## lws_frame_is_binary -

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.

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

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.

## lws_get_library_version -

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

## libwebsockets_get_peer_addresses - Get client address information

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 qotted 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.

## libwebsocket_service_fd - Service polled socket with something waiting

int libwebsocket_service_fd (struct libwebsocket_context * context, struct 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.

## libwebsocket_context_destroy - Destroy the websocket context

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.

## libwebsocket_context_user - get the user data associated with the context

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.

## libwebsocket_service - Service any pending websocket activity

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.

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

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

### Arguments

context
  libwebsockets context
wsi
  Websocket connection instance to get callback for

## 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.

int libwebsocket_callback_on_writable_all_protocol (const struct libwebsocket_protocols * protocol)

### Arguments

protocol
  Protocol whose connections will get callbacks

## libwebsocket_set_timeout - marks the wsi as subject to a timeout

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

## libwebsocket_get_socket_fd - returns the socket file descriptor

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

## libwebsocket_rx_flow_control - Enable and disable socket servicing for receieved packets.

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.

## libwebsocket_rx_flow_allow_all_protocol - Allow all connections with this protocol to receive

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.

## libwebsocket_canonical_hostname - returns this host's hostname

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.

## libwebsocket_create_context - Create the websocket handler

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 can be done in the same process context or a forked process, or another thread,

> 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.

## libwebsockets_get_protocol - Returns a protocol pointer from a websocket connection.

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.

## lws_set_log_level - Set the logging bitfield

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.

## libwebsocket_write - Apply protocol then write data to client

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.

## libwebsockets_serve_http_file - Send a file back to the client using http

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

### 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

### 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 the wsi should be closed. ==0 indicates the file transfer is started and needs more service later, the wsi should be left alone.

## libwebsocket_client_connect - Connect to another websocket server

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.
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

## libwebsocket_client_connect_extended - Connect to another websocket server

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

## callback - User server actions

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_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_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. 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_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 an array of struct lws_tokens, you can use 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_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.

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

### 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` contains the fd, and `len` is the events bitmap (like, POLLIN). 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 the socket desricptor. If you are using the internal polling loop, you can just ignore it.

### LWS_CALLBACK_SET_MODE_POLL_FD

> This callback happens when libwebsockets wants to modify the events for the socket descriptor in `in`. The handler should OR `len` on to the events member of the pollfd struct for this socket descriptor. If you are using the internal polling loop, you can just ignore it.

### LWS_CALLBACK_CLEAR_MODE_POLL_FD

> This callback occurs when libwebsockets wants to modify the events for the socket descriptor in `in`. The handler should AND ~`len` on to the events member of the pollfd struct for this socket descriptor. If you are using the internal polling loop, you can just ignore it.

## extension_callback - Hooks to allow extensions to operate

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;
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.
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.

## 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;
const char * ssl_cert_filepath;
const char * ssl_private_key_filepath;
const char * ssl_ca_filepath;
const char * ssl_cipher_list;
int gid;
int uid;
unsigned int options;
void * user;
int ka_time;
int ka_probes;
int ka_interval;
};

### Members

port
  Port to listen on... you can use 0 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.
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, else ignored
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"
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