libwebsockets-api-doc.html

<h2>lws_write - Apply protocol then write data to client</h2>
<i>int</i>
<b>lws_write</b>
(<i>struct lws *</i> <b>wsi</b>,
<i>unsigned char *</i> <b>buf</b>,
<i>size_t</i> <b>len</b>,
<i>enum lws_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.
<p>
Return may be -1 for a fatal error needing connection close, or a
positive number reflecting the amount of bytes actually sent.  This
can be less than the requested number of bytes due to OS memory
pressure at any given time.
</blockquote>
<hr>
<h2>lws_http_transaction_completed - wait for new http transaction or close</h2>
<i>int</i>
<b>lws_http_transaction_completed</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>websocket connection
</dl>
<h3>Description</h3>
<blockquote>
Returns 1 if the HTTP connection must close now
Returns 0 and resets connection to wait for new HTTP header /
transaction if possible
</blockquote>
<hr>
<h2>lws_serve_http_file - Send a file back to the client using http</h2>
<i>int</i>
<b>lws_serve_http_file</b>
(<i>struct lws *</i> <b>wsi</b>,
<i>const char *</i> <b>file</b>,
<i>const char *</i> <b>content_type</b>,
<i>const char *</i> <b>other_headers</b>,
<i>int</i> <b>other_headers_len</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
<dt><b>other_headers</b>
<dd>NULL or pointer to header string
<dt><b>other_headers_len</b>
<dd>length of the other headers if non-NULL
</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.
<p>
Returning &lt;0 indicates error and the wsi should be closed.  Returning
&gt;0 indicates the file was completely sent and
<b>lws_http_transaction_completed</b> called on the wsi (and close if != 0)
==0 indicates the file transfer is started and needs more service later,
the wsi should be left alone.
</blockquote>
<hr>
<h2>lws_return_http_status - Return simple http status</h2>
<i>int</i>
<b>lws_return_http_status</b>
(<i>struct lws *</i> <b>wsi</b>,
<i>unsigned int</i> <b>code</b>,
<i>const char *</i> <b>html_body</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket instance (available from user callback)
<dt><b>code</b>
<dd>Status index, eg, 404
<dt><b>html_body</b>
<dd>User-readable HTML description &lt; 1KB, or NULL
</dl>
<h3>Description</h3>
<blockquote>
Helper to report HTTP errors back to the client cleanly and
consistently
</blockquote>
<hr>
<h2>lws_client_connect - Connect to another websocket server</h2>
<i>struct lws *</i>
<b>lws_client_connect</b>
(<i>struct lws_context *</i> <b>context</b>,
<i>const char *</i> <b>address</b>,
<i>int</i> <b>port</b>,
<i>int</i> <b>ssl_connection</b>,
<i>const char *</i> <b>path</b>,
<i>const char *</i> <b>host</b>,
<i>const char *</i> <b>origin</b>,
<i>const char *</i> <b>protocol</b>,
<i>int</i> <b>ietf_version_or_minus_one</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
<dt><b>address</b>
<dd>Remote server address, eg, "myserver.com"
<dt><b>port</b>
<dd>Port to connect to on the remote server, eg, 80
<dt><b>ssl_connection</b>
<dd>0 = ws://, 1 = wss:// encrypted, 2 = wss:// allow self
signed certs
<dt><b>path</b>
<dd>Websocket path on server
<dt><b>host</b>
<dd>Hostname on server
<dt><b>origin</b>
<dd>Socket origin name
<dt><b>protocol</b>
<dd>Comma-separated list of protocols being asked for from
the server, or just one.  The server will pick the one it
likes best.  If you don't want to specify a protocol, which is
legal, use NULL here.
<dt><b>ietf_version_or_minus_one</b>
<dd>-1 to ask to connect using the default, latest
protocol supported, or the specific protocol ordinal
</dl>
<h3>Description</h3>
<blockquote>
This function creates a connection to a remote server
</blockquote>
<hr>
<h2>lws_client_connect_extended - Connect to another websocket server</h2>
<i>struct lws *</i>
<b>lws_client_connect_extended</b>
(<i>struct lws_context *</i> <b>context</b>,
<i>const char *</i> <b>address</b>,
<i>int</i> <b>port</b>,
<i>int</i> <b>ssl_connection</b>,
<i>const char *</i> <b>path</b>,
<i>const char *</i> <b>host</b>,
<i>const char *</i> <b>origin</b>,
<i>const char *</i> <b>protocol</b>,
<i>int</i> <b>ietf_version_or_minus_one</b>,
<i>void *</i> <b>userdata</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
<dt><b>address</b>
<dd>Remote server address, eg, "myserver.com"
<dt><b>port</b>
<dd>Port to connect to on the remote server, eg, 80
<dt><b>ssl_connection</b>
<dd>0 = ws://, 1 = wss:// encrypted, 2 = wss:// allow self
signed certs
<dt><b>path</b>
<dd>Websocket path on server
<dt><b>host</b>
<dd>Hostname on server
<dt><b>origin</b>
<dd>Socket origin name
<dt><b>protocol</b>
<dd>Comma-separated list of protocols being asked for from
the server, or just one.  The server will pick the one it
likes best.
<dt><b>ietf_version_or_minus_one</b>
<dd>-1 to ask to connect using the default, latest
protocol supported, or the specific protocol ordinal
<dt><b>userdata</b>
<dd>Pre-allocated user data
</dl>
<h3>Description</h3>
<blockquote>
This function creates a connection to a remote server
</blockquote>
<hr>
<h2>lws_service_fd - Service polled socket with something waiting</h2>
<i>int</i>
<b>lws_service_fd</b>
(<i>struct lws_context *</i> <b>context</b>,
<i>struct lws_pollfd *</i> <b>pollfd</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
<dt><b>pollfd</b>
<dd>The pollfd entry describing the socket fd and which events
happened.
</dl>
<h3>Description</h3>
<blockquote>
This function takes a pollfd that has POLLIN or POLLOUT activity and
services it according to the state of the associated
struct lws.
<p>
The one call deals with all "service" that might happen on a socket
including listen accepts, http files as well as websocket protocol.
<p>
If a pollfd says it has something, you can just pass it to
<b>lws_service_fd</b> whether it is a socket handled by lws or not.
If it sees it is a lws socket, the traffic will be handled and
pollfd-&gt;revents will be zeroed now.
<p>
If the socket is foreign to lws, it leaves revents alone.  So you can
see if you should service yourself by checking the pollfd revents
after letting lws try to service it.
</blockquote>
<hr>
<h2>lws_service - Service any pending websocket activity</h2>
<i>int</i>
<b>lws_service</b>
(<i>struct lws_context *</i> <b>context</b>,
<i>int</i> <b>timeout_ms</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
<dt><b>timeout_ms</b>
<dd>Timeout for poll; 0 means return immediately if nothing needed
service otherwise block and service immediately, returning
after the timeout if nothing needed service.
</dl>
<h3>Description</h3>
<blockquote>
This function deals with any pending websocket traffic, for three
kinds of event.  It handles these events on both server and client
types of connection the same.
<p>
1) Accept new connections to our context's server
<p>
2) Call the receive callback for incoming frame data received by
server or client connections.
<p>
You need to call this service function periodically to all the above
functions to happen; if your application is single-threaded you can
just call it in your main event loop.
<p>
Alternatively you can fork a new process that asynchronously handles
calling this service in a loop.  In that case you are happy if this
call blocks your thread until it needs to take care of something and
would call it with a large nonzero timeout.  Your loop then takes no
CPU while there is nothing happening.
<p>
If you are calling it in a single-threaded app, you don't want it to
wait around blocking other things in your loop from happening, so you
would call it with a timeout_ms of 0, so it returns immediately if
nothing is pending, or as soon as it services whatever was pending.
</blockquote>
<hr>
<h2>lws_frame_is_binary - </h2>
<i>int</i>
<b>lws_frame_is_binary</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>the connection we are inquiring about
</dl>
<h3>Description</h3>
<blockquote>
This is intended to be called from the LWS_CALLBACK_RECEIVE callback if
it's interested to see if the frame it's dealing with was sent in binary
mode.
</blockquote>
<hr>
<h2>lws_remaining_packet_payload - Bytes to come before "overall" rx packet is complete</h2>
<i>size_t</i>
<b>lws_remaining_packet_payload</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket instance (available from user callback)
</dl>
<h3>Description</h3>
<blockquote>
This function is intended to be called from the callback if the
user code is interested in "complete packets" from the client.
libwebsockets just passes through payload as it comes and issues a buffer
additionally when it hits a built-in limit.  The LWS_CALLBACK_RECEIVE
callback handler can use this API to find out if the buffer it has just
been given is the last piece of a "complete packet" from the client --
when that is the case <b>lws_remaining_packet_payload</b> will return
0.
<p>
Many protocols won't care becuse their packets are always small.
</blockquote>
<hr>
<h2>lws_get_peer_addresses - Get client address information</h2>
<i>void</i>
<b>lws_get_peer_addresses</b>
(<i>struct lws *</i> <b>wsi</b>,
<i>lws_sockfd_type</i> <b>fd</b>,
<i>char *</i> <b>name</b>,
<i>int</i> <b>name_len</b>,
<i>char *</i> <b>rip</b>,
<i>int</i> <b>rip_len</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Local struct lws associated with
<dt><b>fd</b>
<dd>Connection socket descriptor
<dt><b>name</b>
<dd>Buffer to take client address name
<dt><b>name_len</b>
<dd>Length of client address name buffer
<dt><b>rip</b>
<dd>Buffer to take client address IP dotted quad
<dt><b>rip_len</b>
<dd>Length of client address IP buffer
</dl>
<h3>Description</h3>
<blockquote>
This function fills in <tt><b>name</b></tt> and <tt><b>rip</b></tt> with the name and IP of
the client connected with socket descriptor <tt><b>fd</b></tt>.  Names may be
truncated if there is not enough room.  If either cannot be
determined, they will be returned as valid zero-length strings.
</blockquote>
<hr>
<h2>lws_context_user - get the user data associated with the context</h2>
<i>LWS_EXTERN void *</i>
<b>lws_context_user</b>
(<i>struct lws_context *</i> <b>context</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
</dl>
<h3>Description</h3>
<blockquote>
This returns the optional user allocation that can be attached to
the context the sockets live in at context_create time.  It's a way
to let all sockets serviced in the same context share data without
using globals statics in the user code.
</blockquote>
<hr>
<h2>lws_callback_all_protocol - Callback all connections using the given protocol with the given reason</h2>
<i>int</i>
<b>lws_callback_all_protocol</b>
(<i>struct lws_context *</i> <b>context</b>,
<i>const struct lws_protocols *</i> <b>protocol</b>,
<i>int</i> <b>reason</b>)
<h3>Arguments</h3>
<dl>
<dt><b>protocol</b>
<dd>Protocol whose connections will get callbacks
<dt><b>reason</b>
<dd>Callback reason index
</dl>
<hr>
<h2>lws_set_timeout - marks the wsi as subject to a timeout</h2>
<i>void</i>
<b>lws_set_timeout</b>
(<i>struct lws *</i> <b>wsi</b>,
<i>enum pending_timeout</i> <b>reason</b>,
<i>int</i> <b>secs</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket connection instance
<dt><b>reason</b>
<dd>timeout reason
<dt><b>secs</b>
<dd>how many seconds
</dl>
<h3>Description</h3>
<blockquote>
<p>
You will not need this unless you are doing something special
</blockquote>
<hr>
<h2>lws_get_socket_fd - returns the socket file descriptor</h2>
<i>int</i>
<b>lws_get_socket_fd</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket connection instance
</dl>
<h3>Description</h3>
<blockquote>
<p>
You will not need this unless you are doing something special
</blockquote>
<hr>
<h2>lws_rx_flow_control - Enable and disable socket servicing for received packets.</h2>
<i>int</i>
<b>lws_rx_flow_control</b>
(<i>struct lws *</i> <b>wsi</b>,
<i>int</i> <b>enable</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket connection instance to get callback for
<dt><b>enable</b>
<dd>0 = disable read servicing for this connection, 1 = enable
</dl>
<h3>Description</h3>
<blockquote>
<p>
If the output side of a server process becomes choked, this allows flow
control for the input side.
</blockquote>
<hr>
<h2>lws_rx_flow_allow_all_protocol - Allow all connections with this protocol to receive</h2>
<i>void</i>
<b>lws_rx_flow_allow_all_protocol</b>
(<i>const struct lws_context *</i> <b>context</b>,
<i>const struct lws_protocols *</i> <b>protocol</b>)
<h3>Arguments</h3>
<dl>
<dt><b>protocol</b>
<dd>all connections using this protocol will be allowed to receive
</dl>
<h3>Description</h3>
<blockquote>
<p>
When the user server code realizes it can accept more input, it can
call this to have the RX flow restriction removed from all connections using
the given protocol.
</blockquote>
<hr>
<h2>lws_canonical_hostname - returns this host's hostname</h2>
<i>const char *</i>
<b>lws_canonical_hostname</b>
(<i>struct lws_context *</i> <b>context</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
</dl>
<h3>Description</h3>
<blockquote>
<p>
This is typically used by client code to fill in the host parameter
when making a client connection.  You can only call it after the context
has been created.
</blockquote>
<hr>
<h2>lws_set_proxy - Setups proxy to lws_context.</h2>
<i>int</i>
<b>lws_set_proxy</b>
(<i>struct lws_context *</i> <b>context</b>,
<i>const char *</i> <b>proxy</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>pointer to struct lws_context you want set proxy to
<dt><b>proxy</b>
<dd>pointer to c string containing proxy in format address:port
</dl>
<h3>Description</h3>
<blockquote>
Returns 0 if proxy string was parsed and proxy was setup.
Returns -1 if <tt><b>proxy</b></tt> is NULL or has incorrect format.
<p>
This is only required if your OS does not provide the http_proxy
environment variable (eg, OSX)
<p>
IMPORTANT! You should call this function right after creation of the
lws_context and before call to connect. If you call this
function after connect behavior is undefined.
This function will override proxy settings made on lws_context
creation with <b>genenv</b> call.
</blockquote>
<hr>
<h2>lws_get_protocol - Returns a protocol pointer from a websocket connection.</h2>
<i>const struct lws_protocols *</i>
<b>lws_get_protocol</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>pointer to struct websocket you want to know the protocol of
</dl>
<h3>Description</h3>
<blockquote>
<p>
Some apis can act on all live connections of a given protocol,
this is how you can get a pointer to the active protocol if needed.
</blockquote>
<hr>
<h2>lws_set_log_level - Set the logging bitfield</h2>
<i>void</i>
<b>lws_set_log_level</b>
(<i>int</i> <b>level</b>,
<i>void (*</i><b>func</b>) <i>(int level, const char *line)</i>)
<h3>Arguments</h3>
<dl>
<dt><b>level</b>
<dd>OR together the LLL_ debug contexts you want output from
</dl>
<h3>Description</h3>
<blockquote>
log level defaults to "err", "warn" and "notice" contexts enabled and
emission on stderr.
</blockquote>
<hr>
<h2>lws_is_ssl - Find out if connection is using SSL</h2>
<i>int</i>
<b>lws_is_ssl</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>websocket connection to check
</dl>
<h3>Description</h3>
<blockquote>
Returns 0 if the connection is not using SSL, 1 if using SSL and
using verified cert, and 2 if using SSL but the cert was not
checked (appears for client wsi told to skip check on connection)
</blockquote>
<hr>
<h2>lws_partial_buffered - find out if lws buffered the last write</h2>
<i>int</i>
<b>lws_partial_buffered</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>websocket connection to check
</dl>
<h3>Description</h3>
<blockquote>
Returns 1 if you cannot use lws_write because the last
write on this connection is still buffered, and can't be cleared without
returning to the service loop and waiting for the connection to be
writeable again.
<p>
If you will try to do &gt;1 lws_write call inside a single
WRITEABLE callback, you must check this after every write and bail if
set, ask for a new writeable callback and continue writing from there.
<p>
This is never set at the start of a writeable callback, but any write
may set it.
</blockquote>
<hr>
<h2>lws_get_library_version - </h2>
<i>const char *</i>
<b>lws_get_library_version</b>
(<i></i> <b>void</b>)
<h3>Arguments</h3>
<dl>
<dt><b>void</b>
<dd>no arguments
</dl>
<h3>Description</h3>
<blockquote>
<p>
returns a const char * to a string like "1.1 178d78c"
representing the library version followed by the git head hash it
was built from
</blockquote>
<hr>
<h2>lws_create_context - Create the websocket handler</h2>
<i>struct lws_context *</i>
<b>lws_create_context</b>
(<i>struct lws_context_creation_info *</i> <b>info</b>)
<h3>Arguments</h3>
<dl>
<dt><b>info</b>
<dd>pointer to struct with parameters
</dl>
<h3>Description</h3>
<blockquote>
This function creates the listening socket (if serving) and takes care
of all initialization in one step.
<p>
After initialization, it returns a struct lws_context * that
represents this server.  After calling, user code needs to take care
of calling <b>lws_service</b> with the context pointer to get the
server's sockets serviced.  This must be done in the same process
context as the initialization call.
<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>lws_context_destroy - Destroy the websocket context</h2>
<i>void</i>
<b>lws_context_destroy</b>
(<i>struct lws_context *</i> <b>context</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
</dl>
<h3>Description</h3>
<blockquote>
This function closes any active connections and then frees the
context.  After calling this, any further use of the context is
undefined.
</blockquote>
<hr>
<h2>lws_callback_on_writable - Request a callback when this socket becomes able to be written to without blocking</h2>
<i>int</i>
<b>lws_callback_on_writable</b>
(<i>struct lws *</i> <b>wsi</b>)
<h3>Arguments</h3>
<dl>
<dt><b>wsi</b>
<dd>Websocket connection instance to get callback for
</dl>
<hr>
<h2>lws_callback_on_writable_all_protocol - Request a callback for all connections using the given protocol when it becomes possible to write to each socket without blocking in turn.</h2>
<i>int</i>
<b>lws_callback_on_writable_all_protocol</b>
(<i>const struct lws_context *</i> <b>context</b>,
<i>const struct lws_protocols *</i> <b>protocol</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>lws_context
<dt><b>protocol</b>
<dd>Protocol whose connections will get callbacks
</dl>
<hr>
<h2>lws_cancel_service - Cancel servicing of pending websocket activity</h2>
<i>void</i>
<b>lws_cancel_service</b>
(<i>struct lws_context *</i> <b>context</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
</dl>
<h3>Description</h3>
<blockquote>
This function let a call to <b>lws_service</b> waiting for a timeout
immediately return.
</blockquote>
<hr>
<h2>lws_cancel_service - Cancel servicing of pending websocket activity</h2>
<i>void</i>
<b>lws_cancel_service</b>
(<i>struct lws_context *</i> <b>context</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
</dl>
<h3>Description</h3>
<blockquote>
This function let a call to <b>lws_service</b> waiting for a timeout
immediately return.
</blockquote>
<hr>
<h2>lws_cancel_service - Cancel servicing of pending websocket activity</h2>
<i>void</i>
<b>lws_cancel_service</b>
(<i>struct lws_context *</i> <b>context</b>)
<h3>Arguments</h3>
<dl>
<dt><b>context</b>
<dd>Websocket context
</dl>
<h3>Description</h3>
<blockquote>
This function let a call to <b>lws_service</b> waiting for a timeout
immediately return.
<p>
There is no <b>poll</b> in MBED3, he will fire callbacks when he feels like
it.
</blockquote>
<hr>
<h2>struct lws_plat_file_ops - Platform-specific file operations</h2>
<b>struct lws_plat_file_ops</b> {<br>
&nbsp; &nbsp; <i>lws_filefd_type (*</i><b>open</b>) <i>(struct lws *wsi, const char *filename,unsigned long *filelen, int flags)</i>;<br>
&nbsp; &nbsp; <i>int (*</i><b>close</b>) <i>(struct lws *wsi, lws_filefd_type fd)</i>;<br>
&nbsp; &nbsp; <i>unsigned long (*</i><b>seek_cur</b>) <i>(struct lws *wsi, lws_filefd_type fd,long offset_from_cur_pos)</i>;<br>
&nbsp; &nbsp; <i>int (*</i><b>read</b>) <i>(struct lws *wsi, lws_filefd_type fd, unsigned long *amount,unsigned char *buf, unsigned long len)</i>;<br>
&nbsp; &nbsp; <i>int (*</i><b>write</b>) <i>(struct lws *wsi, lws_filefd_type fd, unsigned long *amount,unsigned char *buf, unsigned long len)</i>;<br>
};<br>
<h3>Members</h3>
<dl>
<dt><b>open</b>
<dd>Open file (always binary access if plat supports it)
filelen is filled on exit to be the length of the file
flags should be set to O_RDONLY or O_RDWR
<dt><b>close</b>
<dd>Close file
<dt><b>seek_cur</b>
<dd>Seek from current position
<dt><b>read</b>
<dd>Read fron file *amount is set on exit to amount read
<dt><b>write</b>
<dd>Write to file *amount is set on exit as amount written
</dl>
<h3>Description</h3>
<blockquote>
<p>
These provide platform-agnostic ways to deal with filesystem access in the
library and in the user code.
</blockquote>
<hr>
<h2>callback - User server actions</h2>
<i>LWS_EXTERN int</i>
<b>callback</b>
(<i>const struct lws *</i> <b>wsi</b>,
<i>enum lws_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 lws_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 the server completes a handshake with
an incoming client.  If you built the library
with ssl support, <tt><b>in</b></tt> is a pointer to the
ssl struct associated with the connection or
NULL.
</blockquote>
<h3>LWS_CALLBACK_CLIENT_CONNECTION_ERROR</h3>
<blockquote>
the request client connection has
been unable to complete a handshake with the remote server.  If
in is non-NULL, you can find an error string of length len where
it points to.
</blockquote>
<h3>LWS_CALLBACK_CLIENT_FILTER_PRE_ESTABLISH</h3>
<blockquote>
this is the last chance for the
client user code to examine the http headers
and decide to reject the connection.  If the
content in the headers is interesting to the
client (url, etc) it needs to copy it out at
this point since it will be destroyed before
the CLIENT_ESTABLISHED call
</blockquote>
<h3>LWS_CALLBACK_CLIENT_ESTABLISHED</h3>
<blockquote>
after your client connection completed
a handshake with the remote server
</blockquote>
<h3>LWS_CALLBACK_CLOSED</h3>
<blockquote>
when the websocket session ends
</blockquote>
<h3>LWS_CALLBACK_CLOSED_HTTP</h3>
<blockquote>
when a HTTP (non-websocket) session ends
</blockquote>
<h3>LWS_CALLBACK_RECEIVE</h3>
<blockquote>
data has appeared for this server endpoint from a
remote client, it can be found at *in and is
len bytes long
</blockquote>
<h3>LWS_CALLBACK_CLIENT_RECEIVE_PONG</h3>
<blockquote>
if you elected to see PONG packets,
they appear with this callback reason.  PONG
packets only exist in 04+ protocol
</blockquote>
<h3>LWS_CALLBACK_CLIENT_RECEIVE</h3>
<blockquote>
data has appeared from the server for the
client connection, 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>lws_serve_http_file</b> makes it very
simple to send back a file to the client.
Normally after sending the file you are done
with the http connection, since the rest of the
activity will come by websockets from the script
that was delivered by http, so you will want to
return 1; to close and free up the connection.
That's important because it uses a slot in the
total number of client connections allowed set
by MAX_CLIENTS.
</blockquote>
<h3>LWS_CALLBACK_HTTP_BODY</h3>
<blockquote>
the next <tt><b>len</b></tt> bytes data from the http
request body HTTP connection is now available in <tt><b>in</b></tt>.
</blockquote>
<h3>LWS_CALLBACK_HTTP_BODY_COMPLETION</h3>
<blockquote>
the expected amount of http request
body has been delivered
</blockquote>
<h3>LWS_CALLBACK_HTTP_WRITEABLE</h3>
<blockquote>
you can write more down the http protocol
link now.
</blockquote>
<h3>LWS_CALLBACK_HTTP_FILE_COMPLETION</h3>
<blockquote>
a file requested to be send down
http link has completed.
</blockquote>
<h3>LWS_CALLBACK_SERVER_WRITEABLE</h3>
<blockquote>
If you call
<b>lws_callback_on_writable</b> on a connection, you will
get one of these callbacks coming when the connection socket
is able to accept another write packet without blocking.
If it already was able to take another packet without blocking,
you'll get this callback at the next call to the service loop
function.  Notice that CLIENTs get LWS_CALLBACK_CLIENT_WRITEABLE
and servers get LWS_CALLBACK_SERVER_WRITEABLE.
</blockquote>
<h3>LWS_CALLBACK_FILTER_NETWORK_CONNECTION</h3>
<blockquote>
called when a client connects to
the server at network level; the connection is accepted but then
passed to this callback to decide whether to hang up immediately
or not, based on the client IP.  <tt><b>in</b></tt> contains the connection
socket's descriptor. Since the client connection information is
not available yet, <tt><b>wsi</b></tt> still pointing to the main server socket.
Return non-zero to terminate the connection before sending or
receiving anything. Because this happens immediately after the
network connection from the client, there's no websocket protocol
selected yet so this callback is issued only to protocol 0.
</blockquote>
<h3>LWS_CALLBACK_SERVER_NEW_CLIENT_INSTANTIATED</h3>
<blockquote>
A new client just had
been connected, accepted, and instantiated into the pool. This
callback allows setting any relevant property to it. Because this
happens immediately after the instantiation of a new client,
there's no websocket protocol selected yet so this callback is
issued only to protocol 0. Only <tt><b>wsi</b></tt> is defined, pointing to the
new client, and the return value is ignored.
</blockquote>
<h3>LWS_CALLBACK_FILTER_HTTP_CONNECTION</h3>
<blockquote>
called when the request has
been received and parsed from the client, but the response is
not sent yet.  Return non-zero to disallow the connection.
<tt><b>user</b></tt> is a pointer to the connection user space allocation,
<tt><b>in</b></tt> is the URI, eg, "/"
In your handler you can use the public APIs
<b>lws_hdr_total_length</b> / <b>lws_hdr_copy</b> to access all of the
headers using the header enums lws_token_indexes from
libwebsockets.h to check for and read the supported header
presence and content before deciding to allow the http
connection to proceed or to kill the connection.
</blockquote>
<h3>LWS_CALLBACK_FILTER_PROTOCOL_CONNECTION</h3>
<blockquote>
called when the handshake has
been received and parsed from the client, but the response is
not sent yet.  Return non-zero to disallow the connection.
<tt><b>user</b></tt> is a pointer to the connection user space allocation,
<tt><b>in</b></tt> is the requested protocol name
In your handler you can use the public APIs
<b>lws_hdr_total_length</b> / <b>lws_hdr_copy</b> to access all of the
headers using the header enums lws_token_indexes from
libwebsockets.h to check for and read the supported header
presence and content before deciding to allow the handshake
to proceed or to kill the connection.
</blockquote>
<h3>LWS_CALLBACK_OPENSSL_LOAD_EXTRA_CLIENT_VERIFY_CERTS</h3>
<blockquote>
if configured for
including OpenSSL support, this callback allows your user code
to perform extra <b>SSL_CTX_load_verify_locations</b> or similar
calls to direct OpenSSL where to find certificates the client
can use to confirm the remote server identity.  <tt><b>user</b></tt> is the
OpenSSL SSL_CTX*
</blockquote>
<h3>LWS_CALLBACK_OPENSSL_LOAD_EXTRA_SERVER_VERIFY_CERTS</h3>
<blockquote>
if configured for
including OpenSSL support, this callback allows your user code
to load extra certifcates into the server which allow it to
verify the validity of certificates returned by clients.  <tt><b>user</b></tt>
is the server's OpenSSL SSL_CTX*
</blockquote>
<h3>LWS_CALLBACK_OPENSSL_CONTEXT_REQUIRES_PRIVATE_KEY</h3>
<blockquote>
if configured for
including OpenSSL support but no private key file has been specified
(ssl_private_key_filepath is NULL), this callback is called to
allow the user to set the private key directly via libopenssl
and perform further operations if required; this might be useful
in situations where the private key is not directly accessible by
the OS, for example if it is stored on a smartcard
<tt><b>user</b></tt> is the server's OpenSSL SSL_CTX*
</blockquote>
<h3>LWS_CALLBACK_OPENSSL_PERFORM_CLIENT_CERT_VERIFICATION</h3>
<blockquote>
if the
libwebsockets context was created with the option
LWS_SERVER_OPTION_REQUIRE_VALID_OPENSSL_CLIENT_CERT, then this
callback is generated during OpenSSL verification of the cert
sent from the client.  It is sent to protocol[0] callback as
no protocol has been negotiated on the connection yet.
Notice that the libwebsockets context and wsi are both NULL
during this callback.  See
</blockquote>
<h3>http</h3>
<blockquote>
//www.openssl.org/docs/ssl/SSL_CTX_set_verify.html
to understand more detail about the OpenSSL callback that
generates this libwebsockets callback and the meanings of the
arguments passed.  In this callback, <tt><b>user</b></tt> is the x509_ctx,
<tt><b>in</b></tt> is the ssl pointer and <tt><b>len</b></tt> is preverify_ok
Notice that this callback maintains libwebsocket return
conventions, return 0 to mean the cert is OK or 1 to fail it.
This also means that if you don't handle this callback then
the default callback action of returning 0 allows the client
certificates.
</blockquote>
<h3>LWS_CALLBACK_CLIENT_APPEND_HANDSHAKE_HEADER</h3>
<blockquote>
this callback happens
when a client handshake is being compiled.  <tt><b>user</b></tt> is NULL,
<tt><b>in</b></tt> is a char **, it's pointing to a char * which holds the
next location in the header buffer where you can add
headers, and <tt><b>len</b></tt> is the remaining space in the header buffer,
which is typically some hundreds of bytes.  So, to add a canned
cookie, your handler code might look similar to:
<p>
char **p = (char **)in;
<p>
if (len &lt; 100)
return 1;
<p>
*p += sprintf(*p, "Cookie: a=b\x0d\x0a");
<p>
return 0;
<p>
Notice if you add anything, you just have to take care about
the CRLF on the line you added.  Obviously this callback is