net: fix LookupSRV

R=rsc, chris
CC=golang-dev
https://golang.org/cl/2420041

src/pkg/net/dnsclient.go

@@ -196,12 +196,16 @@ func isDomainName(s string) bool {
 	if len(s) == 0 {
 		return false
 	}
+	if len(s) > 255 {
+		return false
+	}
 	if s[len(s)-1] != '.' { // simplify checking loop: make name end in dot
 		s += "."
 	}
 
 	last := byte('.')
 	ok := false // ok once we've seen a letter
+	partlen := 0
 	for i := 0; i < len(s); i++ {
 		c := s[i]
 		switch {
@@ -209,18 +213,25 @@ func isDomainName(s string) bool {
 			return false
 		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_':
 			ok = true
+			partlen++
 		case '0' <= c && c <= '9':
 			// fine
+			partlen++
 		case c == '-':
 			// byte before dash cannot be dot
 			if last == '.' {
 				return false
 			}
+			partlen++
 		case c == '.':
 			// byte before dot cannot be dot, dash
 			if last == '.' || last == '-' {
 				return false
 			}
+			if partlen > 63 || partlen == 0 {
+				return false
+			}
+			partlen = 0
 		}
 		last = c
 	}
@@ -315,9 +326,14 @@ type SRV struct {
 	Weight   uint16
 }
 
-func LookupSRV(name string) (cname string, addrs []*SRV, err os.Error) {
+// LookupSRV tries to resolve an SRV query of the given service,
+// protocol, and domain name, as specified in RFC 2782. In most cases
+// the proto argument can be the same as the corresponding
+// Addr.Network().
+func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err os.Error) {
+	target := "_" + service + "._" + proto + "." + name
 	var records []dnsRR
-	cname, records, err = lookup(name, dnsTypeSRV)
+	cname, records, err = lookup(target, dnsTypeSRV)
 	if err != nil {
 		return
 	}

src/pkg/net/dnsname_test.go

+// 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.
+
+package net
+
+import (
+	"testing"
+)
+
+type testCase struct {
+	name   string
+	result bool
+}
+
+var tests = []testCase{
+	// RFC2181, section 11.
+	testCase{"_xmpp-server._tcp.google.com", true},
+	testCase{"_xmpp-server._tcp.google.com", true},
+	testCase{"foo.com", true},
+	testCase{"1foo.com", true},
+	testCase{"26.0.0.73.com", true},
+	testCase{"fo-o.com", true},
+	testCase{"fo1o.com", true},
+	testCase{"foo1.com", true},
+	testCase{"a.b..com", false},
+}
+
+func getTestCases(ch chan<- *testCase) {
+	defer close(ch)
+	var char59 = ""
+	var char63 = ""
+	var char64 = ""
+	for i := 0; i < 59; i++ {
+		char59 += "a"
+	}
+	char63 = char59 + "aaaa"
+	char64 = char63 + "a"
+
+	for _, tc := range tests {
+		ch <- &tc
+	}
+
+	ch <- &testCase{char63 + ".com", true}
+	ch <- &testCase{char64 + ".com", false}
+	// 255 char name is fine:
+	ch <- &testCase{char59 + "." + char63 + "." + char63 + "." +
+		char63 + ".com",
+		true}
+	// 256 char name is bad:
+	ch <- &testCase{char59 + "a." + char63 + "." + char63 + "." +
+		char63 + ".com",
+		false}
+}
+
+func TestDNSNames(t *testing.T) {
+	ch := make(chan *testCase)
+	go getTestCases(ch)
+	for tc := range ch {
+		if isDomainName(tc.name) != tc.result {
+			t.Errorf("isDomainName(%v) failed: Should be %v",
+				tc.name, tc.result)
+		}
+	}
+}

src/pkg/net/srv_test.go

+// 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.
+
+// TODO It would be nice to use a mock DNS server, to eliminate
+// external dependencies.
+
+package net
+
+import (
+	"testing"
+)
+
+func TestGoogleSRV(t *testing.T) {
+	_, addrs, err := LookupSRV("xmpp-server", "tcp", "google.com")
+	if err != nil {
+		t.Errorf("failed: %s", err)
+	}
+	if len(addrs) == 0 {
+		t.Errorf("no results")
+	}
+}