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// Copyright 2011 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.
// +build darwin freebsd linux netbsd openbsd
package net
import (
"errors"
"sync"
)
var (
protocols map[string]int
onceReadProtocols sync.Once
)
// readProtocols loads contents of /etc/protocols into protocols map
// for quick access.
func readProtocols() {
protocols = make(map[string]int)
if file, err := open("/etc/protocols"); err == nil {
for line, ok := file.readLine(); ok; line, ok = file.readLine() {
// tcp 6 TCP # transmission control protocol
if i := byteIndex(line, '#'); i >= 0 {
line = line[0:i]
}
f := getFields(line)
if len(f) < 2 {
continue
}
if proto, _, ok := dtoi(f[1], 0); ok {
protocols[f[0]] = proto
for _, alias := range f[2:] {
protocols[alias] = proto
}
}
}
file.close()
}
}
// lookupProtocol looks up IP protocol name in /etc/protocols and
// returns correspondent protocol number.
func lookupProtocol(name string) (proto int, err error) {
onceReadProtocols.Do(readProtocols)
proto, found := protocols[name]
if !found {
return 0, errors.New("unknown IP protocol specified: " + name)
}
return
}
// LookupHost looks up the given host using the local resolver.
// It returns an array of that host's addresses.
func LookupHost(host string) (addrs []string, err error) {
addrs, err, ok := cgoLookupHost(host)
if !ok {
addrs, err = goLookupHost(host)
}
return
}
// LookupIP looks up host using the local resolver.
// It returns an array of that host's IPv4 and IPv6 addresses.
func LookupIP(host string) (addrs []IP, err error) {
addrs, err, ok := cgoLookupIP(host)
if !ok {
addrs, err = goLookupIP(host)
}
return
}
// LookupPort looks up the port for the given network and service.
func LookupPort(network, service string) (port int, err error) {
port, err, ok := cgoLookupPort(network, service)
if !ok {
port, err = goLookupPort(network, service)
}
return
}
// LookupCNAME returns the canonical DNS host for the given name.
// Callers that do not care about the canonical name can call
// LookupHost or LookupIP directly; both take care of resolving
// the canonical name as part of the lookup.
func LookupCNAME(name string) (cname string, err error) {
cname, err, ok := cgoLookupCNAME(name)
if !ok {
cname, err = goLookupCNAME(name)
}
return
}
// LookupSRV tries to resolve an SRV query of the given service,
// protocol, and domain name. The proto is "tcp" or "udp".
// The returned records are sorted by priority and randomized
// by weight within a priority.
//
// LookupSRV constructs the DNS name to look up following RFC 2782.
// That is, it looks up _service._proto.name. To accommodate services
// publishing SRV records under non-standard names, if both service
// and proto are empty strings, LookupSRV looks up name directly.
func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
var target string
if service == "" && proto == "" {
target = name
} else {
target = "_" + service + "._" + proto + "." + name
}
var records []dnsRR
cname, records, err = lookup(target, dnsTypeSRV)
if err != nil {
return
}
addrs = make([]*SRV, len(records))
for i, rr := range records {
r := rr.(*dnsRR_SRV)
addrs[i] = &SRV{r.Target, r.Port, r.Priority, r.Weight}
}
byPriorityWeight(addrs).sort()
return
}
// LookupMX returns the DNS MX records for the given domain name sorted by preference.
func LookupMX(name string) (mx []*MX, err error) {
_, records, err := lookup(name, dnsTypeMX)
if err != nil {
return
}
mx = make([]*MX, len(records))
for i, rr := range records {
r := rr.(*dnsRR_MX)
mx[i] = &MX{r.Mx, r.Pref}
}
byPref(mx).sort()
return
}
// LookupTXT returns the DNS TXT records for the given domain name.
func LookupTXT(name string) (txt []string, err error) {
_, records, err := lookup(name, dnsTypeTXT)
if err != nil {
return
}
txt = make([]string, len(records))
for i, r := range records {
txt[i] = r.(*dnsRR_TXT).Txt
}
return
}
// LookupAddr performs a reverse lookup for the given address, returning a list
// of names mapping to that address.
func LookupAddr(addr string) (name []string, err error) {
name = lookupStaticAddr(addr)
if len(name) > 0 {
return
}
var arpa string
arpa, err = reverseaddr(addr)
if err != nil {
return
}
var records []dnsRR
_, records, err = lookup(arpa, dnsTypePTR)
if err != nil {
return
}
name = make([]string, len(records))
for i := range records {
r := records[i].(*dnsRR_PTR)
name[i] = r.Ptr
}
return
}
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