commit 18875eb8602852c764354adbc6a12a7a2bb64f6c
Author: Luca <Luca@hackerspace-bamberg.de>
Date:   Thu Sep 5 01:20:57 2024 +0200

    initial commit

diff --git a/mqtt.lua b/mqtt.lua
new file mode 100644
index 0000000..136a021
--- /dev/null
+++ b/mqtt.lua
@@ -0,0 +1,173 @@
+local net = require("internet")
+
+local read_varint = function (conn, first_byte)
+	local b
+	if first_byte == nil then
+		b = conn:read(1)
+	else
+		b = first_byte
+	end
+
+	local n, s = 0, 0
+	while b ~= nil and b & 0x80 == 0x80 do
+		if s > 21 then
+			return 0, "number too large"
+		end
+
+		n = n + ((b & 0x7F) << s)
+		s = s + 7
+		b = conn:read(1)
+	end
+
+	if b == nil then
+		return n, "eof"
+	end
+
+	return n + (b << s), nil
+end
+
+local MqttClient
+
+function open (address, port)
+	local conn = net.open(address, port)
+	if conn == nil then
+		return nil, "connection failed"
+	end
+
+	return MqttClient:new(conn), nil
+end
+
+function MqttClient:new (conn)
+	local c = c or {}
+	setmetatable(c, self)
+	self.__index = self
+
+	conn.read_varint = read_varint
+	c.conn = conn
+	c.is_connecting = false
+	c.is_connected = false
+
+	return c
+end
+
+function MqttClient:handle ()
+	local data = self.conn:read(2)
+	if data == nil then
+		return "eof"
+	end
+
+	local ptype, length, _ = string.unpack("B B", s)
+
+	local length, err = self.conn:read_varint(length)
+	if err ~= nil then
+		return err
+	end
+
+	if length > 0 then
+		data = self.conn:read(length)
+		if data == nil then
+			return "eof"
+		end
+	else
+		data = ""
+	end
+
+	if ptype & 0xF0 == 0x20 then -- CONNACK
+		if ptype ~= 0x20 or length < 2 then
+			self:disconnect(0x81)
+			return "malformed packet"
+		end
+
+		local flags, reason, _ = string.unpack("B B", data)
+
+		if flags ~= 0 then
+			self:disconnect(0x81)
+			return "malformed packet"
+		end
+
+		if reason > 127 then
+			self.is_connecting = false
+			self.is_connected = false
+			self.conn:close()
+			self.conn = nil
+			return "connection closed by server"
+		elseif reason ~= 0 then
+			self:disconnect(0x81)
+			return "malformed packet"
+		end
+
+		self.is_connecting = false
+		self.is_connected = true
+	elseif ptype == 0x40 then -- PUBACK
+		-- TODO
+	elseif ptype == 0xD0 then -- PINGRESP
+		-- TODO
+	elseif ptype == 0xE0 then -- DISCONNECT
+		-- TODO
+	end
+
+	return nil
+end
+
+function MqttClient:connect (username, password)
+	if self.is_connecting or self.is_connected then
+		return nil
+	end
+
+	local length = 15
+	local flags = 1
+	if username ~= nil then
+		length = length + 2 + #username
+		flags = flags | 0x80
+	end
+	if password ~= nil then
+		length = length + 2 + #password
+		flags = flags | 0x40
+	end
+
+	if length > 127 then
+		return "packet size exceeds current implementation capabilities"
+	end
+
+	local data = string.pack("> B B s2 B B I2 B s2", 0x10, length, "MQTT", 5, flags, 0, 0, "")
+	if username ~= nil then
+		data = data .. string.pack("> s2", username)
+	end
+	if password ~= nil then
+		data = data .. string.pack("> s2", password)
+	end
+
+	local _, err = self.conn:write(data)
+	if err ~= nil then
+		return err
+	end
+
+	self.is_connecting = true
+
+	return nil
+end
+
+function MqttClient:disconnect (reason)
+	if not (self.is_connecting or self.is_connected) then
+		return nil
+	end
+
+	if reason == nil then
+		reason = 0
+	end
+
+	local data = string.pack("> B B B", 0xE0, 1, reason)
+
+	local _, err = self.conn:write(data)
+	if err ~= nil then
+		return err
+	end
+
+	self.is_connecting = false
+	self.is_connected = false
+
+	self.conn:close()
+	self.conn = nil
+
+	return nil
+end