fix: fix bug caused by incorrectly appending compressing file

Signed-off-by: arkbriar <[email protected]>

internal/filechannel/filechannel.go

@@ -1024,33 +1024,20 @@ func (fc *FileChannel) Open() error {
 	return nil
 }
 
-func (fc *FileChannel) compress(ctx context.Context, index uint32) error {
-	select {
-	case <-ctx.Done():
-		return ctx.Err()
-	default:
-	}
-
-	if !fc.segmentManager.Pin(index) {
-		return fmt.Errorf("failed to pin segment index %d", index)
-	}
-	defer fc.segmentManager.Unpin(index)
-
-	plainFile := fc.segmentManager.SegmentFile(index, Plain)
-	compressingFile := fc.segmentManager.SegmentFile(index, Compressing)
-
-	stats, err := os.Stat(plainFile)
+func (fc *FileChannel) compressInner(index uint32, from, to string) error {
+	stats, err := os.Stat(from)
 	if err != nil {
 		return fmt.Errorf("failed to get stats of plain segment file: %w", err)
 	}
 
-	f, err := fs.OpenSequentialFile(plainFile)
+	f, err := fs.OpenSequentialFile(from)
 	if err != nil {
 		return fmt.Errorf("failed to open plain segment file: %w", err)
 	}
 	defer f.Close()
 
-	wf, err := fs.OpenFile(compressingFile, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
+	// Truncate before compressing.
+	wf, err := fs.OpenFile(to, os.O_CREATE|os.O_APPEND|os.O_WRONLY|os.O_TRUNC, 0644)
 	if err != nil {
 		return fmt.Errorf("failed to open compressing segment file: %w", err)
 	}
@@ -1089,6 +1076,30 @@ func (fc *FileChannel) compress(ctx context.Context, index uint32) error {
 		return fmt.Errorf("failed to compress: %w", err)
 	}
 
+	return nil
+}
+
+func (fc *FileChannel) compress(ctx context.Context, index uint32) error {
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+	}
+
+	if !fc.segmentManager.Pin(index) {
+		return fmt.Errorf("failed to pin segment index %d", index)
+	}
+	defer fc.segmentManager.Unpin(index)
+
+	plainFile := fc.segmentManager.SegmentFile(index, Plain)
+	compressingFile := fc.segmentManager.SegmentFile(index, Compressing)
+
+	// Compress.
+	err := fc.compressInner(index, plainFile, compressingFile)
+	if err != nil {
+		return fmt.Errorf("failed to compress: %w", err)
+	}
+
 	// Rename and delete the original file.
 	err = os.Rename(compressingFile, fc.segmentManager.SegmentFile(index, Compressed))
 	if err != nil {