internal/transport: skip log on EOF when reading client preface (#4458)

call_test.go

@@ -160,7 +160,7 @@ func (s *server) start(t *testing.T, port int, maxStreams uint32) {
 		config := &transport.ServerConfig{
 			MaxStreams: maxStreams,
 		}
-		st, err := transport.NewServerTransport("http2", conn, config)
+		st, err := transport.NewServerTransport(conn, config)
 		if err != nil {
 			continue
 		}

internal/transport/http2_server.go

@@ -125,9 +125,14 @@ type http2Server struct {
 	connectionID uint64
 }
 
-// newHTTP2Server constructs a ServerTransport based on HTTP2. ConnectionError is
+// NewServerTransport creates a http2 transport with conn and configuration
-// returned if something goes wrong.
+// options from config.
-func newHTTP2Server(conn net.Conn, config *ServerConfig) (_ ServerTransport, err error) {
+//
+// It returns a non-nil transport and a nil error on success. On failure, it
+// returns a non-nil transport and a nil-error. For a special case where the
+// underlying conn gets closed before the client preface could be read, it
+// returns a nil transport and a nil error.
+func NewServerTransport(conn net.Conn, config *ServerConfig) (_ ServerTransport, err error) {
 	writeBufSize := config.WriteBufferSize
 	readBufSize := config.ReadBufferSize
 	maxHeaderListSize := defaultServerMaxHeaderListSize
@@ -266,6 +271,13 @@ func newHTTP2Server(conn net.Conn, config *ServerConfig) (_ ServerTransport, err
 	// Check the validity of client preface.
 	preface := make([]byte, len(clientPreface))
 	if _, err := io.ReadFull(t.conn, preface); err != nil {
+		// In deployments where a gRPC server runs behind a cloud load balancer
+		// which performs regular TCP level health checks, the connection is
+		// closed immediately by the latter. Skipping the error here will help
+		// reduce log clutter.
+		if err == io.EOF {
+			return nil, nil
+		}
 		return nil, connectionErrorf(false, err, "transport: http2Server.HandleStreams failed to receive the preface from client: %v", err)
 	}
 	if !bytes.Equal(preface, clientPreface) {

internal/transport/transport.go

@@ -532,12 +532,6 @@ type ServerConfig struct {
 	HeaderTableSize       *uint32
 }
 
-// NewServerTransport creates a ServerTransport with conn or non-nil error
-// if it fails.
-func NewServerTransport(protocol string, conn net.Conn, config *ServerConfig) (ServerTransport, error) {
-	return newHTTP2Server(conn, config)
-}
-
 // ConnectOptions covers all relevant options for communicating with the server.
 type ConnectOptions struct {
 	// UserAgent is the application user agent.

internal/transport/transport_test.go

@@ -323,7 +323,7 @@ func (s *server) start(t *testing.T, port int, serverConfig *ServerConfig, ht hT
 		if err != nil {
 			return
 		}
-		transport, err := NewServerTransport("http2", conn, serverConfig)
+		transport, err := NewServerTransport(conn, serverConfig)
 		if err != nil {
 			return
 		}

server.go

@@ -844,10 +844,16 @@ func (s *Server) handleRawConn(lisAddr string, rawConn net.Conn) {
 		// ErrConnDispatched means that the connection was dispatched away from
 		// gRPC; those connections should be left open.
 		if err != credentials.ErrConnDispatched {
+			// In deployments where a gRPC server runs behind a cloud load
+			// balancer which performs regular TCP level health checks, the
+			// connection is closed immediately by the latter. Skipping the
+			// error here will help reduce log clutter.
+			if err != io.EOF {
 				s.mu.Lock()
 				s.errorf("ServerHandshake(%q) failed: %v", rawConn.RemoteAddr(), err)
 				s.mu.Unlock()
 				channelz.Warningf(logger, s.channelzID, "grpc: Server.Serve failed to complete security handshake from %q: %v", rawConn.RemoteAddr(), err)
+			}
 			rawConn.Close()
 		}
 		rawConn.SetDeadline(time.Time{})
@@ -897,7 +903,7 @@ func (s *Server) newHTTP2Transport(c net.Conn, authInfo credentials.AuthInfo) tr
 		MaxHeaderListSize:     s.opts.maxHeaderListSize,
 		HeaderTableSize:       s.opts.headerTableSize,
 	}
-	st, err := transport.NewServerTransport("http2", c, config)
+	st, err := transport.NewServerTransport(c, config)
 	if err != nil {
 		s.mu.Lock()
 		s.errorf("NewServerTransport(%q) failed: %v", c.RemoteAddr(), err)