mount: fix hang on errored upload

In certain circumstances if an upload failed then the mount could hang
indefinitely. This was fixed by closing the read pipe after the Put
completed.  This will cause the write side to return a pipe closed
error fixing the hang.

Fixes #1498

cmd/mountlib/write.go

@@ -13,7 +13,6 @@ type WriteFileHandle struct {
 	mu          sync.Mutex
 	closed      bool // set if handle has been closed
 	remote      string
-	pipeReader  *io.PipeReader
 	pipeWriter  *io.PipeWriter
 	o           fs.Object
 	result      chan error
@@ -39,10 +38,16 @@ func newWriteFileHandle(d *Dir, f *File, src fs.ObjectInfo) (*WriteFileHandle, e
 		file:   f,
 		hash:   hash,
 	}
-	fh.pipeReader, fh.pipeWriter = io.Pipe()
+	var pipeReader *io.PipeReader
-	r := fs.NewAccountSizeName(fh.pipeReader, 0, src.Remote()).WithBuffer() // account the transfer
+	pipeReader, fh.pipeWriter = io.Pipe()
 	go func() {
+		r := fs.NewAccountSizeName(pipeReader, 0, src.Remote()).WithBuffer() // account the transfer
 		o, err := d.f.Put(r, src)
+		if err != nil {
+			fs.Errorf(fh.remote, "WriteFileHandle.New Put failed: %v", err)
+		}
+		// Close the Account and thus the pipeReader so the pipeWriter fails with ErrClosedPipe
+		_ = r.Close()
 		fh.o = o
 		fh.result <- err
 	}()
@@ -120,14 +125,10 @@ func (fh *WriteFileHandle) close() error {
 	fh.file.addWriters(-1)
 	writeCloseErr := fh.pipeWriter.Close()
 	err := <-fh.result
-	readCloseErr := fh.pipeReader.Close()
 	if err == nil {
 		fh.file.setObject(fh.o)
 		err = writeCloseErr
 	}
-	if err == nil {
-		err = readCloseErr
-	}
 	if err == nil && fh.hash != nil {
 		for hashType, srcSum := range fh.hash.Sums() {
 			dstSum, err := fh.o.Hash(hashType)