libgo/go/net/lookup.go

   1 // Copyright 2012 The Go Authors.  All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package net
   6
   7 import (
   8         "time"
   9 )
  10
  11 // LookupHost looks up the given host using the local resolver.
  12 // It returns an array of that host's addresses.
  13 func LookupHost(host string) (addrs []string, err error) {
  14         return lookupHost(host)
  15 }
  16
  17 func lookupHostDeadline(host string, deadline time.Time) (addrs []string, err error) {
  18         if deadline.IsZero() {
  19                 return lookupHost(host)
  20         }
  21
  22         // TODO(bradfitz): consider pushing the deadline down into the
  23         // name resolution functions. But that involves fixing it for
  24         // the native Go resolver, cgo, Windows, etc.
  25         //
  26         // In the meantime, just use a goroutine. Most users affected
  27         // by http://golang.org/issue/2631 are due to TCP connections
  28         // to unresponsive hosts, not DNS.
  29         timeout := deadline.Sub(time.Now())
  30         if timeout <= 0 {
  31                 err = errTimeout
  32                 return
  33         }
  34         t := time.NewTimer(timeout)
  35         defer t.Stop()
  36         type res struct {
  37                 addrs []string
  38                 err   error
  39         }
  40         resc := make(chan res, 1)
  41         go func() {
  42                 a, err := lookupHost(host)
  43                 resc <- res{a, err}
  44         }()
  45         select {
  46         case <-t.C:
  47                 err = errTimeout
  48         case r := <-resc:
  49                 addrs, err = r.addrs, r.err
  50         }
  51         return
  52 }
  53
  54 // LookupIP looks up host using the local resolver.
  55 // It returns an array of that host's IPv4 and IPv6 addresses.
  56 func LookupIP(host string) (addrs []IP, err error) {
  57         return lookupIP(host)
  58 }
  59
  60 // LookupPort looks up the port for the given network and service.
  61 func LookupPort(network, service string) (port int, err error) {
  62         return lookupPort(network, service)
  63 }
  64
  65 // LookupCNAME returns the canonical DNS host for the given name.
  66 // Callers that do not care about the canonical name can call
  67 // LookupHost or LookupIP directly; both take care of resolving
  68 // the canonical name as part of the lookup.
  69 func LookupCNAME(name string) (cname string, err error) {
  70         return lookupCNAME(name)
  71 }
  72
  73 // LookupSRV tries to resolve an SRV query of the given service,
  74 // protocol, and domain name.  The proto is "tcp" or "udp".
  75 // The returned records are sorted by priority and randomized
  76 // by weight within a priority.
  77 //
  78 // LookupSRV constructs the DNS name to look up following RFC 2782.
  79 // That is, it looks up _service._proto.name.  To accommodate services
  80 // publishing SRV records under non-standard names, if both service
  81 // and proto are empty strings, LookupSRV looks up name directly.
  82 func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
  83         return lookupSRV(service, proto, name)
  84 }
  85
  86 // LookupMX returns the DNS MX records for the given domain name sorted by preference.
  87 func LookupMX(name string) (mx []*MX, err error) {
  88         return lookupMX(name)
  89 }
  90
  91 // LookupNS returns the DNS NS records for the given domain name.
  92 func LookupNS(name string) (ns []*NS, err error) {
  93         return lookupNS(name)
  94 }
  95
  96 // LookupTXT returns the DNS TXT records for the given domain name.
  97 func LookupTXT(name string) (txt []string, err error) {
  98         return lookupTXT(name)
  99 }
 100
 101 // LookupAddr performs a reverse lookup for the given address, returning a list
 102 // of names mapping to that address.
 103 func LookupAddr(addr string) (name []string, err error) {
 104         return lookupAddr(addr)
 105 }