summaryrefslogtreecommitdiff
path: root/src/net/dnsmsg.go
diff options
context:
space:
mode:
Diffstat (limited to 'src/net/dnsmsg.go')
-rw-r--r--src/net/dnsmsg.go887
1 files changed, 887 insertions, 0 deletions
diff --git a/src/net/dnsmsg.go b/src/net/dnsmsg.go
new file mode 100644
index 000000000..161afb2a5
--- /dev/null
+++ b/src/net/dnsmsg.go
@@ -0,0 +1,887 @@
+// 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. See RFC 1035.
+//
+// This is intended to support name resolution during Dial.
+// It doesn't have to be blazing fast.
+//
+// Each message structure has a Walk method that is used by
+// a generic pack/unpack routine. 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
+
+// Packet formats
+
+// Wire constants.
+const (
+ // valid dnsRR_Header.Rrtype and dnsQuestion.qtype
+ dnsTypeA = 1
+ dnsTypeNS = 2
+ dnsTypeMD = 3
+ dnsTypeMF = 4
+ dnsTypeCNAME = 5
+ dnsTypeSOA = 6
+ dnsTypeMB = 7
+ dnsTypeMG = 8
+ dnsTypeMR = 9
+ dnsTypeNULL = 10
+ dnsTypeWKS = 11
+ dnsTypePTR = 12
+ dnsTypeHINFO = 13
+ dnsTypeMINFO = 14
+ dnsTypeMX = 15
+ dnsTypeTXT = 16
+ dnsTypeAAAA = 28
+ dnsTypeSRV = 33
+
+ // valid dnsQuestion.qtype only
+ dnsTypeAXFR = 252
+ dnsTypeMAILB = 253
+ dnsTypeMAILA = 254
+ dnsTypeALL = 255
+
+ // valid dnsQuestion.qclass
+ dnsClassINET = 1
+ dnsClassCSNET = 2
+ dnsClassCHAOS = 3
+ dnsClassHESIOD = 4
+ dnsClassANY = 255
+
+ // dnsMsg.rcode
+ dnsRcodeSuccess = 0
+ dnsRcodeFormatError = 1
+ dnsRcodeServerFailure = 2
+ dnsRcodeNameError = 3
+ dnsRcodeNotImplemented = 4
+ dnsRcodeRefused = 5
+)
+
+// A dnsStruct describes how to iterate over its fields to emulate
+// reflective marshalling.
+type dnsStruct interface {
+ // Walk iterates over fields of a structure and calls f
+ // with a reference to that field, the name of the field
+ // and a tag ("", "domain", "ipv4", "ipv6") specifying
+ // particular encodings. Possible concrete types
+ // for v are *uint16, *uint32, *string, or []byte, and
+ // *int, *bool in the case of dnsMsgHdr.
+ // Whenever f returns false, Walk must stop and return
+ // false, and otherwise return true.
+ Walk(f func(v interface{}, name, tag string) (ok bool)) (ok bool)
+}
+
+// The wire format for the DNS packet header.
+type dnsHeader struct {
+ Id uint16
+ Bits uint16
+ Qdcount, Ancount, Nscount, Arcount uint16
+}
+
+func (h *dnsHeader) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return f(&h.Id, "Id", "") &&
+ f(&h.Bits, "Bits", "") &&
+ f(&h.Qdcount, "Qdcount", "") &&
+ f(&h.Ancount, "Ancount", "") &&
+ f(&h.Nscount, "Nscount", "") &&
+ f(&h.Arcount, "Arcount", "")
+}
+
+const (
+ // dnsHeader.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 dnsQuestion struct {
+ Name string `net:"domain-name"` // `net:"domain-name"` specifies encoding; see packers below
+ Qtype uint16
+ Qclass uint16
+}
+
+func (q *dnsQuestion) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return f(&q.Name, "Name", "domain") &&
+ f(&q.Qtype, "Qtype", "") &&
+ f(&q.Qclass, "Qclass", "")
+}
+
+// DNS responses (resource records).
+// There are many types of messages,
+// but they all share the same header.
+type dnsRR_Header struct {
+ Name string `net:"domain-name"`
+ Rrtype uint16
+ Class uint16
+ Ttl uint32
+ Rdlength uint16 // length of data after header
+}
+
+func (h *dnsRR_Header) Header() *dnsRR_Header {
+ return h
+}
+
+func (h *dnsRR_Header) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return f(&h.Name, "Name", "domain") &&
+ f(&h.Rrtype, "Rrtype", "") &&
+ f(&h.Class, "Class", "") &&
+ f(&h.Ttl, "Ttl", "") &&
+ f(&h.Rdlength, "Rdlength", "")
+}
+
+type dnsRR interface {
+ dnsStruct
+ Header() *dnsRR_Header
+}
+
+// Specific DNS RR formats for each query type.
+
+type dnsRR_CNAME struct {
+ Hdr dnsRR_Header
+ Cname string `net:"domain-name"`
+}
+
+func (rr *dnsRR_CNAME) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_CNAME) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Cname, "Cname", "domain")
+}
+
+type dnsRR_HINFO struct {
+ Hdr dnsRR_Header
+ Cpu string
+ Os string
+}
+
+func (rr *dnsRR_HINFO) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_HINFO) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Cpu, "Cpu", "") && f(&rr.Os, "Os", "")
+}
+
+type dnsRR_MB struct {
+ Hdr dnsRR_Header
+ Mb string `net:"domain-name"`
+}
+
+func (rr *dnsRR_MB) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_MB) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Mb, "Mb", "domain")
+}
+
+type dnsRR_MG struct {
+ Hdr dnsRR_Header
+ Mg string `net:"domain-name"`
+}
+
+func (rr *dnsRR_MG) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_MG) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Mg, "Mg", "domain")
+}
+
+type dnsRR_MINFO struct {
+ Hdr dnsRR_Header
+ Rmail string `net:"domain-name"`
+ Email string `net:"domain-name"`
+}
+
+func (rr *dnsRR_MINFO) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_MINFO) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Rmail, "Rmail", "domain") && f(&rr.Email, "Email", "domain")
+}
+
+type dnsRR_MR struct {
+ Hdr dnsRR_Header
+ Mr string `net:"domain-name"`
+}
+
+func (rr *dnsRR_MR) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_MR) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Mr, "Mr", "domain")
+}
+
+type dnsRR_MX struct {
+ Hdr dnsRR_Header
+ Pref uint16
+ Mx string `net:"domain-name"`
+}
+
+func (rr *dnsRR_MX) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_MX) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Pref, "Pref", "") && f(&rr.Mx, "Mx", "domain")
+}
+
+type dnsRR_NS struct {
+ Hdr dnsRR_Header
+ Ns string `net:"domain-name"`
+}
+
+func (rr *dnsRR_NS) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_NS) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Ns, "Ns", "domain")
+}
+
+type dnsRR_PTR struct {
+ Hdr dnsRR_Header
+ Ptr string `net:"domain-name"`
+}
+
+func (rr *dnsRR_PTR) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_PTR) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Ptr, "Ptr", "domain")
+}
+
+type dnsRR_SOA struct {
+ Hdr dnsRR_Header
+ Ns string `net:"domain-name"`
+ Mbox string `net:"domain-name"`
+ Serial uint32
+ Refresh uint32
+ Retry uint32
+ Expire uint32
+ Minttl uint32
+}
+
+func (rr *dnsRR_SOA) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_SOA) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) &&
+ f(&rr.Ns, "Ns", "domain") &&
+ f(&rr.Mbox, "Mbox", "domain") &&
+ f(&rr.Serial, "Serial", "") &&
+ f(&rr.Refresh, "Refresh", "") &&
+ f(&rr.Retry, "Retry", "") &&
+ f(&rr.Expire, "Expire", "") &&
+ f(&rr.Minttl, "Minttl", "")
+}
+
+type dnsRR_TXT struct {
+ Hdr dnsRR_Header
+ Txt string // not domain name
+}
+
+func (rr *dnsRR_TXT) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_TXT) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.Txt, "Txt", "")
+}
+
+type dnsRR_SRV struct {
+ Hdr dnsRR_Header
+ Priority uint16
+ Weight uint16
+ Port uint16
+ Target string `net:"domain-name"`
+}
+
+func (rr *dnsRR_SRV) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_SRV) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) &&
+ f(&rr.Priority, "Priority", "") &&
+ f(&rr.Weight, "Weight", "") &&
+ f(&rr.Port, "Port", "") &&
+ f(&rr.Target, "Target", "domain")
+}
+
+type dnsRR_A struct {
+ Hdr dnsRR_Header
+ A uint32 `net:"ipv4"`
+}
+
+func (rr *dnsRR_A) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_A) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(&rr.A, "A", "ipv4")
+}
+
+type dnsRR_AAAA struct {
+ Hdr dnsRR_Header
+ AAAA [16]byte `net:"ipv6"`
+}
+
+func (rr *dnsRR_AAAA) Header() *dnsRR_Header {
+ return &rr.Hdr
+}
+
+func (rr *dnsRR_AAAA) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return rr.Hdr.Walk(f) && f(rr.AAAA[:], "AAAA", "ipv6")
+}
+
+// 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() dnsRR{
+ dnsTypeCNAME: func() dnsRR { return new(dnsRR_CNAME) },
+ dnsTypeHINFO: func() dnsRR { return new(dnsRR_HINFO) },
+ dnsTypeMB: func() dnsRR { return new(dnsRR_MB) },
+ dnsTypeMG: func() dnsRR { return new(dnsRR_MG) },
+ dnsTypeMINFO: func() dnsRR { return new(dnsRR_MINFO) },
+ dnsTypeMR: func() dnsRR { return new(dnsRR_MR) },
+ dnsTypeMX: func() dnsRR { return new(dnsRR_MX) },
+ dnsTypeNS: func() dnsRR { return new(dnsRR_NS) },
+ dnsTypePTR: func() dnsRR { return new(dnsRR_PTR) },
+ dnsTypeSOA: func() dnsRR { return new(dnsRR_SOA) },
+ dnsTypeTXT: func() dnsRR { return new(dnsRR_TXT) },
+ dnsTypeSRV: func() dnsRR { return new(dnsRR_SRV) },
+ dnsTypeA: func() dnsRR { return new(dnsRR_A) },
+ dnsTypeAAAA: func() dnsRR { return new(dnsRR_AAAA) },
+}
+
+// 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
+}
+
+// packStruct packs a structure into msg at specified offset off, and
+// returns off1 such that msg[off:off1] is the encoded data.
+func packStruct(any dnsStruct, msg []byte, off int) (off1 int, ok bool) {
+ ok = any.Walk(func(field interface{}, name, tag string) bool {
+ switch fv := field.(type) {
+ default:
+ println("net: dns: unknown packing type")
+ return false
+ case *uint16:
+ i := *fv
+ if off+2 > len(msg) {
+ return false
+ }
+ msg[off] = byte(i >> 8)
+ msg[off+1] = byte(i)
+ off += 2
+ case *uint32:
+ i := *fv
+ msg[off] = byte(i >> 24)
+ msg[off+1] = byte(i >> 16)
+ msg[off+2] = byte(i >> 8)
+ msg[off+3] = byte(i)
+ off += 4
+ case []byte:
+ n := len(fv)
+ if off+n > len(msg) {
+ return false
+ }
+ copy(msg[off:off+n], fv)
+ off += n
+ case *string:
+ s := *fv
+ switch tag {
+ default:
+ println("net: dns: unknown string tag", tag)
+ return false
+ case "domain":
+ off, ok = packDomainName(s, msg, off)
+ if !ok {
+ return false
+ }
+ case "":
+ // Counted string: 1 byte length.
+ if len(s) > 255 || off+1+len(s) > len(msg) {
+ return false
+ }
+ msg[off] = byte(len(s))
+ off++
+ off += copy(msg[off:], s)
+ }
+ }
+ return true
+ })
+ if !ok {
+ return len(msg), false
+ }
+ return off, true
+}
+
+// unpackStruct decodes msg[off:] into the given structure, and
+// returns off1 such that msg[off:off1] is the encoded data.
+func unpackStruct(any dnsStruct, msg []byte, off int) (off1 int, ok bool) {
+ ok = any.Walk(func(field interface{}, name, tag string) bool {
+ switch fv := field.(type) {
+ default:
+ println("net: dns: unknown packing type")
+ return false
+ case *uint16:
+ if off+2 > len(msg) {
+ return false
+ }
+ *fv = uint16(msg[off])<<8 | uint16(msg[off+1])
+ off += 2
+ case *uint32:
+ if off+4 > len(msg) {
+ return false
+ }
+ *fv = uint32(msg[off])<<24 | uint32(msg[off+1])<<16 |
+ uint32(msg[off+2])<<8 | uint32(msg[off+3])
+ off += 4
+ case []byte:
+ n := len(fv)
+ if off+n > len(msg) {
+ return false
+ }
+ copy(fv, msg[off:off+n])
+ off += n
+ case *string:
+ var s string
+ switch tag {
+ default:
+ println("net: dns: unknown string tag", tag)
+ return false
+ case "domain":
+ s, off, ok = unpackDomainName(msg, off)
+ if !ok {
+ return false
+ }
+ case "":
+ if off >= len(msg) || off+1+int(msg[off]) > len(msg) {
+ return 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)
+ }
+ *fv = s
+ }
+ return true
+ })
+ if !ok {
+ return len(msg), false
+ }
+ return off, true
+}
+
+// Generic struct printer. Prints fields with tag "ipv4" or "ipv6"
+// as IP addresses.
+func printStruct(any dnsStruct) string {
+ s := "{"
+ i := 0
+ any.Walk(func(val interface{}, name, tag string) bool {
+ i++
+ if i > 1 {
+ s += ", "
+ }
+ s += name + "="
+ switch tag {
+ case "ipv4":
+ i := *val.(*uint32)
+ s += IPv4(byte(i>>24), byte(i>>16), byte(i>>8), byte(i)).String()
+ case "ipv6":
+ i := val.([]byte)
+ s += IP(i).String()
+ default:
+ var i int64
+ switch v := val.(type) {
+ default:
+ // can't really happen.
+ s += "<unknown type>"
+ return true
+ case *string:
+ s += *v
+ return true
+ case []byte:
+ s += string(v)
+ return true
+ case *bool:
+ if *v {
+ s += "true"
+ } else {
+ s += "false"
+ }
+ return true
+ case *int:
+ i = int64(*v)
+ case *uint:
+ i = int64(*v)
+ case *uint8:
+ i = int64(*v)
+ case *uint16:
+ i = int64(*v)
+ case *uint32:
+ i = int64(*v)
+ case *uint64:
+ i = int64(*v)
+ case *uintptr:
+ i = int64(*v)
+ }
+ s += itoa(int(i))
+ }
+ return true
+ })
+ s += "}"
+ return s
+}
+
+// Resource record packer.
+func packRR(rr dnsRR, 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 dnsRR, off1 int, ok bool) {
+ // unpack just the header, to find the rr type and length
+ var h dnsRR_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 dnsMsgHdr struct {
+ id uint16
+ response bool
+ opcode int
+ authoritative bool
+ truncated bool
+ recursion_desired bool
+ recursion_available bool
+ rcode int
+}
+
+func (h *dnsMsgHdr) Walk(f func(v interface{}, name, tag string) bool) bool {
+ return f(&h.id, "id", "") &&
+ f(&h.response, "response", "") &&
+ f(&h.opcode, "opcode", "") &&
+ f(&h.authoritative, "authoritative", "") &&
+ f(&h.truncated, "truncated", "") &&
+ f(&h.recursion_desired, "recursion_desired", "") &&
+ f(&h.recursion_available, "recursion_available", "") &&
+ f(&h.rcode, "rcode", "")
+}
+
+type dnsMsg struct {
+ dnsMsgHdr
+ question []dnsQuestion
+ answer []dnsRR
+ ns []dnsRR
+ extra []dnsRR
+}
+
+func (dns *dnsMsg) Pack() (msg []byte, ok bool) {
+ var dh dnsHeader
+
+ // Convert convenient dnsMsg into wire-like dnsHeader.
+ 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 = packRR(answer[i], msg, off)
+ }
+ for i := 0; i < len(ns); i++ {
+ off, ok = packRR(ns[i], msg, off)
+ }
+ for i := 0; i < len(extra); i++ {
+ off, ok = packRR(extra[i], msg, off)
+ }
+ if !ok {
+ return nil, false
+ }
+ return msg[0:off], true
+}
+
+func (dns *dnsMsg) Unpack(msg []byte) bool {
+ // Header.
+ var dh dnsHeader
+ 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([]dnsQuestion, dh.Qdcount)
+ dns.answer = make([]dnsRR, 0, dh.Ancount)
+ dns.ns = make([]dnsRR, 0, dh.Nscount)
+ dns.extra = make([]dnsRR, 0, dh.Arcount)
+
+ var rec dnsRR
+
+ for i := 0; i < len(dns.question); i++ {
+ off, ok = unpackStruct(&dns.question[i], msg, off)
+ }
+ for i := 0; i < int(dh.Ancount); i++ {
+ rec, off, ok = unpackRR(msg, off)
+ if !ok {
+ return false
+ }
+ dns.answer = append(dns.answer, rec)
+ }
+ for i := 0; i < int(dh.Nscount); i++ {
+ rec, off, ok = unpackRR(msg, off)
+ if !ok {
+ return false
+ }
+ dns.ns = append(dns.ns, rec)
+ }
+ for i := 0; i < int(dh.Arcount); i++ {
+ rec, off, ok = unpackRR(msg, off)
+ if !ok {
+ return false
+ }
+ dns.extra = append(dns.extra, rec)
+ }
+ // if off != len(msg) {
+ // println("extra bytes in dns packet", off, "<", len(msg));
+ // }
+ return true
+}
+
+func (dns *dnsMsg) String() string {
+ s := "DNS: " + printStruct(&dns.dnsMsgHdr) + "\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 2.39.1) at 2024-06-13 19:18:23 +0000