DNS messages

R=r
DELTA=685  (683 added, 0 deleted, 2 changed)
OCL=20926
CL=20951

src/lib/net/Makefile

@@ -3,7 +3,7 @@
 # license that can be found in the LICENSE file.
 
 # DO NOT EDIT.  Automatically generated by gobuild.
-# gobuild -m fd_darwin.go fd.go net.go net_darwin.go ip.go >Makefile
+# gobuild -m fd_darwin.go fd.go net.go net_darwin.go ip.go dnsmsg.go >Makefile
 O=6
 GC=$(O)g
 CC=$(O)c -w
@@ -34,6 +34,7 @@ coverage: packages
 O1=\
 	fd_$(GOOS).$O\
 	ip.$O\
+	dnsmsg.$O\
 
 O2=\
 	fd.$O\
@@ -45,7 +46,7 @@ O3=\
 net.a: a1 a2 a3
 
 a1:	$(O1)
-	$(AR) grc net.a fd_$(GOOS).$O ip.$O
+	$(AR) grc net.a fd_$(GOOS).$O ip.$O dnsmsg.$O
 	rm -f $(O1)
 
 a2:	$(O2)

src/lib/net/dnsmsg.go

@@ -0,0 +1,683 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// DNS packet assembly.
+//
+// This is intended to support name resolution during net.Dial.
+// It doesn't have to be blazing fast.
+//
+// Rather than write the usual handful of routines to pack and
+// unpack every message that can appear on the wire, we use
+// reflection to write a generic pack/unpack for structs and then
+// use it.  Thus, if in the future we need to define new message
+// structs, no new pack/unpack/printing code needs to be written.
+//
+// The first half of this file defines the DNS message formats.
+// The second half implements the conversion to and from wire format.
+// A few of the structure elements have string tags to aid the
+// generic pack/unpack routines.
+//
+// TODO(rsc)  There are enough names defined in this file that they're all
+// prefixed with DNS_.  Perhaps put this in its own package later.
+
+package net
+
+import (
+	"fmt";
+	"os";
+	"reflect";
+)
+
+// Packet formats
+
+// Wire constants.
+export const (
+	// valid DNS_RR_Header.rrtype and DNS_Question.qtype
+	DNS_TypeA = 1;
+	DNS_TypeNS = 2;
+	DNS_TypeMD = 3;
+	DNS_TypeMF = 4;
+	DNS_TypeCNAME = 5;
+	DNS_TypeSOA = 6;
+	DNS_TypeMB = 7;
+	DNS_TypeMG = 8;
+	DNS_TypeMR = 9;
+	DNS_TypeNULL = 10;
+	DNS_TypeWKS = 11;
+	DNS_TypePTR = 12;
+	DNS_TypeHINFO = 13;
+	DNS_TypeMINFO = 14;
+	DNS_TypeMX = 15;
+	DNS_TypeTXT = 16;
+
+	// valid DNS_Question.qtype only
+	DNS_TypeAXFR = 252;
+	DNS_TypeMAILB = 253;
+	DNS_TypeMAILA = 254;
+	DNS_TypeALL = 255;
+
+	// valid DNS_Question.qclass
+	DNS_ClassINET = 1;
+	DNS_ClassCSNET = 2;
+	DNS_ClassCHAOS = 3;
+	DNS_ClassHESIOD = 4;
+	DNS_ClassANY = 255;
+)
+
+// The wire format for the DNS packet header.
+type DNS_Header struct {
+	id uint16;
+	bits uint16;
+	qdcount, ancount, nscount, arcount uint16;
+}
+
+const (
+	// DNS_Header.bits
+	QR = 1<<15;	// query/response (response=1)
+	AA = 1<<10;	// authoritative
+	TC = 1<<9;	// truncated
+	RD = 1<<8;	// recursion desired
+	RA = 1<<7;	// recursion available
+)
+
+// DNS queries.
+export type DNS_Question struct {
+	name string "domain-name";	// "domain-name" specifies encoding; see packers below
+	qtype uint16;
+	qclass uint16;
+}
+
+// DNS responses (resource records).
+// There are many types of messages,
+// but they all share the same header.
+export type DNS_RR_Header struct {
+	name string "domain-name";
+	rrtype uint16;
+	class uint16;
+	ttl uint32;
+	rdlength uint16;	// length of data after header
+}
+
+func (h *DNS_RR_Header) Header() *DNS_RR_Header {
+	return h
+}
+
+export type DNS_RR interface {
+	Header() *DNS_RR_Header
+}
+
+
+// Specific DNS RR formats for each query type.
+
+export type DNS_RR_CNAME struct {
+	DNS_RR_Header;
+	cname string "domain-name";
+}
+
+export type DNS_RR_HINFO struct {
+	DNS_RR_Header;
+	cpu string;
+	os string;
+}
+
+export type DNS_RR_MB struct {
+	DNS_RR_Header;
+	mb string "domain-name";
+}
+
+export type DNS_RR_MG struct {
+	DNS_RR_Header;
+	mg string "domain-name";
+}
+
+export type DNS_RR_MINFO struct {
+	DNS_RR_Header;
+	rmail string "domain-name";
+	email string "domain-name";
+}
+
+export type DNS_RR_MR struct {
+	DNS_RR_Header;
+	mr string "domain-name";
+}
+
+export type DNS_RR_MX struct {
+	DNS_RR_Header;
+	pref uint16;
+	mx string "domain-name";
+}
+
+export type DNS_RR_NS struct {
+	DNS_RR_Header;
+	ns string "domain-name";
+}
+
+export type DNS_RR_PTR struct {
+	DNS_RR_Header;
+	ptr string "domain-name";
+}
+
+export type DNS_RR_SOA struct {
+	DNS_RR_Header;
+	ns string "domain-name";
+	mbox string "domain-name";
+	serial uint32;
+	refresh uint32;
+	retry uint32;
+	expire uint32;
+	minttl uint32;
+}
+
+export type DNS_RR_TXT struct {
+	DNS_RR_Header;
+	txt string;	// not domain name
+}
+
+export type DNS_RR_A struct {
+	DNS_RR_Header;
+	a uint32 "ipv4";
+}
+
+
+// Packing and unpacking.
+//
+// All the packers and unpackers take a (msg *[]byte, off int)
+// and return (off1 int, ok bool).  If they return ok==false, they
+// also return off1==len(msg), so that the next unpacker will
+// also fail.  This lets us avoid checks of ok until the end of a
+// packing sequence.
+
+// Map of constructors for each RR wire type.
+var rr_mk = map[int]*()DNS_RR {
+	DNS_TypeCNAME: func() DNS_RR { return new(DNS_RR_CNAME) },
+	DNS_TypeHINFO: func() DNS_RR { return new(DNS_RR_HINFO) },
+	DNS_TypeMB: func() DNS_RR { return new(DNS_RR_MB) },
+	DNS_TypeMG: func() DNS_RR { return new(DNS_RR_MG) },
+	DNS_TypeMINFO: func() DNS_RR { return new(DNS_RR_MINFO) },
+	DNS_TypeMR: func() DNS_RR { return new(DNS_RR_MR) },
+	DNS_TypeMX: func() DNS_RR { return new(DNS_RR_MX) },
+	DNS_TypeNS: func() DNS_RR { return new(DNS_RR_NS) },
+	DNS_TypePTR: func() DNS_RR { return new(DNS_RR_PTR) },
+	DNS_TypeSOA: func() DNS_RR { return new(DNS_RR_SOA) },
+	DNS_TypeTXT: func() DNS_RR { return new(DNS_RR_TXT) },
+	DNS_TypeA: func() DNS_RR { return new(DNS_RR_A) },
+}
+
+// Pack a domain name s into msg[off:].
+// Domain names are a sequence of counted strings
+// split at the dots.  They end with a zero-length string.
+func PackDomainName(s string, msg *[]byte, off int) (off1 int, ok bool) {
+	// Add trailing dot to canonicalize name.
+	if n := len(s); n == 0 || s[n-1] != '.' {
+		s += ".";
+	}
+
+	// Each dot ends a segment of the name.
+	// We trade each dot byte for a length byte.
+	// There is also a trailing zero.
+	// Check that we have all the space we need.
+	tot := len(s) + 1;
+	if off+tot > len(msg) {
+		return len(msg), false
+	}
+
+	// Emit sequence of counted strings, chopping at dots.
+	begin := 0;
+	for i := 0; i < len(s); i++ {
+		if s[i] == '.' {
+			if i - begin >= 1<<6 { // top two bits of length must be clear
+				return len(msg), false
+			}
+			msg[off] = byte(i - begin);
+			off++;
+			for j := begin; j < i; j++ {
+				msg[off] = s[j];
+				off++;
+			}
+			begin = i+1;
+		}
+	}
+	msg[off] = 0;
+	off++;
+	return off, true
+}
+
+// Unpack a domain name.
+// In addition to the simple sequences of counted strings above,
+// domain names are allowed to refer to strings elsewhere in the
+// packet, to avoid repeating common suffixes when returning
+// many entries in a single domain.  The pointers are marked
+// by a length byte with the top two bits set.  Ignoring those
+// two bits, that byte and the next give a 14 bit offset from msg[0]
+// where we should pick up the trail.
+// Note that if we jump elsewhere in the packet,
+// we return off1 == the offset after the first pointer we found,
+// which is where the next record will start.
+// In theory, the pointers are only allowed to jump backward.
+// We let them jump anywhere and stop jumping after a while.
+func UnpackDomainName(msg *[]byte, off int) (s string, off1 int, ok bool) {
+	s = "";
+	ptr := 0;	// number of pointers followed
+Loop:
+	for {
+		if off >= len(msg) {
+			return "", len(msg), false
+		}
+		c := int(msg[off]);
+		off++;
+		switch c&0xC0 {
+		case 0x00:
+			if c == 0x00 {
+				// end of name
+				break Loop
+			}
+			// literal string
+			if off+c > len(msg) {
+				return "", len(msg), false
+			}
+			s += string(msg[off:off+c]) + ".";
+			off += c;
+		case 0xC0:
+			// pointer to somewhere else in msg.
+			// remember location after first ptr,
+			// since that's how many bytes we consumed.
+			// also, don't follow too many pointers --
+			// maybe there's a loop.
+			if off >= len(msg) {
+				return "", len(msg), false
+			}
+			c1 := msg[off];
+			off++;
+			if ptr == 0 {
+				off1 = off
+			}
+			if ptr++; ptr > 10 {
+				return "", len(msg), false
+			}
+			off = (c^0xC0)<<8 | int(c1);
+		default:
+			// 0x80 and 0x40 are reserved
+			return "", len(msg), false
+		}
+	}
+	if ptr == 0 {
+		off1 = off
+	}
+	return s, off1, true
+}
+
+// Pack a reflect.StructValue into msg.  Struct members can only be uint16, uint32, string,
+// and other (often anonymous) structs.
+func PackStructValue(val reflect.StructValue, msg *[]byte, off int) (off1 int, ok bool) {
+	for i := 0; i < val.Len(); i++ {
+		fld := val.Field(i);
+		name, typ, tag, xxx := val.Type().(reflect.StructType).Field(i);
+		switch fld.Kind() {
+		default:
+			fmt.fprintf(os.Stderr, "net: dns: unknown packing type %v", fld.Type());
+			return len(msg), false;
+		case reflect.StructKind:
+			off, ok = PackStructValue(fld.(reflect.StructValue), msg, off);
+		case reflect.Uint16Kind:
+			i := fld.(reflect.Uint16Value).Get();
+			if off+2 > len(msg) {
+				return len(msg), false
+			}
+			msg[off] = byte(i>>8);
+			msg[off+1] = byte(i);
+			off += 2;
+		case reflect.Uint32Kind:
+			i := fld.(reflect.Uint32Value).Get();
+			if off+4 > len(msg) {
+				return len(msg), false
+			}
+			msg[off] = byte(i>>24);
+			msg[off+1] = byte(i>>16);
+			msg[off+2] = byte(i>>8);
+			msg[off+4] = byte(i);
+			off += 4;
+		case reflect.StringKind:
+			// There are multiple string encodings.
+			// The tag distinguishes ordinary strings from domain names.
+			s := fld.(reflect.StringValue).Get();
+			switch tag {
+			default:
+				fmt.fprintf(os.Stderr, "net: dns: unknown string tag %v", tag);
+				return len(msg), false;
+			case "domain-name":
+				off, ok = PackDomainName(s, msg, off);
+				if !ok {
+					return len(msg), false
+				}
+			case "":
+				// Counted string: 1 byte length.
+				if len(s) > 255 || off + 1 + len(s) > len(msg) {
+					return len(msg), false
+				}
+				msg[off] = byte(len(s));
+				off++;
+				for i := 0; i < len(s); i++ {
+					msg[off+i] = s[i];
+				}
+				off += len(s);
+			}
+		}
+	}
+	return off, true
+}
+
+func PackStruct(any interface{}, msg *[]byte, off int) (off1 int, ok bool) {
+	val := reflect.NewValue(any).(reflect.PtrValue).Sub().(reflect.StructValue);
+	off, ok = PackStructValue(val, msg, off);
+	return off, ok
+}
+
+// Unpack a reflect.StructValue from msg.
+// Same restrictions as PackStructValue.
+func UnpackStructValue(val reflect.StructValue, msg *[]byte, off int) (off1 int, ok bool) {
+	for i := 0; i < val.Len(); i++ {
+		name, typ, tag, xxx := val.Type().(reflect.StructType).Field(i);
+		fld := val.Field(i);
+		switch fld.Kind() {
+		default:
+			fmt.fprintf(os.Stderr, "net: dns: unknown packing type %v", fld.Type());
+			return len(msg), false;
+		case reflect.StructKind:
+			off, ok = UnpackStructValue(fld.(reflect.StructValue), msg, off);
+		case reflect.Uint16Kind:
+			if off+2 > len(msg) {
+				return len(msg), false
+			}
+			i := uint16(msg[off])<<8 | uint16(msg[off+1]);
+			fld.(reflect.Uint16Value).Set(i);
+			off += 2;
+		case reflect.Uint32Kind:
+			if off+4 > len(msg) {
+				return len(msg), false
+			}
+			i := uint32(msg[off])<<24 | uint32(msg[off+1])<<16 | uint32(msg[off+2])<<8 | uint32(msg[off+3]);
+			fld.(reflect.Uint32Value).Set(i);
+			off += 4;
+		case reflect.StringKind:
+			var s string;
+			switch tag {
+			default:
+				fmt.fprintf(os.Stderr, "net: dns: unknown string tag %v", tag);
+				return len(msg), false;
+			case "domain-name":
+				s, off, ok = UnpackDomainName(msg, off);
+				if !ok {
+					return len(msg), false
+				}
+			case "":
+				if off >= len(msg) || off+1+int(msg[off]) > len(msg) {
+					return len(msg), false
+				}
+				n := int(msg[off]);
+				off++;
+				b := new([]byte, n);
+				for i := 0; i < n; i++ {
+					b[i] = msg[off+i];
+				}
+				off += n;
+				s = string(b);
+			}
+			fld.(reflect.StringValue).Set(s);
+		}
+	}
+	return off, true
+}
+
+func UnpackStruct(any interface{}, msg *[]byte, off int) (off1 int, ok bool) {
+	val := reflect.NewValue(any).(reflect.PtrValue).Sub().(reflect.StructValue);
+	off, ok = UnpackStructValue(val, msg, off);
+	return off, ok
+}
+
+// Generic struct printer.
+// Doesn't care about the string tag "domain-name",
+// but does look for an "ipv4" tag on uint32 variables,
+// printing them as IP addresses.
+func PrintStructValue(val reflect.StructValue) string {
+	s := "{";
+	for i := 0; i < val.Len(); i++ {
+		if i > 0 {
+			s += ", ";
+		}
+		name, typ, tag, xxx := val.Type().(reflect.StructType).Field(i);
+		fld := val.Field(i);
+		if name != "" && name != "?" {	// BUG? Shouldn't the reflect library hide "?" ?
+			s += name + "=";
+		}
+		kind := fld.Kind();
+		switch {
+		case kind == reflect.StructKind:
+			s += PrintStructValue(fld.(reflect.StructValue));
+		case kind == reflect.Uint32Kind && tag == "ipv4":
+			i := fld.(reflect.Uint32Value).Get();
+			s += fmt.sprintf("%d.%d.%d.%d", (i>>24)&0xFF, (i>>16)&0xFF, (i>>8)&0xFF, i&0xFF);
+		default:
+			s += fmt.sprint(fld.Interface())
+		}
+	}
+	s += "}";
+	return s;
+}
+
+func PrintStruct(any interface{}) string {
+	val := reflect.NewValue(any).(reflect.PtrValue).Sub().(reflect.StructValue);
+	s := PrintStructValue(val);
+	return s
+}
+
+// Resource record packer.
+func PackRR(rr DNS_RR, msg *[]byte, off int) (off2 int, ok bool) {
+	var off1 int;
+	// pack twice, once to find end of header
+	// and again to find end of packet.
+	// a bit inefficient but this doesn't need to be fast.
+	// off1 is end of header
+	// off2 is end of rr
+	off1, ok = PackStruct(rr.Header(), msg, off);
+	off2, ok = PackStruct(rr, msg, off);
+	if !ok {
+		return len(msg), false
+	}
+	// pack a third time; redo header with correct data length
+	rr.Header().rdlength = uint16(off2 - off1);
+	PackStruct(rr.Header(), msg, off);
+	return off2, true
+}
+
+// Resource record unpacker.
+func UnpackRR(msg *[]byte, off int) (rr DNS_RR, off1 int, ok bool) {
+	// unpack just the header, to find the rr type and length
+	var h DNS_RR_Header;
+	off0 := off;
+	if off, ok = UnpackStruct(&h, msg, off); !ok {
+		return nil, len(msg), false
+	}
+	end := off+int(h.rdlength);
+
+	// make an rr of that type and re-unpack.
+	// again inefficient but doesn't need to be fast.
+	mk, known := rr_mk[int(h.rrtype)];
+	if !known {
+		return &h, end, true
+	}
+	rr = mk();
+	off, ok = UnpackStruct(rr, msg, off0);
+	if off != end {
+		return &h, end, true
+	}
+	return rr, off, ok
+}
+
+// Usable representation of a DNS packet.
+
+// A manually-unpacked version of (id, bits).
+// This is in its own struct for easy printing.
+type DNS_Msg_Top struct {
+	id uint16;
+	response bool;
+	opcode int;
+	authoritative bool;
+	truncated bool;
+	recursion_desired bool;
+	recursion_available bool;
+	rcode int;
+}
+
+export type DNS_Msg struct {
+	DNS_Msg_Top;
+	question *[]DNS_Question;
+	answer *[]DNS_RR;
+	ns *[]DNS_RR;
+	extra *[]DNS_RR;
+}
+
+var no_questions = new([]DNS_Question, 0)
+var no_rr = new([]DNS_RR, 0)
+
+func (dns *DNS_Msg) Pack() (msg *[]byte, ok bool) {
+	var dh DNS_Header;
+
+	// Convert convenient DNS_Msg into wire-like DNS_Header.
+	dh.id = dns.id;
+	dh.bits = uint16(dns.opcode)<<11 | uint16(dns.rcode);
+	if dns.recursion_available {
+		dh.bits |= RA;
+	}
+	if dns.recursion_desired {
+		dh.bits |= RD;
+	}
+	if dns.truncated {
+		dh.bits |= TC;
+	}
+	if dns.authoritative {
+		dh.bits |= AA;
+	}
+	if dns.response {
+		dh.bits |= QR;
+	}
+
+	// Prepare variable sized arrays; paper over nils.
+	var question *[]DNS_Question;
+	var answer, ns, extra *[]DNS_RR;
+	if question = dns.question; question == nil {
+		question = no_questions
+	}
+	if answer = dns.answer; answer == nil {
+		answer = no_rr
+	}
+	if ns = dns.ns; ns == nil {
+		ns = no_rr
+	}
+	if extra = dns.extra; extra == nil {
+		extra = no_rr
+	}
+
+	dh.qdcount = uint16(len(question));
+	dh.ancount = uint16(len(answer));
+	dh.nscount = uint16(len(ns));
+	dh.arcount = uint16(len(extra));
+
+	// Could work harder to calculate message size,
+	// but this is far more than we need and not
+	// big enough to hurt the allocator.
+	msg = new([]byte, 2000);
+
+	// Pack it in: header and then the pieces.
+	off := 0;
+	off, ok = PackStruct(&dh, msg, off);
+	for i := 0; i < len(question); i++ {
+		off, ok = PackStruct(&question[i], msg, off);
+	}
+	for i := 0; i < len(answer); i++ {
+		off, ok = PackStruct(answer[i], msg, off);
+	}
+	for i := 0; i < len(ns); i++ {
+		off, ok = PackStruct(ns[i], msg, off);
+	}
+	for i := 0; i < len(extra); i++ {
+		off, ok = PackStruct(extra[i], msg, off);
+	}
+	if !ok {
+		return nil, false
+	}
+	return msg[0:off], true
+}
+
+func (dns *DNS_Msg) Unpack(msg *[]byte) bool {
+	// Header.
+	var dh DNS_Header;
+	off := 0;
+	var ok bool;
+	if off, ok = UnpackStruct(&dh, msg, off); !ok {
+		return false
+	}
+	dns.id = dh.id;
+	dns.response = (dh.bits & QR) != 0;
+	dns.opcode = int(dh.bits >> 11) & 0xF;
+	dns.authoritative = (dh.bits & AA) != 0;
+	dns.truncated = (dh.bits & TC) != 0;
+	dns.recursion_desired = (dh.bits & RD) != 0;
+	dns.recursion_available = (dh.bits & RA) != 0;
+	dns.rcode = int(dh.bits & 0xF);
+
+	// Arrays.
+	dns.question = new([]DNS_Question, dh.qdcount);
+	dns.answer = new([]DNS_RR, dh.ancount);
+	dns.ns = new([]DNS_RR, dh.nscount);
+	dns.extra = new([]DNS_RR, dh.arcount);
+
+	for i := 0; i < len(dns.question); i++ {
+		off, ok = UnpackStruct(&dns.question[i], msg, off);
+	}
+	for i := 0; i < len(dns.answer); i++ {
+		dns.answer[i], off, ok = UnpackRR(msg, off);
+	}
+	for i := 0; i < len(dns.ns); i++ {
+		dns.ns[i], off, ok = UnpackRR(msg, off);
+	}
+	for i := 0; i < len(dns.extra); i++ {
+		dns.extra[i], off, ok = UnpackRR(msg, off);
+	}
+	if !ok {
+		return false
+	}
+//	if off != len(msg) {
+//		println("extra bytes in dns packet", off, "<", len(msg));
+//	}
+	return true
+}
+
+func (dns *DNS_Msg) String() string {
+	s := "DNS: "+PrintStruct(&dns.DNS_Msg_Top)+"\n";
+	if dns.question != nil && len(dns.question) > 0 {
+		s += "-- Questions\n";
+		for i := 0; i < len(dns.question); i++ {
+			s += PrintStruct(&dns.question[i])+"\n";
+		}
+	}
+	if dns.answer != nil && len(dns.answer) > 0 {
+		s += "-- Answers\n";
+		for i := 0; i < len(dns.answer); i++ {
+			s += PrintStruct(dns.answer[i])+"\n";
+		}
+	}
+	if dns.ns != nil && len(dns.ns) > 0 {
+		s += "-- Name servers\n";
+		for i := 0; i < len(dns.ns); i++ {
+			s += PrintStruct(dns.ns[i])+"\n";
+		}
+	}
+	if dns.extra != nil && len(dns.extra) > 0 {
+		s += "-- Extra\n";
+		for i := 0; i < len(dns.extra); i++ {
+			s += PrintStruct(dns.extra[i])+"\n";
+		}
+	}
+	return s;
+}