Register and use default balancers and resolvers (#1551)

balancer/balancer.go

@@ -33,8 +33,6 @@ import (
 var (
 	// m is a map from name to balancer builder.
 	m = make(map[string]Builder)
-	// defaultBuilder is the default balancer to use.
-	defaultBuilder Builder // TODO(bar) install pickfirst as default.
 )
 
 // Register registers the balancer builder to the balancer map.
@@ -44,13 +42,12 @@ func Register(b Builder) {
 }
 
 // Get returns the resolver builder registered with the given name.
-// If no builder is register with the name, the default pickfirst will
+// If no builder is register with the name, nil will be returned.
-// be used.
 func Get(name string) Builder {
 	if b, ok := m[name]; ok {
 		return b
 	}
-	return defaultBuilder
+	return nil
 }
 
 // SubConn represents a gRPC sub connection.

balancer/roundrobin/roundrobin_test.go

@@ -16,7 +16,7 @@
  *
  */
 
-package roundrobin
+package roundrobin_test
 
 import (
 	"fmt"
@@ -27,6 +27,7 @@ import (
 
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/codes"
 	_ "google.golang.org/grpc/grpclog/glogger"
 	"google.golang.org/grpc/peer"
@@ -36,6 +37,8 @@ import (
 	"google.golang.org/grpc/test/leakcheck"
 )
 
+var rr = balancer.Get("roundrobin")
+
 type testServer struct {
 	testpb.TestServiceServer
 }
@@ -99,7 +102,7 @@ func TestOneBackend(t *testing.T) {
 	}
 	defer test.cleanup()
 
-	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(newBuilder()))
+	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(rr))
 	if err != nil {
 		t.Fatalf("failed to dial: %v", err)
 	}
@@ -131,7 +134,7 @@ func TestBackendsRoundRobin(t *testing.T) {
 	}
 	defer test.cleanup()
 
-	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(newBuilder()))
+	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(rr))
 	if err != nil {
 		t.Fatalf("failed to dial: %v", err)
 	}
@@ -190,7 +193,7 @@ func TestAddressesRemoved(t *testing.T) {
 	}
 	defer test.cleanup()
 
-	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(newBuilder()))
+	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(rr))
 	if err != nil {
 		t.Fatalf("failed to dial: %v", err)
 	}
@@ -232,7 +235,7 @@ func TestCloseWithPendingRPC(t *testing.T) {
 	}
 	defer test.cleanup()
 
-	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(newBuilder()))
+	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(rr))
 	if err != nil {
 		t.Fatalf("failed to dial: %v", err)
 	}
@@ -266,7 +269,7 @@ func TestNewAddressWhileBlocking(t *testing.T) {
 	}
 	defer test.cleanup()
 
-	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(newBuilder()))
+	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(rr))
 	if err != nil {
 		t.Fatalf("failed to dial: %v", err)
 	}
@@ -315,7 +318,7 @@ func TestOneServerDown(t *testing.T) {
 	}
 	defer test.cleanup()
 
-	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(newBuilder()))
+	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(rr))
 	if err != nil {
 		t.Fatalf("failed to dial: %v", err)
 	}
@@ -408,7 +411,7 @@ func TestAllServersDown(t *testing.T) {
 	}
 	defer test.cleanup()
 
-	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(newBuilder()))
+	cc, err := grpc.Dial(r.Scheme()+":///test.server", grpc.WithInsecure(), grpc.WithBalancerBuilder(rr))
 	if err != nil {
 		t.Fatalf("failed to dial: %v", err)
 	}

balancer_conn_wrappers.go

@@ -73,7 +73,7 @@ func (b *scStateUpdateBuffer) load() {
 	}
 }
 
-// get returns the channel that receives a recvMsg in the buffer.
+// get returns the channel that the scStateUpdate will be sent to.
 //
 // Upon receiving, the caller should call load to send another
 // scStateChangeTuple onto the channel if there is any.
@@ -96,6 +96,8 @@ type ccBalancerWrapper struct {
 	stateChangeQueue *scStateUpdateBuffer
 	resolverUpdateCh chan *resolverUpdate
 	done             chan struct{}
+
+	subConns map[*acBalancerWrapper]struct{}
 }
 
 func newCCBalancerWrapper(cc *ClientConn, b balancer.Builder, bopts balancer.BuildOptions) *ccBalancerWrapper {
@@ -104,6 +106,7 @@ func newCCBalancerWrapper(cc *ClientConn, b balancer.Builder, bopts balancer.Bui
 		stateChangeQueue: newSCStateUpdateBuffer(),
 		resolverUpdateCh: make(chan *resolverUpdate, 1),
 		done:             make(chan struct{}),
+		subConns:         make(map[*acBalancerWrapper]struct{}),
 	}
 	go ccb.watcher()
 	ccb.balancer = b.Build(ccb, bopts)
@@ -117,8 +120,20 @@ func (ccb *ccBalancerWrapper) watcher() {
 		select {
 		case t := <-ccb.stateChangeQueue.get():
 			ccb.stateChangeQueue.load()
+			select {
+			case <-ccb.done:
+				ccb.balancer.Close()
+				return
+			default:
+			}
 			ccb.balancer.HandleSubConnStateChange(t.sc, t.state)
 		case t := <-ccb.resolverUpdateCh:
+			select {
+			case <-ccb.done:
+				ccb.balancer.Close()
+				return
+			default:
+			}
 			ccb.balancer.HandleResolvedAddrs(t.addrs, t.err)
 		case <-ccb.done:
 		}
@@ -126,6 +141,9 @@ func (ccb *ccBalancerWrapper) watcher() {
 		select {
 		case <-ccb.done:
 			ccb.balancer.Close()
+			for acbw := range ccb.subConns {
+				ccb.cc.removeAddrConn(acbw.getAddrConn(), errConnDrain)
+			}
 			return
 		default:
 		}
@@ -171,7 +189,10 @@ func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer
 		return nil, err
 	}
 	acbw := &acBalancerWrapper{ac: ac}
+	acbw.ac.mu.Lock()
 	ac.acbw = acbw
+	acbw.ac.mu.Unlock()
+	ccb.subConns[acbw] = struct{}{}
 	return acbw, nil
 }
 
@@ -181,6 +202,7 @@ func (ccb *ccBalancerWrapper) RemoveSubConn(sc balancer.SubConn) {
 	if !ok {
 		return
 	}
+	delete(ccb.subConns, acbw)
 	ccb.cc.removeAddrConn(acbw.getAddrConn(), errConnDrain)
 }
 

balancer_switching_test.go

@@ -0,0 +1,133 @@
+/*
+ *
+ * Copyright 2017 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 (
+	"fmt"
+	"math"
+	"testing"
+	"time"
+
+	"golang.org/x/net/context"
+	_ "google.golang.org/grpc/grpclog/glogger"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/resolver/manual"
+	"google.golang.org/grpc/test/leakcheck"
+)
+
+func checkPickFirst(cc *ClientConn, servers []*server) error {
+	var (
+		req   = "port"
+		reply string
+		err   error
+	)
+	connected := false
+	for i := 0; i < 1000; i++ {
+		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); ErrorDesc(err) == servers[0].port {
+			if connected {
+				// connected is set to false if peer is not server[0]. So if
+				// connected is true here, this is the second time we saw
+				// server[0] in a row. Break because pickfirst is in effect.
+				break
+			}
+			connected = true
+		} else {
+			connected = false
+		}
+		time.Sleep(time.Millisecond)
+	}
+	if !connected {
+		return fmt.Errorf("pickfirst is not in effect after 1 second, EmptyCall() = _, %v, want _, %v", err, servers[0].port)
+	}
+	// The following RPCs should all succeed with the first server.
+	for i := 0; i < 3; i++ {
+		err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+		if ErrorDesc(err) != servers[0].port {
+			return fmt.Errorf("Index %d: want peer %v, got peer %v", i, servers[0].port, err)
+		}
+	}
+	return nil
+}
+
+func checkRoundRobin(cc *ClientConn, servers []*server) error {
+	var (
+		req   = "port"
+		reply string
+		err   error
+	)
+
+	// Make sure connections to all servers are up.
+	for i := 0; i < 2; i++ {
+		// Do this check twice, otherwise the first RPC's transport may still be
+		// picked by the closing pickfirst balancer, and the test becomes flaky.
+		for _, s := range servers {
+			var up bool
+			for i := 0; i < 1000; i++ {
+				if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); ErrorDesc(err) == s.port {
+					up = true
+					break
+				}
+				time.Sleep(time.Millisecond)
+			}
+			if !up {
+				return fmt.Errorf("server %v is not up within 1 second", s.port)
+			}
+		}
+	}
+
+	serverCount := len(servers)
+	for i := 0; i < 3*serverCount; i++ {
+		err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+		if ErrorDesc(err) != servers[i%serverCount].port {
+			return fmt.Errorf("Index %d: want peer %v, got peer %v", i, servers[i%serverCount].port, err)
+		}
+	}
+	return nil
+}
+
+func TestSwitchBalancer(t *testing.T) {
+	defer leakcheck.Check(t)
+	r, rcleanup := manual.GenerateAndRegisterManualResolver()
+	defer rcleanup()
+
+	numServers := 2
+	servers, _, scleanup := startServers(t, numServers, math.MaxInt32)
+	defer scleanup()
+
+	cc, err := Dial(r.Scheme()+":///test.server", WithInsecure(), WithCodec(testCodec{}))
+	if err != nil {
+		t.Fatalf("failed to dial: %v", err)
+	}
+	defer cc.Close()
+	r.NewAddress([]resolver.Address{{Addr: servers[0].addr}, {Addr: servers[1].addr}})
+	// The default balancer is pickfirst.
+	if err := checkPickFirst(cc, servers); err != nil {
+		t.Fatalf("check pickfirst returned non-nil error: %v", err)
+	}
+	// Switch to roundrobin.
+	cc.switchBalancer("roundrobin")
+	if err := checkRoundRobin(cc, servers); err != nil {
+		t.Fatalf("check roundrobin returned non-nil error: %v", err)
+	}
+	// Switch to pickfirst.
+	cc.switchBalancer("pickfirst")
+	if err := checkPickFirst(cc, servers); err != nil {
+		t.Fatalf("check pickfirst returned non-nil error: %v", err)
+	}
+}

balancer_test.go

@@ -31,6 +31,10 @@ import (
 	_ "google.golang.org/grpc/grpclog/glogger"
 	"google.golang.org/grpc/naming"
 	"google.golang.org/grpc/test/leakcheck"
+
+	// V1 balancer tests use passthrough resolver instead of dns.
+	// TODO(bar) remove this when removing v1 balaner entirely.
+	_ "google.golang.org/grpc/resolver/passthrough"
 )
 
 type testWatcher struct {
@@ -117,7 +121,7 @@ func TestNameDiscovery(t *testing.T) {
 	numServers := 2
 	servers, r, cleanup := startServers(t, numServers, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -151,7 +155,7 @@ func TestEmptyAddrs(t *testing.T) {
 	defer leakcheck.Check(t)
 	servers, r, cleanup := startServers(t, 1, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -185,7 +189,7 @@ func TestRoundRobin(t *testing.T) {
 	numServers := 3
 	servers, r, cleanup := startServers(t, numServers, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -230,7 +234,7 @@ func TestCloseWithPendingRPC(t *testing.T) {
 	defer leakcheck.Check(t)
 	servers, r, cleanup := startServers(t, 1, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -282,7 +286,7 @@ func TestGetOnWaitChannel(t *testing.T) {
 	defer leakcheck.Check(t)
 	servers, r, cleanup := startServers(t, 1, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -328,7 +332,7 @@ func TestOneServerDown(t *testing.T) {
 	numServers := 2
 	servers, r, cleanup := startServers(t, numServers, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -381,7 +385,7 @@ func TestOneAddressRemoval(t *testing.T) {
 	numServers := 2
 	servers, r, cleanup := startServers(t, numServers, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -439,7 +443,7 @@ func TestOneAddressRemoval(t *testing.T) {
 func checkServerUp(t *testing.T, currentServer *server) {
 	req := "port"
 	port := currentServer.port
-	cc, err := Dial("localhost:"+port, WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///localhost:"+port, WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -457,7 +461,7 @@ func TestPickFirstEmptyAddrs(t *testing.T) {
 	defer leakcheck.Check(t)
 	servers, r, cleanup := startServers(t, 1, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -489,7 +493,7 @@ func TestPickFirstCloseWithPendingRPC(t *testing.T) {
 	defer leakcheck.Check(t)
 	servers, r, cleanup := startServers(t, 1, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -543,7 +547,7 @@ func TestPickFirstOrderAllServerUp(t *testing.T) {
 	numServers := 3
 	servers, r, cleanup := startServers(t, numServers, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -656,7 +660,7 @@ func TestPickFirstOrderOneServerDown(t *testing.T) {
 	numServers := 3
 	servers, r, cleanup := startServers(t, numServers, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}
@@ -747,7 +751,7 @@ func TestPickFirstOneAddressRemoval(t *testing.T) {
 	numServers := 2
 	servers, r, cleanup := startServers(t, numServers, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("localhost:"+servers[0].port, WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
+	cc, err := Dial("passthrough:///localhost:"+servers[0].port, WithBalancer(pickFirstBalancerV1(r)), WithBlock(), WithInsecure(), WithCodec(testCodec{}))
 	if err != nil {
 		t.Fatalf("Failed to create ClientConn: %v", err)
 	}

balancer_v1_wrapper.go

@@ -19,6 +19,7 @@
 package grpc
 
 import (
+	"strings"
 	"sync"
 
 	"golang.org/x/net/context"
@@ -34,7 +35,13 @@ type balancerWrapperBuilder struct {
 }
 
 func (bwb *balancerWrapperBuilder) Build(cc balancer.ClientConn, opts balancer.BuildOptions) balancer.Balancer {
-	bwb.b.Start(cc.Target(), BalancerConfig{
+	targetAddr := cc.Target()
+	targetSplitted := strings.Split(targetAddr, ":///")
+	if len(targetSplitted) >= 2 {
+		targetAddr = targetSplitted[1]
+	}
+
+	bwb.b.Start(targetAddr, BalancerConfig{
 		DialCreds: opts.DialCreds,
 		Dialer:    opts.Dialer,
 	})
@@ -43,6 +50,7 @@ func (bwb *balancerWrapperBuilder) Build(cc balancer.ClientConn, opts balancer.B
 		balancer:   bwb.b,
 		pickfirst:  pickfirst,
 		cc:         cc,
+		targetAddr: targetAddr,
 		startCh:    make(chan struct{}),
 		conns:      make(map[resolver.Address]balancer.SubConn),
 		connSt:     make(map[balancer.SubConn]*scState),
@@ -69,6 +77,7 @@ type balancerWrapper struct {
 	pickfirst bool
 
 	cc         balancer.ClientConn
+	targetAddr string // Target without the scheme.
 
 	// To aggregate the connectivity state.
 	csEvltr *connectivityStateEvaluator
@@ -93,7 +102,7 @@ func (bw *balancerWrapper) lbWatcher() {
 	if notifyCh == nil {
 		// There's no resolver in the balancer. Connect directly.
 		a := resolver.Address{
-			Addr: bw.cc.Target(),
+			Addr: bw.targetAddr,
 			Type: resolver.Backend,
 		}
 		sc, err := bw.cc.NewSubConn([]resolver.Address{a}, balancer.NewSubConnOptions{})
@@ -103,7 +112,7 @@ func (bw *balancerWrapper) lbWatcher() {
 			bw.mu.Lock()
 			bw.conns[a] = sc
 			bw.connSt[sc] = &scState{
-				addr: Address{Addr: bw.cc.Target()},
+				addr: Address{Addr: bw.targetAddr},
 				s:    connectivity.Idle,
 			}
 			bw.mu.Unlock()

clientconn.go

@@ -31,11 +31,13 @@ import (
 	"golang.org/x/net/context"
 	"golang.org/x/net/trace"
 	"google.golang.org/grpc/balancer"
+	_ "google.golang.org/grpc/balancer/roundrobin" // To register roundrobin.
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/grpclog"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/resolver"
+	_ "google.golang.org/grpc/resolver/dns" // To register dns resolver.
 	"google.golang.org/grpc/stats"
 	"google.golang.org/grpc/transport"
 )
@@ -435,42 +437,6 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 		cc.authority = target
 	}
 
-	if cc.dopts.balancerBuilder != nil {
-		var credsClone credentials.TransportCredentials
-		if creds != nil {
-			credsClone = creds.Clone()
-		}
-		buildOpts := balancer.BuildOptions{
-			DialCreds: credsClone,
-			Dialer:    cc.dopts.copts.Dialer,
-		}
-		// Build should not take long time. So it's ok to not have a goroutine for it.
-		// TODO(bar) init balancer after first resolver result to support service config balancer.
-		cc.balancerWrapper = newCCBalancerWrapper(cc, cc.dopts.balancerBuilder, buildOpts)
-	} else {
-		waitC := make(chan error, 1)
-		go func() {
-			defer close(waitC)
-			// No balancer, or no resolver within the balancer.  Connect directly.
-			ac, err := cc.newAddrConn([]resolver.Address{{Addr: target}})
-			if err != nil {
-				waitC <- err
-				return
-			}
-			if err := ac.connect(cc.dopts.block); err != nil {
-				waitC <- err
-				return
-			}
-		}()
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		case err := <-waitC:
-			if err != nil {
-				return nil, err
-			}
-		}
-	}
 	if cc.dopts.scChan != nil && !scSet {
 		// Blocking wait for the initial service config.
 		select {
@@ -486,20 +452,27 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 		go cc.scWatcher()
 	}
 
+	var credsClone credentials.TransportCredentials
+	if creds := cc.dopts.copts.TransportCredentials; creds != nil {
+		credsClone = creds.Clone()
+	}
+	cc.balancerBuildOpts = balancer.BuildOptions{
+		DialCreds: credsClone,
+		Dialer:    cc.dopts.copts.Dialer,
+	}
+
+	if cc.dopts.balancerBuilder != nil {
+		cc.customBalancer = true
+		// Build should not take long time. So it's ok to not have a goroutine for it.
+		cc.balancerWrapper = newCCBalancerWrapper(cc, cc.dopts.balancerBuilder, cc.balancerBuildOpts)
+	}
+
 	// Build the resolver.
 	cc.resolverWrapper, err = newCCResolverWrapper(cc)
 	if err != nil {
 		return nil, fmt.Errorf("failed to build resolver: %v", err)
 	}
 
-	if cc.balancerWrapper != nil && cc.resolverWrapper == nil {
-		// TODO(bar) there should always be a resolver (DNS as the default).
-		// Unblock balancer initialization with a fake resolver update if there's no resolver.
-		// The balancer wrapper will not read the addresses, so an empty list works.
-		// TODO(bar) remove this after the real resolver is started.
-		cc.balancerWrapper.handleResolvedAddrs([]resolver.Address{}, nil)
-	}
-
 	// A blocking dial blocks until the clientConn is ready.
 	if cc.dopts.block {
 		for {
@@ -570,9 +543,9 @@ type ClientConn struct {
 	dopts     dialOptions
 	csMgr     *connectivityStateManager
 
-	balancerWrapper *ccBalancerWrapper
+	customBalancer    bool // If this is true, switching balancer will be disabled.
+	balancerBuildOpts balancer.BuildOptions
 	resolverWrapper   *ccResolverWrapper
-
 	blockingpicker    *pickerWrapper
 
 	mu    sync.RWMutex
@@ -580,6 +553,9 @@ type ClientConn struct {
 	conns map[*addrConn]struct{}
 	// Keepalive parameter can be updated if a GoAway is received.
 	mkp             keepalive.ClientParameters
+	curBalancerName string
+	curAddresses    []resolver.Address
+	balancerWrapper *ccBalancerWrapper
 }
 
 // WaitForStateChange waits until the connectivity.State of ClientConn changes from sourceState or
@@ -622,6 +598,71 @@ func (cc *ClientConn) scWatcher() {
 	}
 }
 
+func (cc *ClientConn) handleResolvedAddrs(addrs []resolver.Address, err error) {
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
+	if cc.conns == nil {
+		return
+	}
+
+	// TODO(bar switching) when grpclb is submitted, check address type and start grpclb.
+	if !cc.customBalancer && cc.balancerWrapper == nil {
+		// No customBalancer was specified by DialOption, and this is the first
+		// time handling resolved addresses, create a pickfirst balancer.
+		builder := newPickfirstBuilder()
+		cc.curBalancerName = builder.Name()
+		cc.balancerWrapper = newCCBalancerWrapper(cc, builder, cc.balancerBuildOpts)
+	}
+
+	// TODO(bar switching) compare addresses, if there's no update, don't notify balancer.
+	cc.curAddresses = addrs
+	cc.balancerWrapper.handleResolvedAddrs(addrs, nil)
+}
+
+// switchBalancer starts the switching from current balancer to the balancer with name.
+func (cc *ClientConn) switchBalancer(name string) {
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
+	if cc.conns == nil {
+		return
+	}
+	grpclog.Infof("ClientConn switching balancer to %q", name)
+
+	if cc.customBalancer {
+		grpclog.Infoln("ignoring service config balancer configuration: WithBalancer DialOption used instead")
+		return
+	}
+
+	if cc.curBalancerName == name {
+		return
+	}
+
+	// TODO(bar switching) change this to two steps: drain and close.
+	// Keep track of sc in wrapper.
+	cc.balancerWrapper.close()
+
+	builder := balancer.Get(name)
+	if builder == nil {
+		grpclog.Infof("failed to get balancer builder for: %v (this should never happen...)", name)
+		builder = newPickfirstBuilder()
+	}
+	cc.curBalancerName = builder.Name()
+	cc.balancerWrapper = newCCBalancerWrapper(cc, builder, cc.balancerBuildOpts)
+	cc.balancerWrapper.handleResolvedAddrs(cc.curAddresses, nil)
+}
+
+func (cc *ClientConn) handleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return
+	}
+	// TODO(bar switching) send updates to all balancer wrappers when balancer
+	// gracefully switching is supported.
+	cc.balancerWrapper.handleSubConnStateChange(sc, s)
+	cc.mu.Unlock()
+}
+
 // newAddrConn creates an addrConn for addrs and adds it to cc.conns.
 func (cc *ClientConn) newAddrConn(addrs []resolver.Address) (*addrConn, error) {
 	ac := &addrConn{
@@ -670,11 +711,7 @@ func (ac *addrConn) connect(block bool) error {
 		return nil
 	}
 	ac.state = connectivity.Connecting
-	if ac.cc.balancerWrapper != nil {
+	ac.cc.handleSubConnStateChange(ac.acbw, ac.state)
-		ac.cc.balancerWrapper.handleSubConnStateChange(ac.acbw, ac.state)
-	} else {
-		ac.cc.csMgr.updateState(ac.state)
-	}
 	ac.mu.Unlock()
 
 	if block {
@@ -756,31 +793,6 @@ func (cc *ClientConn) GetMethodConfig(method string) MethodConfig {
 }
 
 func (cc *ClientConn) getTransport(ctx context.Context, failfast bool) (transport.ClientTransport, func(balancer.DoneInfo), error) {
-	if cc.balancerWrapper == nil {
-		// If balancer is nil, there should be only one addrConn available.
-		cc.mu.RLock()
-		if cc.conns == nil {
-			cc.mu.RUnlock()
-			// TODO this function returns toRPCErr and non-toRPCErr. Clean up
-			// the errors in ClientConn.
-			return nil, nil, toRPCErr(ErrClientConnClosing)
-		}
-		var ac *addrConn
-		for ac = range cc.conns {
-			// Break after the first iteration to get the first addrConn.
-			break
-		}
-		cc.mu.RUnlock()
-		if ac == nil {
-			return nil, nil, errConnClosing
-		}
-		t, err := ac.wait(ctx, false /*hasBalancer*/, failfast)
-		if err != nil {
-			return nil, nil, err
-		}
-		return t, nil, nil
-	}
-
 	t, done, err := cc.blockingpicker.pick(ctx, failfast, balancer.PickOptions{})
 	if err != nil {
 		return nil, nil, toRPCErr(err)
@@ -800,13 +812,18 @@ func (cc *ClientConn) Close() error {
 	conns := cc.conns
 	cc.conns = nil
 	cc.csMgr.updateState(connectivity.Shutdown)
+
+	rWrapper := cc.resolverWrapper
+	cc.resolverWrapper = nil
+	bWrapper := cc.balancerWrapper
+	cc.balancerWrapper = nil
 	cc.mu.Unlock()
 	cc.blockingpicker.close()
-	if cc.resolverWrapper != nil {
+	if rWrapper != nil {
-		cc.resolverWrapper.close()
+		rWrapper.close()
 	}
-	if cc.balancerWrapper != nil {
+	if bWrapper != nil {
-		cc.balancerWrapper.close()
+		bWrapper.close()
 	}
 	for ac := range conns {
 		ac.tearDown(ErrClientConnClosing)
@@ -877,11 +894,7 @@ func (ac *addrConn) resetTransport() error {
 		return errConnClosing
 	}
 	ac.state = connectivity.TransientFailure
-	if ac.cc.balancerWrapper != nil {
+	ac.cc.handleSubConnStateChange(ac.acbw, ac.state)
-		ac.cc.balancerWrapper.handleSubConnStateChange(ac.acbw, ac.state)
-	} else {
-		ac.cc.csMgr.updateState(ac.state)
-	}
 	if ac.ready != nil {
 		close(ac.ready)
 		ac.ready = nil
@@ -906,12 +919,7 @@ func (ac *addrConn) resetTransport() error {
 		}
 		ac.printf("connecting")
 		ac.state = connectivity.Connecting
-		// TODO(bar) remove condition once we always have a balancer.
+		ac.cc.handleSubConnStateChange(ac.acbw, ac.state)
-		if ac.cc.balancerWrapper != nil {
-			ac.cc.balancerWrapper.handleSubConnStateChange(ac.acbw, ac.state)
-		} else {
-			ac.cc.csMgr.updateState(ac.state)
-		}
 		// copy ac.addrs in case of race
 		addrsIter := make([]resolver.Address, len(ac.addrs))
 		copy(addrsIter, ac.addrs)
@@ -953,11 +961,7 @@ func (ac *addrConn) resetTransport() error {
 				return errConnClosing
 			}
 			ac.state = connectivity.Ready
-			if ac.cc.balancerWrapper != nil {
+			ac.cc.handleSubConnStateChange(ac.acbw, ac.state)
-				ac.cc.balancerWrapper.handleSubConnStateChange(ac.acbw, ac.state)
-			} else {
-				ac.cc.csMgr.updateState(ac.state)
-			}
 			t := ac.transport
 			ac.transport = newTransport
 			if t != nil {
@@ -973,11 +977,7 @@ func (ac *addrConn) resetTransport() error {
 		}
 		ac.mu.Lock()
 		ac.state = connectivity.TransientFailure
-		if ac.cc.balancerWrapper != nil {
+		ac.cc.handleSubConnStateChange(ac.acbw, ac.state)
-			ac.cc.balancerWrapper.handleSubConnStateChange(ac.acbw, ac.state)
-		} else {
-			ac.cc.csMgr.updateState(ac.state)
-		}
 		if ac.ready != nil {
 			close(ac.ready)
 			ac.ready = nil
@@ -1111,11 +1111,7 @@ func (ac *addrConn) tearDown(err error) {
 	}
 	ac.state = connectivity.Shutdown
 	ac.tearDownErr = err
-	if ac.cc.balancerWrapper != nil {
+	ac.cc.handleSubConnStateChange(ac.acbw, ac.state)
-		ac.cc.balancerWrapper.handleSubConnStateChange(ac.acbw, ac.state)
-	} else {
-		ac.cc.csMgr.updateState(ac.state)
-	}
 	if ac.events != nil {
 		ac.events.Finish()
 		ac.events = nil

clientconn_test.go

@@ -30,6 +30,7 @@ import (
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/naming"
+	_ "google.golang.org/grpc/resolver/passthrough"
 	"google.golang.org/grpc/test/leakcheck"
 	"google.golang.org/grpc/testdata"
 )
@@ -47,7 +48,7 @@ func TestConnectivityStates(t *testing.T) {
 	defer leakcheck.Check(t)
 	servers, resolver, cleanup := startServers(t, 2, math.MaxUint32)
 	defer cleanup()
-	cc, err := Dial("foo.bar.com", WithBalancer(RoundRobin(resolver)), WithInsecure())
+	cc, err := Dial("passthrough:///foo.bar.com", WithBalancer(RoundRobin(resolver)), WithInsecure())
 	if err != nil {
 		t.Fatalf("Dial(\"foo.bar.com\", WithBalancer(_)) = _, %v, want _ <nil>", err)
 	}
@@ -82,7 +83,7 @@ func TestConnectivityStates(t *testing.T) {
 
 func TestDialTimeout(t *testing.T) {
 	defer leakcheck.Check(t)
-	conn, err := Dial("Non-Existent.Server:80", WithTimeout(time.Millisecond), WithBlock(), WithInsecure())
+	conn, err := Dial("passthrough:///Non-Existent.Server:80", WithTimeout(time.Millisecond), WithBlock(), WithInsecure())
 	if err == nil {
 		conn.Close()
 	}
@@ -97,7 +98,7 @@ func TestTLSDialTimeout(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to create credentials %v", err)
 	}
-	conn, err := Dial("Non-Existent.Server:80", WithTransportCredentials(creds), WithTimeout(time.Millisecond), WithBlock())
+	conn, err := Dial("passthrough:///Non-Existent.Server:80", WithTransportCredentials(creds), WithTimeout(time.Millisecond), WithBlock())
 	if err == nil {
 		conn.Close()
 	}
@@ -113,7 +114,7 @@ func TestDefaultAuthority(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Dial(_, _) = _, %v, want _, <nil>", err)
 	}
-	conn.Close()
+	defer conn.Close()
 	if conn.authority != target {
 		t.Fatalf("%v.authority = %v, want %v", conn, conn.authority, target)
 	}
@@ -126,11 +127,11 @@ func TestTLSServerNameOverwrite(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to create credentials %v", err)
 	}
-	conn, err := Dial("Non-Existent.Server:80", WithTransportCredentials(creds))
+	conn, err := Dial("passthrough:///Non-Existent.Server:80", WithTransportCredentials(creds))
 	if err != nil {
 		t.Fatalf("Dial(_, _) = _, %v, want _, <nil>", err)
 	}
-	conn.Close()
+	defer conn.Close()
 	if conn.authority != overwriteServerName {
 		t.Fatalf("%v.authority = %v, want %v", conn, conn.authority, overwriteServerName)
 	}
@@ -139,11 +140,11 @@ func TestTLSServerNameOverwrite(t *testing.T) {
 func TestWithAuthority(t *testing.T) {
 	defer leakcheck.Check(t)
 	overwriteServerName := "over.write.server.name"
-	conn, err := Dial("Non-Existent.Server:80", WithInsecure(), WithAuthority(overwriteServerName))
+	conn, err := Dial("passthrough:///Non-Existent.Server:80", WithInsecure(), WithAuthority(overwriteServerName))
 	if err != nil {
 		t.Fatalf("Dial(_, _) = _, %v, want _, <nil>", err)
 	}
-	conn.Close()
+	defer conn.Close()
 	if conn.authority != overwriteServerName {
 		t.Fatalf("%v.authority = %v, want %v", conn, conn.authority, overwriteServerName)
 	}
@@ -156,11 +157,11 @@ func TestWithAuthorityAndTLS(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to create credentials %v", err)
 	}
-	conn, err := Dial("Non-Existent.Server:80", WithTransportCredentials(creds), WithAuthority("no.effect.authority"))
+	conn, err := Dial("passthrough:///Non-Existent.Server:80", WithTransportCredentials(creds), WithAuthority("no.effect.authority"))
 	if err != nil {
 		t.Fatalf("Dial(_, _) = _, %v, want _, <nil>", err)
 	}
-	conn.Close()
+	defer conn.Close()
 	if conn.authority != overwriteServerName {
 		t.Fatalf("%v.authority = %v, want %v", conn, conn.authority, overwriteServerName)
 	}
@@ -231,11 +232,11 @@ func TestCredentialsMisuse(t *testing.T) {
 		t.Fatalf("Failed to create authenticator %v", err)
 	}
 	// Two conflicting credential configurations
-	if _, err := Dial("Non-Existent.Server:80", WithTransportCredentials(tlsCreds), WithBlock(), WithInsecure()); err != errCredentialsConflict {
+	if _, err := Dial("passthrough:///Non-Existent.Server:80", WithTransportCredentials(tlsCreds), WithBlock(), WithInsecure()); err != errCredentialsConflict {
 		t.Fatalf("Dial(_, _) = _, %v, want _, %v", err, errCredentialsConflict)
 	}
 	// security info on insecure connection
-	if _, err := Dial("Non-Existent.Server:80", WithPerRPCCredentials(securePerRPCCredentials{}), WithBlock(), WithInsecure()); err != errTransportCredentialsMissing {
+	if _, err := Dial("passthrough:///Non-Existent.Server:80", WithPerRPCCredentials(securePerRPCCredentials{}), WithBlock(), WithInsecure()); err != errTransportCredentialsMissing {
 		t.Fatalf("Dial(_, _) = _, %v, want _, %v", err, errTransportCredentialsMissing)
 	}
 }
@@ -263,10 +264,11 @@ func TestWithBackoffMaxDelay(t *testing.T) {
 
 func testBackoffConfigSet(t *testing.T, expected *BackoffConfig, opts ...DialOption) {
 	opts = append(opts, WithInsecure())
-	conn, err := Dial("foo:80", opts...)
+	conn, err := Dial("passthrough:///foo:80", opts...)
 	if err != nil {
 		t.Fatalf("unexpected error dialing connection: %v", err)
 	}
+	defer conn.Close()
 
 	if conn.dopts.bs == nil {
 		t.Fatalf("backoff config not set")
@@ -280,39 +282,6 @@ func testBackoffConfigSet(t *testing.T, expected *BackoffConfig, opts ...DialOpt
 	if actual != *expected {
 		t.Fatalf("unexpected backoff config on connection: %v, want %v", actual, expected)
 	}
-	conn.Close()
-}
-
-type testErr struct {
-	temp bool
-}
-
-func (e *testErr) Error() string {
-	return "test error"
-}
-
-func (e *testErr) Temporary() bool {
-	return e.temp
-}
-
-var nonTemporaryError = &testErr{false}
-
-func nonTemporaryErrorDialer(addr string, timeout time.Duration) (net.Conn, error) {
-	return nil, nonTemporaryError
-}
-
-func TestDialWithBlockErrorOnNonTemporaryErrorDialer(t *testing.T) {
-	defer leakcheck.Check(t)
-	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
-	defer cancel()
-	if _, err := DialContext(ctx, "", WithInsecure(), WithDialer(nonTemporaryErrorDialer), WithBlock(), FailOnNonTempDialError(true)); err != nonTemporaryError {
-		t.Fatalf("Dial(%q) = %v, want %v", "", err, nonTemporaryError)
-	}
-
-	// Without FailOnNonTempDialError, gRPC will retry to connect, and dial should exit with time out error.
-	if _, err := DialContext(ctx, "", WithInsecure(), WithDialer(nonTemporaryErrorDialer), WithBlock()); err != context.DeadlineExceeded {
-		t.Fatalf("Dial(%q) = %v, want %v", "", err, context.DeadlineExceeded)
-	}
 }
 
 // emptyBalancer returns an empty set of servers.

pickfirst.go

@@ -57,14 +57,20 @@ func (b *pickfirstBalancer) HandleResolvedAddrs(addrs []resolver.Address, err er
 			return
 		}
 		b.cc.UpdateBalancerState(connectivity.Idle, &picker{sc: b.sc})
+		b.sc.Connect()
 	} else {
 		b.sc.UpdateAddresses(addrs)
+		b.sc.Connect()
 	}
 }
 
 func (b *pickfirstBalancer) HandleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
 	grpclog.Infof("pickfirstBalancer: HandleSubConnStateChange: %p, %v", sc, s)
-	if b.sc != sc || s == connectivity.Shutdown {
+	if b.sc != sc {
+		grpclog.Infof("pickfirstBalancer: ignored state change because sc is not recognized")
+		return
+	}
+	if s == connectivity.Shutdown {
 		b.sc = nil
 		return
 	}
@@ -93,3 +99,7 @@ func (p *picker) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.
 	}
 	return p.sc, nil, nil
 }
+
+func init() {
+	balancer.Register(newPickfirstBuilder())
+}

resolver/resolver.go

@@ -24,7 +24,7 @@ var (
 	// m is a map from scheme to resolver builder.
 	m = make(map[string]Builder)
 	// defaultScheme is the default scheme to use.
-	defaultScheme string
+	defaultScheme = "dns"
 )
 
 // TODO(bar) install dns resolver in init(){}.

resolver_conn_wrapper.go

@@ -19,6 +19,7 @@
 package grpc
 
 import (
+	"fmt"
 	"strings"
 
 	"google.golang.org/grpc/grpclog"
@@ -56,19 +57,13 @@ func parseTarget(target string) (ret resolver.Target) {
 // newCCResolverWrapper parses cc.target for scheme and gets the resolver
 // builder for this scheme. It then builds the resolver and starts the
 // monitoring goroutine for it.
-//
-// This function could return nil, nil, in tests for old behaviors.
-// TODO(bar) never return nil, nil when DNS becomes the default resolver.
 func newCCResolverWrapper(cc *ClientConn) (*ccResolverWrapper, error) {
 	target := parseTarget(cc.target)
 	grpclog.Infof("dialing to target with scheme: %q", target.Scheme)
 
 	rb := resolver.Get(target.Scheme)
 	if rb == nil {
-		// TODO(bar) return error when DNS becomes the default (implemented and
+		return nil, fmt.Errorf("could not get resolver for scheme: %q", target.Scheme)
-		// registered by DNS package).
-		grpclog.Infof("could not get resolver for scheme: %q", target.Scheme)
-		return nil, nil
 	}
 
 	ccr := &ccResolverWrapper{
@@ -100,13 +95,19 @@ func (ccr *ccResolverWrapper) watcher() {
 
 		select {
 		case addrs := <-ccr.addrCh:
-			grpclog.Infof("ccResolverWrapper: sending new addresses to balancer wrapper: %v", addrs)
+			select {
-			// TODO(bar switching) this should never be nil. Pickfirst should be default.
+			case <-ccr.done:
-			if ccr.cc.balancerWrapper != nil {
+				return
-				// TODO(bar switching) create balancer if it's nil?
+			default:
-				ccr.cc.balancerWrapper.handleResolvedAddrs(addrs, nil)
 			}
+			grpclog.Infof("ccResolverWrapper: sending new addresses to cc: %v", addrs)
+			ccr.cc.handleResolvedAddrs(addrs, nil)
 		case sc := <-ccr.scCh:
+			select {
+			case <-ccr.done:
+				return
+			default:
+			}
 			grpclog.Infof("ccResolverWrapper: got new service config: %v", sc)
 		case <-ccr.done:
 			return

test/end2end_test.go

@@ -559,8 +559,6 @@ func (te *test) startServer(ts testpb.TestServiceServer) {
 			te.t.Fatalf("Failed to generate credentials %v", err)
 		}
 		sopts = append(sopts, grpc.Creds(creds))
-	case "clientAlwaysFailCred":
-		sopts = append(sopts, grpc.Creds(clientAlwaysFailCred{}))
 	case "clientTimeoutCreds":
 		sopts = append(sopts, grpc.Creds(&clientTimeoutCreds{}))
 	}
@@ -634,15 +632,13 @@ func (te *test) clientConn() *grpc.ClientConn {
 			te.t.Fatalf("Failed to load credentials: %v", err)
 		}
 		opts = append(opts, grpc.WithTransportCredentials(creds))
-	case "clientAlwaysFailCred":
-		opts = append(opts, grpc.WithTransportCredentials(clientAlwaysFailCred{}))
 	case "clientTimeoutCreds":
 		opts = append(opts, grpc.WithTransportCredentials(&clientTimeoutCreds{}))
 	default:
 		opts = append(opts, grpc.WithInsecure())
 	}
 	// TODO(bar) switch balancer case "pickfirst".
-	var scheme string
+	scheme := "passthrough:///"
 	switch te.e.balancer {
 	case "v1":
 		opts = append(opts, grpc.WithBalancer(grpc.RoundRobin(nil)))
@@ -652,7 +648,6 @@ func (te *test) clientConn() *grpc.ClientConn {
 			te.t.Fatalf("got nil when trying to get roundrobin balancer builder")
 		}
 		opts = append(opts, grpc.WithBalancerBuilder(rr))
-		scheme = "passthrough:///"
 	}
 	if te.clientInitialWindowSize > 0 {
 		opts = append(opts, grpc.WithInitialWindowSize(te.clientInitialWindowSize))
@@ -670,6 +665,9 @@ func (te *test) clientConn() *grpc.ClientConn {
 		// Only do a blocking dial if server is up.
 		opts = append(opts, grpc.WithBlock())
 	}
+	if te.srvAddr == "" {
+		te.srvAddr = "client.side.only.test"
+	}
 	var err error
 	te.cc, err = grpc.Dial(scheme+te.srvAddr, opts...)
 	if err != nil {
@@ -4068,44 +4066,6 @@ func testClientRequestBodyErrorCancelStreamingInput(t *testing.T, e env) {
 	})
 }
 
-const clientAlwaysFailCredErrorMsg = "clientAlwaysFailCred always fails"
-
-var errClientAlwaysFailCred = errors.New(clientAlwaysFailCredErrorMsg)
-
-type clientAlwaysFailCred struct{}
-
-func (c clientAlwaysFailCred) ClientHandshake(ctx context.Context, addr string, rawConn net.Conn) (net.Conn, credentials.AuthInfo, error) {
-	return nil, nil, errClientAlwaysFailCred
-}
-func (c clientAlwaysFailCred) ServerHandshake(rawConn net.Conn) (net.Conn, credentials.AuthInfo, error) {
-	return rawConn, nil, nil
-}
-func (c clientAlwaysFailCred) Info() credentials.ProtocolInfo {
-	return credentials.ProtocolInfo{}
-}
-func (c clientAlwaysFailCred) Clone() credentials.TransportCredentials {
-	return nil
-}
-func (c clientAlwaysFailCred) OverrideServerName(s string) error {
-	return nil
-}
-
-func TestDialWithBlockErrorOnBadCertificates(t *testing.T) {
-	te := newTest(t, env{name: "bad-cred", network: "tcp", security: "clientAlwaysFailCred", balancer: "v1"})
-	te.startServer(&testServer{security: te.e.security})
-	defer te.tearDown()
-
-	var (
-		err  error
-		opts []grpc.DialOption
-	)
-	opts = append(opts, grpc.WithTransportCredentials(clientAlwaysFailCred{}), grpc.WithBlock())
-	te.cc, err = grpc.Dial(te.srvAddr, opts...)
-	if err != errClientAlwaysFailCred {
-		te.t.Fatalf("Dial(%q) = %v, want %v", te.srvAddr, err, errClientAlwaysFailCred)
-	}
-}
-
 type clientTimeoutCreds struct {
 	timeoutReturned bool
 }