1 files changed, 610 insertions, 0 deletions
diff --git a/src/net/lookup.go b/src/net/lookup.go
new file mode 100644
index 0000000..4135122
--- /dev/null
+++ b/src/net/lookup.go
@@ -0,0 +1,610 @@
+// 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.
+//
+// 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)
+}
+
+// LookupIP looks up host for the given network using the local resolver.
+// It returns a slice of that host's IP addresses of the type specified by
+// network.
+// network must be one of "ip", "ip4" or "ip6".
+func (r *Resolver) LookupIP(ctx context.Context, network, host string) ([]IP, error) {
+	afnet, _, err := parseNetwork(ctx, network, false)
+	if err != nil {
+		return nil, err
+	}
+	switch afnet {
+	case "ip", "ip4", "ip6":
+	default:
+		return nil, UnknownNetworkError(network)
+	}
+	addrs, err := r.internetAddrList(ctx, afnet, host)
+	if err != nil {
+		return nil, err
+	}
+	ips := make([]IP, 0, len(addrs))
+	for _, addr := range addrs {
+		ips = append(ips, addr.(*IPAddr).IP)
+	}
+	return ips, nil
+}
+
+// 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.
+//
+// The returned canonical name is validated to be a properly
+// formatted presentation-format domain name.
+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.
+//
+// The returned canonical name is validated to be a properly
+// formatted presentation-format domain name.
+func (r *Resolver) LookupCNAME(ctx context.Context, host string) (string, error) {
+	cname, err := r.lookupCNAME(ctx, host)
+	if err != nil {
+		return "", err
+	}
+	if !isDomainName(cname) {
+		return "", &DNSError{Err: errMalformedDNSRecordsDetail, Name: host}
+	}
+	return cname, nil
+}
+
+// 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.
+//
+// The returned service names are validated to be properly
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+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.
+//
+// The returned service names are validated to be properly
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+func (r *Resolver) LookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
+	cname, addrs, err := r.lookupSRV(ctx, service, proto, name)
+	if err != nil {
+		return "", nil, err
+	}
+	if cname != "" && !isDomainName(cname) {
+		return "", nil, &DNSError{Err: "SRV header name is invalid", Name: name}
+	}
+	filteredAddrs := make([]*SRV, 0, len(addrs))
+	for _, addr := range addrs {
+		if addr == nil {
+			continue
+		}
+		if !isDomainName(addr.Target) {
+			continue
+		}
+		filteredAddrs = append(filteredAddrs, addr)
+	}
+	if len(addrs) != len(filteredAddrs) {
+		return cname, filteredAddrs, &DNSError{Err: errMalformedDNSRecordsDetail, Name: name}
+	}
+	return cname, filteredAddrs, nil
+}
+
+// LookupMX returns the DNS MX records for the given domain name sorted by preference.
+//
+// The returned mail server names are validated to be properly
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+//
+// LookupMX uses context.Background internally; to specify the context, use
+// Resolver.LookupMX.
+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.
+//
+// The returned mail server names are validated to be properly
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+func (r *Resolver) LookupMX(ctx context.Context, name string) ([]*MX, error) {
+	records, err := r.lookupMX(ctx, name)
+	if err != nil {
+		return nil, err
+	}
+	filteredMX := make([]*MX, 0, len(records))
+	for _, mx := range records {
+		if mx == nil {
+			continue
+		}
+		// Bypass the hostname validity check for targets which contain only a dot,
+		// as this is used to represent a 'Null' MX record.
+		if mx.Host != "." && !isDomainName(mx.Host) {
+			continue
+		}
+		filteredMX = append(filteredMX, mx)
+	}
+	if len(records) != len(filteredMX) {
+		return filteredMX, &DNSError{Err: errMalformedDNSRecordsDetail, Name: name}
+	}
+	return filteredMX, nil
+}
+
+// LookupNS returns the DNS NS records for the given domain name.
+//
+// The returned name server names are validated to be properly
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+//
+// LookupNS uses context.Background internally; to specify the context, use
+// Resolver.LookupNS.
+func LookupNS(name string) ([]*NS, error) {
+	return DefaultResolver.LookupNS(context.Background(), name)
+}
+
+// LookupNS returns the DNS NS records for the given domain name.
+//
+// The returned name server names are validated to be properly
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+func (r *Resolver) LookupNS(ctx context.Context, name string) ([]*NS, error) {
+	records, err := r.lookupNS(ctx, name)
+	if err != nil {
+		return nil, err
+	}
+	filteredNS := make([]*NS, 0, len(records))
+	for _, ns := range records {
+		if ns == nil {
+			continue
+		}
+		if !isDomainName(ns.Host) {
+			continue
+		}
+		filteredNS = append(filteredNS, ns)
+	}
+	if len(records) != len(filteredNS) {
+		return filteredNS, &DNSError{Err: errMalformedDNSRecordsDetail, Name: name}
+	}
+	return filteredNS, nil
+}
+
+// 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.
+//
+// The returned names are validated to be properly formatted presentation-format
+// domain names. If the response contains invalid names, those records are filtered
+// out and an error will be returned alongside the the remaining results, if any.
+//
+// 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.
+//
+// The returned names are validated to be properly formatted presentation-format
+// domain names. If the response contains invalid names, those records are filtered
+// out and an error will be returned alongside the the remaining results, if any.
+func (r *Resolver) LookupAddr(ctx context.Context, addr string) ([]string, error) {
+	names, err := r.lookupAddr(ctx, addr)
+	if err != nil {
+		return nil, err
+	}
+	filteredNames := make([]string, 0, len(names))
+	for _, name := range names {
+		if isDomainName(name) {
+			filteredNames = append(filteredNames, name)
+		}
+	}
+	if len(names) != len(filteredNames) {
+		return filteredNames, &DNSError{Err: errMalformedDNSRecordsDetail, Name: addr}
+	}
+	return filteredNames, nil
+}
+
+// errMalformedDNSRecordsDetail is the DNSError detail which is returned when a Resolver.Lookup...
+// method recieves DNS records which contain invalid DNS names. This may be returned alongside
+// results which have had the malformed records filtered out.
+var errMalformedDNSRecordsDetail = "DNS response contained records which contain invalid names"