138 lines
4.1 KiB
Go
138 lines
4.1 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package net
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import "time"
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// protocols contains minimal mappings between internet protocol
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// names and numbers for platforms that don't have a complete list of
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// protocol numbers.
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//
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// See http://www.iana.org/assignments/protocol-numbers
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var protocols = map[string]int{
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"icmp": 1, "ICMP": 1,
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"igmp": 2, "IGMP": 2,
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"tcp": 6, "TCP": 6,
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"udp": 17, "UDP": 17,
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"ipv6-icmp": 58, "IPV6-ICMP": 58, "IPv6-ICMP": 58,
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}
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// LookupHost looks up the given host using the local resolver.
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// It returns an array of that host's addresses.
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func LookupHost(host string) (addrs []string, err error) {
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return lookupHost(host)
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}
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// LookupIP looks up host using the local resolver.
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// It returns an array of that host's IPv4 and IPv6 addresses.
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func LookupIP(host string) (addrs []IP, err error) {
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return lookupIPMerge(host)
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}
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var lookupGroup singleflight
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// lookupIPMerge wraps lookupIP, but makes sure that for any given
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// host, only one lookup is in-flight at a time. The returned memory
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// is always owned by the caller.
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func lookupIPMerge(host string) (addrs []IP, err error) {
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addrsi, err, shared := lookupGroup.Do(host, func() (interface{}, error) {
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return lookupIP(host)
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})
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if err != nil {
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return nil, err
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}
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addrs = addrsi.([]IP)
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if shared {
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clone := make([]IP, len(addrs))
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copy(clone, addrs)
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addrs = clone
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}
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return addrs, nil
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}
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func lookupIPDeadline(host string, deadline time.Time) (addrs []IP, err error) {
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if deadline.IsZero() {
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return lookupIPMerge(host)
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}
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// TODO(bradfitz): consider pushing the deadline down into the
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// name resolution functions. But that involves fixing it for
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// the native Go resolver, cgo, Windows, etc.
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//
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// In the meantime, just use a goroutine. Most users affected
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// by http://golang.org/issue/2631 are due to TCP connections
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// to unresponsive hosts, not DNS.
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timeout := deadline.Sub(time.Now())
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if timeout <= 0 {
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err = errTimeout
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return
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}
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t := time.NewTimer(timeout)
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defer t.Stop()
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type res struct {
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addrs []IP
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err error
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}
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resc := make(chan res, 1)
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go func() {
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a, err := lookupIPMerge(host)
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resc <- res{a, err}
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}()
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select {
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case <-t.C:
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err = errTimeout
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case r := <-resc:
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addrs, err = r.addrs, r.err
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}
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return
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}
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// LookupPort looks up the port for the given network and service.
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func LookupPort(network, service string) (port int, err error) {
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return lookupPort(network, service)
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}
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// LookupCNAME returns the canonical DNS host for the given name.
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// Callers that do not care about the canonical name can call
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// LookupHost or LookupIP directly; both take care of resolving
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// the canonical name as part of the lookup.
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func LookupCNAME(name string) (cname string, err error) {
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return lookupCNAME(name)
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}
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// LookupSRV tries to resolve an SRV query of the given service,
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// protocol, and domain name. The proto is "tcp" or "udp".
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// The returned records are sorted by priority and randomized
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// by weight within a priority.
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//
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// LookupSRV constructs the DNS name to look up following RFC 2782.
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// That is, it looks up _service._proto.name. To accommodate services
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// publishing SRV records under non-standard names, if both service
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// and proto are empty strings, LookupSRV looks up name directly.
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func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
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return lookupSRV(service, proto, name)
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}
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// LookupMX returns the DNS MX records for the given domain name sorted by preference.
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func LookupMX(name string) (mx []*MX, err error) {
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return lookupMX(name)
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}
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// LookupNS returns the DNS NS records for the given domain name.
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func LookupNS(name string) (ns []*NS, err error) {
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return lookupNS(name)
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}
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// LookupTXT returns the DNS TXT records for the given domain name.
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func LookupTXT(name string) (txt []string, err error) {
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return lookupTXT(name)
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}
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// LookupAddr performs a reverse lookup for the given address, returning a list
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// of names mapping to that address.
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func LookupAddr(addr string) (name []string, err error) {
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return lookupAddr(addr)
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}
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