mirror of
https://github.com/octoleo/restic.git
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2104 lines
53 KiB
Go
2104 lines
53 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package dnsmessage provides a mostly RFC 1035 compliant implementation of
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// DNS message packing and unpacking.
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//
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// This implementation is designed to minimize heap allocations and avoid
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// unnecessary packing and unpacking as much as possible.
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package dnsmessage
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import (
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"errors"
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)
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// Message formats
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// A Type is a type of DNS request and response.
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type Type uint16
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// A Class is a type of network.
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type Class uint16
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// An OpCode is a DNS operation code.
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type OpCode uint16
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// An RCode is a DNS response status code.
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type RCode uint16
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// Wire constants.
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const (
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// ResourceHeader.Type and Question.Type
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TypeA Type = 1
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TypeNS Type = 2
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TypeCNAME Type = 5
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TypeSOA Type = 6
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TypePTR Type = 12
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TypeMX Type = 15
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TypeTXT Type = 16
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TypeAAAA Type = 28
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TypeSRV Type = 33
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// Question.Type
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TypeWKS Type = 11
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TypeHINFO Type = 13
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TypeMINFO Type = 14
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TypeAXFR Type = 252
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TypeALL Type = 255
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// ResourceHeader.Class and Question.Class
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ClassINET Class = 1
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ClassCSNET Class = 2
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ClassCHAOS Class = 3
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ClassHESIOD Class = 4
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// Question.Class
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ClassANY Class = 255
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// Message.Rcode
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RCodeSuccess RCode = 0
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RCodeFormatError RCode = 1
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RCodeServerFailure RCode = 2
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RCodeNameError RCode = 3
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RCodeNotImplemented RCode = 4
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RCodeRefused RCode = 5
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)
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var (
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// ErrNotStarted indicates that the prerequisite information isn't
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// available yet because the previous records haven't been appropriately
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// parsed, skipped or finished.
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ErrNotStarted = errors.New("parsing/packing of this type isn't available yet")
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// ErrSectionDone indicated that all records in the section have been
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// parsed or finished.
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ErrSectionDone = errors.New("parsing/packing of this section has completed")
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errBaseLen = errors.New("insufficient data for base length type")
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errCalcLen = errors.New("insufficient data for calculated length type")
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errReserved = errors.New("segment prefix is reserved")
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errTooManyPtr = errors.New("too many pointers (>10)")
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errInvalidPtr = errors.New("invalid pointer")
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errNilResouceBody = errors.New("nil resource body")
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errResourceLen = errors.New("insufficient data for resource body length")
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errSegTooLong = errors.New("segment length too long")
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errZeroSegLen = errors.New("zero length segment")
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errResTooLong = errors.New("resource length too long")
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errTooManyQuestions = errors.New("too many Questions to pack (>65535)")
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errTooManyAnswers = errors.New("too many Answers to pack (>65535)")
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errTooManyAuthorities = errors.New("too many Authorities to pack (>65535)")
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errTooManyAdditionals = errors.New("too many Additionals to pack (>65535)")
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errNonCanonicalName = errors.New("name is not in canonical format (it must end with a .)")
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errStringTooLong = errors.New("character string exceeds maximum length (255)")
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errCompressedSRV = errors.New("compressed name in SRV resource data")
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)
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// Internal constants.
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const (
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// packStartingCap is the default initial buffer size allocated during
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// packing.
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//
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// The starting capacity doesn't matter too much, but most DNS responses
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// Will be <= 512 bytes as it is the limit for DNS over UDP.
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packStartingCap = 512
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// uint16Len is the length (in bytes) of a uint16.
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uint16Len = 2
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// uint32Len is the length (in bytes) of a uint32.
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uint32Len = 4
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// headerLen is the length (in bytes) of a DNS header.
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//
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// A header is comprised of 6 uint16s and no padding.
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headerLen = 6 * uint16Len
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)
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type nestedError struct {
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// s is the current level's error message.
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s string
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// err is the nested error.
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err error
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}
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// nestedError implements error.Error.
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func (e *nestedError) Error() string {
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return e.s + ": " + e.err.Error()
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}
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// Header is a representation of a DNS message header.
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type Header struct {
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ID uint16
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Response bool
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OpCode OpCode
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Authoritative bool
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Truncated bool
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RecursionDesired bool
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RecursionAvailable bool
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RCode RCode
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}
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func (m *Header) pack() (id uint16, bits uint16) {
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id = m.ID
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bits = uint16(m.OpCode)<<11 | uint16(m.RCode)
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if m.RecursionAvailable {
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bits |= headerBitRA
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}
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if m.RecursionDesired {
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bits |= headerBitRD
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}
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if m.Truncated {
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bits |= headerBitTC
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}
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if m.Authoritative {
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bits |= headerBitAA
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}
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if m.Response {
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bits |= headerBitQR
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}
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return
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}
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// Message is a representation of a DNS message.
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type Message struct {
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Header
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Questions []Question
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Answers []Resource
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Authorities []Resource
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Additionals []Resource
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}
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type section uint8
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const (
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sectionNotStarted section = iota
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sectionHeader
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sectionQuestions
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sectionAnswers
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sectionAuthorities
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sectionAdditionals
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sectionDone
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headerBitQR = 1 << 15 // query/response (response=1)
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headerBitAA = 1 << 10 // authoritative
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headerBitTC = 1 << 9 // truncated
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headerBitRD = 1 << 8 // recursion desired
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headerBitRA = 1 << 7 // recursion available
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)
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var sectionNames = map[section]string{
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sectionHeader: "header",
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sectionQuestions: "Question",
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sectionAnswers: "Answer",
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sectionAuthorities: "Authority",
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sectionAdditionals: "Additional",
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}
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// header is the wire format for a DNS message header.
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type header struct {
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id uint16
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bits uint16
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questions uint16
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answers uint16
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authorities uint16
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additionals uint16
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}
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func (h *header) count(sec section) uint16 {
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switch sec {
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case sectionQuestions:
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return h.questions
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case sectionAnswers:
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return h.answers
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case sectionAuthorities:
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return h.authorities
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case sectionAdditionals:
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return h.additionals
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}
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return 0
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}
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// pack appends the wire format of the header to msg.
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func (h *header) pack(msg []byte) []byte {
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msg = packUint16(msg, h.id)
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msg = packUint16(msg, h.bits)
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msg = packUint16(msg, h.questions)
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msg = packUint16(msg, h.answers)
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msg = packUint16(msg, h.authorities)
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return packUint16(msg, h.additionals)
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}
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func (h *header) unpack(msg []byte, off int) (int, error) {
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newOff := off
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var err error
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if h.id, newOff, err = unpackUint16(msg, newOff); err != nil {
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return off, &nestedError{"id", err}
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}
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if h.bits, newOff, err = unpackUint16(msg, newOff); err != nil {
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return off, &nestedError{"bits", err}
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}
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if h.questions, newOff, err = unpackUint16(msg, newOff); err != nil {
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return off, &nestedError{"questions", err}
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}
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if h.answers, newOff, err = unpackUint16(msg, newOff); err != nil {
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return off, &nestedError{"answers", err}
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}
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if h.authorities, newOff, err = unpackUint16(msg, newOff); err != nil {
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return off, &nestedError{"authorities", err}
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}
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if h.additionals, newOff, err = unpackUint16(msg, newOff); err != nil {
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return off, &nestedError{"additionals", err}
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}
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return newOff, nil
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}
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func (h *header) header() Header {
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return Header{
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ID: h.id,
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Response: (h.bits & headerBitQR) != 0,
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OpCode: OpCode(h.bits>>11) & 0xF,
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Authoritative: (h.bits & headerBitAA) != 0,
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Truncated: (h.bits & headerBitTC) != 0,
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RecursionDesired: (h.bits & headerBitRD) != 0,
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RecursionAvailable: (h.bits & headerBitRA) != 0,
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RCode: RCode(h.bits & 0xF),
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}
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}
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// A Resource is a DNS resource record.
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type Resource struct {
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Header ResourceHeader
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Body ResourceBody
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}
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// A ResourceBody is a DNS resource record minus the header.
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type ResourceBody interface {
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// pack packs a Resource except for its header.
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pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error)
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// realType returns the actual type of the Resource. This is used to
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// fill in the header Type field.
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realType() Type
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}
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// pack appends the wire format of the Resource to msg.
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func (r *Resource) pack(msg []byte, compression map[string]int, compressionOff int) ([]byte, error) {
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if r.Body == nil {
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return msg, errNilResouceBody
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}
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oldMsg := msg
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r.Header.Type = r.Body.realType()
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msg, length, err := r.Header.pack(msg, compression, compressionOff)
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if err != nil {
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return msg, &nestedError{"ResourceHeader", err}
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}
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preLen := len(msg)
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msg, err = r.Body.pack(msg, compression, compressionOff)
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if err != nil {
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return msg, &nestedError{"content", err}
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}
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if err := r.Header.fixLen(msg, length, preLen); err != nil {
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return oldMsg, err
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}
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return msg, nil
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}
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// A Parser allows incrementally parsing a DNS message.
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//
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// When parsing is started, the Header is parsed. Next, each Question can be
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// either parsed or skipped. Alternatively, all Questions can be skipped at
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// once. When all Questions have been parsed, attempting to parse Questions
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// will return (nil, nil) and attempting to skip Questions will return
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// (true, nil). After all Questions have been either parsed or skipped, all
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// Answers, Authorities and Additionals can be either parsed or skipped in the
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// same way, and each type of Resource must be fully parsed or skipped before
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// proceeding to the next type of Resource.
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//
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// Note that there is no requirement to fully skip or parse the message.
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type Parser struct {
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msg []byte
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header header
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section section
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off int
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index int
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resHeaderValid bool
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resHeader ResourceHeader
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}
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// Start parses the header and enables the parsing of Questions.
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func (p *Parser) Start(msg []byte) (Header, error) {
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if p.msg != nil {
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*p = Parser{}
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}
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p.msg = msg
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var err error
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if p.off, err = p.header.unpack(msg, 0); err != nil {
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return Header{}, &nestedError{"unpacking header", err}
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}
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p.section = sectionQuestions
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return p.header.header(), nil
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}
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func (p *Parser) checkAdvance(sec section) error {
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if p.section < sec {
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return ErrNotStarted
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}
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if p.section > sec {
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return ErrSectionDone
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}
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p.resHeaderValid = false
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if p.index == int(p.header.count(sec)) {
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p.index = 0
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p.section++
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return ErrSectionDone
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}
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return nil
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}
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func (p *Parser) resource(sec section) (Resource, error) {
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var r Resource
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var err error
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r.Header, err = p.resourceHeader(sec)
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if err != nil {
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return r, err
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}
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p.resHeaderValid = false
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r.Body, p.off, err = unpackResourceBody(p.msg, p.off, r.Header)
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if err != nil {
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return Resource{}, &nestedError{"unpacking " + sectionNames[sec], err}
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}
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p.index++
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return r, nil
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}
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func (p *Parser) resourceHeader(sec section) (ResourceHeader, error) {
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if p.resHeaderValid {
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return p.resHeader, nil
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}
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if err := p.checkAdvance(sec); err != nil {
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return ResourceHeader{}, err
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}
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var hdr ResourceHeader
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off, err := hdr.unpack(p.msg, p.off)
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if err != nil {
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return ResourceHeader{}, err
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}
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p.resHeaderValid = true
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p.resHeader = hdr
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p.off = off
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return hdr, nil
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}
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func (p *Parser) skipResource(sec section) error {
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if p.resHeaderValid {
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newOff := p.off + int(p.resHeader.Length)
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if newOff > len(p.msg) {
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return errResourceLen
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}
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p.off = newOff
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p.resHeaderValid = false
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p.index++
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return nil
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}
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if err := p.checkAdvance(sec); err != nil {
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return err
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}
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var err error
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p.off, err = skipResource(p.msg, p.off)
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if err != nil {
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return &nestedError{"skipping: " + sectionNames[sec], err}
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}
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p.index++
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return nil
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}
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// Question parses a single Question.
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func (p *Parser) Question() (Question, error) {
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if err := p.checkAdvance(sectionQuestions); err != nil {
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return Question{}, err
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}
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var name Name
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off, err := name.unpack(p.msg, p.off)
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if err != nil {
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return Question{}, &nestedError{"unpacking Question.Name", err}
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}
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typ, off, err := unpackType(p.msg, off)
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if err != nil {
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return Question{}, &nestedError{"unpacking Question.Type", err}
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}
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class, off, err := unpackClass(p.msg, off)
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if err != nil {
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return Question{}, &nestedError{"unpacking Question.Class", err}
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}
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p.off = off
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p.index++
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return Question{name, typ, class}, nil
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}
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// AllQuestions parses all Questions.
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func (p *Parser) AllQuestions() ([]Question, error) {
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// Multiple questions are valid according to the spec,
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// but servers don't actually support them. There will
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// be at most one question here.
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//
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// Do not pre-allocate based on info in p.header, since
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// the data is untrusted.
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qs := []Question{}
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for {
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q, err := p.Question()
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if err == ErrSectionDone {
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return qs, nil
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}
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if err != nil {
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return nil, err
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}
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qs = append(qs, q)
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}
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}
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// SkipQuestion skips a single Question.
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func (p *Parser) SkipQuestion() error {
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if err := p.checkAdvance(sectionQuestions); err != nil {
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return err
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}
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off, err := skipName(p.msg, p.off)
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if err != nil {
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return &nestedError{"skipping Question Name", err}
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}
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if off, err = skipType(p.msg, off); err != nil {
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return &nestedError{"skipping Question Type", err}
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}
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if off, err = skipClass(p.msg, off); err != nil {
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return &nestedError{"skipping Question Class", err}
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}
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p.off = off
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p.index++
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return nil
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}
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// SkipAllQuestions skips all Questions.
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func (p *Parser) SkipAllQuestions() error {
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for {
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if err := p.SkipQuestion(); err == ErrSectionDone {
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return nil
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} else if err != nil {
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return err
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}
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}
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}
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// AnswerHeader parses a single Answer ResourceHeader.
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func (p *Parser) AnswerHeader() (ResourceHeader, error) {
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return p.resourceHeader(sectionAnswers)
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}
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// Answer parses a single Answer Resource.
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func (p *Parser) Answer() (Resource, error) {
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return p.resource(sectionAnswers)
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}
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// AllAnswers parses all Answer Resources.
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func (p *Parser) AllAnswers() ([]Resource, error) {
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// The most common query is for A/AAAA, which usually returns
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// a handful of IPs.
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//
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// Pre-allocate up to a certain limit, since p.header is
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// untrusted data.
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n := int(p.header.answers)
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if n > 20 {
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n = 20
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}
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as := make([]Resource, 0, n)
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for {
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a, err := p.Answer()
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if err == ErrSectionDone {
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return as, nil
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}
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if err != nil {
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return nil, err
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}
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as = append(as, a)
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}
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}
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// SkipAnswer skips a single Answer Resource.
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func (p *Parser) SkipAnswer() error {
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return p.skipResource(sectionAnswers)
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}
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// SkipAllAnswers skips all Answer Resources.
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func (p *Parser) SkipAllAnswers() error {
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for {
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if err := p.SkipAnswer(); err == ErrSectionDone {
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return nil
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} else if err != nil {
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return err
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}
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}
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}
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// AuthorityHeader parses a single Authority ResourceHeader.
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func (p *Parser) AuthorityHeader() (ResourceHeader, error) {
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return p.resourceHeader(sectionAuthorities)
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}
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// Authority parses a single Authority Resource.
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func (p *Parser) Authority() (Resource, error) {
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return p.resource(sectionAuthorities)
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}
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// AllAuthorities parses all Authority Resources.
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func (p *Parser) AllAuthorities() ([]Resource, error) {
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// Authorities contains SOA in case of NXDOMAIN and friends,
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// otherwise it is empty.
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//
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|
// 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
|
|
}
|
|
|
|
// 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
|
|
}
|
|
|
|
// 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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, length, 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
|
|
}
|
|
|
|
// pack appends the wire format of the ResourceHeader to oldMsg.
|
|
//
|
|
// The bytes where length was packed are returned as a slice so they can be
|
|
// updated after the rest of the Resource has been packed.
|
|
func (h *ResourceHeader) pack(oldMsg []byte, compression map[string]int, compressionOff int) (msg []byte, length []byte, err error) {
|
|
msg = oldMsg
|
|
if msg, err = h.Name.pack(msg, compression, compressionOff); err != nil {
|
|
return oldMsg, nil, &nestedError{"Name", err}
|
|
}
|
|
msg = packType(msg, h.Type)
|
|
msg = packClass(msg, h.Class)
|
|
msg = packUint32(msg, h.TTL)
|
|
lenBegin := len(msg)
|
|
msg = packUint16(msg, h.Length)
|
|
return msg, msg[lenBegin : lenBegin+uint16Len], 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
|
|
}
|
|
|
|
func (h *ResourceHeader) fixLen(msg []byte, length []byte, 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(length[:0], uint16(conLen))
|
|
h.Length = uint16(conLen)
|
|
|
|
return nil
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
func (n Name) String() string {
|
|
return string(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
|
|
}
|
|
|
|
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"
|
|
}
|
|
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)
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
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)
|
|
}
|
|
|
|
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)
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
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
|
|
}
|
|
|
|
// 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
|
|
}
|