rclone: Give rclone time to finish before closing stdin pipe

Calling `Close()` on the rclone backend sometimes failed during test
execution with 'signal: Broken pipe'. The stdio connection closed both
the stdin and stdout file descriptors at the same moment, therefore
giving rclone no chance to properly send any final http2 data frames.

Now the stdin connection to rclone is closed first and will only be
forcefully closed after a timeout. In case rclone exits before the
timeout then the stdio connection will be closed normally.

internal/backend/rclone/backend.go

@@ -197,7 +197,7 @@ func newBackend(cfg Config, lim limiter.Limiter) (*Backend, error) {
 		debug.Log("Wait returned %v", err)
 		be.waitResult = err
 		// close our side of the pipes to rclone
-		stdioConn.Close()
+		stdioConn.CloseAll()
 		close(waitCh)
 	}()
 
@@ -314,7 +314,7 @@ func (be *Backend) Close() error {
 		debug.Log("rclone exited")
 	case <-time.After(waitForExit):
 		debug.Log("timeout, closing file descriptors")
-		err := be.conn.Close()
+		err := be.conn.CloseAll()
 		if err != nil {
 			return err
 		}

internal/backend/rclone/stdio_conn.go

@@ -12,10 +12,11 @@ import (
 
 // StdioConn implements a net.Conn via stdin/stdout.
 type StdioConn struct {
-	stdin  *os.File
-	stdout *os.File
-	cmd    *exec.Cmd
-	close  sync.Once
+	stdin    *os.File
+	stdout   *os.File
+	cmd      *exec.Cmd
+	closeIn  sync.Once
+	closeOut sync.Once
 }
 
 func (s *StdioConn) Read(p []byte) (int, error) {
@@ -28,21 +29,25 @@ func (s *StdioConn) Write(p []byte) (int, error) {
 	return n, err
 }
 
-// Close closes both streams.
+// Close closes the stream to the child process.
 func (s *StdioConn) Close() (err error) {
-	s.close.Do(func() {
-		debug.Log("close stdio connection")
-		var errs []error
+	s.closeOut.Do(func() {
+		debug.Log("close stdio send connection")
+		err = s.stdout.Close()
+	})
 
-		for _, f := range []func() error{s.stdin.Close, s.stdout.Close} {
-			err := f()
-			if err != nil {
-				errs = append(errs, err)
-			}
-		}
+	return err
+}
 
-		if len(errs) > 0 {
-			err = errs[0]
+// CloseAll closes both streams.
+func (s *StdioConn) CloseAll() (err error) {
+	err = s.Close()
+
+	s.closeIn.Do(func() {
+		debug.Log("close stdio receive connection")
+		err2 := s.stdin.Close()
+		if err == nil {
+			err = err2
 		}
 	})