client: add WithResolvers options for specifying client-local resolve…

…rs (#3320)

clientconn.go

@@ -243,7 +243,7 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 		// Only try to parse target when resolver builder is not already set.
 		cc.parsedTarget = parseTarget(cc.target)
 		grpclog.Infof("parsed scheme: %q", cc.parsedTarget.Scheme)
-		cc.dopts.resolverBuilder = resolver.Get(cc.parsedTarget.Scheme)
+		cc.dopts.resolverBuilder = cc.getResolver(cc.parsedTarget.Scheme)
 		if cc.dopts.resolverBuilder == nil {
 			// If resolver builder is still nil, the parsed target's scheme is
 			// not registered. Fallback to default resolver and set Endpoint to
@@ -253,7 +253,7 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 				Scheme:   resolver.GetDefaultScheme(),
 				Endpoint: target,
 			}
-			cc.dopts.resolverBuilder = resolver.Get(cc.parsedTarget.Scheme)
+			cc.dopts.resolverBuilder = cc.getResolver(cc.parsedTarget.Scheme)
 		}
 	} else {
 		cc.parsedTarget = resolver.Target{Endpoint: target}
@@ -1542,3 +1542,12 @@ func (c *channelzChannel) ChannelzMetric() *channelz.ChannelInternalMetric {
 // Deprecated: This error is never returned by grpc and should not be
 // referenced by users.
 var ErrClientConnTimeout = errors.New("grpc: timed out when dialing")
+
+func (cc *ClientConn) getResolver(scheme string) resolver.Builder {
+	for _, rb := range cc.dopts.resolvers {
+		if cc.parsedTarget.Scheme == rb.Scheme() {
+			return rb
+		}
+	}
+	return resolver.Get(cc.parsedTarget.Scheme)
+}

clientconn_state_transition_test.go

@@ -320,7 +320,7 @@ func (s) TestStateTransitions_TriesAllAddrsBeforeTransientFailure(t *testing.T)
 		{Addr: lis1.Addr().String()},
 		{Addr: lis2.Addr().String()},
 	}})
-	client, err := DialContext(ctx, "this-gets-overwritten", WithInsecure(), WithBalancerName(stateRecordingBalancerName), withResolverBuilder(rb))
+	client, err := DialContext(ctx, "whatever:///this-gets-overwritten", WithInsecure(), WithBalancerName(stateRecordingBalancerName), WithResolvers(rb))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -414,7 +414,7 @@ func (s) TestStateTransitions_MultipleAddrsEntersReady(t *testing.T) {
 		{Addr: lis1.Addr().String()},
 		{Addr: lis2.Addr().String()},
 	}})
-	client, err := DialContext(ctx, "this-gets-overwritten", WithInsecure(), WithBalancerName(stateRecordingBalancerName), withResolverBuilder(rb))
+	client, err := DialContext(ctx, "whatever:///this-gets-overwritten", WithInsecure(), WithBalancerName(stateRecordingBalancerName), WithResolvers(rb))
 	if err != nil {
 		t.Fatal(err)
 	}

clientconn_test.go

@@ -539,10 +539,10 @@ func (s) TestDial_OneBackoffPerRetryGroup(t *testing.T) {
 		{Addr: lis1.Addr().String()},
 		{Addr: lis2.Addr().String()},
 	}})
-	client, err := DialContext(ctx, "this-gets-overwritten",
+	client, err := DialContext(ctx, "whatever:///this-gets-overwritten",
 		WithInsecure(),
 		WithBalancerName(stateRecordingBalancerName),
-		withResolverBuilder(rb),
+		WithResolvers(rb),
 		withMinConnectDeadline(getMinConnectTimeout))
 	if err != nil {
 		t.Fatal(err)
@@ -1085,9 +1085,9 @@ func (s) TestUpdateAddresses_RetryFromFirstAddr(t *testing.T) {
 	rb := manual.NewBuilderWithScheme("whatever")
 	rb.InitialState(resolver.State{Addresses: addrsList})
 
-	client, err := Dial("this-gets-overwritten",
+	client, err := Dial("whatever:///this-gets-overwritten",
 		WithInsecure(),
-		withResolverBuilder(rb),
+		WithResolvers(rb),
 		withBackoff(noBackoff{}),
 		WithBalancerName(stateRecordingBalancerName),
 		withMinConnectDeadline(func() time.Duration { return time.Hour }))

dialoptions.go

@@ -73,6 +73,7 @@ type dialOptions struct {
 	// resolver.ResolveNow(). The user will have no need to configure this, but
 	// we need to be able to configure this in tests.
 	resolveNowBackoff func(int) time.Duration
+	resolvers         []resolver.Builder
 }
 
 // DialOption configures how we set up the connection.
@@ -589,3 +590,15 @@ func withResolveNowBackoff(f func(int) time.Duration) DialOption {
 		o.resolveNowBackoff = f
 	})
 }
+
+// WithResolvers allows a list of resolver implementations to be registered
+// locally with the ClientConn without needing to be globally registered via
+// resolver.Register.  They will be matched against the scheme used for the
+// current Dial only, and will take precedence over the global registry.
+//
+// This API is EXPERIMENTAL.
+func WithResolvers(rs ...resolver.Builder) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.resolvers = rs
+	})
+}