net: case insensitivity of DNS labels in built-in stub resolver

This change adds support for case insensitivity of DNS labels to
built-in DNS stub resolver as described in RFC 4343.

Fixes #9215.

Change-Id: Ia752fe71866a3bfa3ea08371985b799d419ddea3
Reviewed-on: https://go-review.googlesource.com/3685
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/net/dnsclient.go b/src/net/dnsclient.go
index 56e2a9496512cde18a990c2ab0412996ac8c1f4a..099ea45ebaf2c169cf074b656b9ae0251bf97791 100644 (file)
--- a/src/net/dnsclient.go
+++ b/src/net/dnsclient.go
@@ -94,7 +94,7 @@ Cname:
                                continue
                        }
                        h := rr.Header()
-                       if h.Class == dnsClassINET && h.Name == name {
+                       if h.Class == dnsClassINET && equalASCIILabel(h.Name, name) {
                                switch h.Rrtype {
                                case qtype:
                                        addrs = append(addrs, rr)
@@ -114,6 +114,26 @@ Cname:
        return "", nil, &DNSError{Err: "too many redirects", Name: name, Server: server}
 }
 
+func equalASCIILabel(x, y string) bool {
+       if len(x) != len(y) {
+               return false
+       }
+       for i := 0; i < len(x); i++ {
+               a := x[i]
+               b := y[i]
+               if 'A' <= a && a <= 'Z' {
+                       a += 0x20
+               }
+               if 'A' <= b && b <= 'Z' {
+                       b += 0x20
+               }
+               if a != b {
+                       return false
+               }
+       }
+       return true
+}
+
 func isDomainName(s string) bool {
        // See RFC 1035, RFC 3696.
        if len(s) == 0 {

diff --git a/src/net/dnsmsg_test.go b/src/net/dnsmsg_test.go
index c39dbdb049d63058f8e2df942de151a366304590..159a03e5252a6e301991148cafea7a4067ff35fc 100644 (file)
--- a/src/net/dnsmsg_test.go
+++ b/src/net/dnsmsg_test.go
@@ -18,7 +18,7 @@ func TestDNSParseSRVReply(t *testing.T) {
        msg := new(dnsMsg)
        ok := msg.Unpack(data)
        if !ok {
-               t.Fatalf("unpacking packet failed")
+               t.Fatal("unpacking packet failed")
        }
        msg.String() // exercise this code path
        if g, e := len(msg.answer), 5; g != e {
@@ -32,13 +32,19 @@ func TestDNSParseSRVReply(t *testing.T) {
                        t.Errorf("answer[%d] = %T; want *dnsRR_SRV", idx, rr)
                }
        }
-       _, addrs, err := answer("_xmpp-server._tcp.google.com.", "foo:53", msg, uint16(dnsTypeSRV))
-       if err != nil {
-               t.Fatalf("answer: %v", err)
-       }
-       if g, e := len(addrs), 5; g != e {
-               t.Errorf("len(addrs) = %d; want %d", g, e)
-               t.Logf("addrs = %#v", addrs)
+       for _, name := range [...]string{
+               "_xmpp-server._tcp.google.com.",
+               "_XMPP-Server._TCP.Google.COM.",
+               "_XMPP-SERVER._TCP.GOOGLE.COM.",
+       } {
+               _, addrs, err := answer(name, "foo:53", msg, uint16(dnsTypeSRV))
+               if err != nil {
+                       t.Error(err)
+               }
+               if g, e := len(addrs), 5; g != e {
+                       t.Errorf("len(addrs) = %d; want %d", g, e)
+                       t.Logf("addrs = %#v", addrs)
+               }
        }
        // repack and unpack.
        data2, ok := msg.Pack()
@@ -46,9 +52,9 @@ func TestDNSParseSRVReply(t *testing.T) {
        msg2.Unpack(data2)
        switch {
        case !ok:
-               t.Errorf("failed to repack message")
+               t.Error("failed to repack message")
        case !reflect.DeepEqual(msg, msg2):
-               t.Errorf("repacked message differs from original")
+               t.Error("repacked message differs from original")
        }
 }