docs/reference/client-howto.xml

<?xml version="1.0"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
               "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">
<refentry id="libsoup-client-howto">
<refmeta>
<refentrytitle>libsoup Client Basics</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>LIBSOUP Library</refmiscinfo>
</refmeta>

<refnamediv>
<refname>libsoup Client Basics</refname><refpurpose>Client-side tutorial</refpurpose>
</refnamediv>

<refsect2>
<para>
This section explains how to use <application>libsoup</application> as
an HTTP client using several new APIs introduced in version 2.42. If
you want to be compatible with older versions of
<application>libsoup</application>, consult the documentation for that
version.
</para>
</refsect2>

<refsect2>
<title>Creating a <type>SoupSession</type></title>

<para>
The first step in using the client API is to create a <link
linkend="SoupSession"><type>SoupSession</type></link>. The session object
encapsulates all of the state that <application>libsoup</application>
is keeping on behalf of your program; cached HTTP connections,
authentication information, etc.
</para>

<para>
When you create the session with <link
linkend="soup-session-new-with-options"><function>soup_session_new_with_options</function></link>,
you can specify various additional options:
</para>

<variablelist>
    <varlistentry>
	<term><link linkend="SOUP-SESSION-MAX-CONNS:CAPS"><literal>SOUP_SESSION_MAX_CONNS</literal></link></term>
	<listitem><para>
	    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.
	</para></listitem>
    </varlistentry>
    <varlistentry>
	<term><link linkend="SOUP-SESSION-MAX-CONNS-PER-HOST:CAPS"><literal>SOUP_SESSION_MAX_CONNS_PER_HOST</literal></link></term>
	<listitem><para>
	    Allows you to set the maximum total number of connections
	    the session will have open <emphasis>to a single
	    host</emphasis> at one time. The default value is 2.
	</para></listitem>
    </varlistentry>
    <varlistentry>
	<term><link linkend="SOUP-SESSION-USER-AGENT:CAPS"><literal>SOUP_SESSION_USER_AGENT</literal></link></term>
	<listitem><para>
	    Allows you to set a User-Agent string that will be sent
	    on all outgoing requests.
	</para></listitem>
    </varlistentry>
    <varlistentry>
	<term><link linkend="SOUP-SESSION-ACCEPT-LANGUAGE:CAPS"><literal>SOUP_SESSION_ACCEPT_LANGUAGE</literal></link>
	and <link linkend="SOUP-SESSION-ACCEPT-LANGUAGE-AUTO:CAPS"><literal>SOUP_SESSION_ACCEPT_LANGUAGE_AUTO</literal></link></term>
	<listitem><para>
	    Allow you to set an Accept-Language header on all outgoing
	    requests. <literal>SOUP_SESSION_ACCEPT_LANGUAGE</literal>
	    takes a list of language tags to use, while
	    <literal>SOUP_SESSION_ACCEPT_LANGUAGE_AUTO</literal>
	    automatically generates the list from the user's locale
	    settings.
	</para></listitem>
    </varlistentry>
    <varlistentry>
	<term><link linkend="SOUP-SESSION-HTTP-ALIASES:CAPS"><literal>SOUP_SESSION_HTTP_ALIASES</literal></link>
	and <link linkend="SOUP-SESSION-HTTPS-ALIASES:CAPS"><literal>SOUP_SESSION_HTTPS_ALIASES</literal></link></term>
	<listitem><para>
	    Allow you to tell the session to recognize additional URI
	    schemes as aliases for "<literal>http</literal>" or
	    <literal>https</literal>. You can set this if you are
	    using URIs with schemes like "<literal>dav</literal>" or
	    "<literal>webcal</literal>" (and in particular, you need
	    to set this if the server you are talking to might return
	    redirects with such a scheme).
	</para></listitem>
    </varlistentry>
    <varlistentry>
	<term><link linkend="SOUP-SESSION-PROXY-RESOLVER:CAPS"><literal>SOUP_SESSION_PROXY_RESOLVER</literal></link> and <link linkend="SOUP-SESSION-PROXY-URI:CAPS"><literal>SOUP_SESSION_PROXY_URI</literal></link></term>
	<listitem>
	    <para>
		<link linkend="SOUP-SESSION-PROXY-RESOLVER:CAPS"><literal>SOUP_SESSION_PROXY_RESOLVER</literal></link>
		specifies a <link
		linkend="GProxyResolver"><type>GProxyResolver</type></link>
		to use to determine the HTTP proxies to use. By default,
		this is set to the resolver returned by <link
		linkend="g-proxy-resolver-get-default"><function>g_proxy_resolver_get_default</function></link>,
		so you do not need to set it yourself.
	    </para>
	    <para>
		Alternatively, if you want all requests to go through a
		single proxy, you can set <link
		linkend="SOUP-SESSION-PROXY-URI:CAPS"><literal>SOUP_SESSION_PROXY_URI</literal></link>.
	    </para>
	</listitem>
    </varlistentry>
    <varlistentry>
	<term><link linkend="SOUP-SESSION-ADD-FEATURE:CAPS"><literal>SOUP_SESSION_ADD_FEATURE</literal></link> and <link linkend="SOUP-SESSION-ADD-FEATURE-BY-TYPE:CAPS"><literal>SOUP_SESSION_ADD_FEATURE_BY_TYPE</literal></link></term>
	<listitem><para>
	    These allow you to specify <link
	    linkend="SoupSessionFeature"><type>SoupSessionFeature</type></link>s
	    (discussed <link linkend="session-features">below</link>)
	    to add at construct-time.
	</para></listitem>
    </varlistentry>
</variablelist>

<para>
Other properties are also available; see the <link
linkend="SoupSession"><type>SoupSession</type></link> documentation for
more details.
</para>

<para>
If you don't need to specify any options, you can just use <link
linkend="soup-session-new"><function>soup_session_new</function></link>,
which takes no arguments.
</para>

</refsect2>

<refsect2 id="session-features">
<title>Session features</title>

<para>
Additional session functionality is provided as <link
linkend="SoupSessionFeature"><type>SoupSessionFeature</type></link>s,
which can be added to a session, via the <link
linkend="SOUP-SESSION-ADD-FEATURE:CAPS"><literal>SOUP_SESSION_ADD_FEATURE</literal></link>
and <link
linkend="SOUP-SESSION-ADD-FEATURE-BY-TYPE:CAPS"><literal>SOUP_SESSION_ADD_FEATURE_BY_TYPE</literal></link>
options at session-construction-time, or afterward via the <link
linkend="soup-session-add-feature"><function>soup_session_add_feature</function></link>
and <link
linkend="soup-session-add-feature-by-type"><function>soup_session_add_feature_by_type</function></link>
functions.
</para>

<para>
A <link
linkend="SoupContentDecoder"><type>SoupContentDecoder</type></link> is
added for you automatically. This advertises to servers that the
client supports compression, and automatically decompresses compressed
responses.
</para>

<para>
Some other available features that you can add include:
</para>

<variablelist>
    <varlistentry>
	<term><link linkend="SoupLogger"><type>SoupLogger</type></link></term>
	<listitem><para>
	    A debugging aid, which logs all of libsoup's HTTP traffic
	    to <literal>stdout</literal> (or another place you specify).
	</para></listitem>
    </varlistentry>
    <varlistentry>
	<term>
	    <link linkend="SoupCookieJar"><type>SoupCookieJar</type></link>,
	    <link linkend="SoupCookieJarText"><type>SoupCookieJarText</type></link>,
	    and <link linkend="SoupCookieJarDB"><type>SoupCookieJarDB</type></link>
	</term>
	<listitem><para>
	    Support for HTTP cookies. <type>SoupCookieJar</type>
	    provides non-persistent cookie storage, while
	    <type>SoupCookieJarText</type> uses a text file to keep
	    track of cookies between sessions, and
	    <type>SoupCookieJarDB</type> uses a
	    <application>SQLite</application> database.
	</para></listitem>
    </varlistentry>
    <varlistentry>
	<term><link linkend="SoupContentSniffer"><type>SoupContentSniffer</type></link></term>
	<listitem><para>
	    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.
	</para></listitem>
    </varlistentry>
</variablelist>

<para>
Use the "add_feature_by_type" property/function to add features that
don't require any configuration (such as <link
linkend="SoupContentSniffer"><type>SoupContentSniffer</type></link>),
and the "add_feature" property/function to add features that must be
constructed first (such as <link
linkend="SoupLogger"><type>SoupLogger</type></link>). For example, an
application might do something like the following:
</para>

<informalexample><programlisting>
	session = soup_session_new_with_options (
		SOUP_SESSION_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);
	}
</programlisting></informalexample>

</refsect2>

<refsect2>
<title>Creating and Sending SoupMessages</title>

<para>
Once you have a session, you send HTTP requests using <link
linkend="SoupMessage"><type>SoupMessage</type></link>. In the simplest
case, you only need to create the message and it's ready to send:
</para>

<informalexample><programlisting>
	SoupMessage *msg;

	msg = soup_message_new ("GET", "http://example.com/");
</programlisting></informalexample>

<para>
In more complicated cases, you can use various <link
linkend="SoupMessage">SoupMessage</link>, <link
linkend="SoupMessageHeaders">SoupMessageHeaders</link>, and <link
linkend="SoupMessageBody">SoupMessageBody</link> methods to set the
request headers and body of the message:
</para>

<informalexample><programlisting>
	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);
</programlisting></informalexample>

<para>
(Although this is a bad example, because
<application>libsoup</application> actually has convenience methods
for dealing with <link linkend="libsoup-2.4-HTML-Form-Support">HTML
forms</link>, as well as <link
linkend="libsoup-2.4-XMLRPC-Support">XML-RPC</link>.)
</para>

<para>
You can also use <link
linkend="soup-message-set-flags"><function>soup_message_set_flags</function></link>
to change some default behaviors. For example, by default,
<type>SoupSession</type> automatically handles responses from the
server that redirect to another URL. If you would like to handle these
yourself, you can set the <link linkend="SOUP-MESSAGE-NO-REDIRECT:CAPS"><literal>SOUP_MESSAGE_NO_REDIRECT</literal></link>
flag.
</para>

<refsect3>
<title>Sending a Message Synchronously</title>

<para>
To send a message and wait for the response, use <link
linkend="soup-session-send"><function>soup_session_send</function></link>:
</para>

<informalexample><programlisting>
	GInputStream *stream;
	GError *error = NULL;

	stream = soup_session_send (session, msg, cancellable, &amp;error);
</programlisting></informalexample>

<para>
At the point when <function>soup_session_send</function> returns, the
request will have been sent, and the response headers read back in;
you can examine the message's <structfield>status_code</structfield>,
<structfield>reason_phrase</structfield>, and
<structfield>response_headers</structfield> fields to see the response
metadata. To get the response body, read from the returned <link
linkend="GInputStream"><type>GInputStream</type></link>, and close it
when you are done.
</para>

<para>
Note that <function>soup_session_send</function> 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
<structfield>status_code</structfield> field to determine whether the
request was successful or not at the HTTP level (ie, "<literal>200
OK</literal>" vs "<literal>401 Bad Request</literal>").
</para>

<para>
If you would prefer to have <application>libsoup</application> gather
the response body for you and then return it all at once, you can use
the older
<link linkend="soup-session-send-message"><function>soup_session_send_message</function></link>
API:
</para>

<informalexample><programlisting>
	guint status;

	status = soup_session_send_message (session, msg);
</programlisting></informalexample>

<para>
In this case, the response body will be available in the message's
<structfield>response_body</structfield> field, and transport-level
errors will be indicated in the <structfield>status_code</structfield>
field via special pseudo-HTTP-status codes like <link
linkend="SOUP-STATUS-CANT-CONNECT:CAPS"><literal>SOUP_STATUS_CANT_CONNECT</literal></link>.
</para>

</refsect3>

<refsect3>
<title>Sending a Message Asynchronously</title>

<para>
To send a message asynchronously, use <link
linkend="soup-session-send-async"><function>soup_session_send_async</function></link>:
</para>

<informalexample><programlisting>
{
	...
	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, &amp;error);
	...
}
</programlisting></informalexample>

<para>
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
<link linkend="GAsyncReadyCallback"><type>GAsyncReadyCallback</type></link>
style.
</para>

<para>
As with synchronous sending, there is also an alternate API, <link
linkend="soup-session-queue-message"><function>soup_session_queue_message</function></link>,
in which your callback is not invoked until the response has been
completely read:
</para>

<informalexample><programlisting>
{
	...
	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 */
}
</programlisting></informalexample>

<para>
<link
linkend="soup-session-queue-message"><function>soup_session_queue_message</function></link>
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.
</para>

</refsect3>

</refsect2>

<refsect2>
<title>Processing the Response</title>

<para>
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 <literal>SoupMessage</literal> to decide what
to do next. The <structfield>status_code</structfield> and
<structfield>reason_phrase</structfield> fields contain the numeric
status and textual status response from the server.
<structfield>response_headers</structfield> contains the response
headers, which you can investigate using <link
linkend="soup-message-headers-get"><function>soup_message_headers_get</function></link>
and <link
linkend="soup-message-headers-foreach"><function>soup_message_headers_foreach</function></link>.
</para>

<para>
<link
linkend="SoupMessageHeaders"><type>SoupMessageHeaders</type></link>
automatically parses several important headers in
<structfield>response_headers</structfield> for you and provides
specialized accessors for them. Eg, <link
linkend="soup-message-headers-get-content-type"><function>soup_message_headers_get_content_type</function></link>.
There are several generic methods such as <link
linkend="soup-header-parse-param-list"><function>soup_header_parse_param_list</function></link>
(for parsing an attribute-list-type header) and <link
linkend="soup-header-contains"><function>soup_header_contains</function></link>
(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
<function>g_strsplit</function> or <function>strstr</function>.
</para>

</refsect2>

<refsect2>
<title>Handling Authentication</title>

<para>
<type>SoupSession</type> 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
<link linkend="SoupSession-authenticate">authenticate</link> signal,
providing you with a <link
linkend="SoupAuth"><type>SoupAuth</type></link> 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 <link
linkend="soup-auth-authenticate"><function>soup_auth_authenticate</function></link>
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
<function>soup_auth_authenticate</function>, the session will just
return the message to the application with its 401 or 407 status.)
</para>

<para>
If the server doesn't accept the username and password provided, the
session will emit <link
linkend="SoupSession-authenticate">authenticate</link> again, with the
<literal>retrying</literal> parameter set to <literal>TRUE</literal>. 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 <literal>authenticate</literal> again and again until the
provided username/password successfully authenticates, or until the
signal handler fails to call <link
linkend="soup-auth-authenticate"><function>soup_auth_authenticate</function></link>,
at which point <application>libsoup</application> will allow the
message to fail (with status 401 or 407).
</para>

<para>
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 <link
linkend="soup-session-pause-message"><function>soup_session_pause_message</function></link>
on the message before returning from the signal handler, and
<function>g_object_ref</function> the <type>SoupAuth</type>. Then,
later on, after calling <function>soup_auth_authenticate</function>
(or deciding not to), call <link
linkend="soup-session-unpause-message"><function>soup_session_unpause_message</function></link>
to resume the paused message.
</para>

<para>
By default, NTLM authentication is not enabled. To add NTLM support to
a session, call:
</para>

<informalexample><programlisting>
	soup_session_add_feature_by_type (session, SOUP_TYPE_AUTH_NTLM);
</programlisting></informalexample>

<para>
(You can also disable Basic or Digest authentication by calling <link
linkend="soup-session-remove-feature-by-type"><function>soup_session_remove_feature_by_type</function></link>
on <link linkend="SOUP-TYPE-AUTH-BASIC:CAPS"><literal>SOUP_TYPE_AUTH_BASIC</literal></link>
or <link linkend="SOUP-TYPE-AUTH-DIGEST:CAPS"><literal>SOUP_TYPE_AUTH_DIGEST</literal></link>.)
</para>

</refsect2>

<refsect2>
<title>Multi-threaded usage</title>

<para>
A <link linkend="SoupSession"><type>SoupSession</type></link> 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 <link linkend="GMainContext"><type>GMainContext</type></link>.
</para>

<para>
<link linkend="SoupMessage"><type>SoupMessage</type></link> is
<emphasis>not</emphasis> 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.
</para>

</refsect2>

<refsect2>
<title>Sample Programs</title>

<para>
A few sample programs are available in the
<application>libsoup</application> sources, in the
<literal>examples</literal> directory:
</para>

<itemizedlist>
    <listitem><para>
	<emphasis role="bold"><literal>get</literal></emphasis> is a simple command-line
	HTTP GET utility using the asynchronous API.
    </para></listitem>

    <listitem><para>
	<emphasis role="bold"><literal>simple-proxy</literal></emphasis> uses both the
	client and server APIs to create a simple (and not very
	RFC-compliant) proxy server. It shows how to use the <link
	linkend="SoupMessageFlags"><literal>SOUP_MESSAGE_OVERWRITE_CHUNKS</literal></link>
	flag when reading a message to save memory by processing each
	chunk of the message as it is read, rather than accumulating
	them all into a single buffer to process all at the end.
    </para></listitem>
</itemizedlist>

<para>
More complicated examples are available in GNOME git.
</para>

</refsect2>

</refentry>