<h2>callback - User server actions</h2>
<i>int</i>
<b>callback</b>
(<i>struct libwebsocket *</i> <b>wsi</b>,
<i>enum libwebsocket_callback_reasons</i> <b>reason</b>,
<i>void *</i> <b>user</b>,
<i>void *</i> <b>in</b>,
<i>size_t</i> <b>len</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Opaque websocket instance pointer
<dt><b>reason</b>
<dd>The reason for the call
<dt><b>user</b>
<dd>Pointer to per-session user data allocated by library
<dt><b>in</b>
<dd>Pointer used for some callback reasons
<dt><b>len</b>
<dd>Length set for some callback reasons
</dl>
<h3>Description</h3>
<blockquote>
This callback is the way the user controls what is served.  All the
protocol detail is hidden and handled by the library.
<p>
For each connection / session there is user data allocated that is
pointed to by "user".  You set the size of this user data area when
the library is initialized with libwebsocket_create_server.
<p>
You get an opportunity to initialize user data when called back with
LWS_CALLBACK_ESTABLISHED reason.
</blockquote>
<h3>LWS_CALLBACK_ESTABLISHED</h3>
<blockquote>
after successful websocket handshake
</blockquote>
<h3>LWS_CALLBACK_CLOSED</h3>
<blockquote>
when the websocket session ends
</blockquote>
<h3>LWS_CALLBACK_SEND</h3>
<blockquote>
opportunity to send to client (you would use
<b>libwebsocket_write</b> taking care about the
special buffer requirements
</blockquote>
<h3>LWS_CALLBACK_RECEIVE</h3>
<blockquote>
data has appeared for the server, it can be
found at *in and is len bytes long
</blockquote>
<h3>LWS_CALLBACK_HTTP</h3>
<blockquote>
an http request has come from a client that is not
asking to upgrade the connection to a websocket
one.  This is a chance to serve http content,
for example, to send a script to the client
which will then open the websockets connection.
<tt><b>in</b></tt> points to the URI path requested and 
<b>libwebsockets_serve_http_file</b> makes it very
simple to send back a file to the client.
</blockquote>
<hr>
<h2>libwebsocket_create_server - Create the listening websockets server</h2>
<i>int</i>
<b>libwebsocket_create_server</b>
(<i>int</i> <b>port</b>,
<i>const struct libwebsocket_protocols *</i> <b>protocols</b>,
<i>const char *</i> <b>ssl_cert_filepath</b>,
<i>const char *</i> <b>ssl_private_key_filepath</b>,
<i>int</i> <b>gid</b>,
<i>int</i> <b>uid</b>)
<h3>Arguments</h3>
<dl>
<dt><b>port</b>
<dd>Port to listen on
<dt><b>protocols</b>
<dd>Array of structures listing supported protocols and a protocol-
specific callback for each one.  The list is ended with an
entry that has a NULL callback pointer.
<dt><b>ssl_cert_filepath</b>
<dd>If libwebsockets was compiled to use ssl, and you want
to listen using SSL, set to the filepath to fetch the
server cert from, otherwise NULL for unencrypted
<dt><b>ssl_private_key_filepath</b>
<dd>filepath to private key if wanting SSL mode,
else ignored
<dt><b>gid</b>
<dd>group id to change to after setting listen socket, or -1.
<dt><b>uid</b>
<dd>user id to change to after setting listen socket, or -1.
</dl>
<h3>Description</h3>
<blockquote>
This function creates the listening socket and takes care
of all initialization in one step.
<p>
It does not return since it sits in a service loop and operates via the
callbacks given in <tt><b>protocol</b></tt>.  User code should fork before calling
<b>libwebsocket_create_server</b> if it wants to do other things in
parallel other than serve websockets.
<p>
The protocol callback functions are called for a handful of events
including http requests coming in, websocket connections becoming
established, and data arriving; it's also called periodically to allow
async transmission.
<p>
HTTP requests are sent always to the FIRST protocol in <tt><b>protocol</b></tt>, since
at that time websocket protocol has not been negotiated.  Other
protocols after the first one never see any HTTP callack activity.
<p>
The server created is a simple http server by default; part of the
websocket standard is upgrading this http connection to a websocket one.
<p>
This allows the same server to provide files like scripts and favicon /
images or whatever over http and dynamic data over websockets all in
one place; they're all handled in the user callback.
</blockquote>
<hr>
<h2>libwebsocket_write - Apply protocol then write data to client</h2>
<i>int</i>
<b>libwebsocket_write</b>
(<i>struct libwebsocket *</i> <b>wsi</b>,
<i>unsigned char *</i> <b>buf</b>,
<i>size_t</i> <b>len</b>,
<i>enum libwebsocket_write_protocol</i> <b>protocol</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket instance (available from user callback)
<dt><b>buf</b>
<dd>The data to send.  For data being sent on a websocket
connection (ie, not default http), this buffer MUST have
LWS_SEND_BUFFER_PRE_PADDING bytes valid BEFORE the pointer
and an additional LWS_SEND_BUFFER_POST_PADDING bytes valid
in the buffer after (buf + len).  This is so the protocol
header and trailer data can be added in-situ.
<dt><b>len</b>
<dd>Count of the data bytes in the payload starting from buf
<dt><b>protocol</b>
<dd>Use LWS_WRITE_HTTP to reply to an http connection, and one
of LWS_WRITE_BINARY or LWS_WRITE_TEXT to send appropriate
data on a websockets connection.  Remember to allow the extra
bytes before and after buf if LWS_WRITE_BINARY or LWS_WRITE_TEXT
are used.
</dl>
<h3>Description</h3>
<blockquote>
This function provides the way to issue data back to the client
for both http and websocket protocols.
<p>
In the case of sending using websocket protocol, be sure to allocate
valid storage before and after buf as explained above.  This scheme
allows maximum efficiency of sending data and protocol in a single
packet while not burdening the user code with any protocol knowledge.
</blockquote>
<hr>
<h2>libwebsockets_serve_http_file - Send a file back to the client using http</h2>
<i>int</i>
<b>libwebsockets_serve_http_file</b>
(<i>struct libwebsocket *</i> <b>wsi</b>,
<i>const char *</i> <b>file</b>,
<i>const char *</i> <b>content_type</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket instance (available from user callback)
<dt><b>file</b>
<dd>The file to issue over http
<dt><b>content_type</b>
<dd>The http content type, eg, text/html
</dl>
<h3>Description</h3>
<blockquote>
This function is intended to be called from the callback in response
to http requests from the client.  It allows the callback to issue
local files down the http link in a single step.
</blockquote>
<hr>
<h2>struct libwebsocket_protocols - List of protocols and handlers server supports.</h2>
<b>struct libwebsocket_protocols</b> {<br>
&nbsp; &nbsp; <i>const char *</i> <b>name</b>;<br>
&nbsp; &nbsp; <i>int (*</i><b>callback</b>) <i>(struct libwebsocket * wsi,enum libwebsocket_callback_reasons reason, void * user,void *in, size_t len)</i>;<br>
&nbsp; &nbsp; <i>size_t</i> <b>per_session_data_size</b>;<br>
};<br>
<h3>Members</h3>
<dl>
<dt><b>name</b>
<dd>Protocol name that must match the one given in the client
Javascript new WebSocket(url, 'protocol') name
<dt><b>callback</b>
<dd>The service callback used for this protocol.  It allows the
service action for an entire protocol to be encapsulated in
the protocol-specific callback
<dt><b>per_session_data_size</b>
<dd>Each new connection using this protocol gets
this much memory allocated on connection establishment and
freed on connection takedown.  A pointer to this per-connection
allocation is passed into the callback in the 'user' parameter
</dl>
<h3>Description</h3>
<blockquote>
This structure represents one protocol supported by the server.  An
array of these structures is passed to <b>libwebsocket_create_server</b>
allows as many protocols as you like to be handled by one server.
</blockquote>
<hr>