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// 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.
// Package dnsmessage provides a mostly RFC 1035 compliant implementation of
// DNS message packing and unpacking.
//
// The package also supports messages with Extension Mechanisms for DNS
// (EDNS(0)) as defined in RFC 6891.
//
// This implementation is designed to minimize heap allocations and avoid
// unnecessary packing and unpacking as much as possible.
package dnsmessage
import (
"errors"
)
// Message formats
// A Type is a type of DNS request and response.
type Type uint16
const (
// ResourceHeader.Type and Question.Type
TypeA Type = 1
TypeNS Type = 2
TypeCNAME Type = 5
TypeSOA Type = 6
TypePTR Type = 12
TypeMX Type = 15
TypeTXT Type = 16
TypeAAAA Type = 28
TypeSRV Type = 33
TypeOPT Type = 41
// Question.Type
TypeWKS Type = 11
TypeHINFO Type = 13
TypeMINFO Type = 14
TypeAXFR Type = 252
TypeALL Type = 255
)
var typeNames = map[Type]string{
TypeA: "TypeA",
TypeNS: "TypeNS",
TypeCNAME: "TypeCNAME",
TypeSOA: "TypeSOA",
TypePTR: "TypePTR",
TypeMX: "TypeMX",
TypeTXT: "TypeTXT",
TypeAAAA: "TypeAAAA",
TypeSRV: "TypeSRV",
TypeOPT: "TypeOPT",
TypeWKS: "TypeWKS",
TypeHINFO: "TypeHINFO",
TypeMINFO: "TypeMINFO",
TypeAXFR: "TypeAXFR",
TypeALL: "TypeALL",
}
// String implements fmt.Stringer.String.
func (t Type) String() string {
if n, ok := typeNames[t]; ok {
return n
}
return printUint16(uint16(t))
}
// GoString implements fmt.GoStringer.GoString.
func (t Type) GoString() string {
if n, ok := typeNames[t]; ok {
return "dnsmessage." + n
}
return printUint16(uint16(t))
}
// A Class is a type of network.
type Class uint16
const (
// ResourceHeader.Class and Question.Class
ClassINET Class = 1
ClassCSNET Class = 2
ClassCHAOS Class = 3
ClassHESIOD Class = 4
// Question.Class
ClassANY Class = 255
)
var classNames = map[Class]string{
ClassINET: "ClassINET",
ClassCSNET: "ClassCSNET",
ClassCHAOS: "ClassCHAOS",
ClassHESIOD: "ClassHESIOD",
ClassANY: "ClassANY",
}
// String implements fmt.Stringer.String.
func (c Class) String() string {
if n, ok := classNames[c]; ok {
return n
}
return printUint16(uint16(c))
}
// GoString implements fmt.GoStringer.GoString.
func (c Class) GoString() string {
if n, ok := classNames[c]; ok {
return "dnsmessage." + n
}
return printUint16(uint16(c))
}
// An OpCode is a DNS operation code.
type OpCode uint16
// GoString implements fmt.GoStringer.GoString.
func (o OpCode) GoString() string {
return printUint16(uint16(o))
}
// An RCode is a DNS response status code.
type RCode uint16
const (
// Message.Rcode
RCodeSuccess RCode = 0
RCodeFormatError RCode = 1
RCodeServerFailure RCode = 2
RCodeNameError RCode = 3
RCodeNotImplemented RCode = 4
RCodeRefused RCode = 5
)
var rCodeNames = map[RCode]string{
RCodeSuccess: "RCodeSuccess",
RCodeFormatError: "RCodeFormatError",
RCodeServerFailure: "RCodeServerFailure",
RCodeNameError: "RCodeNameError",
RCodeNotImplemented: "RCodeNotImplemented",
RCodeRefused: "RCodeRefused",
}
// String implements fmt.Stringer.String.
func (r RCode) String() string {
if n, ok := rCodeNames[r]; ok {
return n
}
return printUint16(uint16(r))
}
// GoString implements fmt.GoStringer.GoString.
func (r RCode) GoString() string {
if n, ok := rCodeNames[r]; ok {
return "dnsmessage." + n
}
return printUint16(uint16(r))
}
func printPaddedUint8(i uint8) string {
b := byte(i)
return string([]byte{
b/100 + '0',
b/10%10 + '0',
b%10 + '0',
})
}
func printUint8Bytes(buf []byte, i uint8) []byte {
b := byte(i)
if i >= 100 {
buf = append(buf, b/100+'0')
}
if i >= 10 {
buf = append(buf, b/10%10+'0')
}
return append(buf, b%10+'0')
}
func printByteSlice(b []byte) string {
if len(b) == 0 {
return ""
}
buf := make([]byte, 0, 5*len(b))
buf = printUint8Bytes(buf, uint8(b[0]))
for _, n := range b[1:] {
buf = append(buf, ',', ' ')
buf = printUint8Bytes(buf, uint8(n))
}
return string(buf)
}
const hexDigits = "0123456789abcdef"
func printString(str []byte) string {
buf := make([]byte, 0, len(str))
for i := 0; i < len(str); i++ {
c := str[i]
if c == '.' || c == '-' || c == ' ' ||
'A' <= c && c <= 'Z' ||
'a' <= c && c <= 'z' ||
'0' <= c && c <= '9' {
buf = append(buf, c)
continue
}
upper := c >> 4
lower := (c << 4) >> 4
buf = append(
buf,
'\\',
'x',
hexDigits[upper],
hexDigits[lower],
)
}
return string(buf)
}
func printUint16(i uint16) string {
return printUint32(uint32(i))
}
func printUint32(i uint32) string {
// Max value is 4294967295.
buf := make([]byte, 10)
for b, d := buf, uint32(1000000000); d > 0; d /= 10 {
b[0] = byte(i/d%10 + '0')
if b[0] == '0' && len(b) == len(buf) && len(buf) > 1 {
buf = buf[1:]
}
b = b[1:]
i %= d
}
return string(buf)
}
func printBool(b bool) string {
if b {
return "true"
}
return "false"
}
var (
// ErrNotStarted indicates that the prerequisite information isn't
// available yet because the previous records haven't been appropriately
// parsed, skipped or finished.
ErrNotStarted = errors.New("parsing/packing of this type isn't available yet")
// ErrSectionDone indicated that all records in the section have been
// parsed or finished.
ErrSectionDone = errors.New("parsing/packing of this section has completed")
errBaseLen = errors.New("insufficient data for base length type")
errCalcLen = errors.New("insufficient data for calculated length type")
errReserved = errors.New("segment prefix is reserved")
errTooManyPtr = errors.New("too many pointers (>10)")
errInvalidPtr = errors.New("invalid pointer")
errNilResouceBody = errors.New("nil resource body")
errResourceLen = errors.New("insufficient data for resource body length")
errSegTooLong = errors.New("segment length too long")
errZeroSegLen = errors.New("zero length segment")
errResTooLong = errors.New("resource length too long")
errTooManyQuestions = errors.New("too many Questions to pack (>65535)")
errTooManyAnswers = errors.New("too many Answers to pack (>65535)")
errTooManyAuthorities = errors.New("too many Authorities to pack (>65535)")
errTooManyAdditionals = errors.New("too many Additionals to pack (>65535)")
errNonCanonicalName = errors.New("name is not in canonical format (it must end with a .)")
errStringTooLong = errors.New("character string exceeds maximum length (255)")
errCompressedSRV = errors.New("compressed name in SRV resource data")
)
// Internal constants.
const (
// packStartingCap is the default initial buffer size allocated during
// packing.
//
// The starting capacity doesn't matter too much, but most DNS responses
// Will be <= 512 bytes as it is the limit for DNS over UDP.
packStartingCap = 512
// uint16Len is the length (in bytes) of a uint16.
uint16Len = 2
// uint32Len is the length (in bytes) of a uint32.
uint32Len = 4
// headerLen is the length (in bytes) of a DNS header.
//
// A header is comprised of 6 uint16s and no padding.
headerLen = 6 * uint16Len
)
type nestedError struct {
// s is the current level's error message.
s string
// err is the nested error.
err error
}
// nestedError implements error.Error.
func (e *nestedError) Error() string {
return e.s + ": " + e.err.Error()
}
// Header is a representation of a DNS message header.
type Header struct {
ID uint16
Response bool
OpCode OpCode
Authoritative bool
Truncated bool
RecursionDesired bool
RecursionAvailable bool
RCode RCode
}
func (m *Header) pack() (id uint16, bits uint16) {
id = m.ID
bits = uint16(m.OpCode)<<11 | uint16(m.RCode)
if m.RecursionAvailable {
bits |= headerBitRA
}
if m.RecursionDesired {
bits |= headerBitRD
}
if m.Truncated {
bits |= headerBitTC
}
if m.Authoritative {
bits |= headerBitAA
}
if m.Response {
bits |= headerBitQR
}
return
}
// GoString implements fmt.GoStringer.GoString.
func (m *Header) GoString() string {
return "dnsmessage.Header{" +
"ID: " + printUint16(m.ID) + ", " +
"Response: " + printBool(m.Response) + ", " +
"OpCode: " + m.OpCode.GoString() + ", " +
"Authoritative: " + printBool(m.Authoritative) + ", " +
"Truncated: " + printBool(m.Truncated) + ", " +
"RecursionDesired: " + printBool(m.RecursionDesired) + ", " +
"RecursionAvailable: " + printBool(m.RecursionAvailable) + ", " +
"RCode: " + m.RCode.GoString() + "}"
}
// Message is a representation of a DNS message.
type Message struct {
Header
Questions []Question
Answers []Resource
Authorities []Resource
Additionals []Resource
}
type section uint8
const (
sectionNotStarted section = iota
sectionHeader
sectionQuestions
sectionAnswers
sectionAuthorities
sectionAdditionals
sectionDone
headerBitQR = 1 << 15 // query/response (response=1)
headerBitAA = 1 << 10 // authoritative
headerBitTC = 1 << 9 // truncated
headerBitRD = 1 << 8 // recursion desired
headerBitRA = 1 << 7 // recursion available
)
var sectionNames = map[section]string{
sectionHeader: "header",
sectionQuestions: "Question",
sectionAnswers: "Answer",
sectionAuthorities: "Authority",
sectionAdditionals: "Additional",
}
// header is the wire format for a DNS message header.
type header struct {
id uint16
bits uint16
questions uint16
answers uint16
authorities uint16
additionals uint16
}
func (h *header) count(sec section) uint16 {
switch sec {
case sectionQuestions:
return h.questions
case sectionAnswers:
return h.answers
case sectionAuthorities:
return h.authorities
case sectionAdditionals:
return h.additionals
}
return 0
}
// pack appends the wire format of the header to msg.
func (h *header) pack(msg []byte) []byte {
msg = packUint16(msg, h.id)
msg = packUint16(msg, h.bits)
msg = packUint16(msg, h.questions)
msg = packUint16(msg, h.answers)
msg = packUint16(msg, h.authorities)
return packUint16(msg, h.additionals)
}
func (h *header) unpack(msg []byte, off int) (int, error) {
newOff := off
var err error
if h.id, newOff, err = unpackUint16(msg, newOff); err != nil {
return off, &nestedError{"id", err}
}
if h.bits, newOff, err = unpackUint16(msg, newOff); err != nil {
return off, &nestedError{"bits", err}
}
if h.questions, newOff, err = unpackUint16(msg, newOff); err != nil {
return off, &nestedError{"questions", err}
}
if h.answers, newOff, err = unpackUint16(msg, newOff); err != nil {
return off, &nestedError{"answers", err}
}
if h.authorities, newOff, err = unpackUint16(msg, newOff); err != nil {
return off, &nestedError{"authorities", err}
}
if h.additionals, newOff, err = unpackUint16(msg, newOff); err != nil {
return off, &nestedError{"additionals", err}
}
return newOff, nil
}
func (h *header) header() Header {
return Header{
ID: h.id,
Response: (h.bits & headerBitQR) != 0,
OpCode: OpCode(h.bits>>11) & 0xF,
Authoritative: (h.bits & headerBitAA) != 0,
Truncated: (h.bits & headerBitTC) != 0,
RecursionDesired: (h.bits & headerBitRD) != 0,
RecursionAvailable: (h.bits & headerBitRA) != 0,
RCode: RCode(h.bits & 0xF),
}
}
// A Resource is a DNS resource record.
type Resource struct {
Header ResourceHeader
Body ResourceBody
}
func (r *Resource) GoString() string {
return "dnsmessage.Resource{" +
"Header: " + r.Header.GoString() +
", Body: &" + r.Body.GoString() +
"}"
}
// A ResourceBody is a DNS resource record minus the header.
type ResourceBody interface {
// pack packs a Resource except for its header.
pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error)
// realType returns the actual type of the Resource. This is used to
// fill in the header Type field.
realType() Type
// GoString implements fmt.GoStringer.GoString.
GoString() string
}
// pack appends the wire format of the Resource to msg.
func (r *Resource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
if r.Body == nil {
return msg, errNilResouceBody
}
oldMsg := msg
r.Header.Type = r.Body.realType()
msg, lenOff, err := r.Header.pack(msg, compression, compressionOff)
if err != nil {
return msg, &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
msg, err = r.Body.pack(msg, compression, compressionOff)
if err != nil {
return msg, &nestedError{"content", err}
}
if err := r.Header.fixLen(msg, lenOff, preLen); err != nil {
return oldMsg, err
}
return msg, nil
}
// A Parser allows incrementally parsing a DNS message.
//
// When parsing is started, the Header is parsed. Next, each Question can be
// either parsed or skipped. Alternatively, all Questions can be skipped at
// once. When all Questions have been parsed, attempting to parse Questions
// will return (nil, nil) and attempting to skip Questions will return
// (true, nil). After all Questions have been either parsed or skipped, all
// Answers, Authorities and Additionals can be either parsed or skipped in the
// same way, and each type of Resource must be fully parsed or skipped before
// proceeding to the next type of Resource.
//
// Note that there is no requirement to fully skip or parse the message.
type Parser struct {
msg []byte
header header
section section
off int
index int
resHeaderValid bool
resHeader ResourceHeader
}
// Start parses the header and enables the parsing of Questions.
func (p *Parser) Start(msg []byte) (Header, error) {
if p.msg != nil {
*p = Parser{}
}
p.msg = msg
var err error
if p.off, err = p.header.unpack(msg, 0); err != nil {
return Header{}, &nestedError{"unpacking header", err}
}
p.section = sectionQuestions
return p.header.header(), nil
}
func (p *Parser) checkAdvance(sec section) error {
if p.section < sec {
return ErrNotStarted
}
if p.section > sec {
return ErrSectionDone
}
p.resHeaderValid = false
if p.index == int(p.header.count(sec)) {
p.index = 0
p.section++
return ErrSectionDone
}
return nil
}
func (p *Parser) resource(sec section) (Resource, error) {
var r Resource
var err error
r.Header, err = p.resourceHeader(sec)
if err != nil {
return r, err
}
p.resHeaderValid = false
r.Body, p.off, err = unpackResourceBody(p.msg, p.off, r.Header)
if err != nil {
return Resource{}, &nestedError{"unpacking " + sectionNames[sec], err}
}
p.index++
return r, nil
}
func (p *Parser) resourceHeader(sec section) (ResourceHeader, error) {
if p.resHeaderValid {
return p.resHeader, nil
}
if err := p.checkAdvance(sec); err != nil {
return ResourceHeader{}, err
}
var hdr ResourceHeader
off, err := hdr.unpack(p.msg, p.off)
if err != nil {
return ResourceHeader{}, err
}
p.resHeaderValid = true
p.resHeader = hdr
p.off = off
return hdr, nil
}
func (p *Parser) skipResource(sec section) error {
if p.resHeaderValid {
newOff := p.off + int(p.resHeader.Length)
if newOff > len(p.msg) {
return errResourceLen
}
p.off = newOff
p.resHeaderValid = false
p.index++
return nil
}
if err := p.checkAdvance(sec); err != nil {
return err
}
var err error
p.off, err = skipResource(p.msg, p.off)
if err != nil {
return &nestedError{"skipping: " + sectionNames[sec], err}
}
p.index++
return nil
}
// Question parses a single Question.
func (p *Parser) Question() (Question, error) {
if err := p.checkAdvance(sectionQuestions); err != nil {
return Question{}, err
}
var name Name
off, err := name.unpack(p.msg, p.off)
if err != nil {
return Question{}, &nestedError{"unpacking Question.Name", err}
}
typ, off, err := unpackType(p.msg, off)
if err != nil {
return Question{}, &nestedError{"unpacking Question.Type", err}
}
class, off, err := unpackClass(p.msg, off)
if err != nil {
return Question{}, &nestedError{"unpacking Question.Class", err}
}
p.off = off
p.index++
return Question{name, typ, class}, nil
}
// AllQuestions parses all Questions.
func (p *Parser) AllQuestions() ([]Question, error) {
// Multiple questions are valid according to the spec,
// but servers don't actually support them. There will
// be at most one question here.
//
// Do not pre-allocate based on info in p.header, since
// the data is untrusted.
qs := []Question{}
for {
q, err := p.Question()
if err == ErrSectionDone {
return qs, nil
}
if err != nil {
return nil, err
}
qs = append(qs, q)
}
}
// SkipQuestion skips a single Question.
func (p *Parser) SkipQuestion() error {
if err := p.checkAdvance(sectionQuestions); err != nil {
return err
}
off, err := skipName(p.msg, p.off)
if err != nil {
return &nestedError{"skipping Question Name", err}
}
if off, err = skipType(p.msg, off); err != nil {
return &nestedError{"skipping Question Type", err}
}
if off, err = skipClass(p.msg, off); err != nil {
return &nestedError{"skipping Question Class", err}
}
p.off = off
p.index++
return nil
}
// SkipAllQuestions skips all Questions.
func (p *Parser) SkipAllQuestions() error {
for {
if err := p.SkipQuestion(); err == ErrSectionDone {
return nil
} else if err != nil {
return err
}
}
}
// AnswerHeader parses a single Answer ResourceHeader.
func (p *Parser) AnswerHeader() (ResourceHeader, error) {
return p.resourceHeader(sectionAnswers)
}
// Answer parses a single Answer Resource.
func (p *Parser) Answer() (Resource, error) {
return p.resource(sectionAnswers)
}
// AllAnswers parses all Answer Resources.
func (p *Parser) AllAnswers() ([]Resource, error) {
// The most common query is for A/AAAA, which usually returns
// a handful of IPs.
//
// Pre-allocate up to a certain limit, since p.header is
// untrusted data.
n := int(p.header.answers)
if n > 20 {
n = 20
}
as := make([]Resource, 0, n)
for {
a, err := p.Answer()
if err == ErrSectionDone {
return as, nil
}
if err != nil {
return nil, err
}
as = append(as, a)
}
}
// SkipAnswer skips a single Answer Resource.
func (p *Parser) SkipAnswer() error {
return p.skipResource(sectionAnswers)
}
// SkipAllAnswers skips all Answer Resources.
func (p *Parser) SkipAllAnswers() error {
for {
if err := p.SkipAnswer(); err == ErrSectionDone {
return nil
} else if err != nil {
return err
}
}
}
// AuthorityHeader parses a single Authority ResourceHeader.
func (p *Parser) AuthorityHeader() (ResourceHeader, error) {
return p.resourceHeader(sectionAuthorities)
}
// Authority parses a single Authority Resource.
func (p *Parser) Authority() (Resource, error) {
return p.resource(sectionAuthorities)
}
// AllAuthorities parses all Authority Resources.
func (p *Parser) AllAuthorities() ([]Resource, error) {
// Authorities contains SOA in case of NXDOMAIN and friends,
// otherwise it is empty.
//
// Pre-allocate up to a certain limit, since p.header is
// untrusted data.
n := int(p.header.authorities)
if n > 10 {
n = 10
}
as := make([]Resource, 0, n)
for {
a, err := p.Authority()
if err == ErrSectionDone {
return as, nil
}
if err != nil {
return nil, err
}
as = append(as, a)
}
}
// SkipAuthority skips a single Authority Resource.
func (p *Parser) SkipAuthority() error {
return p.skipResource(sectionAuthorities)
}
// SkipAllAuthorities skips all Authority Resources.
func (p *Parser) SkipAllAuthorities() error {
for {
if err := p.SkipAuthority(); err == ErrSectionDone {
return nil
} else if err != nil {
return err
}
}
}
// AdditionalHeader parses a single Additional ResourceHeader.
func (p *Parser) AdditionalHeader() (ResourceHeader, error) {
return p.resourceHeader(sectionAdditionals)
}
// Additional parses a single Additional Resource.
func (p *Parser) Additional() (Resource, error) {
return p.resource(sectionAdditionals)
}
// AllAdditionals parses all Additional Resources.
func (p *Parser) AllAdditionals() ([]Resource, error) {
// Additionals usually contain OPT, and sometimes A/AAAA
// glue records.
//
// Pre-allocate up to a certain limit, since p.header is
// untrusted data.
n := int(p.header.additionals)
if n > 10 {
n = 10
}
as := make([]Resource, 0, n)
for {
a, err := p.Additional()
if err == ErrSectionDone {
return as, nil
}
if err != nil {
return nil, err
}
as = append(as, a)
}
}
// SkipAdditional skips a single Additional Resource.
func (p *Parser) SkipAdditional() error {
return p.skipResource(sectionAdditionals)
}
// SkipAllAdditionals skips all Additional Resources.
func (p *Parser) SkipAllAdditionals() error {
for {
if err := p.SkipAdditional(); err == ErrSectionDone {
return nil
} else if err != nil {
return err
}
}
}
// CNAMEResource parses a single CNAMEResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) CNAMEResource() (CNAMEResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeCNAME {
return CNAMEResource{}, ErrNotStarted
}
r, err := unpackCNAMEResource(p.msg, p.off)
if err != nil {
return CNAMEResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// MXResource parses a single MXResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) MXResource() (MXResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeMX {
return MXResource{}, ErrNotStarted
}
r, err := unpackMXResource(p.msg, p.off)
if err != nil {
return MXResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// NSResource parses a single NSResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) NSResource() (NSResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeNS {
return NSResource{}, ErrNotStarted
}
r, err := unpackNSResource(p.msg, p.off)
if err != nil {
return NSResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// PTRResource parses a single PTRResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) PTRResource() (PTRResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypePTR {
return PTRResource{}, ErrNotStarted
}
r, err := unpackPTRResource(p.msg, p.off)
if err != nil {
return PTRResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// SOAResource parses a single SOAResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) SOAResource() (SOAResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeSOA {
return SOAResource{}, ErrNotStarted
}
r, err := unpackSOAResource(p.msg, p.off)
if err != nil {
return SOAResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// TXTResource parses a single TXTResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) TXTResource() (TXTResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeTXT {
return TXTResource{}, ErrNotStarted
}
r, err := unpackTXTResource(p.msg, p.off, p.resHeader.Length)
if err != nil {
return TXTResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// SRVResource parses a single SRVResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) SRVResource() (SRVResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeSRV {
return SRVResource{}, ErrNotStarted
}
r, err := unpackSRVResource(p.msg, p.off)
if err != nil {
return SRVResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// AResource parses a single AResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) AResource() (AResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeA {
return AResource{}, ErrNotStarted
}
r, err := unpackAResource(p.msg, p.off)
if err != nil {
return AResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// AAAAResource parses a single AAAAResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) AAAAResource() (AAAAResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeAAAA {
return AAAAResource{}, ErrNotStarted
}
r, err := unpackAAAAResource(p.msg, p.off)
if err != nil {
return AAAAResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// OPTResource parses a single OPTResource.
//
// One of the XXXHeader methods must have been called before calling this
// method.
func (p *Parser) OPTResource() (OPTResource, error) {
if !p.resHeaderValid || p.resHeader.Type != TypeOPT {
return OPTResource{}, ErrNotStarted
}
r, err := unpackOPTResource(p.msg, p.off, p.resHeader.Length)
if err != nil {
return OPTResource{}, err
}
p.off += int(p.resHeader.Length)
p.resHeaderValid = false
p.index++
return r, nil
}
// Unpack parses a full Message.
func (m *Message) Unpack(msg []byte) error {
var p Parser
var err error
if m.Header, err = p.Start(msg); err != nil {
return err
}
if m.Questions, err = p.AllQuestions(); err != nil {
return err
}
if m.Answers, err = p.AllAnswers(); err != nil {
return err
}
if m.Authorities, err = p.AllAuthorities(); err != nil {
return err
}
if m.Additionals, err = p.AllAdditionals(); err != nil {
return err
}
return nil
}
// Pack packs a full Message.
func (m *Message) Pack() ([]byte, error) {
return m.AppendPack(make([]byte, 0, packStartingCap))
}
// AppendPack is like Pack but appends the full Message to b and returns the
// extended buffer.
func (m *Message) AppendPack(b []byte) ([]byte, error) {
// Validate the lengths. It is very unlikely that anyone will try to
// pack more than 65535 of any particular type, but it is possible and
// we should fail gracefully.
if len(m.Questions) > int(^uint16(0)) {
return nil, errTooManyQuestions
}
if len(m.Answers) > int(^uint16(0)) {
return nil, errTooManyAnswers
}
if len(m.Authorities) > int(^uint16(0)) {
return nil, errTooManyAuthorities
}
if len(m.Additionals) > int(^uint16(0)) {
return nil, errTooManyAdditionals
}
var h header
h.id, h.bits = m.Header.pack()
h.questions = uint16(len(m.Questions))
h.answers = uint16(len(m.Answers))
h.authorities = uint16(len(m.Authorities))
h.additionals = uint16(len(m.Additionals))
compressionOff := len(b)
msg := h.pack(b)
// RFC 1035 allows (but does not require) compression for packing. RFC
// 1035 requires unpacking implementations to support compression, so
// unconditionally enabling it is fine.
//
// DNS lookups are typically done over UDP, and RFC 1035 states that UDP
// DNS messages can be a maximum of 512 bytes long. Without compression,
// many DNS response messages are over this limit, so enabling
// compression will help ensure compliance.
compression := map[string]int{}
for i := range m.Questions {
var err error
if msg, err = m.Questions[i].pack(msg, compression, compressionOff); err != nil {
return nil, &nestedError{"packing Question", err}
}
}
for i := range m.Answers {
var err error
if msg, err = m.Answers[i].pack(msg, compression, compressionOff); err != nil {
return nil, &nestedError{"packing Answer", err}
}
}
for i := range m.Authorities {
var err error
if msg, err = m.Authorities[i].pack(msg, compression, compressionOff); err != nil {
return nil, &nestedError{"packing Authority", err}
}
}
for i := range m.Additionals {
var err error
if msg, err = m.Additionals[i].pack(msg, compression, compressionOff); err != nil {
return nil, &nestedError{"packing Additional", err}
}
}
return msg, nil
}
// GoString implements fmt.GoStringer.GoString.
func (m *Message) GoString() string {
s := "dnsmessage.Message{Header: " + m.Header.GoString() + ", " +
"Questions: []dnsmessage.Question{"
if len(m.Questions) > 0 {
s += m.Questions[0].GoString()
for _, q := range m.Questions[1:] {
s += ", " + q.GoString()
}
}
s += "}, Answers: []dnsmessage.Resource{"
if len(m.Answers) > 0 {
s += m.Answers[0].GoString()
for _, a := range m.Answers[1:] {
s += ", " + a.GoString()
}
}
s += "}, Authorities: []dnsmessage.Resource{"
if len(m.Authorities) > 0 {
s += m.Authorities[0].GoString()
for _, a := range m.Authorities[1:] {
s += ", " + a.GoString()
}
}
s += "}, Additionals: []dnsmessage.Resource{"
if len(m.Additionals) > 0 {
s += m.Additionals[0].GoString()
for _, a := range m.Additionals[1:] {
s += ", " + a.GoString()
}
}
return s + "}}"
}
// A Builder allows incrementally packing a DNS message.
//
// Example usage:
// buf := make([]byte, 2, 514)
// b := NewBuilder(buf, Header{...})
// b.EnableCompression()
// // Optionally start a section and add things to that section.
// // Repeat adding sections as necessary.
// buf, err := b.Finish()
// // If err is nil, buf[2:] will contain the built bytes.
type Builder struct {
// msg is the storage for the message being built.
msg []byte
// section keeps track of the current section being built.
section section
// header keeps track of what should go in the header when Finish is
// called.
header header
// start is the starting index of the bytes allocated in msg for header.
start int
// compression is a mapping from name suffixes to their starting index
// in msg.
compression map[string]int
}
// NewBuilder creates a new builder with compression disabled.
//
// Note: Most users will want to immediately enable compression with the
// EnableCompression method. See that method's comment for why you may or may
// not want to enable compression.
//
// The DNS message is appended to the provided initial buffer buf (which may be
// nil) as it is built. The final message is returned by the (*Builder).Finish
// method, which may return the same underlying array if there was sufficient
// capacity in the slice.
func NewBuilder(buf []byte, h Header) Builder {
if buf == nil {
buf = make([]byte, 0, packStartingCap)
}
b := Builder{msg: buf, start: len(buf)}
b.header.id, b.header.bits = h.pack()
var hb [headerLen]byte
b.msg = append(b.msg, hb[:]...)
b.section = sectionHeader
return b
}
// EnableCompression enables compression in the Builder.
//
// Leaving compression disabled avoids compression related allocations, but can
// result in larger message sizes. Be careful with this mode as it can cause
// messages to exceed the UDP size limit.
//
// According to RFC 1035, section 4.1.4, the use of compression is optional, but
// all implementations must accept both compressed and uncompressed DNS
// messages.
//
// Compression should be enabled before any sections are added for best results.
func (b *Builder) EnableCompression() {
b.compression = map[string]int{}
}
func (b *Builder) startCheck(s section) error {
if b.section <= sectionNotStarted {
return ErrNotStarted
}
if b.section > s {
return ErrSectionDone
}
return nil
}
// StartQuestions prepares the builder for packing Questions.
func (b *Builder) StartQuestions() error {
if err := b.startCheck(sectionQuestions); err != nil {
return err
}
b.section = sectionQuestions
return nil
}
// StartAnswers prepares the builder for packing Answers.
func (b *Builder) StartAnswers() error {
if err := b.startCheck(sectionAnswers); err != nil {
return err
}
b.section = sectionAnswers
return nil
}
// StartAuthorities prepares the builder for packing Authorities.
func (b *Builder) StartAuthorities() error {
if err := b.startCheck(sectionAuthorities); err != nil {
return err
}
b.section = sectionAuthorities
return nil
}
// StartAdditionals prepares the builder for packing Additionals.
func (b *Builder) StartAdditionals() error {
if err := b.startCheck(sectionAdditionals); err != nil {
return err
}
b.section = sectionAdditionals
return nil
}
func (b *Builder) incrementSectionCount() error {
var count *uint16
var err error
switch b.section {
case sectionQuestions:
count = &b.header.questions
err = errTooManyQuestions
case sectionAnswers:
count = &b.header.answers
err = errTooManyAnswers
case sectionAuthorities:
count = &b.header.authorities
err = errTooManyAuthorities
case sectionAdditionals:
count = &b.header.additionals
err = errTooManyAdditionals
}
if *count == ^uint16(0) {
return err
}
*count++
return nil
}
// Question adds a single Question.
func (b *Builder) Question(q Question) error {
if b.section < sectionQuestions {
return ErrNotStarted
}
if b.section > sectionQuestions {
return ErrSectionDone
}
msg, err := q.pack(b.msg, b.compression, b.start)
if err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
func (b *Builder) checkResourceSection() error {
if b.section < sectionAnswers {
return ErrNotStarted
}
if b.section > sectionAdditionals {
return ErrSectionDone
}
return nil
}
// CNAMEResource adds a single CNAMEResource.
func (b *Builder) CNAMEResource(h ResourceHeader, r CNAMEResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"CNAMEResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// MXResource adds a single MXResource.
func (b *Builder) MXResource(h ResourceHeader, r MXResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"MXResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// NSResource adds a single NSResource.
func (b *Builder) NSResource(h ResourceHeader, r NSResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"NSResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// PTRResource adds a single PTRResource.
func (b *Builder) PTRResource(h ResourceHeader, r PTRResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"PTRResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// SOAResource adds a single SOAResource.
func (b *Builder) SOAResource(h ResourceHeader, r SOAResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"SOAResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// TXTResource adds a single TXTResource.
func (b *Builder) TXTResource(h ResourceHeader, r TXTResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"TXTResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// SRVResource adds a single SRVResource.
func (b *Builder) SRVResource(h ResourceHeader, r SRVResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"SRVResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// AResource adds a single AResource.
func (b *Builder) AResource(h ResourceHeader, r AResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"AResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// AAAAResource adds a single AAAAResource.
func (b *Builder) AAAAResource(h ResourceHeader, r AAAAResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"AAAAResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// OPTResource adds a single OPTResource.
func (b *Builder) OPTResource(h ResourceHeader, r OPTResource) error {
if err := b.checkResourceSection(); err != nil {
return err
}
h.Type = r.realType()
msg, lenOff, err := h.pack(b.msg, b.compression, b.start)
if err != nil {
return &nestedError{"ResourceHeader", err}
}
preLen := len(msg)
if msg, err = r.pack(msg, b.compression, b.start); err != nil {
return &nestedError{"OPTResource body", err}
}
if err := h.fixLen(msg, lenOff, preLen); err != nil {
return err
}
if err := b.incrementSectionCount(); err != nil {
return err
}
b.msg = msg
return nil
}
// Finish ends message building and generates a binary message.
func (b *Builder) Finish() ([]byte, error) {
if b.section < sectionHeader {
return nil, ErrNotStarted
}
b.section = sectionDone
// Space for the header was allocated in NewBuilder.
b.header.pack(b.msg[b.start:b.start])
return b.msg, nil
}
// A ResourceHeader is the header of a DNS resource record. There are
// many types of DNS resource records, but they all share the same header.
type ResourceHeader struct {
// Name is the domain name for which this resource record pertains.
Name Name
// Type is the type of DNS resource record.
//
// This field will be set automatically during packing.
Type Type
// Class is the class of network to which this DNS resource record
// pertains.
Class Class
// TTL is the length of time (measured in seconds) which this resource
// record is valid for (time to live). All Resources in a set should
// have the same TTL (RFC 2181 Section 5.2).
TTL uint32
// Length is the length of data in the resource record after the header.
//
// This field will be set automatically during packing.
Length uint16
}
// GoString implements fmt.GoStringer.GoString.
func (h *ResourceHeader) GoString() string {
return "dnsmessage.ResourceHeader{" +
"Name: " + h.Name.GoString() + ", " +
"Type: " + h.Type.GoString() + ", " +
"Class: " + h.Class.GoString() + ", " +
"TTL: " + printUint32(h.TTL) + ", " +
"Length: " + printUint16(h.Length) + "}"
}
// pack appends the wire format of the ResourceHeader to oldMsg.
//
// lenOff is the offset in msg where the Length field was packed.
func (h *ResourceHeader) pack(oldMsg []byte, compression map[string]int, compressionOff int) (msg []byte, lenOff int, err error) {
msg = oldMsg
if msg, err = h.Name.pack(msg, compression, compressionOff); err != nil {
return oldMsg, 0, &nestedError{"Name", err}
}
msg = packType(msg, h.Type)
msg = packClass(msg, h.Class)
msg = packUint32(msg, h.TTL)
lenOff = len(msg)
msg = packUint16(msg, h.Length)
return msg, lenOff, nil
}
func (h *ResourceHeader) unpack(msg []byte, off int) (int, error) {
newOff := off
var err error
if newOff, err = h.Name.unpack(msg, newOff); err != nil {
return off, &nestedError{"Name", err}
}
if h.Type, newOff, err = unpackType(msg, newOff); err != nil {
return off, &nestedError{"Type", err}
}
if h.Class, newOff, err = unpackClass(msg, newOff); err != nil {
return off, &nestedError{"Class", err}
}
if h.TTL, newOff, err = unpackUint32(msg, newOff); err != nil {
return off, &nestedError{"TTL", err}
}
if h.Length, newOff, err = unpackUint16(msg, newOff); err != nil {
return off, &nestedError{"Length", err}
}
return newOff, nil
}
// fixLen updates a packed ResourceHeader to include the length of the
// ResourceBody.
//
// lenOff is the offset of the ResourceHeader.Length field in msg.
//
// preLen is the length that msg was before the ResourceBody was packed.
func (h *ResourceHeader) fixLen(msg []byte, lenOff int, preLen int) error {
conLen := len(msg) - preLen
if conLen > int(^uint16(0)) {
return errResTooLong
}
// Fill in the length now that we know how long the content is.
packUint16(msg[lenOff:lenOff], uint16(conLen))
h.Length = uint16(conLen)
return nil
}
// EDNS(0) wire constants.
const (
edns0Version = 0
edns0DNSSECOK = 0x00008000
ednsVersionMask = 0x00ff0000
edns0DNSSECOKMask = 0x00ff8000
)
// SetEDNS0 configures h for EDNS(0).
//
// The provided extRCode must be an extedned RCode.
func (h *ResourceHeader) SetEDNS0(udpPayloadLen int, extRCode RCode, dnssecOK bool) error {
h.Name = Name{Data: [nameLen]byte{'.'}, Length: 1} // RFC 6891 section 6.1.2
h.Type = TypeOPT
h.Class = Class(udpPayloadLen)
h.TTL = uint32(extRCode) >> 4 << 24
if dnssecOK {
h.TTL |= edns0DNSSECOK
}
return nil
}
// DNSSECAllowed reports whether the DNSSEC OK bit is set.
func (h *ResourceHeader) DNSSECAllowed() bool {
return h.TTL&edns0DNSSECOKMask == edns0DNSSECOK // RFC 6891 section 6.1.3
}
// ExtendedRCode returns an extended RCode.
//
// The provided rcode must be the RCode in DNS message header.
func (h *ResourceHeader) ExtendedRCode(rcode RCode) RCode {
if h.TTL&ednsVersionMask == edns0Version { // RFC 6891 section 6.1.3
return RCode(h.TTL>>24<<4) | rcode
}
return rcode
}
func skipResource(msg []byte, off int) (int, error) {
newOff, err := skipName(msg, off)
if err != nil {
return off, &nestedError{"Name", err}
}
if newOff, err = skipType(msg, newOff); err != nil {
return off, &nestedError{"Type", err}
}
if newOff, err = skipClass(msg, newOff); err != nil {
return off, &nestedError{"Class", err}
}
if newOff, err = skipUint32(msg, newOff); err != nil {
return off, &nestedError{"TTL", err}
}
length, newOff, err := unpackUint16(msg, newOff)
if err != nil {
return off, &nestedError{"Length", err}
}
if newOff += int(length); newOff > len(msg) {
return off, errResourceLen
}
return newOff, nil
}
// packUint16 appends the wire format of field to msg.
func packUint16(msg []byte, field uint16) []byte {
return append(msg, byte(field>>8), byte(field))
}
func unpackUint16(msg []byte, off int) (uint16, int, error) {
if off+uint16Len > len(msg) {
return 0, off, errBaseLen
}
return uint16(msg[off])<<8 | uint16(msg[off+1]), off + uint16Len, nil
}
func skipUint16(msg []byte, off int) (int, error) {
if off+uint16Len > len(msg) {
return off, errBaseLen
}
return off + uint16Len, nil
}
// packType appends the wire format of field to msg.
func packType(msg []byte, field Type) []byte {
return packUint16(msg, uint16(field))
}
func unpackType(msg []byte, off int) (Type, int, error) {
t, o, err := unpackUint16(msg, off)
return Type(t), o, err
}
func skipType(msg []byte, off int) (int, error) {
return skipUint16(msg, off)
}
// packClass appends the wire format of field to msg.
func packClass(msg []byte, field Class) []byte {
return packUint16(msg, uint16(field))
}
func unpackClass(msg []byte, off int) (Class, int, error) {
c, o, err := unpackUint16(msg, off)
return Class(c), o, err
}
func skipClass(msg []byte, off int) (int, error) {
return skipUint16(msg, off)
}
// packUint32 appends the wire format of field to msg.
func packUint32(msg []byte, field uint32) []byte {
return append(
msg,
byte(field>>24),
byte(field>>16),
byte(field>>8),
byte(field),
)
}
func unpackUint32(msg []byte, off int) (uint32, int, error) {
if off+uint32Len > len(msg) {
return 0, off, errBaseLen
}
v := uint32(msg[off])<<24 | uint32(msg[off+1])<<16 | uint32(msg[off+2])<<8 | uint32(msg[off+3])
return v, off + uint32Len, nil
}
func skipUint32(msg []byte, off int) (int, error) {
if off+uint32Len > len(msg) {
return off, errBaseLen
}
return off + uint32Len, nil
}
// packText appends the wire format of field to msg.
func packText(msg []byte, field string) ([]byte, error) {
l := len(field)
if l > 255 {
return nil, errStringTooLong
}
msg = append(msg, byte(l))
msg = append(msg, field...)
return msg, nil
}
func unpackText(msg []byte, off int) (string, int, error) {
if off >= len(msg) {
return "", off, errBaseLen
}
beginOff := off + 1
endOff := beginOff + int(msg[off])
if endOff > len(msg) {
return "", off, errCalcLen
}
return string(msg[beginOff:endOff]), endOff, nil
}
func skipText(msg []byte, off int) (int, error) {
if off >= len(msg) {
return off, errBaseLen
}
endOff := off + 1 + int(msg[off])
if endOff > len(msg) {
return off, errCalcLen
}
return endOff, nil
}
// packBytes appends the wire format of field to msg.
func packBytes(msg []byte, field []byte) []byte {
return append(msg, field...)
}
func unpackBytes(msg []byte, off int, field []byte) (int, error) {
newOff := off + len(field)
if newOff > len(msg) {
return off, errBaseLen
}
copy(field, msg[off:newOff])
return newOff, nil
}
func skipBytes(msg []byte, off int, field []byte) (int, error) {
newOff := off + len(field)
if newOff > len(msg) {
return off, errBaseLen
}
return newOff, nil
}
const nameLen = 255
// A Name is a non-encoded domain name. It is used instead of strings to avoid
// allocations.
type Name struct {
Data [nameLen]byte
Length uint8
}
// NewName creates a new Name from a string.
func NewName(name string) (Name, error) {
if len([]byte(name)) > nameLen {
return Name{}, errCalcLen
}
n := Name{Length: uint8(len(name))}
copy(n.Data[:], []byte(name))
return n, nil
}
// MustNewName creates a new Name from a string and panics on error.
func MustNewName(name string) Name {
n, err := NewName(name)
if err != nil {
panic("creating name: " + err.Error())
}
return n
}
// String implements fmt.Stringer.String.
func (n Name) String() string {
return string(n.Data[:n.Length])
}
// GoString implements fmt.GoStringer.GoString.
func (n *Name) GoString() string {
return `dnsmessage.MustNewName("` + printString(n.Data[:n.Length]) + `")`
}
// pack appends the wire format of the Name to msg.
//
// Domain names are a sequence of counted strings split at the dots. They end
// with a zero-length string. Compression can be used to reuse domain suffixes.
//
// The compression map will be updated with new domain suffixes. If compression
// is nil, compression will not be used.
func (n *Name) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
oldMsg := msg
// Add a trailing dot to canonicalize name.
if n.Length == 0 || n.Data[n.Length-1] != '.' {
return oldMsg, errNonCanonicalName
}
// Allow root domain.
if n.Data[0] == '.' && n.Length == 1 {
return append(msg, 0), nil
}
// Emit sequence of counted strings, chopping at dots.
for i, begin := 0, 0; i < int(n.Length); i++ {
// Check for the end of the segment.
if n.Data[i] == '.' {
// The two most significant bits have special meaning.
// It isn't allowed for segments to be long enough to
// need them.
if i-begin >= 1<<6 {
return oldMsg, errSegTooLong
}
// Segments must have a non-zero length.
if i-begin == 0 {
return oldMsg, errZeroSegLen
}
msg = append(msg, byte(i-begin))
for j := begin; j < i; j++ {
msg = append(msg, n.Data[j])
}
begin = i + 1
continue
}
// We can only compress domain suffixes starting with a new
// segment. A pointer is two bytes with the two most significant
// bits set to 1 to indicate that it is a pointer.
if (i == 0 || n.Data[i-1] == '.') && compression != nil {
if ptr, ok := compression[string(n.Data[i:])]; ok {
// Hit. Emit a pointer instead of the rest of
// the domain.
return append(msg, byte(ptr>>8|0xC0), byte(ptr)), nil
}
// Miss. Add the suffix to the compression table if the
// offset can be stored in the available 14 bytes.
if len(msg) <= int(^uint16(0)>>2) {
compression[string(n.Data[i:])] = len(msg) - compressionOff
}
}
}
return append(msg, 0), nil
}
// unpack unpacks a domain name.
func (n *Name) unpack(msg []byte, off int) (int, error) {
return n.unpackCompressed(msg, off, true /* allowCompression */)
}
func (n *Name) unpackCompressed(msg []byte, off int, allowCompression bool) (int, error) {
// currOff is the current working offset.
currOff := off
// newOff is the offset where the next record will start. Pointers lead
// to data that belongs to other names and thus doesn't count towards to
// the usage of this name.
newOff := off
// ptr is the number of pointers followed.
var ptr int
// Name is a slice representation of the name data.
name := n.Data[:0]
Loop:
for {
if currOff >= len(msg) {
return off, errBaseLen
}
c := int(msg[currOff])
currOff++
switch c & 0xC0 {
case 0x00: // String segment
if c == 0x00 {
// A zero length signals the end of the name.
break Loop
}
endOff := currOff + c
if endOff > len(msg) {
return off, errCalcLen
}
name = append(name, msg[currOff:endOff]...)
name = append(name, '.')
currOff = endOff
case 0xC0: // Pointer
if !allowCompression {
return off, errCompressedSRV
}
if currOff >= len(msg) {
return off, errInvalidPtr
}
c1 := msg[currOff]
currOff++
if ptr == 0 {
newOff = currOff
}
// Don't follow too many pointers, maybe there's a loop.
if ptr++; ptr > 10 {
return off, errTooManyPtr
}
currOff = (c^0xC0)<<8 | int(c1)
default:
// Prefixes 0x80 and 0x40 are reserved.
return off, errReserved
}
}
if len(name) == 0 {
name = append(name, '.')
}
if len(name) > len(n.Data) {
return off, errCalcLen
}
n.Length = uint8(len(name))
if ptr == 0 {
newOff = currOff
}
return newOff, nil
}
func skipName(msg []byte, off int) (int, error) {
// newOff is the offset where the next record will start. Pointers lead
// to data that belongs to other names and thus doesn't count towards to
// the usage of this name.
newOff := off
Loop:
for {
if newOff >= len(msg) {
return off, errBaseLen
}
c := int(msg[newOff])
newOff++
switch c & 0xC0 {
case 0x00:
if c == 0x00 {
// A zero length signals the end of the name.
break Loop
}
// literal string
newOff += c
if newOff > len(msg) {
return off, errCalcLen
}
case 0xC0:
// Pointer to somewhere else in msg.
// Pointers are two bytes.
newOff++
// Don't follow the pointer as the data here has ended.
break Loop
default:
// Prefixes 0x80 and 0x40 are reserved.
return off, errReserved
}
}
return newOff, nil
}
// A Question is a DNS query.
type Question struct {
Name Name
Type Type
Class Class
}
// pack appends the wire format of the Question to msg.
func (q *Question) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
msg, err := q.Name.pack(msg, compression, compressionOff)
if err != nil {
return msg, &nestedError{"Name", err}
}
msg = packType(msg, q.Type)
return packClass(msg, q.Class), nil
}
// GoString implements fmt.GoStringer.GoString.
func (q *Question) GoString() string {
return "dnsmessage.Question{" +
"Name: " + q.Name.GoString() + ", " +
"Type: " + q.Type.GoString() + ", " +
"Class: " + q.Class.GoString() + "}"
}
func unpackResourceBody(msg []byte, off int, hdr ResourceHeader) (ResourceBody, int, error) {
var (
r ResourceBody
err error
name string
)
switch hdr.Type {
case TypeA:
var rb AResource
rb, err = unpackAResource(msg, off)
r = &rb
name = "A"
case TypeNS:
var rb NSResource
rb, err = unpackNSResource(msg, off)
r = &rb
name = "NS"
case TypeCNAME:
var rb CNAMEResource
rb, err = unpackCNAMEResource(msg, off)
r = &rb
name = "CNAME"
case TypeSOA:
var rb SOAResource
rb, err = unpackSOAResource(msg, off)
r = &rb
name = "SOA"
case TypePTR:
var rb PTRResource
rb, err = unpackPTRResource(msg, off)
r = &rb
name = "PTR"
case TypeMX:
var rb MXResource
rb, err = unpackMXResource(msg, off)
r = &rb
name = "MX"
case TypeTXT:
var rb TXTResource
rb, err = unpackTXTResource(msg, off, hdr.Length)
r = &rb
name = "TXT"
case TypeAAAA:
var rb AAAAResource
rb, err = unpackAAAAResource(msg, off)
r = &rb
name = "AAAA"
case TypeSRV:
var rb SRVResource
rb, err = unpackSRVResource(msg, off)
r = &rb
name = "SRV"
case TypeOPT:
var rb OPTResource
rb, err = unpackOPTResource(msg, off, hdr.Length)
r = &rb
name = "OPT"
}
if err != nil {
return nil, off, &nestedError{name + " record", err}
}
if r == nil {
return nil, off, errors.New("invalid resource type: " + string(hdr.Type+'0'))
}
return r, off + int(hdr.Length), nil
}
// A CNAMEResource is a CNAME Resource record.
type CNAMEResource struct {
CNAME Name
}
func (r *CNAMEResource) realType() Type {
return TypeCNAME
}
// pack appends the wire format of the CNAMEResource to msg.
func (r *CNAMEResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
return r.CNAME.pack(msg, compression, compressionOff)
}
// GoString implements fmt.GoStringer.GoString.
func (r *CNAMEResource) GoString() string {
return "dnsmessage.CNAMEResource{CNAME: " + r.CNAME.GoString() + "}"
}
func unpackCNAMEResource(msg []byte, off int) (CNAMEResource, error) {
var cname Name
if _, err := cname.unpack(msg, off); err != nil {
return CNAMEResource{}, err
}
return CNAMEResource{cname}, nil
}
// An MXResource is an MX Resource record.
type MXResource struct {
Pref uint16
MX Name
}
func (r *MXResource) realType() Type {
return TypeMX
}
// pack appends the wire format of the MXResource to msg.
func (r *MXResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
oldMsg := msg
msg = packUint16(msg, r.Pref)
msg, err := r.MX.pack(msg, compression, compressionOff)
if err != nil {
return oldMsg, &nestedError{"MXResource.MX", err}
}
return msg, nil
}
// GoString implements fmt.GoStringer.GoString.
func (r *MXResource) GoString() string {
return "dnsmessage.MXResource{" +
"Pref: " + printUint16(r.Pref) + ", " +
"MX: " + r.MX.GoString() + "}"
}
func unpackMXResource(msg []byte, off int) (MXResource, error) {
pref, off, err := unpackUint16(msg, off)
if err != nil {
return MXResource{}, &nestedError{"Pref", err}
}
var mx Name
if _, err := mx.unpack(msg, off); err != nil {
return MXResource{}, &nestedError{"MX", err}
}
return MXResource{pref, mx}, nil
}
// An NSResource is an NS Resource record.
type NSResource struct {
NS Name
}
func (r *NSResource) realType() Type {
return TypeNS
}
// pack appends the wire format of the NSResource to msg.
func (r *NSResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
return r.NS.pack(msg, compression, compressionOff)
}
// GoString implements fmt.GoStringer.GoString.
func (r *NSResource) GoString() string {
return "dnsmessage.NSResource{NS: " + r.NS.GoString() + "}"
}
func unpackNSResource(msg []byte, off int) (NSResource, error) {
var ns Name
if _, err := ns.unpack(msg, off); err != nil {
return NSResource{}, err
}
return NSResource{ns}, nil
}
// A PTRResource is a PTR Resource record.
type PTRResource struct {
PTR Name
}
func (r *PTRResource) realType() Type {
return TypePTR
}
// pack appends the wire format of the PTRResource to msg.
func (r *PTRResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
return r.PTR.pack(msg, compression, compressionOff)
}
// GoString implements fmt.GoStringer.GoString.
func (r *PTRResource) GoString() string {
return "dnsmessage.PTRResource{PTR: " + r.PTR.GoString() + "}"
}
func unpackPTRResource(msg []byte, off int) (PTRResource, error) {
var ptr Name
if _, err := ptr.unpack(msg, off); err != nil {
return PTRResource{}, err
}
return PTRResource{ptr}, nil
}
// An SOAResource is an SOA Resource record.
type SOAResource struct {
NS Name
MBox Name
Serial uint32
Refresh uint32
Retry uint32
Expire uint32
// MinTTL the is the default TTL of Resources records which did not
// contain a TTL value and the TTL of negative responses. (RFC 2308
// Section 4)
MinTTL uint32
}
func (r *SOAResource) realType() Type {
return TypeSOA
}
// pack appends the wire format of the SOAResource to msg.
func (r *SOAResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
oldMsg := msg
msg, err := r.NS.pack(msg, compression, compressionOff)
if err != nil {
return oldMsg, &nestedError{"SOAResource.NS", err}
}
msg, err = r.MBox.pack(msg, compression, compressionOff)
if err != nil {
return oldMsg, &nestedError{"SOAResource.MBox", err}
}
msg = packUint32(msg, r.Serial)
msg = packUint32(msg, r.Refresh)
msg = packUint32(msg, r.Retry)
msg = packUint32(msg, r.Expire)
return packUint32(msg, r.MinTTL), nil
}
// GoString implements fmt.GoStringer.GoString.
func (r *SOAResource) GoString() string {
return "dnsmessage.SOAResource{" +
"NS: " + r.NS.GoString() + ", " +
"MBox: " + r.MBox.GoString() + ", " +
"Serial: " + printUint32(r.Serial) + ", " +
"Refresh: " + printUint32(r.Refresh) + ", " +
"Retry: " + printUint32(r.Retry) + ", " +
"Expire: " + printUint32(r.Expire) + ", " +
"MinTTL: " + printUint32(r.MinTTL) + "}"
}
func unpackSOAResource(msg []byte, off int) (SOAResource, error) {
var ns Name
off, err := ns.unpack(msg, off)
if err != nil {
return SOAResource{}, &nestedError{"NS", err}
}
var mbox Name
if off, err = mbox.unpack(msg, off); err != nil {
return SOAResource{}, &nestedError{"MBox", err}
}
serial, off, err := unpackUint32(msg, off)
if err != nil {
return SOAResource{}, &nestedError{"Serial", err}
}
refresh, off, err := unpackUint32(msg, off)
if err != nil {
return SOAResource{}, &nestedError{"Refresh", err}
}
retry, off, err := unpackUint32(msg, off)
if err != nil {
return SOAResource{}, &nestedError{"Retry", err}
}
expire, off, err := unpackUint32(msg, off)
if err != nil {
return SOAResource{}, &nestedError{"Expire", err}
}
minTTL, _, err := unpackUint32(msg, off)
if err != nil {
return SOAResource{}, &nestedError{"MinTTL", err}
}
return SOAResource{ns, mbox, serial, refresh, retry, expire, minTTL}, nil
}
// A TXTResource is a TXT Resource record.
type TXTResource struct {
TXT []string
}
func (r *TXTResource) realType() Type {
return TypeTXT
}
// pack appends the wire format of the TXTResource to msg.
func (r *TXTResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
oldMsg := msg
for _, s := range r.TXT {
var err error
msg, err = packText(msg, s)
if err != nil {
return oldMsg, err
}
}
return msg, nil
}
// GoString implements fmt.GoStringer.GoString.
func (r *TXTResource) GoString() string {
s := "dnsmessage.TXTResource{TXT: []string{"
if len(r.TXT) == 0 {
return s + "}}"
}
s += `"` + printString([]byte(r.TXT[0]))
for _, t := range r.TXT[1:] {
s += `", "` + printString([]byte(t))
}
return s + `"}}`
}
func unpackTXTResource(msg []byte, off int, length uint16) (TXTResource, error) {
txts := make([]string, 0, 1)
for n := uint16(0); n < length; {
var t string
var err error
if t, off, err = unpackText(msg, off); err != nil {
return TXTResource{}, &nestedError{"text", err}
}
// Check if we got too many bytes.
if length-n < uint16(len(t))+1 {
return TXTResource{}, errCalcLen
}
n += uint16(len(t)) + 1
txts = append(txts, t)
}
return TXTResource{txts}, nil
}
// An SRVResource is an SRV Resource record.
type SRVResource struct {
Priority uint16
Weight uint16
Port uint16
Target Name // Not compressed as per RFC 2782.
}
func (r *SRVResource) realType() Type {
return TypeSRV
}
// pack appends the wire format of the SRVResource to msg.
func (r *SRVResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
oldMsg := msg
msg = packUint16(msg, r.Priority)
msg = packUint16(msg, r.Weight)
msg = packUint16(msg, r.Port)
msg, err := r.Target.pack(msg, nil, compressionOff)
if err != nil {
return oldMsg, &nestedError{"SRVResource.Target", err}
}
return msg, nil
}
// GoString implements fmt.GoStringer.GoString.
func (r *SRVResource) GoString() string {
return "dnsmessage.SRVResource{" +
"Priority: " + printUint16(r.Priority) + ", " +
"Weight: " + printUint16(r.Weight) + ", " +
"Port: " + printUint16(r.Port) + ", " +
"Target: " + r.Target.GoString() + "}"
}
func unpackSRVResource(msg []byte, off int) (SRVResource, error) {
priority, off, err := unpackUint16(msg, off)
if err != nil {
return SRVResource{}, &nestedError{"Priority", err}
}
weight, off, err := unpackUint16(msg, off)
if err != nil {
return SRVResource{}, &nestedError{"Weight", err}
}
port, off, err := unpackUint16(msg, off)
if err != nil {
return SRVResource{}, &nestedError{"Port", err}
}
var target Name
if _, err := target.unpackCompressed(msg, off, false /* allowCompression */); err != nil {
return SRVResource{}, &nestedError{"Target", err}
}
return SRVResource{priority, weight, port, target}, nil
}
// An AResource is an A Resource record.
type AResource struct {
A [4]byte
}
func (r *AResource) realType() Type {
return TypeA
}
// pack appends the wire format of the AResource to msg.
func (r *AResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
return packBytes(msg, r.A[:]), nil
}
// GoString implements fmt.GoStringer.GoString.
func (r *AResource) GoString() string {
return "dnsmessage.AResource{" +
"A: [4]byte{" + printByteSlice(r.A[:]) + "}}"
}
func unpackAResource(msg []byte, off int) (AResource, error) {
var a [4]byte
if _, err := unpackBytes(msg, off, a[:]); err != nil {
return AResource{}, err
}
return AResource{a}, nil
}
// An AAAAResource is an AAAA Resource record.
type AAAAResource struct {
AAAA [16]byte
}
func (r *AAAAResource) realType() Type {
return TypeAAAA
}
// GoString implements fmt.GoStringer.GoString.
func (r *AAAAResource) GoString() string {
return "dnsmessage.AAAAResource{" +
"AAAA: [16]byte{" + printByteSlice(r.AAAA[:]) + "}}"
}
// pack appends the wire format of the AAAAResource to msg.
func (r *AAAAResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
return packBytes(msg, r.AAAA[:]), nil
}
func unpackAAAAResource(msg []byte, off int) (AAAAResource, error) {
var aaaa [16]byte
if _, err := unpackBytes(msg, off, aaaa[:]); err != nil {
return AAAAResource{}, err
}
return AAAAResource{aaaa}, nil
}
// An OPTResource is an OPT pseudo Resource record.
//
// The pseudo resource record is part of the extension mechanisms for DNS
// as defined in RFC 6891.
type OPTResource struct {
Options []Option
}
// An Option represents a DNS message option within OPTResource.
//
// The message option is part of the extension mechanisms for DNS as
// defined in RFC 6891.
type Option struct {
Code uint16 // option code
Data []byte
}
// GoString implements fmt.GoStringer.GoString.
func (o *Option) GoString() string {
return "dnsmessage.Option{" +
"Code: " + printUint16(o.Code) + ", " +
"Data: []byte{" + printByteSlice(o.Data) + "}}"
}
func (r *OPTResource) realType() Type {
return TypeOPT
}
func (r *OPTResource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
for _, opt := range r.Options {
msg = packUint16(msg, opt.Code)
l := uint16(len(opt.Data))
msg = packUint16(msg, l)
msg = packBytes(msg, opt.Data)
}
return msg, nil
}
// GoString implements fmt.GoStringer.GoString.
func (r *OPTResource) GoString() string {
s := "dnsmessage.OPTResource{Options: []dnsmessage.Option{"
if len(r.Options) == 0 {
return s + "}}"
}
s += r.Options[0].GoString()
for _, o := range r.Options[1:] {
s += ", " + o.GoString()
}
return s + "}}"
}
func unpackOPTResource(msg []byte, off int, length uint16) (OPTResource, error) {
var opts []Option
for oldOff := off; off < oldOff+int(length); {
var err error
var o Option
o.Code, off, err = unpackUint16(msg, off)
if err != nil {
return OPTResource{}, &nestedError{"Code", err}
}
var l uint16
l, off, err = unpackUint16(msg, off)
if err != nil {
return OPTResource{}, &nestedError{"Data", err}
}
o.Data = make([]byte, l)
if copy(o.Data, msg[off:]) != int(l) {
return OPTResource{}, &nestedError{"Data", errCalcLen}
}
off += int(l)
opts = append(opts, o)
}
return OPTResource{opts}, nil
}
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