Add async dns query

lualib/dns.lua

@@ -0,0 +1,290 @@
+--[[
+	lua dns resolver library
+	See  https://github.com/xjdrew/levent/blob/master/levent/dns.lua for more detail
+
+-- resource record type:
+-- TYPE            value and meaning
+-- A               1 a host address
+-- NS              2 an authoritative name server
+-- MD              3 a mail destination (Obsolete - use MX)
+-- MF              4 a mail forwarder (Obsolete - use MX)
+-- CNAME           5 the canonical name for an alias
+-- SOA             6 marks the start of a zone of authority
+-- MB              7 a mailbox domain name (EXPERIMENTAL)
+-- MG              8 a mail group member (EXPERIMENTAL)
+-- MR              9 a mail rename domain name (EXPERIMENTAL)
+-- NULL            10 a null RR (EXPERIMENTAL)
+-- WKS             11 a well known service description
+-- PTR             12 a domain name pointer
+-- HINFO           13 host information
+-- MINFO           14 mailbox or mail list information
+-- MX              15 mail exchange
+-- TXT             16 text strings
+-- AAAA            28 a ipv6 host address
+-- only appear in the question section:
+-- AXFR            252 A request for a transfer of an entire zone
+-- MAILB           253 A request for mailbox-related records (MB, MG or MR)
+-- MAILA           254 A request for mail agent RRs (Obsolete - see MX)
+-- *               255 A request for all records
+--
+-- resource recode class:
+-- IN              1 the Internet
+-- CS              2 the CSNET class (Obsolete - used only for examples in some obsolete RFCs)
+-- CH              3 the CHAOS class
+-- HS              4 Hesiod [Dyer 87]
+-- only appear in the question section:
+-- *               255 any class
+-- ]]
+
+--[[
+-- struct header {
+--  uint16_t tid     # identifier assigned by the program that generates any kind of query.
+--  uint16_t flags   # flags
+--  uint16_t qdcount # the number of entries in the question section.
+--  uint16_t ancount # the number of resource records in the answer section.
+--  uint16_t nscount # the number of name server resource records in the authority records section.
+--  uint16_t arcount # the number of resource records in the additional records section.
+-- }
+--
+-- request body:
+-- struct request {
+--  string name
+--  uint16_t atype
+--  uint16_t class
+-- }
+--
+-- response body:
+-- struct response {
+--  string name
+--  uint16_t atype
+--  uint16_t class
+--  uint16_t ttl
+--  uint16_t rdlength
+--  string rdata
+-- }
+--]]
+
+local skynet = require "skynet"
+local socket = require "socket"
+
+local MAX_DOMAIN_LEN = 1024
+local MAX_LABEL_LEN = 63
+local MAX_PACKET_LEN = 2048
+local DNS_HEADER_LEN = 12
+
+local QTYPE = {
+	A = 1,
+	CNAME = 5,
+	AAAA = 28,
+}
+
+local QCLASS = {
+	IN = 1,
+}
+
+local dns = {}
+
+local function verify_domain_name(name)
+	if #name > MAX_DOMAIN_LEN then
+		return false
+	end
+	if not name:match("^[%l%d-%.]+$") then
+		return false
+	end
+	for w in name:gmatch("([%w-]+)%.?") do
+		if #w > MAX_LABEL_LEN then
+			return false
+		end
+	end
+	return true
+end
+
+local next_tid = 1
+local function gen_tid()
+	local tid = next_tid
+	next_tid = next_tid + 1
+	return tid
+end
+
+local function pack_header(t)
+	return string.pack(">HHHHHH",
+		t.tid, t.flags, t.qdcount, t.ancount or 0, t.nscount or 0, t.arcount or 0)
+end
+
+local function pack_question(name, qtype, qclass)
+	local labels = {}
+	for w in name:gmatch("([%w-]+)%.?") do
+		table.insert(labels, string.pack("s1",w))
+	end
+	table.insert(labels, '\0')
+	table.insert(labels, string.pack(">HH", qtype, qclass))
+	return table.concat(labels)
+end
+
+local function unpack_header(chunk)
+	local tid, flags, qdcount, ancount, nscount, arcount, left = string.unpack(">HHHHHH", chunk)
+	return {
+		tid = tid,
+		flags = flags,
+		qdcount = qdcount,
+		ancount = ancount,
+		nscount = nscount,
+		arcount = arcount
+	}, left
+end
+
+-- unpack a resource name
+local function unpack_name(chunk, left)
+	local t = {}
+	local jump_pointer
+	local tag, offset, label
+	while true do
+		tag, left = string.unpack("B", chunk, left)
+		if tag & 0xc0 == 0xc0 then
+			-- pointer
+			offset,left = string.unpack(">H", chunk, left - 1)
+			offset = offset & 0x3fff
+			if not jump_pointer then
+				jump_pointer = left
+			end
+			-- offset is base 0, need to plus 1
+			left = offset + 1
+		elseif tag == 0 then
+			break
+		else
+			label, left = string.unpack("s1", chunk, left - 1)
+			t[#t+1] = label
+		end
+	end
+	return table.concat(t, "."), jump_pointer or left
+end
+
+local function unpack_question(chunk, left)
+	local name, left = unpack_name(chunk, left)
+	local atype, class, left = string.unpack(">HH", chunk, left)
+	return {
+		name = name,
+		atype = atype,
+		class = class
+	}, left
+end
+
+local function unpack_answer(chunk, left)
+	local name, left = unpack_name(chunk, left)
+	local atype, class, ttl, rdata, left = string.unpack(">HHI4s2", chunk, left)
+	return {
+		name = name,
+		atype = atype,
+		class = class,
+		ttl = ttl,
+		rdata = rdata
+	},left
+end
+
+local function unpack_rdata(qtype, chunk)
+	if qtype == QTYPE.A then
+		local a,b,c,d = string.unpack("BBBB", chunk)
+		return string.format("%d.%d.%d.%d", a,b,c,d)
+	elseif qtype == QTYPE.AAAA then
+		local a,b,c,d,e,f,g,h = string.unpack(">HHHHHHHH", chunk)
+		return string.format("%x:%x:%x:%x:%x:%x:%x:%x", a, b, c, d, e, f, g, h)
+	else
+		error("Error qtype " .. qtype)
+	end
+end
+
+local dns_server
+local request_pool = {}
+
+local function resolve(content)
+	if #content < DNS_HEADER_LEN then
+		-- drop
+		skynet.error("Recv an invalid package when dns query")
+		return
+	end
+	local answer_header,left = unpack_header(content)
+	-- verify answer
+	assert(answer_header.qdcount == 1, "malformed packet")
+
+	local resp = request_pool[answer_header.tid]
+	if not resp then
+		skynet.error("Recv an invalid tid when dns query")
+		return
+	end
+
+	local question,left = unpack_question(content, left)
+	if question.name ~= resp.name then
+		skynet.error("Recv an invalid name when dns query")
+		return
+	end
+
+	local ttl
+	local answer
+	local answers = {}
+	for i=1, answer_header.ancount do
+		answer, left = unpack_answer(content, left)
+		-- only extract qtype address
+		if answer.atype == resp.qtype then
+			local ip = unpack_rdata(resp.qtype, answer.rdata)
+			ttl = ttl and math.min(ttl, answer.ttl) or answer.ttl
+			answers[#answers+1] = ip
+		end
+	end
+
+	if #answers > 0 then
+		resp.answers = answers
+	end
+
+	skynet.wakeup(resp.co)
+end
+
+function dns.server(server, port)
+	if not server then
+		local f = assert(io.open "/etc/resolv.conf")
+		for line in f:lines() do
+			server = line:match("%s*nameserver%s+([^%s]+)")
+			if server then
+				break
+			end
+		end
+		assert(server, "Can't get nameserver")
+	end
+	dns_server = socket.udp(function(data, sz, from)
+		resolve(skynet.tostring(data,sz))
+	end)
+	socket.udp_connect(dns_server, server, port or 53)
+	return server
+end
+
+local function suspend(tid, name, qtype)
+	local req = {
+		name = name,
+		tid = tid,
+		qtype = qtype,
+		time = skynet.now(),	-- for timeout
+		co = coroutine.running(),
+	}
+	request_pool[tid] = req
+	skynet.wait()
+	local answers = request_pool[tid].answers
+	request_pool[tid] = nil
+	assert(answers, "no ip")
+	return answers[1], answers
+end
+
+function dns.resolve(name, ipv6)
+	local qtype = ipv6 and QTYPE.AAAA or QTYPE.A
+	local name = name:lower()
+	assert(verify_domain_name(name) , "illegal name")
+	local question_header = {
+		tid = gen_tid(),
+		flags = 0x100, -- flags: 00000001 00000000, set RD
+		qdcount = 1,
+	}
+	local req = pack_header(question_header) .. pack_question(name, qtype, QCLASS.IN)
+	assert(dns_server, "Call dns.server fist")
+	socket.write(dns_server, req)
+	return suspend(question_header.tid, name, qtype)
+end
+
+return dns

test/testdns.lua

@@ -0,0 +1,11 @@
+local skynet = require "skynet"
+local dns = require "dns"
+
+skynet.start(function()
+	print("nameserver:", dns.server())	-- set nameserver
+	-- you can specify the server like dns.server("8.8.4.4", 53)
+	local ip, ips = dns.resolve "github.com"
+	for k,v in ipairs(ips) do
+		print("github.com",v)
+	end
+end)