Websocket Module

Since Origin / Contributor Maintainer Source
2016-08-02 Luís Fonseca Luís Fonseca websocket.c

A websocket client module that implements RFC6455 (version 13) and provides a simple interface to send and receive messages.

The implementation supports fragmented messages, automatically respondes to ping requests and periodically pings if the server isn't communicating.

SSL/TLS support

Take note of constraints documented in the net module.

websocket.createClient()

Creates a new websocket client. This client should be stored in a variable and will provide all the functions to handle a connection.

When the connection becomes closed, the same client can still be reused - the callback functions are kept - and you can connect again to any server.

Before disposing the client, make sure to call ws:close().

Syntax

websocket.createClient()

Parameters

none

Returns

websocketclient

Example

local ws = websocket.createClient()
-- ...
ws:close()
ws = nil

websocket.client:close()

Closes a websocket connection. The client issues a close frame and attemtps to gracefully close the websocket. If server doesn't reply, the connection is terminated after a small timeout.

This function can be called even if the websocket isn't connected.

This function must always be called before disposing the reference to the websocket client.

Syntax

websocket:close()

Parameters

none

Returns

nil

Example

ws = websocket.createClient()
ws:close()
ws:close() -- nothing will happen

ws = nil -- fully dispose the client as Lua will now gc it

websocket.client:config(params)

Configures websocket client instance.

Syntax

websocket:config(params)

Parameters

  • params table with configuration parameters. Following keys are recognized:
  • headers table of extra request headers affecting every request

Returns

nil

Example

ws = websocket.createClient()
ws:config({headers={['User-Agent']='NodeMCU'}})

websocket.client:connect()

Attempts to estabilish a websocket connection to the given URL.

Syntax

websocket:connect(url)

Parameters

  • url the URL for the websocket.

Returns

nil

Example

ws = websocket.createClient()
ws:connect('ws://echo.websocket.org')

If it fails, an error will be delivered via websocket:on("close", handler).

websocket.client:on()

Registers the callback function to handle websockets events (there can be only one handler function registered per event type).

Syntax

websocket:on(eventName, function(ws, ...))

Parameters

  • eventName the type of websocket event to register the callback function. Those events are: connection, receive and close.
  • function(ws, ...) callback function. The function first parameter is always the websocketclient. Other arguments are required depending on the event type. See example for more details. If nil, any previously configured callback is unregistered.

Returns

nil

Example

local ws = websocket.createClient()
ws:on("connection", function(ws)
  print('got ws connection')
end)
ws:on("receive", function(_, msg, opcode)
  print('got message:', msg, opcode) -- opcode is 1 for text message, 2 for binary
end)
ws:on("close", function(_, status)
  print('connection closed', status)
  ws = nil -- required to Lua gc the websocket client
end)

ws:connect('ws://echo.websocket.org')

Note that the close callback is also triggered if any error occurs.

The status code for the close, if not 0 then it represents an error, as described in the following table.

Status Code Explanation
0 User requested close or the connection was terminated gracefully
-1 Failed to extract protocol from URL
-2 Hostname is too large (>256 chars)
-3 Invalid port number (must be >0 and <= 65535)
-4 Failed to extract hostname
-5 DNS failed to lookup hostname
-6 Server requested termination
-7 Server sent invalid handshake HTTP response (i.e. server sent a bad key)
-8 to -14 Failed to allocate memory to receive message
-15 Server not following FIN bit protocol correctly
-16 Failed to allocate memory to send message
-17 Server is not switching protocols
-18 Connect timeout
-19 Server is not responding to health checks nor communicating
-99 to -999 Well, something bad has happenned

websocket.client:send()

Sends a message through the websocket connection.

Syntax

websocket:send(message, opcode)

Parameters

  • message the data to send.
  • opcode optionally set the opcode (default: 1, text message)

Returns

nil or an error if socket is not connected

Example

ws = websocket.createClient()
ws:on("connection", function()
  ws:send('hello!')
end)
ws:connect('ws://echo.websocket.org')