342 lines
7.6 KiB
Go
342 lines
7.6 KiB
Go
// Copyright 2011 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 (
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"context"
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"errors"
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"internal/bytealg"
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"internal/itoa"
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"io"
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"os"
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)
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func query(ctx context.Context, filename, query string, bufSize int) (addrs []string, err error) {
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queryAddrs := func() (addrs []string, err error) {
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file, err := os.OpenFile(filename, os.O_RDWR, 0)
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if err != nil {
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return nil, err
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}
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defer file.Close()
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_, err = file.Seek(0, io.SeekStart)
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if err != nil {
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return nil, err
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}
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_, err = file.WriteString(query)
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if err != nil {
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return nil, err
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}
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_, err = file.Seek(0, io.SeekStart)
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if err != nil {
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return nil, err
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}
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buf := make([]byte, bufSize)
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for {
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n, _ := file.Read(buf)
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if n <= 0 {
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break
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}
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addrs = append(addrs, string(buf[:n]))
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}
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return addrs, nil
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}
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type ret struct {
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addrs []string
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err error
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}
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ch := make(chan ret, 1)
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go func() {
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addrs, err := queryAddrs()
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ch <- ret{addrs: addrs, err: err}
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}()
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select {
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case r := <-ch:
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return r.addrs, r.err
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case <-ctx.Done():
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return nil, &DNSError{
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Name: query,
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Err: ctx.Err().Error(),
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IsTimeout: ctx.Err() == context.DeadlineExceeded,
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}
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}
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}
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func queryCS(ctx context.Context, net, host, service string) (res []string, err error) {
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switch net {
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case "tcp4", "tcp6":
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net = "tcp"
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case "udp4", "udp6":
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net = "udp"
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}
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if host == "" {
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host = "*"
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}
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return query(ctx, netdir+"/cs", net+"!"+host+"!"+service, 128)
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}
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func queryCS1(ctx context.Context, net string, ip IP, port int) (clone, dest string, err error) {
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ips := "*"
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if len(ip) != 0 && !ip.IsUnspecified() {
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ips = ip.String()
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}
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lines, err := queryCS(ctx, net, ips, itoa.Itoa(port))
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if err != nil {
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return
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}
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f := getFields(lines[0])
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if len(f) < 2 {
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return "", "", errors.New("bad response from ndb/cs")
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}
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clone, dest = f[0], f[1]
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return
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}
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func queryDNS(ctx context.Context, addr string, typ string) (res []string, err error) {
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return query(ctx, netdir+"/dns", addr+" "+typ, 1024)
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}
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// toLower returns a lower-case version of in. Restricting us to
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// ASCII is sufficient to handle the IP protocol names and allow
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// us to not depend on the strings and unicode packages.
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func toLower(in string) string {
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for _, c := range in {
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if 'A' <= c && c <= 'Z' {
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// Has upper case; need to fix.
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out := []byte(in)
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for i := 0; i < len(in); i++ {
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c := in[i]
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if 'A' <= c && c <= 'Z' {
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c += 'a' - 'A'
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}
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out[i] = c
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}
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return string(out)
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}
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}
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return in
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}
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// lookupProtocol looks up IP protocol name and returns
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// the corresponding protocol number.
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func lookupProtocol(ctx context.Context, name string) (proto int, err error) {
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lines, err := query(ctx, netdir+"/cs", "!protocol="+toLower(name), 128)
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if err != nil {
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return 0, err
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}
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if len(lines) == 0 {
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return 0, UnknownNetworkError(name)
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}
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f := getFields(lines[0])
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if len(f) < 2 {
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return 0, UnknownNetworkError(name)
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}
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s := f[1]
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if n, _, ok := dtoi(s[bytealg.IndexByteString(s, '=')+1:]); ok {
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return n, nil
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}
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return 0, UnknownNetworkError(name)
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}
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func (*Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
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// Use netdir/cs instead of netdir/dns because cs knows about
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// host names in local network (e.g. from /lib/ndb/local)
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lines, err := queryCS(ctx, "net", host, "1")
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if err != nil {
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dnsError := &DNSError{Err: err.Error(), Name: host}
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if stringsHasSuffix(err.Error(), "dns failure") {
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dnsError.Err = errNoSuchHost.Error()
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dnsError.IsNotFound = true
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}
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return nil, dnsError
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}
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loop:
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for _, line := range lines {
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f := getFields(line)
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if len(f) < 2 {
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continue
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}
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addr := f[1]
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if i := bytealg.IndexByteString(addr, '!'); i >= 0 {
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addr = addr[:i] // remove port
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}
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if ParseIP(addr) == nil {
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continue
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}
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// only return unique addresses
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for _, a := range addrs {
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if a == addr {
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continue loop
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}
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}
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addrs = append(addrs, addr)
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}
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return
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}
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func (r *Resolver) lookupIP(ctx context.Context, _, host string) (addrs []IPAddr, err error) {
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lits, err := r.lookupHost(ctx, host)
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if err != nil {
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return
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}
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for _, lit := range lits {
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host, zone := splitHostZone(lit)
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if ip := ParseIP(host); ip != nil {
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addr := IPAddr{IP: ip, Zone: zone}
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addrs = append(addrs, addr)
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}
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}
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return
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}
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func (*Resolver) lookupPort(ctx context.Context, network, service string) (port int, err error) {
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switch network {
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case "tcp4", "tcp6":
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network = "tcp"
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case "udp4", "udp6":
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network = "udp"
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}
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lines, err := queryCS(ctx, network, "127.0.0.1", toLower(service))
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if err != nil {
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return
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}
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unknownPortError := &AddrError{Err: "unknown port", Addr: network + "/" + service}
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if len(lines) == 0 {
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return 0, unknownPortError
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}
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f := getFields(lines[0])
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if len(f) < 2 {
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return 0, unknownPortError
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}
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s := f[1]
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if i := bytealg.IndexByteString(s, '!'); i >= 0 {
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s = s[i+1:] // remove address
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}
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if n, _, ok := dtoi(s); ok {
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return n, nil
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}
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return 0, unknownPortError
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}
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func (*Resolver) lookupCNAME(ctx context.Context, name string) (cname string, err error) {
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lines, err := queryDNS(ctx, name, "cname")
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if err != nil {
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if stringsHasSuffix(err.Error(), "dns failure") || stringsHasSuffix(err.Error(), "resource does not exist; negrcode 0") {
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cname = name + "."
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err = nil
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}
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return
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}
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if len(lines) > 0 {
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if f := getFields(lines[0]); len(f) >= 3 {
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return f[2] + ".", nil
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}
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}
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return "", errors.New("bad response from ndb/dns")
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}
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func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*SRV, err error) {
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var target string
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if service == "" && proto == "" {
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target = name
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} else {
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target = "_" + service + "._" + proto + "." + name
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}
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lines, err := queryDNS(ctx, target, "srv")
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if err != nil {
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return
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}
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for _, line := range lines {
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f := getFields(line)
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if len(f) < 6 {
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continue
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}
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port, _, portOk := dtoi(f[4])
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priority, _, priorityOk := dtoi(f[3])
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weight, _, weightOk := dtoi(f[2])
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if !(portOk && priorityOk && weightOk) {
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continue
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}
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addrs = append(addrs, &SRV{absDomainName(f[5]), uint16(port), uint16(priority), uint16(weight)})
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cname = absDomainName(f[0])
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}
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byPriorityWeight(addrs).sort()
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return
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}
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func (*Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error) {
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lines, err := queryDNS(ctx, name, "mx")
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if err != nil {
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return
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}
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for _, line := range lines {
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f := getFields(line)
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if len(f) < 4 {
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continue
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}
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if pref, _, ok := dtoi(f[2]); ok {
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mx = append(mx, &MX{absDomainName(f[3]), uint16(pref)})
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}
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}
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byPref(mx).sort()
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return
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}
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func (*Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error) {
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lines, err := queryDNS(ctx, name, "ns")
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if err != nil {
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return
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}
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for _, line := range lines {
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f := getFields(line)
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if len(f) < 3 {
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continue
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}
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ns = append(ns, &NS{absDomainName(f[2])})
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}
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return
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}
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func (*Resolver) lookupTXT(ctx context.Context, name string) (txt []string, err error) {
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lines, err := queryDNS(ctx, name, "txt")
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if err != nil {
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return
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}
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for _, line := range lines {
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if i := bytealg.IndexByteString(line, '\t'); i >= 0 {
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txt = append(txt, line[i+1:])
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}
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}
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return
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}
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func (*Resolver) lookupAddr(ctx context.Context, addr string) (name []string, err error) {
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arpa, err := reverseaddr(addr)
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if err != nil {
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return
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}
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lines, err := queryDNS(ctx, arpa, "ptr")
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if err != nil {
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return
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}
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for _, line := range lines {
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f := getFields(line)
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if len(f) < 3 {
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continue
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}
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name = append(name, absDomainName(f[2]))
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}
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return
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}
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// concurrentThreadsLimit returns the number of threads we permit to
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// run concurrently doing DNS lookups.
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func concurrentThreadsLimit() int {
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return 500
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}
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