Writer: fix #170

writer.go

@@ -144,9 +144,8 @@ func (w *Writer) write(data []byte, safe bool) error {
 	return nil
 }
 
-// Close closes the Writer, flushing any unwritten data to the underlying io.Writer,
-// but does not close the underlying io.Writer.
-func (w *Writer) Close() (err error) {
+// Flush any buffered data to the underlying writer immediately.
+func (w *Writer) Flush() (err error) {
 	switch w.state.state {
 	case writeState:
 	case errorState:
@@ -162,13 +161,22 @@ func (w *Writer) Close() (err error) {
 		}
 		w.idx = 0
 	}
-	err = w.frame.CloseW(w.src, w.num)
+	return nil
+}
+
+// Close closes the Writer, flushing any unwritten data to the underlying writer
+// without closing it.
+func (w *Writer) Close() error {
+	if err := w.Flush(); err != nil {
+		return err
+	}
+	err := w.frame.CloseW(w.src, w.num)
 	// It is now safe to free the buffer.
 	if w.data != nil {
 		lz4block.Put(w.data)
 		w.data = nil
 	}
-	return
+	return err
 }
 
 // Reset clears the state of the Writer w such that it is equivalent to its

writer_test.go

@@ -228,6 +228,29 @@ func TestIssue71(t *testing.T) {
 	}
 }
 
+func TestWriterFlush(t *testing.T) {
+	out := new(bytes.Buffer)
+	zw := lz4.NewWriter(out)
+	if err := zw.Apply(); err != nil {
+		t.Fatal(err)
+	}
+	data := strings.Repeat("0123456789", 100)
+	if _, err := zw.Write([]byte(data)); err != nil {
+		t.Fatal(err)
+	}
+	// header only
+	if got, want := out.Len(), 7; got != want {
+		t.Fatalf("got %d, want %d", got, want)
+	}
+	if err := zw.Flush(); err != nil {
+		t.Fatal(err)
+	}
+	// header + data
+	if got, want := out.Len(), 7; got == want {
+		t.Fatalf("got %d, want %d", got, want)
+	}
+}
+
 func TestWriterLegacy(t *testing.T) {
 	goldenFiles := []string{
 		"testdata/vmlinux_LZ4_19377",