net: fix lookupHost on Plan 9

CL 532217 added the newDNSError function.

However, the implementation was not correct on
Plan 9, which lead TestLookupNoSuchHost to fail.

This change fixes lookupHost on Plan 9.

Fixes #67096.

Change-Id: I39271f7d588b19c1b1608f18a24d871460be09cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/582236
Reviewed-by: Joedian Reid <joedian@google.com>
Run-TryBot: David du Colombier <0intro@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>

2 files changed, 9 insertions, 14 deletions

diff --git a/src/net/lookup_plan9.go b/src/net/lookup_plan9.go
index 2532a0e967..588174b1fc 100644
--- a/src/net/lookup_plan9.go
+++ b/src/net/lookup_plan9.go
@@ -109,17 +109,11 @@ func queryDNS(ctx context.Context, addr string, typ string) (res []string, err e
 func handlePlan9DNSError(err error, name string) error {
 	if stringsHasSuffix(err.Error(), "dns: name does not exist") ||
 		stringsHasSuffix(err.Error(), "dns: resource does not exist; negrcode 0") ||
-		stringsHasSuffix(err.Error(), "dns: resource does not exist; negrcode") {
-		return &DNSError{
-			Err:        errNoSuchHost.Error(),
-			Name:       name,
-			IsNotFound: true,
-		}
-	}
-	return &DNSError{
-		Err:  err.Error(),
-		Name: name,
+		stringsHasSuffix(err.Error(), "dns: resource does not exist; negrcode") ||
+		stringsHasSuffix(err.Error(), "dns failure") {
+		err = errNoSuchHost
 	}
+	return newDNSError(err, name, "")
 }
 
 // toLower returns a lower-case version of in. Restricting us to
@@ -169,10 +163,7 @@ func (*Resolver) lookupHost(ctx context.Context, host string) (addrs []string, e
 	// host names in local network (e.g. from /lib/ndb/local)
 	lines, err := queryCS(ctx, "net", host, "1")
 	if err != nil {
-		if stringsHasSuffix(err.Error(), "dns failure") {
-			err = errNoSuchHost
-		}
-		return nil, newDNSError(err, host, "")
+		return nil, handlePlan9DNSError(err, host)
 	}
 loop:
 	for _, line := range lines {
diff --git a/src/net/lookup_test.go b/src/net/lookup_test.go
index bd58498fbc..97b37f2841 100644
--- a/src/net/lookup_test.go
+++ b/src/net/lookup_test.go
@@ -1634,6 +1634,10 @@ func TestLookupNoSuchHost(t *testing.T) {
 }
 
 func TestDNSErrorUnwrap(t *testing.T) {
+	if runtime.GOOS == "plan9" {
+		// The Plan 9 implementation of the resolver doesn't use the Dial function yet. See https://go.dev/cl/409234
+		t.Skip("skipping on plan9")
+	}
 	rDeadlineExcceeded := &Resolver{PreferGo: true, Dial: func(ctx context.Context, network, address string) (Conn, error) {
 		return nil, context.DeadlineExceeded
 	}}