-- mod_net_proxy.lua

-- Copyright (C) 2018 Pascal Mathis <mail@pascalmathis.com>

--

-- Implementation of PROXY protocol versions 1 and 2

-- Specifications: https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt

module:set_global();

-- Imports

local softreq = require "util.dependencies".softreq;

local bit = assert(softreq "bit" or softreq "bit32", "No bit module found. See https://prosody.im/doc/depends#bitop");

local hex = require "util.hex";

local ip = require "util.ip";

local net = require "util.net";

local portmanager = require "core.portmanager";

-- Utility Functions

local function _table_invert(input)

	local output = {};

	for key, value in pairs(input) do

		output[value] = key;

	end

	return output;

end

-- Constants

local ADDR_FAMILY = { UNSPEC = 0x0, INET = 0x1, INET6 = 0x2, UNIX = 0x3 };

local ADDR_FAMILY_STR = _table_invert(ADDR_FAMILY);

local TRANSPORT = { UNSPEC = 0x0, STREAM = 0x1, DGRAM = 0x2 };

local TRANSPORT_STR = _table_invert(TRANSPORT);

local PROTO_MAX_HEADER_LENGTH = 256;

local PROTO_HANDLERS = {

	PROXYv1 = { signature = hex.from("50524F5859"), callback = nil },

	PROXYv2 = { signature = hex.from("0D0A0D0A000D0A515549540A"), callback = nil }

};

local PROTO_HANDLER_STATUS = { SUCCESS = 0, POSTPONE = 1, FAILURE = 2 };

-- Persistent In-Memory Storage

local sessions = {};

local mappings = {};

-- Proxy Data Methods

local proxy_data_mt = {}; proxy_data_mt.__index = proxy_data_mt;

function proxy_data_mt:describe()

	return string.format("proto=%s/%s src=%s:%d dst=%s:%d",

		self:addr_family_str(), self:transport_str(), self:src_addr(), self:src_port(), self:dst_addr(), self:dst_port());

end

function proxy_data_mt:addr_family_str()

	return ADDR_FAMILY_STR[self._addr_family] or ADDR_FAMILY_STR[ADDR_FAMILY.UNSPEC];

end

function proxy_data_mt:transport_str()

	return TRANSPORT_STR[self._transport] or TRANSPORT_STR[TRANSPORT.UNSPEC];

end

function proxy_data_mt:version()

	return self._version;

end

function proxy_data_mt:addr_family()

	return self._addr_family;

end

function proxy_data_mt:transport()

	return self._transport;

end

function proxy_data_mt:src_addr()

	return self._src_addr;

end

function proxy_data_mt:src_port()

	return self._src_port;

end

function proxy_data_mt:dst_addr()

	return self._dst_addr;

end

function proxy_data_mt:dst_port()

	return self._dst_port;

end

-- Protocol Handler Functions

PROTO_HANDLERS["PROXYv1"].callback = function(conn, session)

	local addr_family_mappings = { TCP4 = ADDR_FAMILY.INET, TCP6 = ADDR_FAMILY.INET6 };

	-- Postpone processing if CRLF (PROXYv1 header terminator) does not exist within buffer

	if session.buffer:find("\r\n") == nil then

		return PROTO_HANDLER_STATUS.POSTPONE, nil;

	end

	-- Declare header pattern and match current buffer against pattern

	local header_pattern = "^PROXY (%S+) (%S+) (%S+) (%d+) (%d+)\r\n";

	local addr_family, src_addr, dst_addr, src_port, dst_port = session.buffer:match(header_pattern);

	src_port, dst_port = tonumber(src_port), tonumber(dst_port);

	-- Ensure that header was successfully parsed and contains a valid address family

	if addr_family == nil or src_addr == nil or dst_addr == nil or src_port == nil or dst_port == nil then

		module:log("warn", "Received unparseable PROXYv1 header from %s", conn:ip());

		return PROTO_HANDLER_STATUS.FAILURE, nil;

	end

	if addr_family_mappings[addr_family] == nil then

		module:log("warn", "Received invalid PROXYv1 address family from %s: %s", conn:ip(), addr_family);

		return PROTO_HANDLER_STATUS.FAILURE, nil;

	end

	-- Ensure that received source and destination ports are within 1 and 65535 (0xFFFF)

	if src_port <= 0 or src_port >= 0xFFFF then

		module:log("warn", "Received invalid PROXYv1 source port from %s: %d", conn:ip(), src_port);

		return PROTO_HANDLER_STATUS.FAILURE, nil;

	end

	if dst_port <= 0 or dst_port >= 0xFFFF then

		module:log("warn", "Received invalid PROXYv1 destination port from %s: %d", conn:ip(), dst_port);

		return PROTO_HANDLER_STATUS.FAILURE, nil;

	end

	-- Ensure that received source and destination address can be parsed

	local _, err = ip.new_ip(src_addr);

	if err ~= nil then

		module:log("warn", "Received unparseable PROXYv1 source address from %s: %s", conn:ip(), src_addr);

	end

	_, err = ip.new_ip(dst_addr);

	if err ~= nil then

		module:log("warn", "Received unparseable PROXYv1 destination address from %s: %s", conn:ip(), dst_addr);

		return PROTO_HANDLER_STATUS.FAILURE, nil;

	end

	-- Strip parsed header from session buffer and build proxy data

	session.buffer = session.buffer:gsub(header_pattern, "");

	local proxy_data = {

		_version = 1,

		_addr_family = addr_family, _transport = TRANSPORT.STREAM,

		_src_addr = src_addr, _src_port = src_port,

		_dst_addr = dst_addr, _dst_port = dst_port

	};

	setmetatable(proxy_data, proxy_data_mt);

	-- Return successful response with gathered proxy data

	return PROTO_HANDLER_STATUS.SUCCESS, proxy_data;

end

PROTO_HANDLERS["PROXYv2"].callback = function(conn, session)

	-- Postpone processing if less than 16 bytes are available

	if #session.buffer < 16 then

		return PROTO_HANDLER_STATUS.POSTPONE, nil;

	end

	-- Parse first 16 bytes of protocol header

	local version = bit.rshift(bit.band(session.buffer:byte(13), 0xF0), 4);

	local command = bit.band(session.buffer:byte(13), 0x0F);

	local addr_family = bit.rshift(bit.band(session.buffer:byte(14), 0xF0), 4);

	local transport = bit.band(session.buffer:byte(14), 0x0F);

	local length = bit.bor(session.buffer:byte(16), bit.lshift(session.buffer:byte(15), 8));

	-- Postpone processing if less than 16+<length> bytes are available

	if #session.buffer < 16 + length then

		return PROTO_HANDLER_STATUS.POSTPONE, nil;

	end

	-- Ensure that version number is correct

	if version ~= 0x2 then

		module:log("error", "Received unsupported PROXYv2 version from %s: %d", conn:ip(), version);

		return PROTO_HANDLER_STATUS.FAILURE, nil;

	end

	local payload = session.buffer:sub(17);

	if command == 0x0 then

		-- Gather source/destination addresses and ports from local socket

		local src_addr, src_port = conn:socket():getpeername();

		local dst_addr, dst_port = conn:socket():getsockname();

		-- Build proxy data based on real connection information

		local proxy_data = {

			_version = version,

			_addr_family = addr_family, _transport = transport,

			_src_addr = src_addr, _src_port = src_port,

			_dst_addr = dst_addr, _dst_port = dst_port

		};

		setmetatable(proxy_data, proxy_data_mt);

		-- Return successful response with gathered proxy data

		return PROTO_HANDLER_STATUS.SUCCESS, proxy_data;

	elseif command == 0x1 then

		local offset = 1;

		local src_addr, src_port, dst_addr, dst_port;

		-- Verify transport protocol is either STREAM or DGRAM

		if transport ~= TRANSPORT.STREAM and transport ~= TRANSPORT.DGRAM then

			module:log("warn", "Received unsupported PROXYv2 transport from %s: 0x%02X", conn:ip(), transport);

			return PROTO_HANDLER_STATUS.FAILURE, nil;

		end

		-- Parse source and destination addresses

		if addr_family == ADDR_FAMILY.INET then

		elseif addr_family == ADDR_FAMILY.INET6 then

		elseif addr_family == ADDR_FAMILY.UNIX then

			src_addr = payload:sub(offset, offset + 107); offset = offset + 108;

			dst_addr = payload:sub(offset, offset + 107); offset = offset + 108;

		end

		-- Parse source and destination ports

		if addr_family == ADDR_FAMILY.INET or addr_family == ADDR_FAMILY.INET6 then

			src_port = bit.bor(payload:byte(offset + 1), bit.lshift(payload:byte(offset), 8)); offset = offset + 2;

			-- luacheck: ignore 311

			dst_port = bit.bor(payload:byte(offset + 1), bit.lshift(payload:byte(offset), 8)); offset = offset + 2;

		end

		-- Strip parsed header from session buffer and build proxy data

		session.buffer = session.buffer:sub(17 + length);

		local proxy_data = {

			_version = version,

			_addr_family = addr_family, _transport = transport,

			_src_addr = src_addr, _src_port = src_port,

			_dst_addr = dst_addr, _dst_port = dst_port

		};

		setmetatable(proxy_data, proxy_data_mt);

		-- Return successful response with gathered proxy data

		return PROTO_HANDLER_STATUS.SUCCESS, proxy_data;

	else

		module:log("error", "Received unsupported PROXYv2 command from %s: 0x%02X", conn:ip(), command);

		return PROTO_HANDLER_STATUS.FAILURE, nil;

	end

end

-- Wrap an existing connection with the provided proxy data. This will override several methods of the 'conn' object to

-- return the proxied source instead of the source which initiated the TCP connection. Afterwards, the listener of the

-- connection gets set according to the globally defined port<>service mappings and the methods 'onconnect' and

-- 'onincoming' are being called manually with the current session buffer.

local function wrap_proxy_connection(conn, session, proxy_data)

	-- Override and add functions of 'conn' object when source information has been collected

	conn.proxyip, conn.proxyport = conn.ip, conn.port;

	if proxy_data:src_addr() ~= nil and proxy_data:src_port() ~= nil then

		conn.ip = function()

			return proxy_data:src_addr();

		end

		conn.port = function()

			return proxy_data:src_port();

		end

		conn.clientport = conn.port;

	end

	-- Attempt to find service by processing port<>service mappings

	local mapping = mappings[conn:serverport()];

	if mapping == nil then

		conn:close();

		module:log("error", "Connection %s@%s terminated: Could not find mapping for port %d",

			conn:ip(), conn:proxyip(), conn:serverport());

		return;

	end

	if mapping.service == nil then

		local service = portmanager.get_service(mapping.service_name);

		if service ~= nil then

			mapping.service = service;

		else

			conn:close();

			module:log("error", "Connection %s@%s terminated: Could not process mapping for unknown service %s",

				conn:ip(), conn:proxyip(), mapping.service_name);

			return;

		end

	end

	-- Pass connection to actual service listener and simulate onconnect/onincoming callbacks

	local service_listener = mapping.service.listener;

	module:log("info", "Passing proxied connection %s:%d to service %s", conn:ip(), conn:port(), mapping.service_name);

	conn:setlistener(service_listener);

	if service_listener.onconnect then

		service_listener.onconnect(conn);

	end

	return service_listener.onincoming(conn, session.buffer);

end

-- Network Listener Methods

local listener = {};

function listener.onconnect(conn)

	sessions[conn] = {

		handler = nil;

		buffer = nil;

	};

end

function listener.onincoming(conn, data)

	-- Abort processing if no data has been received

	if not data then

		return;

	end

	-- Lookup session for connection and append received data to buffer

	local session = sessions[conn];

	session.buffer = session.buffer and session.buffer .. data or data;

	-- Attempt to determine protocol handler if not done previously

	if session.handler == nil then

		-- Match current session buffer against all known protocol signatures to determine protocol handler

		for handler_name, handler in pairs(PROTO_HANDLERS) do

			if session.buffer:find("^" .. handler.signature) ~= nil then

				session.handler = handler.callback;

				module:log("debug", "Detected %s connection from %s:%d", handler_name, conn:ip(), conn:port());

				break;

			end

		end

		-- Decide between waiting for a complete header signature or terminating the connection when no handler has been found

		if session.handler == nil then

			-- Terminate connection if buffer size has exceeded tolerable maximum size

			if #session.buffer > PROTO_MAX_HEADER_LENGTH then

				conn:close();

				module:log("warn", "Connection %s:%d terminated: No valid PROXY header within %d bytes",

					conn:ip(), conn:port(), PROTO_MAX_HEADER_LENGTH);

			end

			-- Skip further processing without a valid protocol handler

			module:log("debug", "No valid header signature detected from %s:%d, waiting for more data...",

				conn:ip(), conn:port());

			return;

		end

	end

	-- Execute proxy protocol handler and process response

	local response, proxy_data = session.handler(conn, session);

	if response == PROTO_HANDLER_STATUS.SUCCESS then

		module:log("info", "Received PROXY header from %s: %s", conn:ip(), proxy_data:describe());

		return wrap_proxy_connection(conn, session, proxy_data);

	elseif response == PROTO_HANDLER_STATUS.POSTPONE then

		module:log("debug", "Postponed parsing of incomplete PROXY header received from %s", conn:ip());

		return;

	elseif response == PROTO_HANDLER_STATUS.FAILURE then

		conn:close();

		module:log("warn", "Connection %s terminated: Could not process PROXY header from client, " +

			"see previous log messages.", conn:ip());

		return;

	else

		-- This code should be never reached, but is included for completeness

		conn:close();

		module:log("error", "Connection terminated: Received invalid protocol handler response with code %d", response);

		return;

	end

end

function listener.ondisconnect(conn)

	sessions[conn] = nil;

end