add a test for resolver case sensitivity

resolver_test.go

@@ -0,0 +1,99 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"testing"
+
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/resolver"
+)
+
+type wrapResolverBuilder struct {
+	resolver.Builder
+	scheme string
+}
+
+func (w *wrapResolverBuilder) Scheme() string {
+	return w.scheme
+}
+
+func init() {
+	resolver.Register(&wrapResolverBuilder{Builder: resolver.Get("dns"), scheme: "caseTEST"})
+	resolver.Register(&wrapResolverBuilder{Builder: resolver.Get("dns"), scheme: "caseTest2"})
+	resolver.Register(&wrapResolverBuilder{Builder: resolver.Get("passthrough"), scheme: "caSetest2"})
+}
+
+func (s) TestResolverCaseSensitivity(t *testing.T) {
+	// This should find the "caseTEST" resolver, which is "dns"
+	target := "casetest:///localhost:1234"
+	cc, err := Dial(target, WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		t.Fatalf("Unexpected Dial(%q) error: %v", target, err)
+	}
+	cc.Close()
+
+	// This should find the "caSetest2" resolver instead of the "caseTest2"
+	// resolver, because it was registered later.  "caSetest2" is "passthrough"
+	// and the overwritten one is "dns".  With "passthrough" the dialer should
+	// see the target's address directly, but "dns" would be converted into a
+	// loopback IP (v4 or v6) address.
+	target = "caseTest2:///localhost:1234"
+	addrCh := make(chan string)
+	customDialer := func(ctx context.Context, addr string) (net.Conn, error) {
+		select {
+		case addrCh <- addr:
+		default:
+		}
+		return nil, fmt.Errorf("not dialing with custom dialer")
+	}
+
+	cc, err = Dial(target, WithContextDialer(customDialer), WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		t.Fatalf("Unexpected Dial(%q) error: %v", target, err)
+	}
+	if got, want := <-addrCh, "localhost:1234"; got != want {
+		cc.Close()
+		t.Fatalf("Dialer got address %q; wanted %q", got, want)
+	}
+	cc.Close()
+
+	// Clear addrCh for future use.
+	select {
+	case <-addrCh:
+	default:
+	}
+
+	res := &wrapResolverBuilder{Builder: resolver.Get("dns"), scheme: "CaSetest2"}
+	// This should find the injected resolver instead of the "caSetest2"
+	// globally-registered resolver.  Since it is "dns" instead of passthrough,
+	// we can validate by checking for an address that has been resolved
+	// (i.e. is not "localhost:port").
+	cc, err = Dial(target, WithContextDialer(customDialer), WithResolvers(res), WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		t.Fatalf("Unexpected Dial(%q) error: %v", target, err)
+	}
+	defer cc.Close()
+	if got, wantNot := <-addrCh, "localhost:1234"; got == wantNot {
+		t.Fatalf("Dialer got address %q; wanted something other than %q", got, wantNot)
+	}
+}