path: root/HACKING

==========
COMMITTING
==========

Do NOT commit to this module without permission from a maintainer.
See epiphany.doap for who they are.


==========
CODE STYLE
==========

In order to keep the code nice and clean we have a few requirements you'll
need to stick to in order to get your patch accepted:

- Use 2-space no-tabs for indentation (mandatory on new files, old
  ones will be re-indented eventually. When modifying an existing file
  with 8-space indentation keep the old style please).

- Use K&R style for the braces.

- No braces for one line control clauses.

- Callback functions have a suffix _cb.

- All files have to be encoded in UTF-8.

- Use char/int/double/..., not gchar/gint/gdouble/... types.

- All implementation files must include first "config.h", followed by
  the primary header, followed by a blank line, followed by all the
  local headers sorted alphabetically, followed by a blank line,
  followed by all the system headers sorted alphabetically.

  Headers should follow the same pattern excluding the config.h and
  self file section, for obvious reasons.

- Make comments full sentences. This means proper capitalization and
  punctuation.

- data/kr-gnome-indent.cfg is provided as a reference config file for the
  uncrustify program to get correct indentation in new files.

- There's no space between a type cast and the variable name.

  Right: (int *)foo
  Wrong: (int*) foo


===================
CODE STRUCTURE TIPS
===================

LAYERING
========

The code is currently structured into layers, where higher-level layers have
full access to lower-level layers, but lower-level layers have no access to the
higher layers except via delegate objects. (See EphyEmbedContainer for an
example of a delegate interface that allows embed/ limited access to EphyWindow,
even though EphyWindow is in src/.) The levels are:

 * src/ <-- highest layer, mostly GUI stuff.
 * lib/widgets/ <-- FIXME: very confusing, this layering should be fixed
 * embed/ <-- stuff relating to the web view
 * lib/ <-- lowest layer, helper classes that don't need higher-level stuff

The build system enforces that higher-level layers are not in the include path
of lower-level layers, so you should not be able to break the layering unless
you go out of your way to do so.

GTK APPLICATION AND EPHY SHELL
==============================

Epiphany has one singleton EphyShell object. Its inheritance hierarchy is:

 - GApplication
 --- GtkApplication
 ----- EphyEmbedShell
 ------- EphyShell

There is exactly one instance of EphyShell, and it is also the EphyEmbedShell
and the GtkApplication. Use normal GObject casts to get a pointer to the type
you need.

EphyShell is a singleton object where we put all our global state, so it's kind
of like having a global variable, but more organized. You can access it from
anywhere in src/ using ephy_shell_get_default().

EphyEmbedShell is a separate class from EphyShell for layering purposes. It is
accessible anywhere from embed/ or src/. So if you have global stuff that you
need to access from embed/, you need to put it in EphyEmbedShell, not EphyShell.

IMPORTANT EPIPHANY OBJECTS
==========================

EphyWindow is a subclass of GtkApplicationWindow, which is a subclass of
GtkWindow. It's the window. You can have any number of windows open at a time.
EphyWindow contains (a) an EphyHeaderBar (subclass of GtkHeaderBar), and (b) an
EphyNotebook (subclass of GtkNotebook). EphyNotebook contains one or more tabs,
and each tab is an EphyEmbed. That's worth repeating: an EphyEmbed corresponds
to one browser tab. Each EphyEmbed contains an EphyWebView (subclass of
WebKitWebView). This is the object that actually displays the web page, where
all the web browser magic happens.

IMPORTANT WEBKITGTK+ OBJECTS
============================

WebKitGTK+ is a WebKit port that provides a GTK+ API wrapper around WebKit.

WebKit is really nice. It encapsulates 95% of the complexity of building a web
browser, like the JavaScript engine, HTML layout engine, and actually rendering
the webpage. Epiphany only has to deal with the remaining 5%. The most important
WebKitGTK+ objects are:

 * WebKitWebView (superclass of EphyWebView). Displays the web.
 * WebKitWebContext, a global object that manages shared state among web views.

Epiphany has one EphyWebView per browser tab. It has exactly one
WebKitWebContext, stored by EphyEmbedShell. WARNING: you need to be careful to
use the web context from EphyEmbedShell when using a WebKit API that expects a
WebKitWebContext. Do not use WebKit's default WebKitWebContext; that is, do not
pass NULL to any WebKitWebContext* parameter, and do not use
webkit_web_context_get_default().

WebKitGTK+ API documentation can be found at:

 https://webkitgtk.org/reference/webkit2gtk/unstable/index.html

There is separate documentation for the DOM API:

  https://webkitgtk.org/reference/webkitdomgtk/unstable/index.html

WEBKIT2 PROCESS ARCHITECTURE
============================

WebKit2 has a multiprocess architecture to improve the robustness of the
browser. The UI process (the main epiphany process) runs several subprocesses:

 * Any number of WebKitWebProcesses, which handle rendering web content
 * One WebKitNetworkProcess, which handles most network requests
 * One or zero WebKitDatabaseProcesses, which handles IndexedDB

In WebKitGTK+, by default each WebKitWebView shares the same WebKitWebProcess.
This can reduce overall resource usage, but it results in a less-stable browser
as a crash in one tab will crash all other tabs, and the effects of memory leaks
are greatly amplified. So Epiphany runs a separate WebKitWebProcess for each
browser tab. (This is almost true. Sometimes a tab will create another tab using
JavaScript. In such cases, the web views are "related" and share the same
WebKitWebProcess.) There is a GSettings option to switch back to single-process
mode if required, but we do not claim to support this!

Epiphany uses GtkApplication to ensure uniqueness, so you usually only have one
UI process running at a time. An exception is if you use incognito mode, or
private profile mode (which is only available from the command line). In such
cases, there is no shared state with the main Epiphany browser process.

EPIPHANY WEB EXTENSION
======================

For some Epiphany features, we need to run code in the web process. This code is
called the "web extension" and lives in embed/web-extension/. It is compiled
into a shared library libephywebextension.so and installed in $(pkglibdir) (e.g.
/usr/lib64/epiphany). EphyEmbedShell tells WebKit to look for web extensions
in that location using webkit_web_context_set_web_extensions_directory(), starts
a private D-Bus server (a D-Bus server that is completely separate from the
shared system and session busses), and advertises the address of its D-Bus
server to the web extension by passing it in a GVariant parameter to
webkit_web_context_set_web_extensions_initialization_user_data(). Now the
Epiphany UI process and web extension can communicate back and forth via D-Bus.
EphyWebExtensionProxy encapsulates this IPC in the UI process; EphyEmbedShell
uses it to communicate with the web process.

Epiphany uses script message handlers as an additional form of IPC besides
D-Bus. This allows the web extension to send a WebKitJavascriptResult directly
to the UI process, which is received in EphyEmbedShell. This should generally
be used rather than D-Bus when you need to send a message from the web process
to the UI process.

=========
DEBUGGING
=========

To enable debugging use the configure option --enable-debug.

LOGGING
=======

At execution time, you must enable the log service. To enable the
log service, set the environment variable: EPHY_LOG_MODULES

EPHY_LOG_MODULES variable has the form:

	<moduleName>[:<moduleName>]*

moduleName is a filename.
ex: export EPHY_LOG_MODULES=ephy-window.c:ephy-autocompletion.c
The special log module "all" enables all log modules.

Use the LOG macro to put debug messages in the code.

WARNINGS
========

At execution time, you must enable the service. To enable you to debug
warnings, set the environment variable: EPHY_DEBUG_BREAK

Possible value for EPHY_DEBUG_BREAK variable:

	stack		Prints a stack trace.

	suspend		Use this to stop execution when a warning occurs.
			You can then attach a debugger to the process.

	trap		Use this while running epiphany in a debugger.
			This makes execution stop and gives back control to
			the debugger.


PROFILING
=========

At execution time, you must enable the profiling service. To enable the
profiling service, set the environment variable: EPHY_PROFILING_MODULES

EPHY_PROFILE_MODULES variable has the form:

	<moduleName>[:<moduleName>]*

moduleName is a filename.
ex: export EPHY_PROFILE_MODULES=ephy-window.c:ephy-autocompletion.c
The special profiling module "all" enables all profiling modules.

Use START_PROFILER STOP_PROFILER macros to profile pieces of code.