There's a helper api lws_daemonize built by default that does everything you need to daemonize well, including creating a lock file. If you're making what's basically a daemon, just call this early in your init to fork to a headless background process and exit the starting process.
Notice stdout, stderr, stdin are all redirected to /dev/null to enforce your daemon is headless, so you'll need to sort out alternative logging, by, eg, syslog.
The maximum number of connections the library can deal with is decided when it starts by querying the OS to find out how many file descriptors it is allowed to open (1024 on Fedora for example). It then allocates arrays that allow up to that many connections, minus whatever other file descriptors are in use by the user code.
If you want to restrict that allocation, or increase it, you can use ulimit or similar to change the avaiable number of file descriptors, and when restarted libwebsockets will adapt accordingly.
Directly performing websocket actions from other threads is not allowed. Aside from the internal data being inconsistent in forked() processes, the scope of a wsi (struct websocket) can end at any time during service with the socket closing and the wsi freed.
Websocket write activities should only take place in the LWS_CALLBACK_SERVER_WRITEABLE callback as described below.
Only live connections appear in the user callbacks, so this removes any possibility of trying to used closed and freed wsis.
If you need to service other socket or file descriptors as well as the websocket ones, you can combine them together with the websocket ones in one poll loop, see "External Polling Loop support" below, and still do it all in one thread / process context.
If you insist on trying to use it from multiple threads, take special care if you might simultaneously create more than one context from different threads.
SSL_library_init() is called from the context create api and it also is not reentrant. So at least create the contexts sequentially.
You should only send data on a websocket connection from the user callback LWS_CALLBACK_SERVER_WRITEABLE (or LWS_CALLBACK_CLIENT_WRITEABLE for clients).
If you want to send something, do not just send it but request a callback when the socket is writeable using
lws_callback_on_writable(context, wsi)`` for a specific wsi`, orlws_callback_on_writable_all_protocol(protocol) for all connections using that protocol to get a callback when next writeable.Usually you will get called back immediately next time around the service loop, but if your peer is slow or temporarily inactive the callback will be delayed accordingly. Generating what to write and sending it should be done in the ...WRITEABLE callback.
See the test server code for an example of how to do this.
Libwebsockets may generate additional LWS_CALLBACK_CLIENT_WRITEABLE events if it met network conditions where it had to buffer your send data internally.
So your code for LWS_CALLBACK_CLIENT_WRITEABLE needs to own the decision about what to send, it can't assume that just because the writeable callback came it really is time to send something.
It's quite possible you get an 'extra' writeable callback at any time and just need to return 0 and wait for the expected callback later.
When you want to close a connection, you do it by returning -1 from a callback for that connection.
You can provoke a callback by calling lws_callback_on_writable on the wsi, then notice in the callback you want to close it and just return -1. But usually, the decision to close is made in a callback already and returning -1 is simple.
If the socket knows the connection is dead, because the peer closed or there was an affirmitive network error like a FIN coming, then libwebsockets will take care of closing the connection automatically.
If you have a silently dead connection, it's possible to enter a state where the send pipe on the connection is choked but no ack will ever come, so the dead connection will never become writeable. To cover that, you can use TCP keepalives (see later in this document)
To support fragmented messages you need to check for the final frame of a message with lws_is_final_fragment. This check can be combined with libwebsockets_remaining_packet_payload to gather the whole contents of a message, eg:
case LWS_CALLBACK_RECEIVE:
{
Client * const client = (Client *)user;
const size_t remaining = lws_remaining_packet_payload(wsi);
if (!remaining && lws_is_final_fragment(wsi)) {
if (client->HasFragments()) {
client->AppendMessageFragment(in, len, 0);
in = (void *)client->GetMessage();
len = client->GetMessageLength();
}
client->ProcessMessage((char *)in, len, wsi);
client->ResetMessage();
} else
client->AppendMessageFragment(in, len, remaining);
}
break;
The test app libwebsockets-test-fraggle sources also show how to deal with fragmented messages.
Also using lws_set_log_level api you may provide a custom callback to actually emit the log string. By default, this points to an internal emit function that sends to stderr. Setting it to NULL leaves it as it is instead.
A helper function lwsl_emit_syslog() is exported from the library to simplify logging to syslog. You still need to use setlogmask, openlog and closelog in your user code.
The logging apis are made available for user code.
lwsl_err(...)lwsl_warn(...)lwsl_notice(...)lwsl_info(...)lwsl_debug(...)The difference between notice and info is that notice will be logged by default whereas info is ignored by default.
libwebsockets maintains an internal poll() array for all of its sockets, but you can instead integrate the sockets into an external polling array. That's needed if libwebsockets will cooperate with an existing poll array maintained by another server.
Four callbacks LWS_CALLBACK_ADD_POLL_FD, LWS_CALLBACK_DEL_POLL_FD, LWS_CALLBACK_SET_MODE_POLL_FD and LWS_CALLBACK_CLEAR_MODE_POLL_FD appear in the callback for protocol 0 and allow interface code to manage socket descriptors in other poll loops.
You can pass all pollfds that need service to lws_service_fd(), even if the socket or file does not belong to libwebsockets it is safe.
If libwebsocket handled it, it zeros the pollfd revents field before returning. So you can let libwebsockets try and if pollfd->revents is nonzero on return, you know it needs handling by your code.
The library is ready for use by C++ apps. You can get started quickly by copying the test server
$ cp test-server/test-server.c test.cpp
and building it in C++ like this
$ g++ -DINSTALL_DATADIR=\"/usr/share\" -ocpptest test.cpp -lwebsockets
INSTALL_DATADIR is only needed because the test server uses it as shipped, if you remove the references to it in your app you don't need to define it on the g++ line either.
From v1.2 of the library onwards, the HTTP header content is free()d as soon as the websocket connection is established. For websocket servers, you can copy interesting headers by handling LWS_CALLBACK_FILTER_PROTOCOL_CONNECTION callback, for clients there's a new callback just for this purpose LWS_CALLBACK_CLIENT_FILTER_PRE_ESTABLISH.
It is possible for a connection which is not being used to send to die silently somewhere between the peer and the side not sending. In this case by default TCP will just not report anything and you will never get any more incoming data or sign the link is dead until you try to send.
To deal with getting a notification of that situation, you can choose to enable TCP keepalives on all libwebsockets sockets, when you create the context.
To enable keepalive, set the ka_time member of the context creation parameter struct to a nonzero value (in seconds) at context creation time. You should also fill ka_probes and ka_interval in that case.
With keepalive enabled, the TCP layer will send control packets that should stimulate a response from the peer without affecting link traffic. If the response is not coming, the socket will announce an error at poll() forcing a close.
Note that BSDs don't support keepalive time / probes / interval per-socket like Linux does. On those systems you can enable keepalive by a nonzero value in ka_time, but the systemwide kernel settings for the time / probes/ interval are used, regardless of what nonzero value is in ka_time.
There's a member ssl_cipher_list in the lws_context_creation_info struct which allows the user code to restrict the possible cipher selection at context-creation time.
You might want to look into that to stop the ssl peers selecting a cipher which is too computationally expensive. To use it, point it to a string like
"RC4-MD5:RC4-SHA:AES128-SHA:AES256-SHA:HIGH:!DSS:!aNULL"
if left NULL, then the "DEFAULT" set of ciphers are all possible to select.
When you call lws_client_connect_info(..) and get a wsi back, it does not mean your connection is active. It just means it started trying to connect.
Your client connection is actually active only when you receive LWS_CALLBACK_CLIENT_ESTABLISHED for it.
There's a 5 second timeout for the connection, and it may give up or die for other reasons, if any of that happens you'll get a LWS_CALLBACK_CLIENT_CONNECTION_ERROR callback on protocol 0 instead for the wsi.
After attempting the connection and getting back a non-NULL wsi you should loop calling lws_service() until one of the above callbacks occurs.
As usual, see test-client.c for example code.
lws now exposes his internal platform file abstraction in a way that can be both used by user code to make it platform-agnostic, and be overridden or subclassed by user code. This allows things like handling the URI "directory space" as a virtual filesystem that may or may not be backed by a regular filesystem. One example use is serving files from inside large compressed archive storage without having to unpack anything except the file being requested.
The test server shows how to use it, basically the platform-specific part of lws prepares a file operations structure that lives in the lws context.
The user code can get a pointer to the file operations struct
LWS_VISIBLE LWS_EXTERN struct lws_plat_file_ops * lws_get_fops(struct lws_context *context);
and then can use helpers to also leverage these platform-independent file handling apis
static inline lws_filefd_type lws_plat_file_open(struct lws *wsi, const char *filename, unsigned long *filelen, int flags)
static inline int lws_plat_file_close(struct lws *wsi, lws_filefd_type fd)
static inline unsigned long lws_plat_file_seek_cur(struct lws *wsi, lws_filefd_type fd, long offset_from_cur_pos)
static inline int lws_plat_file_read(struct lws *wsi, lws_filefd_type fd, unsigned long *amount, unsigned char *buf, unsigned long len)
static inline int lws_plat_file_write(struct lws *wsi, lws_filefd_type fd, unsigned long *amount, unsigned char *buf, unsigned long len)
The user code can also override or subclass the file operations, to either wrap or replace them. An example is shown in test server.
ECDH Certs are now supported. Enable the CMake option
cmake .. -DLWS_SSL_SERVER_WITH_ECDH_CERT=1
and the info->options flag
LWS_SERVER_OPTION_SSL_ECDH
to build in support and select it at runtime.
SMP support is integrated into LWS without any internal threading. It's very simple to use, libwebsockets-test-server-pthread shows how to do it, use -j argument there to control the number of service threads up to 32.
Two new members are added to the info struct
unsigned int count_threads; unsigned int fd_limit_per_thread;
leave them at the default 0 to get the normal singlethreaded service loop.
Set count_threads to n to tell lws you will have n simultaneous service threads operating on the context.
There is still a single listen socket on one port, no matter how many service threads.
When a connection is made, it is accepted by the service thread with the least connections active to perform load balancing.
The user code is responsible for spawning n threads running the service loop associated to a specific tsi (Thread Service Index, 0 .. n - 1). See the libwebsockets-test-server-pthread for how to do.
If you leave fd_limit_per_thread at 0, then the process limit of fds is shared between the service threads; if you process was allowed 1024 fds overall then each thread is limited to 1024 / n.
You can set fd_limit_per_thread to a nonzero number to control this manually, eg the overall supported fd limit is less than the process allowance.
You can control the context basic data allocation for multithreading from Cmake using -DLWS_MAX_SMP=, if not given it's set to 32. The serv_buf allocation for the threads (currently 4096) is made at runtime only for active threads.
Because lws will limit the requested number of actual threads supported according to LWS_MAX_SMP, there is an api lws_get_count_threads(context) to discover how many threads were actually allowed when the context was created.
It's required to implement locking in the user code in the same way that libwebsockets-test-server-pthread does it, for the FD locking callbacks.
There is no knowledge or dependency in lws itself about pthreads. How the locking is implemented is entirely up to the user code.
You can select either or both
-DLWS_WITH_LIBEV=1 -DLWS_WITH_LIBUV=1
at cmake configure-time. The user application may use one of the context init options flags
LWS_SERVER_OPTION_LIBEV LWS_SERVER_OPTION_LIBUV
to indicate it will use either of the event libraries.
User code may set per-connection extension options now, using a new api "lws_set_extension_option()".
This should be called from the ESTABLISHED callback like this
lws_set_extension_option(wsi, "permessage-deflate", "rx_buf_size", "12"); /* 1 << 12 */
If the extension is not active (missing or not negotiated for the connection, or extensions are disabled on the library) the call is just returns -1. Otherwise the connection's extension has its named option changed.
The extension may decide to alter or disallow the change, in the example above permessage-deflate restricts the size of his rx output buffer also considering the protocol's rx_buf_size member.
You may open a generic http client connection using the same struct lws_client_connect_info used to create client ws[s] connections.
To stay in http[s], set the optional info member "method" to point to the string "GET" instead of the default NULL.
After the server headers are processed, when payload from the server is available the callback LWS_CALLBACK_RECEIVE_CLIENT_HTTP will be made.
You can choose whether to process the data immediately, or queue a callback when an outgoing socket is writeable to provide flow control, and process the data in the writable callback.
Either way you use the api lws_http_client_read() to access the data, eg
case LWS_CALLBACK_RECEIVE_CLIENT_HTTP:
{
char buffer[1024 + LWS_PRE];
char *px = buffer + LWS_PRE;
int lenx = sizeof(buffer) - LWS_PRE;
lwsl_notice("LWS_CALLBACK_RECEIVE_CLIENT_HTTP\n");
/*
* Often you need to flow control this by something
* else being writable. In that case call the api
* to get a callback when writable here, and do the
* pending client read in the writeable callback of
* the output.
*/
if (lws_http_client_read(wsi, &px, &lenx) < 0)
return -1;
while (lenx--)
putchar(*px++);
}
break;
If you set LWS_SERVER_OPTION_EXPLICIT_VHOSTS options flag when you create your context, it won't create a default vhost using the info struct members for compatibility. Instead you can call lws_create_vhost() afterwards to attach one or more vhosts manually.
LWS_VISIBLE struct lws_vhost * lws_create_vhost(struct lws_context *context, struct lws_context_creation_info *info, struct lws_http_mount *mounts);
lws_create_vhost() uses the same info struct as lws_create_context(), it ignores members related to context and uses the ones meaningful for vhost (marked with VH in libwebsockets.h).
struct lws_context_creation_info {
int port; /* VH */
const char *iface; /* VH */
const struct lws_protocols *protocols; /* VH */
const struct lws_extension *extensions; /* VH */
...
When you attach the vhost, if the vhost's port already has a listen socket then both vhosts share it and use SNI (is SSL in use) or the Host: header from the client to select the right one. Or if no other vhost already listening the a new listen socket is created.
There are some new members but mainly it's stuff you used to set at context creation time.
The last argument to lws_create_vhost() lets you associate a linked list of lws_http_mount structures with that vhost's URL 'namespace', in a similar way that unix lets you mount filesystems into areas of your / filesystem how you like and deal with the contents transparently.
struct lws_http_mount {
struct lws_http_mount *mount_next;
const char *mountpoint; /* mountpoint in http pathspace, eg, "/" */
const char *origin; /* path to be mounted, eg, "/var/www/warmcat.com" */
const char *def; /* default target, eg, "index.html" */
struct lws_protocol_vhost_options *cgienv;
int cgi_timeout;
int cache_max_age;
unsigned int cache_reusable:1;
unsigned int cache_revalidate:1;
unsigned int cache_intermediaries:1;
unsigned char origin_protocol;
unsigned char mountpoint_len;
};
The last mount structure should have a NULL mount_next, otherwise it should point to the 'next' mount structure in your list.
Both the mount structures and the strings must persist until the context is destroyed, since they are not copied but used in place.
.origin_protocol should be one of
enum {
LWSMPRO_HTTP,
LWSMPRO_HTTPS,
LWSMPRO_FILE,
LWSMPRO_CGI,
LWSMPRO_REDIR_HTTP,
LWSMPRO_REDIR_HTTPS,
};
LWSMPRO_FILE is used for mapping url namespace to a filesystem directory and serve it automatically.