Reduce error logs in transport. (#2117)

transport/controlbuf.go

@@ -365,7 +365,17 @@ func newLoopyWriter(s side, fr *framer, cbuf *controlBuffer, bdpEst *bdpEstimato
 const minBatchSize = 1000
 
 // run should be run in a separate goroutine.
-func (l *loopyWriter) run() error {
+func (l *loopyWriter) run() (err error) {
+	defer func() {
+		if err == ErrConnClosing {
+			// Don't log ErrConnClosing as error since it happens
+			// 1. When the connection is closed by some other known issue.
+			// 2. User closed the connection.
+			// 3. A graceful close of connection.
+			infof("transport: loopyWriter.run returning. %v", err)
+			err = nil
+		}
+	}()
 	for {
 		it, err := l.cbuf.get(true)
 		if err != nil {

transport/http2_client.go

@@ -296,10 +296,11 @@ func newHTTP2Client(connectCtx, ctx context.Context, addr TargetInfo, opts Conne
 	go func() {
 		t.loopy = newLoopyWriter(clientSide, t.framer, t.controlBuf, t.bdpEst)
 		err := t.loopy.run()
+		if err != nil {
 			errorf("transport: loopyWriter.run returning. Err: %v", err)
+		}
 		// If it's a connection error, let reader goroutine handle it
 		// since there might be data in the buffers.
-
 		if _, ok := err.(net.Error); !ok {
 			t.conn.Close()
 		}

transport/http2_server.go

@@ -273,8 +273,9 @@ func newHTTP2Server(conn net.Conn, config *ServerConfig) (_ ServerTransport, err
 	go func() {
 		t.loopy = newLoopyWriter(serverSide, t.framer, t.controlBuf, t.bdpEst)
 		t.loopy.ssGoAwayHandler = t.outgoingGoAwayHandler
-		err := t.loopy.run()
+		if err := t.loopy.run(); err != nil {
 			errorf("transport: loopyWriter.run returning. Err: %v", err)
+		}
 		t.conn.Close()
 		close(t.writerDone)
 	}()