File

net/resolvers/service.lua @ 10228:e77bf4222fae

net.server_epoll: Add support for opportunistic writes This tries to flush data to the underlying sockets when receiving writes. This should lead to fewer timer objects being around. On the other hand, this leads to more and smaller writes which may translate to more TCP/IP packets being sent, depending on how the kernel handles this. This trades throughput for lower latency.
author Kim Alvefur <zash@zash.se>
date Wed, 28 Aug 2019 01:41:00 +0200
parent 10121:33f287519bf6
child 10386:cf93a951da37
line wrap: on
line source

local adns = require "net.adns";
local basic = require "net.resolvers.basic";
local unpack = table.unpack or unpack; -- luacheck: ignore 113

local methods = {};
local resolver_mt = { __index = methods };

-- Find the next target to connect to, and
-- pass it to cb()
function methods:next(cb)
	if self.targets then
		if #self.targets == 0 then
			cb(nil);
			return;
		end
		local next_target = table.remove(self.targets, 1);
		self.resolver = basic.new(unpack(next_target, 1, 4));
		self.resolver:next(function (...)
			if ... == nil then
				self:next(cb);
			else
				cb(...);
			end
		end);
		return;
	end

	local targets = {};
	local function ready()
		self.targets = targets;
		self:next(cb);
	end

	-- Resolve DNS to target list
	local dns_resolver = adns.resolver();
	dns_resolver:lookup(function (answer, err)
		if not answer and not err then
			-- net.adns returns nil if there are zero records or nxdomain
			answer = {};
		end
		if answer then
			if #answer == 0 then
				if self.extra and self.extra.default_port then
					table.insert(targets, { self.hostname, self.extra.default_port, self.conn_type, self.extra });
				end
				ready();
				return;
			end

			if #answer == 1 and answer[1].srv.target == "." then -- No service here
				ready();
				return;
			end

			table.sort(answer, function (a, b) return a.srv.priority < b.srv.priority end);
			for _, record in ipairs(answer) do
				table.insert(targets, { record.srv.target, record.srv.port, self.conn_type, self.extra });
			end
		end
		ready();
	end, "_" .. self.service .. "._" .. self.conn_type .. "." .. self.hostname, "SRV", "IN");
end

local function new(hostname, service, conn_type, extra)
	return setmetatable({
		hostname = hostname;
		service = service;
		conn_type = conn_type or "tcp";
		extra = extra;
	}, resolver_mt);
end

return {
	new = new;
};