Preview: dnsclient.go
Size: 5.65 KB
/proc/thread-self/root/opt/golang/1.22.0/src/net/dnsclient.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.
package net
import (
"internal/bytealg"
"internal/itoa"
"sort"
_ "unsafe" // for go:linkname
"golang.org/x/net/dns/dnsmessage"
)
// provided by runtime
//go:linkname runtime_rand runtime.rand
func runtime_rand() uint64
func randInt() int {
return int(uint(runtime_rand()) >> 1) // clear sign bit
}
func randIntn(n int) int {
return randInt() % n
}
// 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 error) {
ip := ParseIP(addr)
if ip == nil {
return "", &DNSError{Err: "unrecognized address", Name: addr}
}
if ip.To4() != nil {
return itoa.Uitoa(uint(ip[15])) + "." + itoa.Uitoa(uint(ip[14])) + "." + itoa.Uitoa(uint(ip[13])) + "." + itoa.Uitoa(uint(ip[12])) + ".in-addr.arpa.", nil
}
// Must be IPv6
buf := make([]byte, 0, len(ip)*4+len("ip6.arpa."))
// Add it, in reverse, to the buffer
for i := len(ip) - 1; i >= 0; i-- {
v := ip[i]
buf = append(buf, hexDigit[v&0xF],
'.',
hexDigit[v>>4],
'.')
}
// Append "ip6.arpa." and return (buf already has the final .)
buf = append(buf, "ip6.arpa."...)
return string(buf), nil
}
func equalASCIIName(x, y dnsmessage.Name) bool {
if x.Length != y.Length {
return false
}
for i := 0; i < int(x.Length); i++ {
a := x.Data[i]
b := y.Data[i]
if 'A' <= a && a <= 'Z' {
a += 0x20
}
if 'A' <= b && b <= 'Z' {
b += 0x20
}
if a != b {
return false
}
}
return true
}
// isDomainName checks if a string is a presentation-format domain name
// (currently restricted to hostname-compatible "preferred name" LDH labels and
// SRV-like "underscore labels"; see golang.org/issue/12421).
func isDomainName(s string) bool {
// The root domain name is valid. See golang.org/issue/45715.
if s == "." {
return true
}
// See RFC 1035, RFC 3696.
// Presentation format has dots before every label except the first, and the
// terminal empty label is optional here because we assume fully-qualified
// (absolute) input. We must therefore reserve space for the first and last
// labels' length octets in wire format, where they are necessary and the
// maximum total length is 255.
// So our _effective_ maximum is 253, but 254 is not rejected if the last
// character is a dot.
l := len(s)
if l == 0 || l > 254 || l == 254 && s[l-1] != '.' {
return false
}
last := byte('.')
nonNumeric := false // true once we've seen a letter or hyphen
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 == '_':
nonNumeric = true
partlen++
case '0' <= c && c <= '9':
// fine
partlen++
case c == '-':
// Byte before dash cannot be dot.
if last == '.' {
return false
}
partlen++
nonNumeric = true
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
}
if last == '-' || partlen > 63 {
return false
}
return nonNumeric
}
// absDomainName returns an absolute domain name which ends with a
// trailing dot to match pure Go reverse resolver and all other lookup
// routines.
// See golang.org/issue/12189.
// But we don't want to add dots for local names from /etc/hosts.
// It's hard to tell so we settle on the heuristic that names without dots
// (like "localhost" or "myhost") do not get trailing dots, but any other
// names do.
func absDomainName(s string) string {
if bytealg.IndexByteString(s, '.') != -1 && s[len(s)-1] != '.' {
s += "."
}
return s
}
// 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) Less(i, j int) bool {
return s[i].Priority < s[j].Priority || (s[i].Priority == s[j].Priority && s[i].Weight < s[j].Weight)
}
func (s byPriorityWeight) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
// shuffleByWeight shuffles SRV records by weight using the algorithm
// described in RFC 2782.
func (addrs byPriorityWeight) shuffleByWeight() {
sum := 0
for _, addr := range addrs {
sum += int(addr.Weight)
}
for sum > 0 && len(addrs) > 1 {
s := 0
n := randIntn(sum)
for i := range addrs {
s += int(addrs[i].Weight)
if s > n {
if i > 0 {
addrs[0], addrs[i] = addrs[i], addrs[0]
}
break
}
}
sum -= int(addrs[0].Weight)
addrs = addrs[1:]
}
}
// sort reorders SRV records as specified in RFC 2782.
func (addrs byPriorityWeight) sort() {
sort.Sort(addrs)
i := 0
for j := 1; j < len(addrs); j++ {
if addrs[i].Priority != addrs[j].Priority {
addrs[i:j].shuffleByWeight()
i = j
}
}
addrs[i:].shuffleByWeight()
}
// 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] }
// sort reorders MX records as specified in RFC 5321.
func (s byPref) sort() {
for i := range s {
j := randIntn(i + 1)
s[i], s[j] = s[j], s[i]
}
sort.Sort(s)
}
// An NS represents a single DNS NS record.
type NS struct {
Host string
}
Directory Contents
Dirs: 9 × Files: 214