net: fix LookupCNAME on Plan 9

Looking up a nonexistent CNAME record on an existing
domain on Plan 9 can return either a "dns failure"
error or a "resource does not exist" error.

Fixes #21335.

Change-Id: Iead8ed4fe3167db06adb4ab7797c52c7efc3ff89
Reviewed-on: https://go-review.googlesource.com/53670
Run-TryBot: David du Colombier <0intro@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Avelino <t@avelino.xxx>

diff --git a/src/net/lookup_plan9.go b/src/net/lookup_plan9.go
index f81e220fc8ce65ff4b262734c96f8cdfd4f3db43..1037b81a3be96f9c0396142a1f1c0774c7448bd1 100644 (file)
--- a/src/net/lookup_plan9.go
+++ b/src/net/lookup_plan9.go
@@ -198,7 +198,7 @@ func (*Resolver) lookupPort(ctx context.Context, network, service string) (port
 func (*Resolver) lookupCNAME(ctx context.Context, name string) (cname string, err error) {
        lines, err := queryDNS(ctx, name, "cname")
        if err != nil {
-               if stringsHasSuffix(err.Error(), "dns failure") {
+               if stringsHasSuffix(err.Error(), "dns failure") || stringsHasSuffix(err.Error(), "resource does not exist; negrcode 0") {
                        cname = name + "."
                        err = nil
                }