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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 net
import (
"bytes"
"fmt"
"os"
"rand"
)
// DNSError represents a DNS lookup error.
type DNSError struct {
Error string // description of the error
Name string // name looked for
Server string // server used
IsTimeout bool
}
func (e *DNSError) String() string {
if e == nil {
return "<nil>"
}
s := "lookup " + e.Name
if e.Server != "" {
s += " on " + e.Server
}
s += ": " + e.Error
return s
}
func (e *DNSError) Timeout() bool { return e.IsTimeout }
func (e *DNSError) Temporary() bool { return e.IsTimeout }
const noSuchHost = "no such host"
// reverseaddr returns the in-addr.arpa. or ip6.arpa. hostname of the IP
// address addr suitable for rDNS (PTR) record lookup or an error if it fails
// to parse the IP address.
func reverseaddr(addr string) (arpa string, err os.Error) {
ip := ParseIP(addr)
if ip == nil {
return "", &DNSError{Error: "unrecognized address", Name: addr}
}
if ip.To4() != nil {
return fmt.Sprintf("%d.%d.%d.%d.in-addr.arpa.", ip[15], ip[14], ip[13], ip[12]), nil
}
// Must be IPv6
var buf bytes.Buffer
// Add it, in reverse, to the buffer
for i := len(ip) - 1; i >= 0; i-- {
s := fmt.Sprintf("%02x", ip[i])
buf.WriteByte(s[1])
buf.WriteByte('.')
buf.WriteByte(s[0])
buf.WriteByte('.')
}
// Append "ip6.arpa." and return (buf already has the final .)
return buf.String() + "ip6.arpa.", nil
}
// Find answer for name in dns message.
// On return, if err == nil, addrs != nil.
func answer(name, server string, dns *dnsMsg, qtype uint16) (cname string, addrs []dnsRR, err os.Error) {
addrs = make([]dnsRR, 0, len(dns.answer))
if dns.rcode == dnsRcodeNameError && dns.recursion_available {
return "", nil, &DNSError{Error: noSuchHost, Name: name}
}
if dns.rcode != dnsRcodeSuccess {
// None of the error codes make sense
// for the query we sent. If we didn't get
// a name error and we didn't get success,
// the server is behaving incorrectly.
return "", nil, &DNSError{Error: "server misbehaving", Name: name, Server: server}
}
// Look for the name.
// Presotto says it's okay to assume that servers listed in
// /etc/resolv.conf are recursive resolvers.
// We asked for recursion, so it should have included
// all the answers we need in this one packet.
Cname:
for cnameloop := 0; cnameloop < 10; cnameloop++ {
addrs = addrs[0:0]
for _, rr := range dns.answer {
if _, justHeader := rr.(*dnsRR_Header); justHeader {
// Corrupt record: we only have a
// header. That header might say it's
// of type qtype, but we don't
// actually have it. Skip.
continue
}
h := rr.Header()
if h.Class == dnsClassINET && h.Name == name {
switch h.Rrtype {
case qtype:
addrs = append(addrs, rr)
case dnsTypeCNAME:
// redirect to cname
name = rr.(*dnsRR_CNAME).Cname
continue Cname
}
}
}
if len(addrs) == 0 {
return "", nil, &DNSError{Error: noSuchHost, Name: name, Server: server}
}
return name, addrs, nil
}
return "", nil, &DNSError{Error: "too many redirects", Name: name, Server: server}
}
func isDomainName(s string) bool {
// See RFC 1035, RFC 3696.
if len(s) == 0 {
return false
}
if len(s) > 255 {
return false
}
if s[len(s)-1] != '.' { // simplify checking loop: make name end in dot
s += "."
}
last := byte('.')
ok := false // ok once we've seen a letter
partlen := 0
for i := 0; i < len(s); i++ {
c := s[i]
switch {
default:
return false
case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_':
ok = true
partlen++
case '0' <= c && c <= '9':
// fine
partlen++
case c == '-':
// byte before dash cannot be dot
if last == '.' {
return false
}
partlen++
case c == '.':
// byte before dot cannot be dot, dash
if last == '.' || last == '-' {
return false
}
if partlen > 63 || partlen == 0 {
return false
}
partlen = 0
}
last = c
}
return ok
}
// An SRV represents a single DNS SRV record.
type SRV struct {
Target string
Port uint16
Priority uint16
Weight uint16
}
// byPriorityWeight sorts SRV records by ascending priority and weight.
type byPriorityWeight []*SRV
func (s byPriorityWeight) Len() int { return len(s) }
func (s byPriorityWeight) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s byPriorityWeight) Less(i, j int) bool {
return s[i].Priority < s[j].Priority ||
(s[i].Priority == s[j].Priority && s[i].Weight < s[j].Weight)
}
// shuffleSRVByWeight shuffles SRV records by weight using the algorithm
// described in RFC 2782.
func shuffleSRVByWeight(addrs []*SRV) {
sum := 0
for _, addr := range addrs {
sum += int(addr.Weight)
}
for sum > 0 && len(addrs) > 1 {
s := 0
n := rand.Intn(sum + 1)
for i := range addrs {
s += int(addrs[i].Weight)
if s >= n {
if i > 0 {
t := addrs[i]
copy(addrs[1:i+1], addrs[0:i])
addrs[0] = t
}
break
}
}
sum -= int(addrs[0].Weight)
addrs = addrs[1:]
}
}
// An MX represents a single DNS MX record.
type MX struct {
Host string
Pref uint16
}
// byPref implements sort.Interface to sort MX records by preference
type byPref []*MX
func (s byPref) Len() int { return len(s) }
func (s byPref) Less(i, j int) bool { return s[i].Pref < s[j].Pref }
func (s byPref) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
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