libsoup Client Basics3LIBSOUP Librarylibsoup Client BasicsClient-side tutorial
This section explains how to use libsoup as
an HTTP client using several new APIs introduced in version 2.42. If
you want to be compatible with older versions of
libsoup, consult the documentation for that
version.
Creating a SoupSession
The first step in using the client API is to create a SoupSession. The session object
encapsulates all of the state that libsoup
is keeping on behalf of your program; cached HTTP connections,
authentication information, etc.
When you create the session with soup_session_new_with_options,
you can specify various additional options:
"max-conns"
Allows you to set the maximum total number of connections
the session will have open at one time. (Once it reaches
this limit, it will either close idle connections, or
wait for existing connections to free up before starting
new requests.) The default value is 10.
"max-conns-per-host"
Allows you to set the maximum total number of connections
the session will have open to a single
host at one time. The default value is 2.
"user-agent"
Allows you to set a User-Agent string that will be sent
on all outgoing requests.
"accept-language"
and "accept-language-auto"
Allow you to set an Accept-Language header on all outgoing
requests. "accept-language"
takes a list of language tags to use, while
"accept-language-auto"
automatically generates the list from the user's locale
settings.
"proxy-resolver""proxy-resolver"
specifies a GProxyResolver
to use to determine the HTTP proxies to use. By default,
this is set to the resolver returned by g_proxy_resolver_get_default,
so you do not need to set it yourself.
"add-feature" and "add-feature-by-type"
These allow you to specify SoupSessionFeatures
(discussed below)
to add at construct-time.
Other properties are also available; see the SoupSession documentation for
more details.
If you don't need to specify any options, you can just use soup_session_new,
which takes no arguments.
Session features
Additional session functionality is provided as SoupSessionFeatures,
which can be added to a session, via the "add-feature"
and "add-feature-by-type"
options at session-construction-time, or afterward via the soup_session_add_feature
and soup_session_add_feature_by_type
functions.
A SoupContentDecoder is
added for you automatically. This advertises to servers that the
client supports compression, and automatically decompresses compressed
responses.
Some other available features that you can add include:
SoupLogger
A debugging aid, which logs all of libsoup's HTTP traffic
to stdout (or another place you specify).
SoupCookieJar,
SoupCookieJarText,
and SoupCookieJarDB
Support for HTTP cookies. SoupCookieJar
provides non-persistent cookie storage, while
SoupCookieJarText uses a text file to keep
track of cookies between sessions, and
SoupCookieJarDB uses a
SQLite database.
SoupContentSniffer
Uses the HTML5 sniffing rules to attempt to
determine the Content-Type of a response when the
server does not identify the Content-Type, or appears to
have provided an incorrect one.
Use the "add_feature_by_type" property/function to add features that
don't require any configuration (such as SoupContentSniffer),
and the "add_feature" property/function to add features that must be
constructed first (such as SoupLogger). For example, an
application might do something like the following:
session = soup_session_new_with_options (
"add-feature-by-type", SOUP_TYPE_CONTENT_SNIFFER,
NULL);
if (debug_level) {
SoupLogger *logger;
logger = soup_logger_new (debug_level, -1);
soup_session_add_feature (session, SOUP_SESSION_FEATURE (logger));
g_object_unref (logger);
}
Creating and Sending SoupMessages
Once you have a session, you send HTTP requests using SoupMessage. In the simplest
case, you only need to create the message and it's ready to send:
SoupMessage *msg;
msg = soup_message_new ("GET", "http://example.com/");
In more complicated cases, you can use various SoupMessage, SoupMessageHeaders, and SoupMessageBody methods to set the
request headers and body of the message:
SoupMessage *msg;
msg = soup_message_new ("POST", "http://example.com/form.cgi");
soup_message_set_request (msg, "application/x-www-form-urlencoded",
SOUP_MEMORY_COPY, formdata, strlen (formdata));
soup_message_headers_append (msg->request_headers, "Referer", referring_url);
(Although this is a bad example, because
libsoup actually has convenience methods
for dealing with HTML
forms.)
You can also use soup_message_set_flags
to change some default behaviors. For example, by default,
SoupSession automatically handles responses from the
server that redirect to another URL. If you would like to handle these
yourself, you can set the SOUP_MESSAGE_NO_REDIRECT
flag.
Sending a Message Synchronously
To send a message and wait for the response, use soup_session_send:
GInputStream *stream;
GError *error = NULL;
stream = soup_session_send (session, msg, cancellable, &error);
At the point when soup_session_send returns, the
request will have been sent, and the response headers read back in;
you can examine the message's status_code,
reason_phrase, and
response_headers fields to see the response
metadata. To get the response body, read from the returned GInputStream, and close it
when you are done.
Note that soup_session_send only returns an error
if a transport-level problem occurs (eg, it could not connect to the
host, or the request was cancelled). Use the message's
status_code field to determine whether the
request was successful or not at the HTTP level (ie, "200
OK" vs "401 Bad Request").
If you would prefer to have libsoup gather
the response body for you and then return it all at once, you can use
the older
soup_session_send_message
API:
guint status;
status = soup_session_send_message (session, msg);
In this case, the response body will be available in the message's
response_body field, and transport-level
errors will be indicated in the status_code
field via special pseudo-HTTP-status codes like SOUP_STATUS_CANT_CONNECT.
Sending a Message Asynchronously
To send a message asynchronously, use soup_session_send_async:
{
...
soup_session_send_async (session, msg, cancellable, my_callback, my_callback_data);
...
}
static void
my_callback (GObject *object, GAsyncResult *result, gpointer user_data)
{
GInputStream *stream;
GError *error = NULL;
stream = soup_session_send_finish (SOUP_SESSION (object), result, &error);
...
}
The message will be added to the session's queue, and eventually (when
control is returned back to the main loop), it will be sent and the
response will be read. When the message has been sent, and its
headers received, the callback will be invoked, in the standard
GAsyncReadyCallback
style.
As with synchronous sending, there is also an alternate API, soup_session_queue_message,
in which your callback is not invoked until the response has been
completely read:
{
...
soup_session_queue_message (session, msg, my_callback, my_callback_data);
...
}
static void
my_callback (SoupSession *session, SoupMessage *msg, gpointer user_data)
{
/* msg->response_body contains the response */
}
soup_session_queue_message
is slightly unusual in that it steals a reference to the message
object, and unrefs it after the last callback is invoked on it. So
when using this API, you should not unref the message yourself.
Processing the Response
Once you have received the initial response from the server,
synchronously or asynchronously, streaming or not, you can look at the
response fields in the SoupMessage to decide what
to do next. The status_code and
reason_phrase fields contain the numeric
status and textual status response from the server.
response_headers contains the response
headers, which you can investigate using soup_message_headers_get_list
and soup_message_headers_foreach.
SoupMessageHeaders
automatically parses several important headers in
response_headers for you and provides
specialized accessors for them. Eg, soup_message_headers_get_content_type.
There are several generic methods such as soup_header_parse_param_list
(for parsing an attribute-list-type header) and soup_header_contains
(for quickly testing if a list-type header contains a particular
token). These handle the various syntactical oddities of parsing HTTP
headers much better than functions like
g_strsplit or strstr.
Handling AuthenticationSoupSession handles most of the details of HTTP
authentication for you. If it receives a 401 ("Unauthorized") or 407
("Proxy Authentication Required") response, the session will emit the
authenticate signal,
providing you with a SoupAuth object indicating the
authentication type ("Basic", "Digest", or "NTLM") and the realm name
provided by the server. If you have a username and password available
(or can generate one), call soup_auth_authenticate
to give the information to libsoup. The session will automatically
requeue the message and try it again with that authentication
information. (If you don't call
soup_auth_authenticate, the session will just
return the message to the application with its 401 or 407 status.)
If the server doesn't accept the username and password provided, the
session will emit authenticate again, with the
retrying parameter set to TRUE. This lets the
application know that the information it provided earlier was
incorrect, and gives it a chance to try again. If this
username/password pair also doesn't work, the session will contine to
emit authenticate again and again until the
provided username/password successfully authenticates, or until the
signal handler fails to call soup_auth_authenticate,
at which point libsoup will allow the
message to fail (with status 401 or 407).
If you need to handle authentication asynchronously (eg, to pop up a
password dialog without recursively entering the main loop), you can
do that as well. Just call soup_session_pause_message
on the message before returning from the signal handler, and
g_object_ref the SoupAuth. Then,
later on, after calling soup_auth_authenticate
(or deciding not to), call soup_session_unpause_message
to resume the paused message.
By default, NTLM authentication is not enabled. To add NTLM support to
a session, call:
soup_session_add_feature_by_type (session, SOUP_TYPE_AUTH_NTLM);
(You can also disable Basic or Digest authentication by calling soup_session_remove_feature_by_type
on SOUP_TYPE_AUTH_BASIC
or SOUP_TYPE_AUTH_DIGEST.)
Multi-threaded usage
A SoupSession can be
used from multiple threads. However, if you are using the async APIs,
then each thread you use the session from must have its own
thread-default GMainContext.
SoupMessage is
not thread-safe, so once you send a message on
the session, you must not interact with it from any thread other than
the one where it was sent.
Sample Programs
A few sample programs are available in the
libsoup sources, in the
examples directory:
get is a simple command-line
HTTP GET utility using the asynchronous API.
simple-proxy uses both the
client and server APIs to create a simple (and not very
RFC-compliant) proxy server.
More complicated examples are available in GNOME git.