Beam: change the prototype of SendPipe() to return a *net.UnixSocket

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Upstream-commit: b637e5f04af010bd1fc6bef93b8512d587d90c46
Component: engine

components/engine/pkg/beam/service.go

@@ -17,11 +17,7 @@ import (
 // not point to a connection, that message will be skipped.
 //
 func Listen(conn *net.UnixConn, name string) (net.Listener, error) {
-	fEndpoint, err := SendPipe(conn, []byte(name))
-	if err != nil {
-		return nil, err
-	}
-	endpoint, err := FdConn(int(fEndpoint.Fd()))
+	endpoint, err := SendPipe(conn, []byte(name))
 	if err != nil {
 		return nil, err
 	}

components/engine/pkg/beam/unix.go

@@ -78,16 +78,25 @@ func Receive(conn *net.UnixConn) ([]byte, *os.File, error) {
 // allows for arbitrarily complex service discovery and retry logic to take place,
 // without complicating application code.
 //
-func SendPipe(conn *net.UnixConn, data []byte) (*os.File, error) {
+func SendPipe(conn *net.UnixConn, data []byte) (endpoint *net.UnixConn, err error) {
 	local, remote, err := SocketPair()
 	if err != nil {
 		return nil, err
 	}
-	if err := Send(conn, data, remote); err != nil {
-		remote.Close()
+	defer func() {
+		if err != nil {
+			local.Close()
+			remote.Close()
+		}
+	}()
+	endpoint, err = FdConn(int(local.Fd()))
+	if err != nil {
 		return nil, err
 	}
-	return local, nil
+	if err := Send(conn, data, remote); err != nil {
+		return nil, err
+	}
+	return endpoint, nil
 }
 
 func receiveUnix(conn *net.UnixConn) ([]byte, []int, error) {