libwebsocket manual

Name:

libwebsocket_cancel_service - Cancel servicing of pending websocket activity

Synopsis:

void libwebsocket_cancel_service (struct libwebsocket_context * context);

Arguments:

context
    Websocket context

Description:

This function let a call to libwebsocket_service waiting for a timeout
immediately return.

Name:

libwebsocket_cancel_service - Cancel servicing of pending websocket activity

Synopsis:

void libwebsocket_cancel_service (struct libwebsocket_context * context);

Arguments:

context
    Websocket context

Description:

This function let a call to libwebsocket_service waiting for a timeout
immediately return.

Name:

libwebsocket_service_fd - Service polled socket with something waiting

Synopsis:

int libwebsocket_service_fd (struct libwebsocket_context * context,
                             struct libwebsocket_pollfd * pollfd);

Arguments:

context
    Websocket context

pollfd
    The pollfd entry describing the socket fd and which events
happened.

Description:

This function takes a pollfd that has POLLIN or POLLOUT activity and
services it according to the state of the associated
struct libwebsocket.

The one call deals with all "service" that might happen on a socket
including listen accepts, http files as well as websocket protocol.

If a pollfd says it has something, you can just pass it to
libwebsocket_serice_fd 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->revents will be zeroed now.

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.

Name:

libwebsocket_service - Service any pending websocket activity

Synopsis:

int libwebsocket_service (struct libwebsocket_context * context,
                          int timeout_ms);

Arguments:

context
    Websocket context

timeout_ms
    Timeout for poll; 0 means return immediately if nothing needed
service otherwise block and service immediately, returning
after the timeout if nothing needed service.

Description:

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.

1) Accept new connections to our context's server

2) Call the receive callback for incoming frame data received by
server or client connections.

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.

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.

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.

Name:

lws_get_library_version -

Synopsis:

const char * lws_get_library_version ( void);

Arguments:

void
    no arguments

Description:

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

Name:

libwebsocket_create_context - Create the websocket handler

Synopsis:

struct libwebsocket_context * libwebsocket_create_context (struct lws_context_creation_info * info);

Arguments:

info
    pointer to struct with parameters

Description:

This function creates the listening socket (if serving) and takes care
of all initialization in one step.

After initialization, it returns a struct libwebsocket_context * that
represents this server.  After calling, user code needs to take care
of calling libwebsocket_service with the context pointer to get the
server's sockets serviced.  This must be done in the same process
context as the initialization call.

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.

HTTP requests are sent always to the FIRST protocol in protocol, since
at that time websocket protocol has not been negotiated.  Other
protocols after the first one never see any HTTP callack activity.

The server created is a simple http server by default; part of the
websocket standard is upgrading this http connection to a websocket one.

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.

Name:

libwebsocket_context_destroy - Destroy the websocket context

Synopsis:

void libwebsocket_context_destroy (struct libwebsocket_context * context);

Arguments:

context
    Websocket context

Description:

This function closes any active connections and then frees the
context.  After calling this, any further use of the context is
undefined.

Name:

libwebsockets_get_peer_addresses - Get client address information

Synopsis:

void libwebsockets_get_peer_addresses (struct libwebsocket_context * context,
                                       struct libwebsocket * wsi,
                                       int fd,
                                       char * name,
                                       int name_len,
                                       char * rip,
                                       int rip_len);

Arguments:

context
    Libwebsockets context

wsi
    Local struct libwebsocket associated with

fd
    Connection socket descriptor

name
    Buffer to take client address name

name_len
    Length of client address name buffer

rip
    Buffer to take client address IP dotted quad

rip_len
    Length of client address IP buffer

Description:

This function fills in name and rip with the name and IP of
the client connected with socket descriptor fd.  Names may be
truncated if there is not enough room.  If either cannot be
determined, they will be returned as valid zero-length strings.

Name:

libwebsocket_context_user - get the user data associated with the context

Synopsis:

LWS_EXTERN void * libwebsocket_context_user (struct libwebsocket_context * context);

Arguments:

context
    Websocket context

Description:

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.

Name:

libwebsocket_callback_all_protocol - Callback all connections using the given protocol with the given reason

Synopsis:

int libwebsocket_callback_all_protocol (const struct libwebsocket_protocols * protocol,
                                        int reason);

Arguments:

protocol
    Protocol whose connections will get callbacks

reason
    Callback reason index

Name:

libwebsocket_set_timeout - marks the wsi as subject to a timeout

Synopsis:

void libwebsocket_set_timeout (struct libwebsocket * wsi,
                               enum pending_timeout reason,
                               int secs);

Arguments:

wsi
    Websocket connection instance

reason
    timeout reason

secs
    how many seconds

Description:

You will not need this unless you are doing something special

Name:

libwebsocket_get_socket_fd - returns the socket file descriptor

Synopsis:

int libwebsocket_get_socket_fd (struct libwebsocket * wsi);

Arguments:

wsi
    Websocket connection instance

Description:

You will not need this unless you are doing something special

Name:

libwebsocket_rx_flow_control - Enable and disable socket servicing for received packets.

Synopsis:

int libwebsocket_rx_flow_control (struct libwebsocket * wsi,
                                  int enable);

Arguments:

wsi
    Websocket connection instance to get callback for

enable
    0 = disable read servicing for this connection, 1 = enable

Description:

If the output side of a server process becomes choked, this allows flow
control for the input side.

Name:

libwebsocket_rx_flow_allow_all_protocol - Allow all connections with this protocol to receive

Synopsis:

void libwebsocket_rx_flow_allow_all_protocol (const struct libwebsocket_protocols * protocol);

Arguments:

protocol
    all connections using this protocol will be allowed to receive

Description:

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.

Name:

libwebsocket_canonical_hostname - returns this host's hostname

Synopsis:

const char * libwebsocket_canonical_hostname (struct libwebsocket_context * context);

Arguments:

context
    Websocket context

Description:

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.

Name:

libwebsocket_set_proxy - Setups proxy to libwebsocket_context.

Synopsis:

int libwebsocket_set_proxy (struct libwebsocket_context * context,
                            const char * proxy);

Arguments:

context
    pointer to struct libwebsocket_context you want set proxy to

proxy
    pointer to c string containing proxy in format address:port

Description:

Returns 0 if proxy string was parsed and proxy was setup.
Returns -1 if proxy is NULL or has incorrect format.

This is only required if your OS does not provide the http_proxy
environment variable (eg, OSX)

IMPORTANT! You should call this function right after creation of the
libwebsocket_context and before call to connect. If you call this
function after connect behavior is undefined.
This function will override proxy settings made on libwebsocket_context
creation with genenv call.

Name:

libwebsockets_get_protocol - Returns a protocol pointer from a websocket connection.

Synopsis:

const struct libwebsocket_protocols * libwebsockets_get_protocol (struct libwebsocket * wsi);

Arguments:

wsi
    pointer to struct websocket you want to know the protocol of

Description:

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.

Name:

lws_set_log_level - Set the logging bitfield

Synopsis:

void lws_set_log_level (int level,
                        void (*log_emit_function) (int level,                                   const char *line);

Arguments:

level
    OR together the LLL_ debug contexts you want output from

log_emit_function
    NULL to leave it as it is, or a user-supplied
function to perform log string emission instead of
the default stderr one.

Description:

log level defaults to "err", "warn" and "notice" contexts enabled and
emission on stderr.

Name:

lws_is_ssl - Find out if connection is using SSL

Synopsis:

int lws_is_ssl (struct libwebsocket * wsi);

Arguments:

wsi
    websocket connection to check

Description:

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)

Name:

lws_partial_buffered - find out if lws buffered the last write

Synopsis:

int lws_partial_buffered (struct libwebsocket * wsi);

Arguments:

wsi
    websocket connection to check

Description:

Returns 1 if you cannot use libwebsocket_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.

If you will try to do >1 libwebsocket_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.

This is never set at the start of a writeable callback, but any write
may set it.

Name:

libwebsocket_client_connect - Connect to another websocket server

Synopsis:

struct libwebsocket * libwebsocket_client_connect (struct libwebsocket_context * context,
                                                   const char * address,
                                                   int port,
                                                   int ssl_connection,
                                                   const char * path,
                                                   const char * host,
                                                   const char * origin,
                                                   const char * protocol,
                                                   int ietf_version_or_minus_one);

Arguments:

context
    Websocket context

address
    Remote server address, eg, "myserver.com"

port
    Port to connect to on the remote server, eg, 80

ssl_connection
    0 = ws://, 1 = wss:// encrypted, 2 = wss:// allow self
signed certs

path
    Websocket path on server

host
    Hostname on server

origin
    Socket origin name

protocol
    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.

ietf_version_or_minus_one
    -1 to ask to connect using the default, latest
protocol supported, or the specific protocol ordinal

Description:

This function creates a connection to a remote server

Name:

libwebsocket_client_connect_extended - Connect to another websocket server

Synopsis:

struct libwebsocket * libwebsocket_client_connect_extended (struct libwebsocket_context * context,
                                                            const char * address,
                                                            int port,
                                                            int ssl_connection,
                                                            const char * path,
                                                            const char * host,
                                                            const char * origin,
                                                            const char * protocol,
                                                            int ietf_version_or_minus_one,
                                                            void * userdata);

Arguments:

context
    Websocket context

address
    Remote server address, eg, "myserver.com"

port
    Port to connect to on the remote server, eg, 80

ssl_connection
    0 = ws://, 1 = wss:// encrypted, 2 = wss:// allow self
signed certs

path
    Websocket path on server

host
    Hostname on server

origin
    Socket origin name

protocol
    Comma-separated list of protocols being asked for from
the server, or just one.  The server will pick the one it
likes best.

ietf_version_or_minus_one
    -1 to ask to connect using the default, latest
protocol supported, or the specific protocol ordinal

userdata
    Pre-allocated user data

Description:

This function creates a connection to a remote server

Name:

lws_http_transaction_completed - wait for new http transaction or close

Synopsis:

int lws_http_transaction_completed (struct libwebsocket * wsi);

Arguments:

wsi
    websocket connection

Description:

Returns 1 if the HTTP connection must close now
Returns 0 and resets connection to wait for new HTTP header /
transaction if possible

Name:

libwebsockets_return_http_status - Return simple http status

Synopsis:

int libwebsockets_return_http_status (struct libwebsocket_context * context,
                                      struct libwebsocket * wsi,
                                      unsigned int code,
                                      const char * html_body);

Arguments:

context
    libwebsockets context

wsi
    Websocket instance (available from user callback)

code
    Status index, eg, 404

html_body
    User-readable HTML description < 1KB, or NULL

Description:

Helper to report HTTP errors back to the client cleanly and
consistently

Name:

libwebsockets_serve_http_file - Send a file back to the client using http

Synopsis:

int libwebsockets_serve_http_file (struct libwebsocket_context * context,
                                   struct libwebsocket * wsi,
                                   const char * file,
                                   const char * content_type,
                                   const char * other_headers,
                                   int other_headers_len);

Arguments:

context
    libwebsockets context

wsi
    Websocket instance (available from user callback)

file
    The file to issue over http

content_type
    The http content type, eg, text/html

other_headers
    NULL or pointer to \0-terminated other header string

other_headers_len
    -- undescribed --

Description:

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.

Returning <0 indicates error and the wsi should be closed.  Returning
>0 indicates the file was completely sent and
lws_http_transaction_completed 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.

Name:

libwebsocket_write - Apply protocol then write data to client

Synopsis:

int libwebsocket_write (struct libwebsocket * wsi,
                        unsigned char * buf,
                        size_t len,
                        enum libwebsocket_write_protocol protocol);

Arguments:

wsi
    Websocket instance (available from user callback)

buf
    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.

len
    Count of the data bytes in the payload starting from buf

protocol
    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.

Description:

This function provides the way to issue data back to the client
for both http and websocket protocols.

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.

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.

Name:

libwebsocket_callback_on_writable - Request a callback when this socket becomes able to be written to without blocking

Synopsis:

int libwebsocket_callback_on_writable (struct libwebsocket_context * context,
                                       struct libwebsocket * wsi);

Arguments:

context
    libwebsockets context

wsi
    Websocket connection instance to get callback for

Name:

libwebsocket_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.

Synopsis:

int libwebsocket_callback_on_writable_all_protocol (const struct libwebsocket_protocols * protocol);

Arguments:

protocol
    Protocol whose connections will get callbacks

Name:

lws_frame_is_binary -

Synopsis:

int lws_frame_is_binary (struct libwebsocket * wsi);

Arguments:

wsi
    the connection we are inquiring about

Description:

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.

Name:

libwebsockets_remaining_packet_payload - Bytes to come before "overall" rx packet is complete

Synopsis:

size_t libwebsockets_remaining_packet_payload (struct libwebsocket * wsi);

Arguments:

wsi
    Websocket instance (available from user callback)

Description:

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 libwebsockets_remaining_packet_payload will return
0.

Many protocols won't care becuse their packets are always small.

Name:

callback - User server actions

Synopsis:

LWS_EXTERN int callback (struct libwebsocket_context * context,
                         struct libwebsocket * wsi,
                         enum libwebsocket_callback_reasons reason,
                         void * user,
                         void * in,
                         size_t len);

Arguments:

context
    Websockets context

wsi
    Opaque websocket instance pointer

reason
    The reason for the call

user
    Pointer to per-session user data allocated by library

in
    Pointer used for some callback reasons

len
    Length set for some callback reasons

Description:

This callback is the way the user controls what is served.  All the
protocol detail is hidden and handled by the library.

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.

You get an opportunity to initialize user data when called back with
LWS_CALLBACK_ESTABLISHED reason.
LWS_CALLBACK_ESTABLISHED:

after the server completes a handshake with
an incoming client
LWS_CALLBACK_CLIENT_CONNECTION_ERROR:

the request client connection has
been unable to complete a handshake with the remote server
LWS_CALLBACK_CLIENT_FILTER_PRE_ESTABLISH:

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
LWS_CALLBACK_CLIENT_ESTABLISHED:

after your client connection completed
a handshake with the remote server
LWS_CALLBACK_CLOSED:

when the websocket session ends
LWS_CALLBACK_CLOSED_HTTP:

when a HTTP (non-websocket) session ends
LWS_CALLBACK_RECEIVE:

data has appeared for this server endpoint from a
remote client, it can be found at *in and is
len bytes long
LWS_CALLBACK_CLIENT_RECEIVE_PONG:

if you elected to see PONG packets,
they appear with this callback reason.  PONG
packets only exist in 04+ protocol
LWS_CALLBACK_CLIENT_RECEIVE:

data has appeared from the server for the
client connection, it can be found at *in and
is len bytes long
LWS_CALLBACK_HTTP:

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.
in points to the URI path requested and
libwebsockets_serve_http_file 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.
LWS_CALLBACK_HTTP_BODY:

the next len bytes data from the http
request body HTTP connection is now available in in.
LWS_CALLBACK_HTTP_BODY_COMPLETION:

the expected amount of http request
body has been delivered
LWS_CALLBACK_HTTP_WRITEABLE:

you can write more down the http protocol
link now.
LWS_CALLBACK_HTTP_FILE_COMPLETION:

a file requested to be send down
http link has completed.
LWS_CALLBACK_SERVER_WRITEABLE:

If you call
libwebsocket_callback_on_writable 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.
LWS_CALLBACK_FILTER_NETWORK_CONNECTION:

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.  in contains the connection
socket's descriptor. Since the client connection information is
not available yet, wsi 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.
LWS_CALLBACK_SERVER_NEW_CLIENT_INSTANTIATED:

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 wsi is defined, pointing to the
new client, and the return value is ignored.
LWS_CALLBACK_FILTER_HTTP_CONNECTION:

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.
user is a pointer to the connection user space allocation,
in is the URI, eg, "/"
In your handler you can use the public APIs
lws_hdr_total_length / lws_hdr_copy 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.
LWS_CALLBACK_FILTER_PROTOCOL_CONNECTION:

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.
user is a pointer to the connection user space allocation,
in is the requested protocol name
In your handler you can use the public APIs
lws_hdr_total_length / lws_hdr_copy 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.
LWS_CALLBACK_OPENSSL_LOAD_EXTRA_CLIENT_VERIFY_CERTS:

if configured for
including OpenSSL support, this callback allows your user code
to perform extra SSL_CTX_load_verify_locations or similar
calls to direct OpenSSL where to find certificates the client
can use to confirm the remote server identity.  user is the
OpenSSL SSL_CTX*
LWS_CALLBACK_OPENSSL_LOAD_EXTRA_SERVER_VERIFY_CERTS:

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.  user
is the server's OpenSSL SSL_CTX*
LWS_CALLBACK_OPENSSL_CONTEXT_REQUIRES_PRIVATE_KEY:

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
user is the server's OpenSSL SSL_CTX*
LWS_CALLBACK_OPENSSL_PERFORM_CLIENT_CERT_VERIFICATION:

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
http:

//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, user is the x509_ctx,
in is the ssl pointer and len 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.
LWS_CALLBACK_CLIENT_APPEND_HANDSHAKE_HEADER:

this callback happens
when a client handshake is being compiled.  user is NULL,
in is a char **, it's pointing to a char * which holds the
next location in the header buffer where you can add
headers, and len 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:

char **p = (char **)in;

if (len < 100)
return 1;

*p += sprintf(*p, "Cookie: a=b\x0d\x0a");

return 0;

Notice if you add anything, you just have to take care about
the CRLF on the line you added.  Obviously this callback is
optional, if you don't handle it everything is fine.

Notice the callback is coming to protocols[0] all the time,
because there is no specific protocol handshook yet.
LWS_CALLBACK_CONFIRM_EXTENSION_OKAY:

When the server handshake code
sees that it does support a requested extension, before
accepting the extension by additing to the list sent back to
the client it gives this callback just to check that it's okay
to use that extension.  It calls back to the requested protocol
and with in being the extension name, len is 0 and user is
valid.  Note though at this time the ESTABLISHED callback hasn't
happened yet so if you initialize user content there, user
content during this callback might not be useful for anything.
Notice this callback comes to protocols[0].
LWS_CALLBACK_CLIENT_CONFIRM_EXTENSION_SUPPORTED:

When a client
connection is being prepared to start a handshake to a server,
each supported extension is checked with protocols[0] callback
with this reason, giving the user code a chance to suppress the
claim to support that extension by returning non-zero.  If
unhandled, by default 0 will be returned and the extension
support included in the header to the server.  Notice this
callback comes to protocols[0].
LWS_CALLBACK_PROTOCOL_INIT:

One-time call per protocol so it can
do initial setup / allocations etc
LWS_CALLBACK_PROTOCOL_DESTROY:

One-time call per protocol indicating
this protocol won't get used at all after this callback, the
context is getting destroyed.  Take the opportunity to
deallocate everything that was allocated by the protocol.
LWS_CALLBACK_WSI_CREATE:

outermost (earliest) wsi create notification
LWS_CALLBACK_WSI_DESTROY:

outermost (latest) wsi destroy notification

The next five reasons are optional and only need taking care of if you
will be integrating libwebsockets sockets into an external polling
array.

For these calls, in points to a struct libwebsocket_pollargs that
contains fd, events and prev_events members
LWS_CALLBACK_ADD_POLL_FD:

libwebsocket deals with its poll loop
internally, but in the case you are integrating with another
server you will need to have libwebsocket sockets share a
polling array with the other server.  This and the other
POLL_FD related callbacks let you put your specialized
poll array interface code in the callback for protocol 0, the
first protocol you support, usually the HTTP protocol in the
serving case.
This callback happens when a socket needs to be
added to the polling loop:

in points to a struct
libwebsocket_pollargs; the fd member of the struct is the file
descriptor, and events contains the active events.

If you are using the internal polling loop (the "service"
callback), you can just ignore these callbacks.
LWS_CALLBACK_DEL_POLL_FD:

This callback happens when a socket descriptor
needs to be removed from an external polling array.  in is
again the struct libwebsocket_pollargs containing the fd member
to be removed.  If you are using the internal polling
loop, you can just ignore it.
LWS_CALLBACK_CHANGE_MODE_POLL_FD:

This callback happens when
libwebsockets wants to modify the events for a connectiion.
in is the struct libwebsocket_pollargs with the fd to change.
The new event mask is in events member and the old mask is in
the prev_events member.
If you are using the internal polling loop, you can just ignore
it.
LWS_CALLBACK_UNLOCK_POLL:

These allow the external poll changes driven
by libwebsockets to participate in an external thread locking
scheme around the changes, so the whole thing is threadsafe.

Name:

extension_callback - Hooks to allow extensions to operate

Synopsis:

LWS_EXTERN int extension_callback (struct libwebsocket_context * context,
                                   struct libwebsocket_extension * ext,
                                   struct libwebsocket * wsi,
                                   enum libwebsocket_extension_callback_reasons reason,
                                   void * user,
                                   void * in,
                                   size_t len);

Arguments:

context
    Websockets context

ext
    This extension

wsi
    Opaque websocket instance pointer

reason
    The reason for the call

user
    Pointer to per-session user data allocated by library

in
    Pointer used for some callback reasons

len
    Length set for some callback reasons

Description:

Each extension that is active on a particular connection receives
callbacks during the connection lifetime to allow the extension to
operate on websocket data and manage itself.

Libwebsockets takes care of allocating and freeing "user" memory for
each active extension on each connection.  That is what is pointed to
by the user parameter.
LWS_EXT_CALLBACK_CONSTRUCT:

called when the server has decided to
select this extension from the list provided by the client,
just before the server will send back the handshake accepting
the connection with this extension active.  This gives the
extension a chance to initialize its connection context found
in user.
LWS_EXT_CALLBACK_CLIENT_CONSTRUCT:

same as LWS_EXT_CALLBACK_CONSTRUCT
but called when client is instantiating this extension.  Some
extensions will work the same on client and server side and then
you can just merge handlers for both CONSTRUCTS.
LWS_EXT_CALLBACK_DESTROY:

called when the connection the extension was
being used on is about to be closed and deallocated.  It's the
last chance for the extension to deallocate anything it has
allocated in the user data (pointed to by user) before the
user data is deleted.  This same callback is used whether you
are in client or server instantiation context.
LWS_EXT_CALLBACK_PACKET_RX_PREPARSE:

when this extension was active on
a connection, and a packet of data arrived at the connection,
it is passed to this callback to give the extension a chance to
change the data, eg, decompress it.  user is pointing to the
extension's private connection context data, in is pointing
to an lws_tokens struct, it consists of a char * pointer called
token, and an int called token_len.  At entry, these are
set to point to the received buffer and set to the content
length.  If the extension will grow the content, it should use
a new buffer allocated in its private user context data and
set the pointed-to lws_tokens members to point to its buffer.
LWS_EXT_CALLBACK_PACKET_TX_PRESEND:

this works the same way as
LWS_EXT_CALLBACK_PACKET_RX_PREPARSE above, except it gives the
extension a chance to change websocket data just before it will
be sent out.  Using the same lws_token pointer scheme in in,
the extension can change the buffer and the length to be
transmitted how it likes.  Again if it wants to grow the
buffer safely, it should copy the data into its own buffer and
set the lws_tokens token pointer to it.

struct libwebsocket_protocols - List of protocols and handlers server supports.

struct libwebsocket_protocols {
    const char * name;
    callback_function * callback;
    size_t per_session_data_size;
    size_t rx_buffer_size;
    unsigned int id;
    void * user;
    struct libwebsocket_context * owning_server;
    int protocol_index;
};

Members:

name
    Protocol name that must match the one given in the client
Javascript new WebSocket(url, 'protocol') name.

callback
    The service callback used for this protocol.  It allows the
service action for an entire protocol to be encapsulated in
the protocol-specific callback

per_session_data_size
    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

rx_buffer_size
    if you want atomic frames delivered to the callback, you
should set this to the size of the biggest legal frame that
you support.  If the frame size is exceeded, there is no
error, but the buffer will spill to the user callback when
full, which you can detect by using
libwebsockets_remaining_packet_payload().  Notice that you
just talk about frame size here, the LWS_SEND_BUFFER_PRE_PADDING
and post-padding are automatically also allocated on top.

id
    ignored by lws, but useful to contain user information bound
to the selected protocol.  For example if this protocol was
called "myprotocol-v2", you might set id to 2, and the user
code that acts differently according to the version can do so by
switch (wsi->protocol->id), user code might use some bits as
capability flags based on selected protocol version, etc.

user
    User provided context data at the protocol level.
Accessible via libwebsockets_get_protocol(wsi)->user
This should not be confused with wsi->user, it is not the same.
The library completely ignores any value in here.

owning_server
    the server init call fills in this opaque pointer when
registering this protocol with the server.

protocol_index
    which protocol we are starting from zero

Description:

This structure represents one protocol supported by the server.  An
array of these structures is passed to libwebsocket_create_server
allows as many protocols as you like to be handled by one server.

The first protocol given has its callback used for user callbacks when
there is no agreed protocol name, that's true during HTTP part of the
connection and true if the client did not send a Protocol:

header.

struct libwebsocket_extension - An extension we know how to cope with

struct libwebsocket_extension {
    const char * name;
    extension_callback_function * callback;
    size_t per_session_data_size;
    void * per_context_private_data;
};

Members:

name
    Formal extension name, eg, "deflate-stream"

callback
    Service callback

per_session_data_size
    Libwebsockets will auto-malloc this much
memory for the use of the extension, a pointer
to it comes in the @user callback parameter

per_context_private_data
    Optional storage for this extension that
is per-context, so it can track stuff across
all sessions, etc, if it wants

struct lws_context_creation_info -

struct lws_context_creation_info {
    int port;
    const char * iface;
    struct libwebsocket_protocols * protocols;
    struct libwebsocket_extension * extensions;
    struct lws_token_limits * token_limits;
    const char * ssl_cert_filepath;
    const char * ssl_private_key_filepath;
    const char * ssl_ca_filepath;
    const char * ssl_cipher_list;
    const char * http_proxy_address;
    unsigned int http_proxy_port;
    int gid;
    int uid;
    unsigned int options;
    void * user;
    int ka_time;
    int ka_probes;
    int ka_interval;
#ifdef LWS_OPENSSL_SUPPORT
    void * provided_client_ssl_ctx;
#else
    void * provided_client_ssl_ctx;
#endif
};

Members:

port
    Port to listen on... you can use CONTEXT_PORT_NO_LISTEN to
suppress listening on any port, that's what you want if you are
not running a websocket server at all but just using it as a
client

iface
    NULL to bind the listen socket to all interfaces, or the
interface name, eg, "eth2"

protocols
    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.
It's not const because we write the owning_server member

extensions
    NULL or array of libwebsocket_extension structs listing the
extensions this context supports.  If you configured with
--without-extensions, you should give NULL here.

token_limits
    NULL or struct lws_token_limits pointer which is initialized
with a token length limit for each possible WSI_TOKEN_***

ssl_cert_filepath
    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

ssl_private_key_filepath
    filepath to private key if wanting SSL mode;
if this is set to NULL but sll_cert_filepath is set, the
OPENSSL_CONTEXT_REQUIRES_PRIVATE_KEY callback is called to allow
setting of the private key directly via openSSL library calls

ssl_ca_filepath
    CA certificate filepath or NULL

ssl_cipher_list
    List of valid ciphers to use (eg,
"RC4-MD5:RC4-SHA:AES128-SHA:AES256-SHA:HIGH:!DSS:!aNULL"
or you can leave it as NULL to get "DEFAULT"

http_proxy_address
    If non-NULL, attempts to proxy via the given address

http_proxy_port
    If http_proxy_address was non-NULL, uses this port at the address

gid
    group id to change to after setting listen socket, or -1.

uid
    user id to change to after setting listen socket, or -1.

options
    0, or LWS_SERVER_OPTION_DEFEAT_CLIENT_MASK

user
    optional user pointer that can be recovered via the context
pointer using libwebsocket_context_user

ka_time
    0 for no keepalive, otherwise apply this keepalive timeout to
all libwebsocket sockets, client or server

ka_probes
    if ka_time was nonzero, after the timeout expires how many
times to try to get a response from the peer before giving up
and killing the connection

ka_interval
    if ka_time was nonzero, how long to wait before each ka_probes
attempt

provided_client_ssl_ctx
    If non-null, swap out libwebsockets ssl
implementation for the one provided by provided_ssl_ctx.
Libwebsockets no longer is responsible for freeing the context
if this option is selected.

provided_client_ssl_ctx
    If non-null, swap out libwebsockets ssl
implementation for the one provided by provided_ssl_ctx.
Libwebsockets no longer is responsible for freeing the context
if this option is selected.