cowboy_websocket_handler

The cowboy_websocket_handler behaviour defines the interface used by Websocket handlers.

The init/3 and websocket_init/3 callbacks will always be called, followed by zero or more calls to websocket_handle/3 and websocket_info/3. The websocket_terminate/3 will always be called last.

Types

None.

Callbacks

init({TransportName, ProtocolName}, Req, Opts) -> {upgrade, protocol, cowboy_websocket} | {upgrade, protocol, cowboy_websocket, Req, Opts}

Types:

• TransportName = tcp | ssl | atom()
• ProtocolName = http | atom()
• Req = cowboy_req:req()
• Opts = any()

Upgrade the protocol to cowboy_websocket.

websocket_init(TransportName, Req, Opts) -> {ok, Req, State} | {ok, Req, State, hibernate} | {ok, Req, State, Timeout} | {ok, Req, State, Timeout, hibernate} | {shutdown, Req}

Types:

• TransportName = tcp | ssl | atom()
• Req = cowboy_req:req()
• Opts = any()
• State = any()
• Timeout = timeout()

Initialize the state for this session.

This function is called before the upgrade to Websocket occurs. It can be used to negotiate Websocket protocol extensions with the client. It will typically be used to register this process to an event manager or a message queue in order to receive the messages the handler wants to process.

The connection will stay up for a duration of up to Timeout milliseconds after it last received data from the socket, at which point it will stop and close the connection. By default this value is set to infinity. It is recommended to either set this value or ensure by any other mechanism that the handler will be closed after a certain period of inactivity.

The hibernate option will hibernate the process until it starts receiving either data from the Websocket connection or Erlang messages.

The shutdown return value can be used to close the connection before upgrading to Websocket.

websocket_handle(InFrame, Req, State) -> {ok, Req, State} | {ok, Req, State, hibernate} | {reply, OutFrame | [OutFrame], Req, State} | {reply, OutFrame | [OutFrame], Req, State, hibernate} | {shutdown, Req, State}

Types:

• InFrame = {text | binary | ping | pong, binary()}
• Req = cowboy_req:req()
• State = any()
• OutFrame = cowboy_websocket:frame()

Handle the data received from the Websocket connection.

This function will be called every time data is received from the Websocket connection.

The shutdown return value can be used to close the connection. A close reply will also result in the connection being closed.

The hibernate option will hibernate the process until it receives new data from the Websocket connection or an Erlang message.

websocket_info(Info, Req, State) -> {ok, Req, State} | {ok, Req, State, hibernate} | {reply, OutFrame | [OutFrame], Req, State} | {reply, OutFrame | [OutFrame], Req, State, hibernate} | {shutdown, Req, State}

Types:

• Info = any()
• Req = cowboy_req:req()
• State = any()
• OutFrame = cowboy_websocket:frame()

Handle the Erlang message received.

This function will be called every time an Erlang message has been received. The message can be any Erlang term.

The shutdown return value can be used to close the connection. A close reply will also result in the connection being closed.

The hibernate option will hibernate the process until it receives another message or new data from the Websocket connection.

websocket_terminate(Reason, Req, State) -> ok

Types:

• Reason = {normal, shutdown | timeout} | {remote, closed} | {remote, cowboy_websocket:close_code(), binary()} | {error, badencoding | badframe | closed | atom()}
• Req = cowboy_req:req()
• State = any()

Perform any necessary cleanup of the state.

The connection will be closed and the process stopped right after this call.