path: root/src/net/lookup.go

// 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 :=