-- mod_limits: Rate-limiting for Prosody

-- Version: Alpha

-- Author: Matthew Wild <mwild1@gmail.com>

-- Because we deal we pre-authed sessions and streams we can't be host-specific

module:set_global();

local filters = require "util.filters";

local throttle = require "util.throttle";

local timer = require "util.timer";

local ceil = math.ceil;

local limits_cfg = module:get_option("limits", {});

local limits_resolution = module:get_option_number("limits_resolution", 1);

local default_bytes_per_second = 3000;

local default_burst = 2;

local rate_units = { b = 1, k = 3, m = 6, g = 9, t = 12 } -- Plan for the future.

local function parse_rate(rate, sess_type)

	local quantity, unit, exp;

	if rate then

		quantity, unit = rate:match("^(%d+) ?([^/]+)/s$");

		exp = quantity and rate_units[unit:sub(1,1):lower()];

	end

	if not exp then

		module:log("error", "Error parsing rate for %s: %q, using default rate (%d bytes/s)", sess_type, rate, default_bytes_per_second);

		return default_bytes_per_second;

	end

	return quantity*(10^exp);

end

local function parse_burst(burst, sess_type)

	if type(burst) == "string" then

		burst = burst:match("^(%d+) ?s$");

	end

	local n_burst = tonumber(burst);

	if not n_burst then

		module:log("error", "Unable to parse burst for %s: %q, using default burst interval (%ds)", sess_type, tostring(burst), default_burst);

	end

	return n_burst or default_burst;

end

-- Process config option into limits table:

-- limits = { c2s = { bytes_per_second = X, burst_seconds = Y } }

local limits = {};

for sess_type, sess_limits in pairs(limits_cfg) do

	limits[sess_type] = {

		bytes_per_second = parse_rate(sess_limits.rate, sess_type);

		burst_seconds = parse_burst(sess_limits.burst, sess_type);

	};

end

local default_filter_set = {};

function default_filter_set.bytes_in(bytes, session)

	local throttle = session.throttle;

	if throttle then

		local ok, balance, outstanding = throttle:poll(#bytes, true);

		if not ok then

			session.log("debug", "Session %q over rate limit (%d) with %d (by %d), pausing", session.full_jid or session.from_host or session.to_host, throttle.max, #bytes, outstanding);

			outstanding = ceil(outstanding);

			session.conn:pause(); -- Read no more data from the connection until there is no outstanding data

			local outstanding_data = bytes:sub(-outstanding);

			bytes = bytes:sub(1, #bytes-outstanding);

			timer.add_task(limits_resolution, function ()

				if not session.conn then return; end

				if throttle:peek(#outstanding_data) then

					session.log("debug", "Resuming paused session");

					session.conn:resume();

				end

				session.log("debug", "mod_limits feeding %d bytes of delayed data into stream", #outstanding_data);

				-- Handle what we can of the outstanding data

				session.data(outstanding_data);

			end);

		end

	end

	return bytes;

end

local type_filters = {

	c2s = default_filter_set;

	s2sin = default_filter_set;

	s2sout = default_filter_set;

};

local function filter_hook(session)

	local session_type = session.type:match("^[^_]+");

	local filter_set, opts = type_filters[session_type], limits[session_type];

	if opts then

		session.throttle = throttle.create(opts.bytes_per_second * opts.burst_seconds, opts.burst_seconds);

		filters.add_filter(session, "bytes/in", filter_set.bytes_in, 1000);

	end

end

function module.load()

	filters.add_filter_hook(filter_hook);

end

function module.unload()

	filters.remove_filter_hook(filter_hook);

end