libgo: update to Go 1.11

[official-gcc.git] / libgo / go / 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
// (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}
}

// 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}
        }
        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) {
        // 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}
        }
        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) ([]IPAddr, error)); alt != nil {
                resolverFunc = alt
        }

        // We don't want a cancelation 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.
        lookupGroupCtx, lookupGroupCancel := context.WithCancel(context.Background())

        dnsWaitGroup.Add(1)
        ch, called := r.getLookupGroup().DoChan(host, func() (interface{}, error) {
                defer dnsWaitGroup.Done()
                return testHookLookupIP(lookupGroupCtx, resolverFunc, 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(host) {
                        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 {
                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)
}