Verawebsockets

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 oject, 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

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