// Copyright 2012 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 (
"context"
"internal/nettrace"
"internal/singleflight"
"sync"
)
// protocols contains minimal mappings between internet protocol
// names and numbers for platforms that don't have a complete list of
// protocol numbers.
//
// See https://www.iana.org/assignments/protocol-numbers
//
// On Unix, this map is augmented by readProtocols via lookupProtocol.
var protocols = map[string]int{
"icmp": 1,
"igmp": 2,
"tcp": 6,
"udp": 17,
"ipv6-icmp": 58,
}
// services contains minimal mappings between services names and port
// numbers for platforms that don't have a complete list of port numbers
// (some Solaris distros, nacl, etc).
//
// See https://www.iana.org/assignments/service-names-port-numbers
//
// On Unix, this map is augmented by readServices via goLookupPort.
var services = map[string]map[string]int{
"udp": {
"domain": 53,
},
"tcp": {
"ftp": 21,
"ftps": 990,
"gopher": 70, // ʕ◔ϖ◔ʔ
"http": 80,
"https": 443,
"imap2": 143,
"imap3": 220,
"imaps": 993,
"pop3": 110,
"pop3s": 995,
"smtp": 25,
"ssh": 22,
"telnet": 23,
},
}
// dnsWaitGroup can be used by tests to wait for all DNS goroutines to
// complete. This avoids races on the test hooks.
var dnsWaitGroup sync.WaitGroup
const maxProtoLength = len("RSVP-E2E-IGNORE") + 10 // with room to grow
func lookupProtocolMap(name string) (int, error) {
var lowerProtocol [maxProtoLength]byte
n := copy(lowerProtocol[:], name)
lowerASCIIBytes(lowerProtocol[:n])
proto, found := protocols[string(lowerProtocol[:n])]
if !found || n != len(name) {
return 0, &AddrError{Err: "unknown IP protocol specified", Addr: name}
}
return proto, nil
}
// maxPortBufSize is the longest reasonable name of a service
// (non-numeric port).
// Currently the longest known IANA-unregistered name is
// "mobility-header", so we use that length, plus some slop in case
// something longer is added in the future.
const maxPortBufSize = len("mobility-header") + 10
func lookupPortMap(network, service string) (port int, error error) {
switch network {
case "tcp4", "tcp6":
network = "tcp"
case "udp4", "udp6":
network = "udp"
}
if m, ok := services[network]; ok {
var lowerService [maxPortBufSize]byte
n := copy(lowerService[:], service)
lowerASCIIBytes(lowerService[:n])
if port, ok := m[string(lowerService[:n])]; ok && n == len(service) {
return port, nil
}
}
return 0, &AddrError{Err: "unknown port", Addr: network + "/" + service}
}
// ipVersion returns the provided network's IP version: '4', '6' or 0
// if network does not end in a '4' or '6' byte.
func ipVersion(network string) byte {
if network == "" {
return 0
}
n := network[len(network)-1]
if n != '4' && n != '6' {
n = 0
}
return n
}
// DefaultResolver is the resolver used by the package-level Lookup
// functions and by Dialers without a specified Resolver.
var DefaultResolver = &Resolver{}
// A Resolver looks up names and numbers.
//
// A nil *Resolver is equivalent to a zero Resolver.
type Resolver struct {
// PreferGo controls whether Go's built-in DNS resolver is preferred
// on platforms where it's available. It is equivalent to setting
// GODEBUG=netdns=go, but scoped to just this resolver.
PreferGo bool
// StrictErrors controls the behavior of temporary errors
// (including timeout, socket errors, and SERVFAIL) when using
// Go's built-in resolver. For a query composed of multiple
// sub-queries (such as an A+AAAA address lookup, or walking the
// DNS search list), this option causes such errors to abort the
// whole query instead of returning a partial result. This is
// not enabled by default because it may affect compatibility
// with resolvers that process AAAA queries incorrectly.
StrictErrors bool
// Dial optionally specifies an alternate dialer for use by
// Go's built-in DNS resolver to make TCP and UDP connections
// to DNS services. The host in the address parameter will
// always be a literal IP address and not a host name, and the
// port in the address parameter will be a literal port number
// and not a service name.
// If the Conn returned is also a PacketConn, sent and received DNS
// messages must adhere to RFC 1035 section 4.2.1, "UDP usage".
// Otherwise, DNS messages transmitted over Conn must adhere
// to RFC 7766 section 5, "Transport Protocol Selection".
// If nil, the default dialer is used.
Dial func(ctx context.Context, network, address string) (Conn, error)
// lookupGroup merges LookupIPAddr calls together for lookups for the same
// host. The lookupGroup key is the LookupIPAddr.host argument.
// The return values are ([]IPAddr, error).
lookupGroup singleflight.Group
// TODO(bradfitz): optional interface impl override hook
// TODO(bradfitz): Timeout time.Duration?
}
func (r *Resolver) preferGo() bool { return r != nil && r.PreferGo }
func (r *Resolver) strictErrors() bool { return r != nil && r.StrictErrors }
func (r *Resolver) getLookupGroup() *singleflight.Group {
if r == nil {
return &DefaultResolver.lookupGroup
}
return &r.lookupGroup
}
// LookupHost looks up the given host using the local resolver.
// It returns a slice of that host's addresses.
func LookupHost(host string) (addrs []string, err error) {
return DefaultResolver.LookupHost(context.Background(), host)
}
// LookupHost looks up the given host using the local resolver.
// It returns a slice of that host's addresses.
func (r *Resolver) LookupHost(ctx context.Context, host string) (addrs []string, err error) {
// Make sure that no matter what we do later, host=="" is rejected.
// parseIP, for example, does accept empty strings.
if host == "" {
return nil, &DNSError{Err: errNoSuchHost.Error(), Name: host, IsNotFound: true}
}
if ip, _ := parseIPZone(host); ip != nil {
return []string{host}, nil
}
return r.lookupHost(ctx, host)
}
// LookupIP looks up host using the local resolver.
// It returns a slice of that host's IPv4 and IPv6 addresses.
func LookupIP(host string) ([]IP, error) {
addrs, err := DefaultResolver.LookupIPAddr(context.Background(), host)
if err != nil {
return nil, err
}
ips := make([]IP, len(addrs))
for i, ia := range addrs {
ips[i] = ia.IP
}
return ips, nil
}
// LookupIPAddr looks up host using the local resolver.
// It returns a slice of that host's IPv4 and IPv6 addresses.
func (r *Resolver) LookupIPAddr(ctx context.Context, host string) ([]IPAddr, error) {
return r.lookupIPAddr(ctx, "ip", host)
}
// onlyValuesCtx is a context that uses an underlying context
// for value lookup if the underlying context hasn't yet expired.
type onlyValuesCtx struct {
context.Context
lookupValues context.Context
}
var _ context.Context = (*onlyValuesCtx)(nil)
// Value performs a lookup if the original context hasn't expired.
func (ovc *onlyValuesCtx) Value(key interface{}) interface{} {
select {
case <-ovc.lookupValues.Done():
return nil
default:
return ovc.lookupValues.Value(key)
}
}
// withUnexpiredValuesPreserved returns a context.Context that only uses lookupCtx
// for its values, otherwise it is never canceled and has no deadline.
// If the lookup context expires, any looked up values will return nil.
// See Issue 28600.
func withUnexpiredValuesPreserved(lookupCtx context.Context) context.Context {
return &onlyValuesCtx{Context: context.Background(), lookupValues: lookupCtx}
}
// lookupIPAddr looks up host using the local resolver and particular network.
// It returns a slice of that host's IPv4 and IPv6 addresses.
func (r *Resolver) lookupIPAddr(ctx context.Context, network, host string) ([]IPAddr, error) {
// Make sure that no matter what we do later, host=="" is rejected.
// parseIP, for example, does accept empty strings.
if host == "" {
return nil, &DNSError{Err: errNoSuchHost.Error(), Name: host, IsNotFound: true}
}
if ip, zone := parseIPZone(host); ip != nil {
return []IPAddr{{IP: ip, Zone: zone}}, nil
}
trace, _ := ctx.Value(nettrace.TraceKey{}).(*nettrace.Trace)
if trace != nil && trace.DNSStart != nil {
trace.DNSStart(host)
}
// The underlying resolver func is lookupIP by default but it
// can be overridden by tests. This is needed by net/http, so it
// uses a context key instead of unexported variables.
resolverFunc := r.lookupIP
if alt, _ := ctx.Value(nettrace.LookupIPAltResolverKey{}).(func(context.Context, string, string) ([]IPAddr, error)); alt != nil {
resolverFunc = alt
}
// We don't want a cancellation of ctx to affect the
// lookupGroup operation. Otherwise if our context gets
// canceled it might cause an error to be returned to a lookup
// using a completely different context. However we need to preserve
// only the values in context. See Issue 28600.
lookupGroupCtx, lookupGroupCancel := context.WithCancel(withUnexpiredValuesPreserved(ctx))
lookupKey := network + "\000" + host
dnsWaitGroup.Add(1)
ch, called := r.getLookupGroup().DoChan(lookupKey, func() (interface{}, error) {
defer dnsWaitGroup.Done()
return testHookLookupIP(lookupGroupCtx, resolverFunc, network, host)
})
if !called {
dnsWaitGroup.Done()
}
select {
case <-ctx.Done():
// Our context was canceled. If we are the only
// goroutine looking up this key, then drop the key
// from the lookupGroup and cancel the lookup.
// If there are other goroutines looking up this key,
// let the lookup continue uncanceled, and let later
// lookups with the same key share the result.
// See issues 8602, 20703, 22724.
if r.getLookupGroup().ForgetUnshared(lookupKey) {
lookupGroupCancel()
} else {
go func() {
<-ch
lookupGroupCancel()
}()
}
err := mapErr(ctx.Err())
if trace != nil && trace.DNSDone != nil {
trace.DNSDone(nil, false, err)
}
return nil, err
case r := <-ch:
lookupGroupCancel()
if trace != nil && trace.DNSDone != nil {
addrs, _ := r.Val.([]IPAddr)
trace.DNSDone(ipAddrsEface(addrs), r.Shared, r.Err)
}
return lookupIPReturn(r.Val, r.Err, r.Shared)
}
}
// lookupIPReturn turns the return values from singleflight.Do into
// the return values from LookupIP.
func lookupIPReturn(addrsi interface{}, err error, shared bool) ([]IPAddr, error) {
if err != nil {
return nil, err
}
addrs := addrsi.([]IPAddr)
if shared {
clone := make([]IPAddr, len(addrs))
copy(clone, addrs)
addrs = clone
}
return addrs, nil
}
// ipAddrsEface returns an empty interface slice of addrs.
func ipAddrsEface(addrs []IPAddr) []interface{} {
s := make([]interface{}, len(addrs))
for i, v := range addrs {
s[i] = v
}
return s
}
// LookupPort looks up the port for the given network and service.
func LookupPort(network, service string) (port int, err error) {
return DefaultResolver.LookupPort(context.Background(), network, service)
}
// LookupPort looks up the port for the given network and service.
func (r *Resolver) LookupPort(ctx context.Context, network, service string) (port int, err error) {
port, needsLookup := parsePort(service)
if needsLookup {
switch network {
case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
case "": // a hint wildcard for Go 1.0 undocumented behavior
network = "ip"
default:
return 0, &AddrError{Err: "unknown network", Addr: network}
}
port, err = r.lookupPort(ctx, network, service)
if err != nil {
return 0, err
}
}
if 0 > port || port > 65535 {
return 0, &AddrError{Err: "invalid port", Addr: service}
}
return port, nil
}
// LookupCNAME returns the canonical name for the given host.
// 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.
//
// A canonical name is the final name after following zero
// or more CNAME records.
// LookupCNAME does not return an error if host does not
// contain DNS "CNAME" records, as long as host resolves to
// address records.
func LookupCNAME(host string) (cname string, err error) {
return DefaultResolver.lookupCNAME(context.Background(), host)
}
// LookupCNAME returns the canonical name for the given host.
// 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.
//
// A canonical name is the final name after following zero
// or more CNAME records.
// LookupCNAME does not return an error if host does not
// contain DNS "CNAME" records, as long as host resolves to
// address records.
func (r *Resolver) LookupCNAME(ctx context.Context, host string) (cname string, err error) {
return r.lookupCNAME(ctx, host)
}
// 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) {
return DefaultResolver.lookupSRV(context.Background(), service, proto, name)
}
// 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 (r *Resolver) LookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*SRV, err error) {
return r.lookupSRV(ctx, service, proto, name)
}
// LookupMX returns the DNS MX records for the given domain name sorted by preference.
func LookupMX(name string) ([]*MX, error) {
return DefaultResolver.lookupMX(context.Background(), name)
}
// LookupMX returns the DNS MX records for the given domain name sorted by preference.
func (r *Resolver) LookupMX(ctx context.Context, name string) ([]*MX, error) {
return r.lookupMX(ctx, name)
}
// LookupNS returns the DNS NS records for the given domain name.
func LookupNS(name string) ([]*NS, error) {
return DefaultResolver.lookupNS(context.Background(), name)
}
// LookupNS returns the DNS NS records for the given domain name.
func (r *Resolver) LookupNS(ctx context.Context, name string) ([]*NS, error) {
return r.lookupNS(ctx, name)
}
// LookupTXT returns the DNS TXT records for the given domain name.
func LookupTXT(name string) ([]string, error) {
return DefaultResolver.lookupTXT(context.Background(), name)
}
// LookupTXT returns the DNS TXT records for the given domain name.
func (r *Resolver) LookupTXT(ctx context.Context, name string) ([]string, error) {
return r.lookupTXT(ctx, name)
}
// LookupAddr performs a reverse lookup for the given address, returning a list
// of names mapping to that address.
//
// When using the host C library resolver, at most one result will be
// returned. To bypass the host resolver, use a custom Resolver.
func LookupAddr(addr string) (names []string, err error) {
return DefaultResolver.lookupAddr(context.Background(), addr)
}
// LookupAddr performs a reverse lookup for the given address, returning a list
// of names mapping to that address.
func (r *Resolver) LookupAddr(ctx context.Context, addr string) (names []string, err error) {
return r.lookupAddr(ctx, addr)
}
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