Verawebsockets

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What is verawebsockets?

verawebsockets is a Lua library based on the libwebsockets v2.4 library (https://libwebsockets.org).

The intention is to provide websockets support for the Luup plugins, which means that verawebsockets can be used from LuaUPnP as well as from standalone Lua scripts.

Functions

create

Creates a websocket object, which must be passed to other functions which require it.

Parameters:

  • url (string): The URL to connect to.
  • event_handlers (table): A table where the index is the event ID, and the value is the callback function name.
  • ssl_settings (table): A table where the index is the SSL setting name, and the value is the SSL setting value.
  • standalone (boolean): Set this to true if using the library from a standalone Lua script, or to false if using the library from LuaUPnP. If not set, the default value is false. If standalone is true, you must call the loop function after you call the connect function.

Returns:

  • wso (websocket): The websocket object.

connect

Connects to the URL from the websocket object.

Parameters:

  • wso (websocket): This is the websocket object returned by the create function.

Returns:

  • nothing

send

Sends a message through the websocket. Parameters:

  • wso (websocket): This is the websocket object returned by the create function.
  • message (string): This is the message to be sent.

Returns:

  • nothing

loop

This function must be called if the create function was called with the standalone parameter set to true. It blocks the main thread, waiting for the service thread to finish execution.

Parameters:

  • none

Returns:

  • nothing

set_log_level

Set how verbose the logs should be.

The default log level is 0, meaning nothing is logged.

If the library is used from LuaUPnP, the logs can be seen in /tmp/log.Init-LuaUPnP

Parameters:

  • log_levels (int or string): log_levels can be either a number, representing a bit mask where each bit is a log level, or the string "all", which means all log levels enabled, and it's the equivalent of setting all the bits in the mask (log_levels = 2047). The available log levels are listed here.


Reference

Event IDs

Since verawebsockets is based on the libwebsockets library, the verawebsockets event IDs are the same as the libwebsockets callback reasons, which are documented here:

https://libwebsockets.org/lws-api-doc-v2.4-stable/html/group__usercb.html

These are the event IDs which are currently supported:

Event ID libwebsockets callback reason Description
1 LWS_CALLBACK_CLIENT_CONNECTION_ERROR Failed to connect to the server. The reason for the failure is passed as parameter to the callback function. Some possible values are:
  • getaddrinfo (ipv6) failed
  • unknown address family
  • getaddrinfo (ipv4) failed
  • set socket opts failed
  • insert wsi failed
  • lws_ssl_client_connect1 failed
  • lws_ssl_client_connect2 failed
  • Peer hung up
  • read failed
  • HS: URI missing
  • HS: Redirect code but no Location
  • HS: URI did not parse
  • HS: Redirect failed
  • HS: Server did not return 200
  • HS: OOM
  • HS: disallowed by client filter
  • HS: disallowed at ESTABLISHED
  • HS: ACCEPT missing
  • HS: ws upgrade response not 101
  • HS: UPGRADE missing
  • HS: Upgrade to something other than websocket
  • HS: CONNECTION missing
  • HS: UPGRADE malformed
  • HS: PROTOCOL malformed
  • HS: Cannot match protocol
  • HS: EXT: list too big
  • HS: EXT: failed setting defaults
  • HS: EXT: failed parsing defaults
  • HS: EXT: failed parsing options
  • HS: EXT: Rejects server options
  • HS: EXT: unknown ext
  • HS: Accept hash wrong
  • HS: Rejected by filter cb
  • HS: OOM
  • HS: SO_SNDBUF failed
  • HS: Rejected at CLIENT_ESTABLISHED
3 LWS_CALLBACK_CLIENT_ESTABLISHED Called after the connection with the server has been established. No parameter is passed to the callback function.
4 LWS_CALLBACK_CLOSED Called after the websocket connection closed. No parameter is passed to the callback function.
8 LWS_CALLBACK_CLIENT_RECEIVE Called when we receive data from the server. The received data is passed as parameter to the callback function.


SSL settings

These are the SSL settings which are currently supported:

SSL setting Description
client_ssl_cert_filepath The certificate the client should present to the server on connection.
client_ssl_private_key_filepath Filepath to the client private key.


Log levels

Log level Description
1 Error
2 Warning
4 Notice
8 Info
16 Debug
32 Parser
64 Header
128 Extensions
256 Client
512 Latency
1024 User


Example

#!/usr/bin/lua
 
local ws = require("verawebsockets")
if not ws then
	print("ERROR: Failed to load the verawebsockets library")
	os.exit(1)
end
 
local g_wso
 
local sslSettings = {
	client_ssl_cert_filepath = "ws.pem"
}
 
local eventHandlers = {
	[1] = "connerror", -- LWS_CALLBACK_CLIENT_CONNECTION_ERROR
	[3] = "open",      -- LWS_CALLBACK_CLIENT_ESTABLISHED
	[4] = "close",     -- LWS_CALLBACK_CLOSED
	[8] = "incoming"   -- LWS_CALLBACK_CLIENT_RECEIVE
}
 
 
function main()
	-- Log only errors and warnings.
	ws.set_log_level(3)
	-- This script is meant to be run standalone, so we set "standalone" to "true".
	g_wso = ws.create {
		["url"] = "wss://echo.websocket.org",
		["ssl_settings"] = sslSettings,
		["event_handlers"] = eventHandlers,
		["standalone"] = true
	}
	if not g_wso then
		print("ERROR: Failed to create connection")
		return 1
	end
	ws.connect(g_wso)
	-- Because we're in standalone mode, call the "loop" function
	-- to prevent the main thread from terminating.
	ws.loop()
	return 0
end
 
 
function connerror (reason)
	print("Connection error: "..(reason or nil))
	os.exit(1)
end
 
 
function open()
	local message = "Hello world!"
	print("Connection successful, send message: ".. message)
	ws.send(g_wso, message);
end
 
 
function close()
	print("Connection closed")
end
 
 
function incoming (data)
	data = data or "nil"
	print("Received message: ".. data)
	if data:match("^Hello world!") then
		ws.send(g_wso, "Hello again!");
	end
end
 
 
os.exit(main())


Further documentation

  • The WebSocket protocol:

https://tools.ietf.org/html/rfc6455

  • The libwebsockets library:

https://libwebsockets.org

  • libwebsockets v2.4 documentation:

https://libwebsockets.org/lws-api-doc-v2.4-stable/html/index.html

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