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Previous: <a href="Thread-safety.html#Thread-safety" accesskey="p" rel="previous">Thread safety</a>, Up: <a href="Introduction-to-the-library.html#Introduction-to-the-library" accesskey="u" rel="up">Introduction to the library</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Callback-functions-1"></a>
<h4 class="subsection">6.1.6 Callback functions</h4>
<a name="index-callback-functions"></a>
<p>There are several cases where <acronym>GnuTLS</acronym> may need out of
band input from your program. This is now implemented using some
callback functions, which your program is expected to register.
</p>
<p>An example of this type of functions are the push and pull callbacks
which are used to specify the functions that will retrieve and send
data to the transport layer.
</p>
<dl compact="compact">
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005ftransport_005fset_005fpush_005ffunction">gnutls_transport_set_push_function</a> (gnutls_session_t <var>session</var>, gnutls_push_func <var>push_func</var>)</code></dt>
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005ftransport_005fset_005fpull_005ffunction">gnutls_transport_set_pull_function</a> (gnutls_session_t <var>session</var>, gnutls_pull_func <var>pull_func</var>)</code></dt>
</dl>
<p>Other callback functions may require more complicated input and data
to be allocated. Such an example is
<a href="Core-TLS-API.html#gnutls_005fsrp_005fset_005fserver_005fcredentials_005ffunction">gnutls_srp_set_server_credentials_function</a>.
All callbacks should allocate and free memory using
<code>gnutls_malloc</code> and <code>gnutls_free</code>.
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