dns/dns.go

// 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.
// Extended and bugfixes by Miek Gieben

// Package dns implements a full featured interface to the DNS.
// The package allows full control over what is send out to the DNS. 
//
// Resource Records are native types. They are not stored in wire format.
// Basic usage pattern for creating new Resource Record:
//
//         r := new(RR_TXT)
//         r.Hdr = RR_Header{Name: "a.miek.nl", Rrtype: TypeTXT, Class: ClassINET, Ttl: 3600}
//         r.TXT = "This is the content of the TXT record"
// 
package dns

import (
	"strconv"
)

// For RFC1982 (Serial Arithmetic) calculations in 32 bits.
const Year68 = 2 << (32 - 1)

// Error represents a DNS error
type Error struct {
	Error   string
	Name    string
	Server  string
	Timeout bool
}

func (e *Error) String() string {
	if e == nil {
		return "<nil>"
	}
	return e.Error
}


type RR interface {
	Header() *RR_Header
	String() string
}

// An RRset is a slice of RRs.
type RRset []RR

func (r RRset) Len() int           { return len(r) }
func (r RRset) Less(i, j int) bool { return r[i].Header().Name < r[j].Header().Name }
func (r RRset) Swap(i, j int)      { r[i], r[j] = r[j], r[i] }

// Check if the RRset is RFC 2181 compliant
func (r RRset) Ok() bool {
	ttl := r[0].Header().Ttl
	name := r[0].Header().Name
	class := r[0].Header().Class
	for _, rr := range r[1:] {
		if rr.Header().Ttl != ttl {
			return false
		}
		if rr.Header().Name != name {
			return false
		}
		if rr.Header().Class != class {
			return false
		}
	}
	return true
}

// DNS resource records.
// There are many types of messages,
// but they all share the same header.
type RR_Header struct {
	Name     string "domain-name"
	Rrtype   uint16
	Class    uint16
	Ttl      uint32
	Rdlength uint16 // length of data after header
}

func (h *RR_Header) Header() *RR_Header {
	return h
}

func (h *RR_Header) String() string {
	var s string

	if h.Rrtype == TypeOPT {
		s = ";"
		// and maybe other things
	}

	if len(h.Name) == 0 {
		s += ".\t"
	} else {
		s += h.Name + "\t"
	}
	s = s + strconv.Itoa(int(h.Ttl)) + "\t"

	if _, ok := Class_str[h.Class]; ok {
		s += Class_str[h.Class] + "\t"
	} else {
		s += "CLASS" + strconv.Itoa(int(h.Class)) + "\t"
	}

	if _, ok := Rr_str[h.Rrtype]; ok {
		s += Rr_str[h.Rrtype] + "\t"
	} else {
		s += "TYPE" + strconv.Itoa(int(h.Rrtype)) + "\t"
	}
	return s
}

// Return the number of labels in a domain name.
func LabelCount(a string) (c uint8) {
	// walk the string and count the dots
	// except when it is escaped
	esc := false
	for _, v := range a {
		switch v {
		case '.':
			if esc {
				esc = !esc
				continue
			}
			c++
		case '\\':
			esc = true
		}
	}
	return
}