacking Byte Arrays @cindex byte packing and unpacking This section describes how to pack and unpack arrays of bytes, usually for binary network protocols. These functions convert byte arrays to alists, and vice versa. The byte array can be represented as a @c FIXME? No multibyte? unibyte string or as a vector of integers, while the alist associates symbols either with fixed-size objects or with recursive sub-alists. To use the functions referred to in this section, load the @code{bindat} library. @c It doesn't have any autoloads. @cindex serializing @cindex deserializing @cindex packing @cindex unpacking Conversion from byte arrays to nested alists is also known as @dfn{deserializing} or @dfn{unpacking}, while going in the opposite direction is also known as @dfn{serializing} or @dfn{packing}. @menu * Bindat Spec:: Describing data layout. * Bindat Functions:: Doing the unpacking and packing. * Bindat Examples:: Samples of what bindat.el can do for you! @end menu @node Bindat Spec @subsection Describing Data Layout To control unpacking and packing, you write a @dfn{data layout specification}, a special nested list describing named and typed @dfn{fields}. This specification controls the length of each field to be processed, and how to pack or unpack it. We normally keep bindat specs in variables whose names end in @samp{-bindat-spec}; that kind of name is automatically recognized as risky. @cindex endianness @cindex big endian @cindex little endian @cindex network byte ordering A field's @dfn{type} describes the size (in bytes) of the object that the field represents and, in the case of multibyte fields, how the bytes are ordered within the field. The two possible orderings are @dfn{big endian} (also known as ``network byte ordering'') and @dfn{little endian}. For instance, the number @code{#x23cd} (decimal 9165) in big endian would be the two bytes @code{#x23} @code{#xcd}; and in little endian, @code{#xcd} @code{#x23}. Here are the possible type values: @table @code @item u8 @itemx byte Unsigned byte, with length 1. @item u16 @itemx word @itemx short Unsigned integer in network byte order, with length 2. @item u24 Unsigned integer in network byte order, with length 3. @item u32 @itemx dword @itemx long Unsigned integer in network byte order, with length 4. Note: These values may be limited by Emacs's integer implementation limits. @item u16r @itemx u24r @itemx u32r Unsigned integer in little endian order, with length 2, 3 and 4, respectively. @item str @var{len} String of length @var{len}. @item strz @var{len} Zero-terminated string, in a fixed-size field with length @var{len}. @item vec @var{len} [@var{type}] Vector of @var{len} elements of type @var{type}, defaulting to bytes. The @var{type} is any of the simple types above, or another vector specified as a list of the form @code{(vec @var{len} [@var{type}])}. @item ip @c FIXME? IPv6? Four-byte vector representing an Internet address. For example: @code{[127 0 0 1]} for localhost. @item bits @var{len} List of set bits in @var{len} bytes. The bytes are taken in big endian order and the bits are numbered starting with @code{8 * @var{len} @minus{} 1} and ending with zero. For example: @code{bits 2} unpacks @code{#x28} @code{#x1c} to @code{(2 3 4 11 13)} and @code{#x1c} @code{#x28} to @code{(3 5 10 11 12)}. @item (eval @var{form}) @var{form} is a Lisp expression evaluated at the moment the field is unpacked or packed. The result of the evaluation should be one of the above-listed type specifications. @end table For a fixed-size field, the length @var{len} is given as an integer specifying the number of bytes in the field. When the length of a field is not fixed, it typically depends on the value of a preceding field. In this case, the length @var{len} can be given either as a list @code{(@var{name} ...)} identifying a @dfn{field name} in the format specified for @code{bindat-get-field} below, or by an expression @code{(eval @var{form})} where @var{form} should evaluate to an integer, specifying the field length. A field specification generally has the form @code{([@var{name}] @var{handler})}, where @var{name} is optional. Don't use names that are symbols meaningful as type specifications (above) or handler specifications (below), since that would be ambiguous. @var{name} can be a symbol or an expression @code{(eval @var{form})}, in which case @var{form} should evaluate to a symbol. @var{handler} describes how to unpack or pack the field and can be one of the following: @table @code @item @var{type} Unpack/pack this field according to the type specification @var{type}. @item eval @var{form} Evaluate @var{form}, a Lisp expression, for side-effect only. If the field name is specified, the value is bound to that field name. @item fill @var{len} Skip @var{len} bytes. In packing, this leaves them unchanged, which normally means they remain zero. In unpacking, this means they are ignored. @item align @var{len} Skip to the next multiple of @var{len} bytes. @item struct @var{spec-name} Process @var{spec-name} as a sub-specification. This describes a structure nested within another structure. @item union @var{form} (@var{tag} @var{spec})@dots{} @c ??? I don't see how one would actually use this. @c ??? what kind of expression would be useful for @var{form}? Evaluate @var{form}, a Lisp expression, find the first @var{tag} that matches it, and process its associated data layout specification @var{spec}. Matching can occur in one of three ways: @itemize @item If a @var{tag} has the form @code{(eval @var{expr})}, evaluate @var{expr} with the variable @code{tag} dynamically bound to the value of @var{form}. A non-@code{nil} result indicates a match. @item @var{tag} matches if it is @code{equal} to the value of @var{form}. @item @var{tag} matches unconditionally if it is @code{t}. @end itemize @item repeat @var{count} @var{field-specs}@dots{} Process the @var{field-specs} recursively, in order, then repeat starting from the first one, processing all the specifications @var{count} times overall. The @var{count} is given using the same formats as a field length---if an @code{eval} form is used, it is evaluated just once. For correct operation, each specification in @var{field-specs} must include a name. @end table For the @code{(eval @var{form})} forms used in a bindat specification, the @var{form} can access and update these dynamically bound variables during evaluation: @table @code @item last Value of the last field processed. @item bindat-raw The data as a byte array. @item bindat-idx Current index (within @code{bindat-raw}) for unpacking or packing. @item struct The alist containing the structured data that have been unpacked so far, or the entire structure being packed. You can use @code{bindat-get-field} to access specific fields of this structure. @item count @itemx index Inside a @code{repeat} block, these contain the maximum number of repetitions (as specified by the @var{count} parameter), and the current repetition number (counting from 0). Setting @code{count} to zero will terminate the inner-most repeat block after the current repetition has completed. @end table @node Bindat Functions @subsection Functions to Unpack and Pack Bytes In the following documentation, @var{spec} refers to a data layout specification, @code{bindat-raw} to a byte array, and @var{struct} to an alist representing unpacked field data. @defun bindat-unpack spec bindat-raw &optional bindat-idx @c FIXME? Again, no multibyte? This function unpacks data from the unibyte string or byte array @code{bindat-raw} according to @var{spec}. Normally, this starts unpacking at the beginning of the byte array, but if @var{bindat-idx} is non-@code{nil}, it specifies a zero-based starting position to use instead. The value is an alist or nested alist in which each element describes one unpacked field. @end defun @defun bindat-get-field struct &rest name This function selects a field's data from the nested alist @var{struct}. Usually @var{struct} was returned by @code{bindat-unpack}. If @var{name} corresponds to just one argument, that means to extract a top-level field value. Multiple @var{name} arguments specify repeated lookup of sub-structures. An integer name acts as an array index. For example, if @var{name} is @code{(a b 2 c)}, that means to find field @code{c} in the third element of subfield @code{b} of field @code{a}. (This corresponds to @code{struct.a.b[2].c} in C.) @end defun Although packing and unpacking operations change the organization of data (in memory), they preserve the data's @dfn{total length}, which is the sum of all the fields' lengths, in bytes. This value is not generally inherent in either the specification or alist alone; instead, both pieces of information contribute to its calculation. Likewise, the length of a string or array being unpacked may be longer than the data's total length as described by the specification. @defun bindat-length spec struct This function returns the total length of the data in @var{struct}, according to @var{spec}. @end defun @defun bindat-pack spec struct &optional bindat-raw bindat-idx This function returns a byte array packed according to @var{spec} from the data in the alist @var{struct}. It normally creates and fills a new byte array starting at the beginning. However, if @var{bindat-raw} is non-@code{nil}, it specifies a pre-allocated unibyte string or vector to pack into. If @var{bindat-idx} is non-@code{nil}, it specifies the starting offset for packing into @code{bindat-raw}. When pre-allocating, you should make sure @code{(length @var{bindat-raw})} meets or exceeds the total length to avoid an out-of-range error. @end defun @defun bindat-ip-to-string ip Convert the Internet address vector @var{ip} to a string in the usual dotted notation. @c FIXME? Does it do IPv6? @example (bindat-ip-to-string [127 0 0 1]) @result{} "127.0.0.1" @end example @end defun @node Bindat Examples @subsection Examples of Byte Unpacking and Packing @c FIXME? This seems a very long example for something that is not used @c very often. As of 25.2, gdb-mi.el is the only user of bindat.el in Emacs. @c Maybe one or both of these examples should just be moved to the @c commentary of bindat.el. Here are two complete examples that use bindat.el. The first shows simple byte packing: @lisp (require 'bindat) (defun rfc868-payload () (bindat-pack '((now-hi u16) (now-lo u16)) ;; Emacs uses Unix epoch, while RFC868 epoch ;; is 1900-01-01 00:00:00, which is 2208988800 ;; (or #x83aa7e80) seconds more. (let ((now (time-add nil '(#x83aa #x7e80)))) `((now-hi . ,(car now)) (now-lo . ,(cadr now)))))) (let ((s (rfc868-payload))) (list (multibyte-string-p s) (mapconcat (lambda (byte) (format "%02x" byte)) s " ") (current-time-string))) @result{} (nil "dc 6d 17 01" "Fri Mar 10 13:13:53 2017") @end lisp The following is an example of defining and unpacking a complex structure. Consider the following C structures: @example struct header @{ unsigned long dest_ip; unsigned long src_ip; unsigned short dest_port; unsigned short src_port; @}; struct data @{ unsigned char type; unsigned char opcode; unsigned short length; /* in network byte order */ unsigned char id[8]; /* null-terminated string */ unsigned char data[/* (length + 3) & ~3 */]; @}; struct packet @{ struct header header; unsigned long counters[2]; /* in little endian order */ unsigned char items; unsigned char filler[3]; struct data item[/* items */]; @}; @end example The corresponding data layout specification is: @lisp (setq header-spec '((dest-ip ip) (src-ip ip) (dest-port u16) (src-port u16))) (setq data-spec '((type u8) (opcode u8) (length u16) ; network byte order (id strz 8) (data vec (length)) (align 4))) (setq packet-spec '((header struct header-spec) (counters vec 2 u32r) ; little endian order (items u8) (fill 3) (item repeat (items) (struct data-spec)))) @end lisp A binary data representation is: @lisp (setq binary-data [ 192 168 1 100 192 168 1 101 01 28 21 32 160 134 1 0 5 1 0 0 2 0 0 0 2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0 1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ]) @end lisp The corresponding decoded structure is: @lisp (setq decoded (bindat-unpack packet-spec binary-data)) @result{} ((header (dest-ip . [192 168 1 100]) (src-ip . [192 168 1 101]) (dest-port . 284) (src-port . 5408)) (counters . [100000 261]) (items . 2) (item ((data . [1 2 3 4 5]) (id . "ABCDEF") (length . 5) (opcode . 3) (type . 2)) ((data . [6 7 8 9 10 11 12]) (id . "BCDEFG") (length . 7) (opcode . 4) (type . 1)))) @end lisp An example of fetching data from this structure: @lisp (bindat-get-field decoded 'item 1 'id) @result{} "BCDEFG" @end lisp