1 files changed, 423 insertions, 0 deletions
diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go
new file mode 100644
index 000000000..7511083f7
--- /dev/null
+++ b/src/net/dnsclient_unix.go
@@ -0,0 +1,423 @@
+// Copyright 2009 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.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+// DNS client: see RFC 1035.
+// Has to be linked into package net for Dial.
+
+// TODO(rsc):
+//	Could potentially handle many outstanding lookups faster.
+//	Could have a small cache.
+//	Random UDP source port (net.Dial should do that for us).
+//	Random request IDs.
+
+package net
+
+import (
+	"errors"
+	"io"
+	"math/rand"
+	"os"
+	"sync"
+	"time"
+)
+
+// A dnsConn represents a DNS transport endpoint.
+type dnsConn interface {
+	Conn
+
+	// readDNSResponse reads a DNS response message from the DNS
+	// transport endpoint and returns the received DNS response
+	// message.
+	readDNSResponse() (*dnsMsg, error)
+
+	// writeDNSQuery writes a DNS query message to the DNS
+	// connection endpoint.
+	writeDNSQuery(*dnsMsg) error
+}
+
+func (c *UDPConn) readDNSResponse() (*dnsMsg, error) {
+	b := make([]byte, 512) // see RFC 1035
+	n, err := c.Read(b)
+	if err != nil {
+		return nil, err
+	}
+	msg := &dnsMsg{}
+	if !msg.Unpack(b[:n]) {
+		return nil, errors.New("cannot unmarshal DNS message")
+	}
+	return msg, nil
+}
+
+func (c *UDPConn) writeDNSQuery(msg *dnsMsg) error {
+	b, ok := msg.Pack()
+	if !ok {
+		return errors.New("cannot marshal DNS message")
+	}
+	if _, err := c.Write(b); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (c *TCPConn) readDNSResponse() (*dnsMsg, error) {
+	b := make([]byte, 1280) // 1280 is a reasonable initial size for IP over Ethernet, see RFC 4035
+	if _, err := io.ReadFull(c, b[:2]); err != nil {
+		return nil, err
+	}
+	l := int(b[0])<<8 | int(b[1])
+	if l > len(b) {
+		b = make([]byte, l)
+	}
+	n, err := io.ReadFull(c, b[:l])
+	if err != nil {
+		return nil, err
+	}
+	msg := &dnsMsg{}
+	if !msg.Unpack(b[:n]) {
+		return nil, errors.New("cannot unmarshal DNS message")
+	}
+	return msg, nil
+}
+
+func (c *TCPConn) writeDNSQuery(msg *dnsMsg) error {
+	b, ok := msg.Pack()
+	if !ok {
+		return errors.New("cannot marshal DNS message")
+	}
+	l := uint16(len(b))
+	b = append([]byte{byte(l >> 8), byte(l)}, b...)
+	if _, err := c.Write(b); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (d *Dialer) dialDNS(network, server string) (dnsConn, error) {
+	switch network {
+	case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
+	default:
+		return nil, UnknownNetworkError(network)
+	}
+	// Calling Dial here is scary -- we have to be sure not to
+	// dial a name that will require a DNS lookup, or Dial will
+	// call back here to translate it. The DNS config parser has
+	// already checked that all the cfg.servers[i] are IP
+	// addresses, which Dial will use without a DNS lookup.
+	c, err := d.Dial(network, server)
+	if err != nil {
+		return nil, err
+	}
+	switch network {
+	case "tcp", "tcp4", "tcp6":
+		return c.(*TCPConn), nil
+	case "udp", "udp4", "udp6":
+		return c.(*UDPConn), nil
+	}
+	panic("unreachable")
+}
+
+// exchange sends a query on the connection and hopes for a response.
+func exchange(server, name string, qtype uint16, timeout time.Duration) (*dnsMsg, error) {
+	d := Dialer{Timeout: timeout}
+	out := dnsMsg{
+		dnsMsgHdr: dnsMsgHdr{
+			recursion_desired: true,
+		},
+		question: []dnsQuestion{
+			{name, qtype, dnsClassINET},
+		},
+	}
+	for _, network := range []string{"udp", "tcp"} {
+		c, err := d.dialDNS(network, server)
+		if err != nil {
+			return nil, err
+		}
+		defer c.Close()
+		if timeout > 0 {
+			c.SetDeadline(time.Now().Add(timeout))
+		}
+		out.id = uint16(rand.Int()) ^ uint16(time.Now().UnixNano())
+		if err := c.writeDNSQuery(&out); err != nil {
+			return nil, err
+		}
+		in, err := c.readDNSResponse()
+		if err != nil {
+			return nil, err
+		}
+		if in.id != out.id {
+			return nil, errors.New("DNS message ID mismatch")
+		}
+		if in.truncated { // see RFC 5966
+			continue
+		}
+		return in, nil
+	}
+	return nil, errors.New("no answer from DNS server")
+}
+
+// Do a lookup for a single name, which must be rooted
+// (otherwise answer will not find the answers).
+func tryOneName(cfg *dnsConfig, name string, qtype uint16) (string, []dnsRR, error) {
+	if len(cfg.servers) == 0 {
+		return "", nil, &DNSError{Err: "no DNS servers", Name: name}
+	}
+	if len(name) >= 256 {
+		return "", nil, &DNSError{Err: "DNS name too long", Name: name}
+	}
+	timeout := time.Duration(cfg.timeout) * time.Second
+	var lastErr error
+	for i := 0; i < cfg.attempts; i++ {
+		for _, server := range cfg.servers {
+			server = JoinHostPort(server, "53")
+			msg, err := exchange(server, name, qtype, timeout)
+			if err != nil {
+				lastErr = &DNSError{
+					Err:    err.Error(),
+					Name:   name,
+					Server: server,
+				}
+				if nerr, ok := err.(Error); ok && nerr.Timeout() {
+					lastErr.(*DNSError).IsTimeout = true
+				}
+				continue
+			}
+			cname, addrs, err := answer(name, server, msg, qtype)
+			if err == nil || err.(*DNSError).Err == noSuchHost {
+				return cname, addrs, err
+			}
+			lastErr = err
+		}
+	}
+	return "", nil, lastErr
+}
+
+func convertRR_A(records []dnsRR) []IP {
+	addrs := make([]IP, len(records))
+	for i, rr := range records {
+		a := rr.(*dnsRR_A).A
+		addrs[i] = IPv4(byte(a>>24), byte(a>>16), byte(a>>8), byte(a))
+	}
+	return addrs
+}
+
+func convertRR_AAAA(records []dnsRR) []IP {
+	addrs := make([]IP, len(records))
+	for i, rr := range records {
+		a := make(IP, IPv6len)
+		copy(a, rr.(*dnsRR_AAAA).AAAA[:])
+		addrs[i] = a
+	}
+	return addrs
+}
+
+var cfg struct {
+	ch        chan struct{}
+	mu        sync.RWMutex // protects dnsConfig and dnserr
+	dnsConfig *dnsConfig
+	dnserr    error
+}
+var onceLoadConfig sync.Once
+
+// Assume dns config file is /etc/resolv.conf here
+func loadDefaultConfig() {
+	loadConfig("/etc/resolv.conf", 5*time.Second, nil)
+}
+
+func loadConfig(resolvConfPath string, reloadTime time.Duration, quit <-chan chan struct{}) {
+	var mtime time.Time
+	cfg.ch = make(chan struct{}, 1)
+	if fi, err := os.Stat(resolvConfPath); err != nil {
+		cfg.dnserr = err
+	} else {
+		mtime = fi.ModTime()
+		cfg.dnsConfig, cfg.dnserr = dnsReadConfig(resolvConfPath)
+	}
+	go func() {
+		for {
+			time.Sleep(reloadTime)
+			select {
+			case qresp := <-quit:
+				qresp <- struct{}{}
+				return
+			case <-cfg.ch:
+			}
+
+			// In case of error, we keep the previous config
+			fi, err := os.Stat(resolvConfPath)
+			if err != nil {
+				continue
+			}
+			// If the resolv.conf mtime didn't change, do not reload
+			m := fi.ModTime()
+			if m.Equal(mtime) {
+				continue
+			}
+			mtime = m
+			// In case of error, we keep the previous config
+			ncfg, err := dnsReadConfig(resolvConfPath)
+			if err != nil || len(ncfg.servers) == 0 {
+				continue
+			}
+			cfg.mu.Lock()
+			cfg.dnsConfig = ncfg
+			cfg.dnserr = nil
+			cfg.mu.Unlock()
+		}
+	}()
+}
+
+func lookup(name string, qtype uint16) (cname string, addrs []dnsRR, err error) {
+	if !isDomainName(name) {
+		return name, nil, &DNSError{Err: "invalid domain name", Name: name}
+	}
+	onceLoadConfig.Do(loadDefaultConfig)
+
+	select {
+	case cfg.ch <- struct{}{}:
+	default:
+	}
+
+	cfg.mu.RLock()
+	defer cfg.mu.RUnlock()
+
+	if cfg.dnserr != nil || cfg.dnsConfig == nil {
+		err = cfg.dnserr
+		return
+	}
+	// If name is rooted (trailing dot) or has enough dots,
+	// try it by itself first.
+	rooted := len(name) > 0 && name[len(name)-1] == '.'
+	if rooted || count(name, '.') >= cfg.dnsConfig.ndots {
+		rname := name
+		if !rooted {
+			rname += "."
+		}
+		// Can try as ordinary name.
+		cname, addrs, err = tryOneName(cfg.dnsConfig, rname, qtype)
+		if rooted || err == nil {
+			return
+		}
+	}
+
+	// Otherwise, try suffixes.
+	for i := 0; i < len(cfg.dnsConfig.search); i++ {
+		rname := name + "." + cfg.dnsConfig.search[i]
+		if rname[len(rname)-1] != '.' {
+			rname += "."
+		}
+		cname, addrs, err = tryOneName(cfg.dnsConfig, rname, qtype)
+		if err == nil {
+			return
+		}
+	}
+
+	// Last ditch effort: try unsuffixed only if we haven't already,
+	// that is, name is not rooted and has less than ndots dots.
+	if count(name, '.') < cfg.dnsConfig.ndots {
+		cname, addrs, err = tryOneName(cfg.dnsConfig, name+".", qtype)
+		if err == nil {
+			return
+		}
+	}
+
+	if e, ok := err.(*DNSError); ok {
+		// Show original name passed to lookup, not suffixed one.
+		// In general we might have tried many suffixes; showing
+		// just one is misleading. See also golang.org/issue/6324.
+		e.Name = name
+	}
+	return
+}
+
+// goLookupHost is the native Go implementation of LookupHost.
+// Used only if cgoLookupHost refuses to handle the request
+// (that is, only if cgoLookupHost is the stub in cgo_stub.go).
+// Normally we let cgo use the C library resolver instead of
+// depending on our lookup code, so that Go and C get the same
+// answers.
+func goLookupHost(name string) (addrs []string, err error) {
+	// Use entries from /etc/hosts if they match.
+	addrs = lookupStaticHost(name)
+	if len(addrs) > 0 {
+		return
+	}
+	ips, err := goLookupIP(name)
+	if err != nil {
+		return
+	}
+	addrs = make([]string, 0, len(ips))
+	for _, ip := range ips {
+		addrs = append(addrs, ip.String())
+	}
+	return
+}
+
+// goLookupIP is the native Go implementation of LookupIP.
+// Used only if cgoLookupIP refuses to handle the request
+// (that is, only if cgoLookupIP is the stub in cgo_stub.go).
+// Normally we let cgo use the C library resolver instead of
+// depending on our lookup code, so that Go and C get the same
+// answers.
+func goLookupIP(name string) (addrs []IP, err error) {
+	// Use entries from /etc/hosts if possible.
+	haddrs := lookupStaticHost(name)
+	if len(haddrs) > 0 {
+		for _, haddr := range haddrs {
+			if ip := ParseIP(haddr); ip != nil {
+				addrs = append(addrs, ip)
+			}
+		}
+		if len(addrs) > 0 {
+			return
+		}
+	}
+	type racer struct {
+		qtype uint16
+		rrs   []dnsRR
+		error
+	}
+	lane := make(chan racer, 1)
+	qtypes := [...]uint16{dnsTypeA, dnsTypeAAAA}
+	for _, qtype := range qtypes {
+		go func(qtype uint16) {
+			_, rrs, err := lookup(name, qtype)
+			lane <- racer{qtype, rrs, err}
+		}(qtype)
+	}
+	var lastErr error
+	for range qtypes {
+		racer := <-lane
+		if racer.error != nil {
+			lastErr = racer.error
+			continue
+		}
+		switch racer.qtype {
+		case dnsTypeA:
+			addrs = append(addrs, convertRR_A(racer.rrs)...)
+		case dnsTypeAAAA:
+			addrs = append(addrs, convertRR_AAAA(racer.rrs)...)
+		}
+	}
+	if len(addrs) == 0 && lastErr != nil {
+		return nil, lastErr
+	}
+	return addrs, nil
+}
+
+// goLookupCNAME is the native Go implementation of LookupCNAME.
+// Used only if cgoLookupCNAME refuses to handle the request
+// (that is, only if cgoLookupCNAME is the stub in cgo_stub.go).
+// Normally we let cgo use the C library resolver instead of
+// depending on our lookup code, so that Go and C get the same
+// answers.
+func goLookupCNAME(name string) (cname string, err error) {
+	_, rr, err := lookup(name, dnsTypeCNAME)
+	if err != nil {
+		return
+	}
+	cname = rr[0].(*dnsRR_CNAME).Cname
+	return
+}