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-rw-r--r--src/pkg/net/dnsmsg.go679
1 files changed, 679 insertions, 0 deletions
diff --git a/src/pkg/net/dnsmsg.go b/src/pkg/net/dnsmsg.go
new file mode 100644
index 000000000..d7a467fc6
--- /dev/null
+++ b/src/pkg/net/dnsmsg.go
@@ -0,0 +1,679 @@
+// 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.
+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;
+
+ // _DNS_Msg.rcode
+ _DNS_RcodeSuccess = 0;
+ _DNS_RcodeFormatError = 1;
+ _DNS_RcodeServerFailure = 2;
+ _DNS_RcodeNameError = 3;
+ _DNS_RcodeNotImplemented = 4;
+ _DNS_RcodeRefused = 5;
+)
+
+// 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.
+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.
+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
+}
+
+type _DNS_RR interface {
+ Header() *_DNS_RR_Header
+}
+
+
+// Specific DNS RR formats for each query type.
+
+type _DNS_RR_CNAME struct {
+ _DNS_RR_Header;
+ cname string "domain-name";
+}
+
+type _DNS_RR_HINFO struct {
+ _DNS_RR_Header;
+ cpu string;
+ os string;
+}
+
+type _DNS_RR_MB struct {
+ _DNS_RR_Header;
+ mb string "domain-name";
+}
+
+type _DNS_RR_MG struct {
+ _DNS_RR_Header;
+ mg string "domain-name";
+}
+
+type _DNS_RR_MINFO struct {
+ _DNS_RR_Header;
+ rmail string "domain-name";
+ email string "domain-name";
+}
+
+type _DNS_RR_MR struct {
+ _DNS_RR_Header;
+ mr string "domain-name";
+}
+
+type _DNS_RR_MX struct {
+ _DNS_RR_Header;
+ pref uint16;
+ mx string "domain-name";
+}
+
+type _DNS_RR_NS struct {
+ _DNS_RR_Header;
+ ns string "domain-name";
+}
+
+type _DNS_RR_PTR struct {
+ _DNS_RR_Header;
+ ptr string "domain-name";
+}
+
+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;
+}
+
+type _DNS_RR_TXT struct {
+ _DNS_RR_Header;
+ txt string; // not domain name
+}
+
+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] func()_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 := make([]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;
+}
+
+type _DNS_Msg struct {
+ __DNS_Msg_Top;
+ question []_DNS_Question;
+ answer []_DNS_RR;
+ ns []_DNS_RR;
+ extra []_DNS_RR;
+}
+
+
+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.
+ question := dns.question;
+ answer := dns.answer;
+ ns := dns.ns;
+ extra := dns.extra;
+
+ 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 = make([]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 = make([]_DNS_Question, dh.qdcount);
+ dns.answer = make([]_DNS_RR, dh.ancount);
+ dns.ns = make([]_DNS_RR, dh.nscount);
+ dns.extra = make([]_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 len(dns.question) > 0 {
+ s += "-- Questions\n";
+ for i := 0; i < len(dns.question); i++ {
+ s += printStruct(&dns.question[i])+"\n";
+ }
+ }
+ if len(dns.answer) > 0 {
+ s += "-- Answers\n";
+ for i := 0; i < len(dns.answer); i++ {
+ s += printStruct(dns.answer[i])+"\n";
+ }
+ }
+ if len(dns.ns) > 0 {
+ s += "-- Name servers\n";
+ for i := 0; i < len(dns.ns); i++ {
+ s += printStruct(dns.ns[i])+"\n";
+ }
+ }
+ if len(dns.extra) > 0 {
+ s += "-- Extra\n";
+ for i := 0; i < len(dns.extra); i++ {
+ s += printStruct(dns.extra[i])+"\n";
+ }
+ }
+ return s;
+}
generated by cgit v1.2.3 (git 2.46.0) at 2025-10-27 02:19:22 +0000