net: use C library resolver on FreeBSD, Linux, OS X / amd64, 386

This CL makes it possible to resolve DNS names on OS X
without offending the Application-Level Firewall.

It also means that cross-compiling from one operating
system to another is no longer possible when using
package net, because cgo needs to be able to sniff around
the local C libraries.  We could special-case this one use
and check in generated files, but it seems more trouble
than it's worth.  Cross compiling is dead anyway.

It is still possible to use either GOARCH=amd64 or GOARCH=386
on typical Linux and OS X x86 systems.

It is also still possible to build GOOS=linux GOARCH=arm on
any system, because arm is for now excluded from this change
(there is no cgo for arm yet).

R=iant, r, mikioh
CC=golang-dev
https://golang.org/cl/4437053

Author: rsc

src/pkg/net/Makefile

@@ -6,7 +6,6 @@ include ../../Make.inc
 
 TARG=net
 GOFILES=\
-	cgo_stub.go\
 	dial.go\
 	dnsmsg.go\
 	fd_$(GOOS).go\
@@ -31,13 +30,19 @@ GOFILES_freebsd=\
 	dnsclient.go\
 	port.go\
 
+CGOFILES_freebsd=\
+	cgo_unix.go\
+
 GOFILES_darwin=\
 	newpollserver.go\
 	fd.go\
 	file.go\
 	dnsconfig.go\
 	dnsclient.go\
 	port.go\
+
+CGOFILES_darwin=\
+	cgo_unix.go\
 
 GOFILES_linux=\
 	newpollserver.go\
@@ -47,10 +52,22 @@ GOFILES_linux=\
 	dnsclient.go\
 	port.go\
 
+ifeq ($(GOARCH),arm)
+# ARM has no cgo, so use the stubs.
+GOFILES_linux+=cgo_stub.go
+else
+CGOFILES_linux=\
+	cgo_unix.go
+endif
+
 GOFILES_windows=\
+	cgo_stub.go\
 	resolv_windows.go\
 	file_windows.go\
 
 GOFILES+=$(GOFILES_$(GOOS))
+ifneq ($(CGOFILES_$(GOOS)),)
+CGOFILES+=$(CGOFILES_$(GOOS))
+endif
 
 include ../../Make.pkg

src/pkg/net/cgo_stub.go

@@ -19,3 +19,7 @@ func cgoLookupPort(network, service string) (port int, err os.Error, completed b
 func cgoLookupIP(name string) (addrs []IP, err os.Error, completed bool) {
 	return nil, nil, false
 }
+
+func cgoLookupCNAME(name string) (cname string, err os.Error, completed bool) {
+	return "", nil, false
+}

src/pkg/net/cgo_unix.go

@@ -0,0 +1,148 @@
+// Copyright 2011 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
+
+/*
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+*/
+import "C"
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+func cgoLookupHost(name string) (addrs []string, err os.Error, completed bool) {
+	ip, err, completed := cgoLookupIP(name)
+	for _, p := range ip {
+		addrs = append(addrs, p.String())
+	}
+	return
+}
+
+func cgoLookupPort(net, service string) (port int, err os.Error, completed bool) {
+	var res *C.struct_addrinfo
+	var hints C.struct_addrinfo
+
+	switch net {
+	case "":
+		// no hints
+	case "tcp", "tcp4", "tcp6":
+		hints.ai_socktype = C.SOCK_STREAM
+		hints.ai_protocol = C.IPPROTO_TCP
+	case "udp", "udp4", "udp6":
+		hints.ai_socktype = C.SOCK_DGRAM
+		hints.ai_protocol = C.IPPROTO_UDP
+	default:
+		return 0, UnknownNetworkError(net), true
+	}
+	if len(net) >= 4 {
+		switch net[3] {
+		case '4':
+			hints.ai_family = C.AF_INET
+		case '6':
+			hints.ai_family = C.AF_INET6
+		}
+	}
+
+	s := C.CString(service)
+	defer C.free(unsafe.Pointer(s))
+	if C.getaddrinfo(nil, s, &hints, &res) == 0 {
+		defer C.freeaddrinfo(res)
+		for r := res; r != nil; r = r.ai_next {
+			switch r.ai_family {
+			default:
+				continue
+			case C.AF_INET:
+				sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.ai_addr))
+				p := (*[2]byte)(unsafe.Pointer(&sa.Port))
+				return int(p[0])<<8 | int(p[1]), nil, true
+			case C.AF_INET6:
+				sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.ai_addr))
+				p := (*[2]byte)(unsafe.Pointer(&sa.Port))
+				return int(p[0])<<8 | int(p[1]), nil, true
+			}
+		}
+	}
+	return 0, &AddrError{"unknown port", net + "/" + service}, true
+}
+
+func cgoLookupIPCNAME(name string) (addrs []IP, cname string, err os.Error, completed bool) {
+	var res *C.struct_addrinfo
+	var hints C.struct_addrinfo
+
+	// NOTE(rsc): In theory there are approximately balanced
+	// arguments for and against including AI_ADDRCONFIG
+	// in the flags (it includes IPv4 results only on IPv4 systems,
+	// and similarly for IPv6), but in practice setting it causes
+	// getaddrinfo to return the wrong canonical name on Linux.
+	// So definitely leave it out.
+	hints.ai_flags = C.AI_ALL | C.AI_V4MAPPED | C.AI_CANONNAME
+
+	h := C.CString(name)
+	defer C.free(unsafe.Pointer(h))
+	gerrno, err := C.getaddrinfo(h, nil, &hints, &res)
+	if gerrno != 0 {
+		var str string
+		if gerrno == C.EAI_NONAME {
+			str = noSuchHost
+		} else if gerrno == C.EAI_SYSTEM {
+			str = err.String()
+		} else {
+			str = C.GoString(C.gai_strerror(gerrno))
+		}
+		return nil, "", &DNSError{Error: str, Name: name}, true
+	}
+	defer C.freeaddrinfo(res)
+	if res != nil {
+		cname = C.GoString(res.ai_canonname)
+		if cname == "" {
+			cname = name
+		}
+		if len(cname) > 0 && cname[len(cname)-1] != '.' {
+			cname += "."
+		}
+	}
+	for r := res; r != nil; r = r.ai_next {
+		// Everything comes back twice, once for UDP and once for TCP.
+		if r.ai_socktype != C.SOCK_STREAM {
+			continue
+		}
+		switch r.ai_family {
+		default:
+			continue
+		case C.AF_INET:
+			sa := (*syscall.RawSockaddrInet4)(unsafe.Pointer(r.ai_addr))
+			addrs = append(addrs, copyIP(sa.Addr[:]))
+		case C.AF_INET6:
+			sa := (*syscall.RawSockaddrInet6)(unsafe.Pointer(r.ai_addr))
+			addrs = append(addrs, copyIP(sa.Addr[:]))
+		}
+	}
+	return addrs, cname, nil, true
+}
+
+func cgoLookupIP(name string) (addrs []IP, err os.Error, completed bool) {
+	addrs, _, err, completed = cgoLookupIPCNAME(name)
+	return
+}
+
+func cgoLookupCNAME(name string) (cname string, err os.Error, completed bool) {
+	_, cname, err, completed = cgoLookupIPCNAME(name)
+	return
+}
+
+func copyIP(x IP) IP {
+	y := make(IP, len(x))
+	copy(y, x)
+	return y
+}

src/pkg/net/dial.go

@@ -30,7 +30,7 @@ func Dial(net, addr string) (c Conn, err os.Error) {
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 		var ra *TCPAddr
-		if ra, err = ResolveTCPAddr(raddr); err != nil {
+		if ra, err = ResolveTCPAddr(net, raddr); err != nil {
 			goto Error
 		}
 		c, err := DialTCP(net, nil, ra)
@@ -40,7 +40,7 @@ func Dial(net, addr string) (c Conn, err os.Error) {
 		return c, nil
 	case "udp", "udp4", "udp6":
 		var ra *UDPAddr
-		if ra, err = ResolveUDPAddr(raddr); err != nil {
+		if ra, err = ResolveUDPAddr(net, raddr); err != nil {
 			goto Error
 		}
 		c, err := DialUDP(net, nil, ra)
@@ -83,7 +83,7 @@ func Listen(net, laddr string) (l Listener, err os.Error) {
 	case "tcp", "tcp4", "tcp6":
 		var la *TCPAddr
 		if laddr != "" {
-			if la, err = ResolveTCPAddr(laddr); err != nil {
+			if la, err = ResolveTCPAddr(net, laddr); err != nil {
 				return nil, err
 			}
 		}
@@ -116,7 +116,7 @@ func ListenPacket(net, laddr string) (c PacketConn, err os.Error) {
 	case "udp", "udp4", "udp6":
 		var la *UDPAddr
 		if laddr != "" {
-			if la, err = ResolveUDPAddr(laddr); err != nil {
+			if la, err = ResolveUDPAddr(net, laddr); err != nil {
 				return nil, err
 			}
 		}

src/pkg/net/dialgoogle_test.go

@@ -78,17 +78,22 @@ func TestDialGoogle(t *testing.T) {
 		googleaddrs[len(googleaddrs)-1] = ""
 	}
 
-	// Insert an actual IP address for google.com
+	// Insert an actual IPv4 address for google.com
 	// into the table.
-
 	addrs, err := LookupIP("www.google.com")
 	if err != nil {
 		t.Fatalf("lookup www.google.com: %v", err)
 	}
-	if len(addrs) == 0 {
-		t.Fatalf("no addresses for www.google.com")
+	var ip IP
+	for _, addr := range addrs {
+		if x := addr.To4(); x != nil {
+			ip = x
+			break
+		}
+	}
+	if ip == nil {
+		t.Fatalf("no IPv4 addresses for www.google.com")
 	}
-	ip := addrs[0].To4()
 
 	for i, s := range googleaddrs {
 		if strings.Contains(s, "%") {

src/pkg/net/dnsclient.go

@@ -307,6 +307,11 @@ func lookup(name string, qtype uint16) (cname string, addrs []dnsRR, err os.Erro
 }
 
 // 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 os.Error) {
 	onceLoadConfig.Do(loadConfig)
 	if dnserr != nil || cfg == nil {
@@ -330,6 +335,11 @@ func goLookupHost(name string) (addrs []string, err os.Error) {
 }
 
 // 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 os.Error) {
 	onceLoadConfig.Do(loadConfig)
 	if dnserr != nil || cfg == nil {
@@ -358,11 +368,13 @@ func goLookupIP(name string) (addrs []IP, err os.Error) {
 	return
 }
 
-// LookupCNAME returns the canonical DNS host for the given name.
-// 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.
-func LookupCNAME(name string) (cname string, err os.Error) {
+// 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 os.Error) {
 	onceLoadConfig.Do(loadConfig)
 	if dnserr != nil || cfg == nil {
 		err = dnserr

src/pkg/net/hosts_test.go

@@ -5,6 +5,7 @@
 package net
 
 import (
+	"sort"
 	"testing"
 )
 
@@ -51,3 +52,17 @@ func TestLookupStaticHost(t *testing.T) {
 	}
 	hostsPath = p
 }
+
+func TestLookupHost(t *testing.T) {
+	// Can't depend on this to return anything in particular,
+	// but if it does return something, make sure it doesn't
+	// duplicate addresses (a common bug due to the way
+	// getaddrinfo works).
+	addrs, _ := LookupHost("localhost")
+	sort.SortStrings(addrs)
+	for i := 0; i+1 < len(addrs); i++ {
+		if addrs[i] == addrs[i+1] {
+			t.Fatalf("LookupHost(\"localhost\") = %v, has duplicate addresses", addrs)
+		}
+	}
+}

src/pkg/net/iprawsock.go

@@ -245,7 +245,7 @@ func hostToIP(host string) (ip IP, err os.Error) {
 			err = err1
 			goto Error
 		}
-		addr = firstSupportedAddr(addrs)
+		addr = firstSupportedAddr(anyaddr, addrs)
 		if addr == nil {
 			// should not happen
 			err = &AddrError{"LookupHost returned invalid address", addrs[0]}