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52f28ce67a
Also introduce libwebsockets_broadcast_foreign() separate from libwebsockets_broadcast() Signed-off-by: Andy Green <andy.green@linaro.org>
116 lines
4.3 KiB
Text
116 lines
4.3 KiB
Text
Daemonization
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-------------
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There's a helper api lws_daemonize built by default that does everything you
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need to daemonize well, including creating a lock file. If you're making
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what's basically a daemon, just call this early in your init to fork to a
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headless background process and exit the starting process.
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Notice stdout, stderr, stdin are all redirected to /dev/null to enforce your
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daemon is headless, so you'll need to sort out alternative logging, by, eg,
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syslog.
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Maximum number of connections
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-----------------------------
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The maximum number of connections the library can deal with is decided when
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it starts by querying the OS to find out how many file descriptors it is
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allowed to open (1024 on Fedora for example). It then allocates arrays that
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allow up to that many connections, minus whatever other file descriptors are
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in use by the user code.
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If you want to restrict that allocation, or increase it, you can use ulimit or
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similar to change the avaiable number of file descriptors, and when restarted
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libwebsockets will adapt accordingly.
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Procedure for sending data from other threads or process contexts
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-----------------------------------------------------------------
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Libwebsockets is carefully designed to work with no blocking in a single thread.
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In some cases where you will add libwebsockets to something else that uses the
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same single thread approach, you can so a safe implementation by combining the
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poll() loops as described in "External Polling loop support" below.
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In other cases, you find you have asynchronous events coming from other thread
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or process contexts and there's not much you can do about it. If you just try
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to randomly send, or broadcast using libwebsockets_broadcast() from these other
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places things will blow up either quickly or when the events on the two threads
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interefere with each other. It's not legal to do this.
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For those situations, you can use libwebsockets_broadcast_foreign(). This
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serializes the data you're sending using a private, per-protocol socket, so the
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service thread picks it up when it's ready, and it is serviced from the service
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thread context only.
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Fragmented messages
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-------------------
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To support fragmented messages you need to check for the final
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frame of a message with libwebsocket_is_final_fragment. This
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check can be combined with libwebsockets_remaining_packet_payload
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to gather the whole contents of a message, eg:
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case LWS_CALLBACK_RECEIVE:
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{
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Client * const client = (Client *)user;
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const size_t remaining = libwebsockets_remaining_packet_payload(wsi);
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if (!remaining && libwebsocket_is_final_fragment(wsi)) {
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if (client->HasFragments()) {
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client->AppendMessageFragment(in, len, 0);
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in = (void *)client->GetMessage();
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len = client->GetMessageLength();
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}
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client->ProcessMessage((char *)in, len, wsi);
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client->ResetMessage();
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} else
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client->AppendMessageFragment(in, len, remaining);
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}
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break;
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The test app llibwebsockets-test-fraggle sources also show how to
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deal with fragmented messages.
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Debug Logging
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-------------
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Also using lws_set_log_level api you may provide a custom callback to actually
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emit the log string. By default, this points to an internal emit function
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that sends to stderr. Setting it to NULL leaves it as it is instead.
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A helper function lwsl_emit_syslog() is exported from the library to simplify
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logging to syslog. You still need to use setlogmask, openlog and closelog
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in your user code.
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The logging apis are made available for user code.
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lwsl_err(...)
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lwsl_warn(...)
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lwsl_notice(...)
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lwsl_info(...)
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lwsl_debug(...)
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The difference between notice and info is that notice will be logged by default
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whereas info is ignored by default.
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External Polling Loop support
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-----------------------------
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libwebsockets maintains an internal poll() array for all of its
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sockets, but you can instead integrate the sockets into an
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external polling array. That's needed if libwebsockets will
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cooperate with an existing poll array maintained by another
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server.
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Four callbacks LWS_CALLBACK_ADD_POLL_FD, LWS_CALLBACK_DEL_POLL_FD,
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LWS_CALLBACK_SET_MODE_POLL_FD and LWS_CALLBACK_CLEAR_MODE_POLL_FD
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appear in the callback for protocol 0 and allow interface code to
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manage socket descriptors in other poll loops.
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