client: synchronously verify server preface in newClientTransport

clientconn.go

@@ -1228,38 +1228,33 @@ func (ac *addrConn) tryAllAddrs(addrs []resolver.Address, connectDeadline time.T
 // address was not successfully connected, or updates ac appropriately with the
 // new transport.
 func (ac *addrConn) createTransport(addr resolver.Address, copts transport.ConnectOptions, connectDeadline time.Time) error {
-	// TODO: Delete prefaceReceived and move the logic to wait for it into the
-	// transport.
-	prefaceReceived := grpcsync.NewEvent()
-	connClosed := grpcsync.NewEvent()
-
 	addr.ServerName = ac.cc.getServerName(addr)
 	hctx, hcancel := context.WithCancel(ac.ctx)
-	hcStarted := false // protected by ac.mu
 
-	onClose := func() {
+	onClose := grpcsync.OnceFunc(func() {
 		ac.mu.Lock()
 		defer ac.mu.Unlock()
-		defer connClosed.Fire()
-		defer hcancel()
-		if !hcStarted || hctx.Err() != nil {
-			// We didn't start the health check or set the state to READY, so
-			// no need to do anything else here.
-			//
-			// OR, we have already cancelled the health check context, meaning
-			// we have already called onClose once for this transport.  In this
-			// case it would be dangerous to clear the transport and update the
-			// state, since there may be a new transport in this addrConn.
+		if ac.state == connectivity.Shutdown {
+			// Already shut down.  tearDown() already cleared the transport and
+			// canceled hctx via ac.ctx, and we expected this connection to be
+			// closed, so do nothing here.
+			return
+		}
+		hcancel()
+		if ac.transport == nil {
+			// We're still connecting to this address, which could error.  Do
+			// not update the connectivity state or resolve; these will happen
+			// at the end of the tryAllAddrs connection loop in the event of an
+			// error.
 			return
 		}
 		ac.transport = nil
-		// Refresh the name resolver
+		// Refresh the name resolver on any connection loss.
 		ac.cc.resolveNow(resolver.ResolveNowOptions{})
-		if ac.state != connectivity.Shutdown {
-			ac.updateConnectivityState(connectivity.Idle, nil)
-		}
-	}
-
+		// Always go idle and wait for the LB policy to initiate a new
+		// connection attempt.
+		ac.updateConnectivityState(connectivity.Idle, nil)
+	})
 	onGoAway := func(r transport.GoAwayReason) {
 		ac.mu.Lock()
 		ac.adjustParams(r)
@@ -1271,74 +1266,42 @@ func (ac *addrConn) createTransport(addr resolver.Address, copts transport.Conne
 	defer cancel()
 	copts.ChannelzParentID = ac.channelzID
 
-	newTr, err := transport.NewClientTransport(connectCtx, ac.cc.ctx, addr, copts, func() { prefaceReceived.Fire() }, onGoAway, onClose)
+	newTr, err := transport.NewClientTransport(connectCtx, ac.cc.ctx, addr, copts, onGoAway, onClose)
 	if err != nil {
 		// newTr is either nil, or closed.
 		hcancel()
 		channelz.Warningf(logger, ac.channelzID, "grpc: addrConn.createTransport failed to connect to %s. Err: %v", addr, err)
 		return err
 	}
 
-	select {
-	case <-connectCtx.Done():
-		// We didn't get the preface in time.
+	ac.mu.Lock()
+	defer ac.mu.Unlock()
+	if ac.state == connectivity.Shutdown {
+		// This can happen if the subConn was removed while in `Connecting`
+		// state. tearDown() would have set the state to `Shutdown`, but
+		// would not have closed the transport since ac.transport would not
+		// have been set at that point.
+		//
+		// We run this in a goroutine because newTr.Close() calls onClose()
+		// inline, which requires locking ac.mu.
+		//
 		// The error we pass to Close() is immaterial since there are no open
 		// streams at this point, so no trailers with error details will be sent
 		// out. We just need to pass a non-nil error.
-		newTr.Close(transport.ErrConnClosing)
-		if connectCtx.Err() == context.DeadlineExceeded {
-			err := errors.New("failed to receive server preface within timeout")
-			channelz.Warningf(logger, ac.channelzID, "grpc: addrConn.createTransport failed to connect to %s: %v", addr, err)
-			return err
-		}
+		go newTr.Close(transport.ErrConnClosing)
 		return nil
-	case <-prefaceReceived.Done():
-		// We got the preface - huzzah! things are good.
-		ac.mu.Lock()
-		defer ac.mu.Unlock()
-		if connClosed.HasFired() {
-			// onClose called first; go idle but do nothing else.
-			if ac.state != connectivity.Shutdown {
-				ac.updateConnectivityState(connectivity.Idle, nil)
-			}
-			return nil
-		}
-		if ac.state == connectivity.Shutdown {
-			// This can happen if the subConn was removed while in `Connecting`
-			// state. tearDown() would have set the state to `Shutdown`, but
-			// would not have closed the transport since ac.transport would not
-			// been set at that point.
-			//
-			// We run this in a goroutine because newTr.Close() calls onClose()
-			// inline, which requires locking ac.mu.
-			//
-			// The error we pass to Close() is immaterial since there are no open
-			// streams at this point, so no trailers with error details will be sent
-			// out. We just need to pass a non-nil error.
-			go newTr.Close(transport.ErrConnClosing)
-			return nil
-		}
-		ac.curAddr = addr
-		ac.transport = newTr
-		hcStarted = true
-		ac.startHealthCheck(hctx) // Will set state to READY if appropriate.
+	}
+	if hctx.Err() != nil {
+		// onClose was already called for this connection, but the connection
+		// was successfully established first.  Consider it a success and set
+		// the new state to Idle.
+		ac.updateConnectivityState(connectivity.Idle, nil)
 		return nil
-	case <-connClosed.Done():
-		// The transport has already closed.  If we received the preface, too,
-		// this is not an error and go idle.
-		select {
-		case <-prefaceReceived.Done():
-			ac.mu.Lock()
-			defer ac.mu.Unlock()
-
-			if ac.state != connectivity.Shutdown {
-				ac.updateConnectivityState(connectivity.Idle, nil)
-			}
-			return nil
-		default:
-			return errors.New("connection closed before server preface received")
-		}
 	}
+	ac.curAddr = addr
+	ac.transport = newTr
+	ac.startHealthCheck(hctx) // Will set state to READY if appropriate.
+	return nil
 }
 
 // startHealthCheck starts the health checking stream (RPC) to watch the health

internal/grpcsync/oncefunc.go

@@ -0,0 +1,32 @@
+/*
+ *
+ * Copyright 2022 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 grpcsync
+
+import (
+	"sync"
+)
+
+// OnceFunc returns a function wrapping f which ensures f is only executed
+// once even if the returned function is executed multiple times.
+func OnceFunc(f func()) func() {
+	var once sync.Once
+	return func() {
+		once.Do(f)
+	}
+}

internal/grpcsync/oncefunc_test.go

@@ -0,0 +1,53 @@
+/*
+ *
+ * Copyright 2022 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 grpcsync
+
+import (
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// TestOnceFunc tests that a OnceFunc is executed only once even with multiple
+// simultaneous callers of it.
+func (s) TestOnceFunc(t *testing.T) {
+	var v int32
+	inc := OnceFunc(func() { atomic.AddInt32(&v, 1) })
+
+	const numWorkers = 100
+	var wg sync.WaitGroup // Blocks until all workers have called inc.
+	wg.Add(numWorkers)
+
+	block := NewEvent() // Signal to worker goroutines to call inc
+
+	for i := 0; i < numWorkers; i++ {
+		go func() {
+			<-block.Done() // Wait for a signal.
+			inc()          // Call the OnceFunc.
+			wg.Done()
+		}()
+	}
+	time.Sleep(time.Millisecond) // Allow goroutines to get to the block.
+	block.Fire()                 // Unblock them.
+	wg.Wait()                    // Wait for them to complete.
+	if v != 1 {
+		t.Fatalf("OnceFunc() called %v times; want 1", v)
+	}
+}