[bug] - Ensure BufferedFileWriter Flushes Buffer Contents to File Correctly (#2943)

* flush butter before writing to file

* revert

* remove redundant Reset

* add test case

Author: ahrav

pkg/writers/buffered_file_writer/bufferedfilewriter.go

@@ -205,7 +205,13 @@ func (w *BufferedFileWriter) Write(data []byte) (int, error) {
 				}
 				return 0, err
 			}
-			w.buf.Reset()
+		}
+	}
+
+	// Write any remaining data in the buffer to the file before writing new data.
+	if w.buf.Len() > 0 {
+		if _, err := w.buf.WriteTo(w.file); err != nil {
+			return 0, fmt.Errorf("error flushing buffer to file: %w", err)
 		}
 	}
 
@@ -273,8 +279,7 @@ func (w *BufferedFileWriter) CloseForWriting() error {
 	defer w.bufPool.Put(w.buf)
 
 	if w.buf.Len() > 0 {
-		_, err := w.buf.WriteTo(w.file)
-		if err != nil {
+		if _, err := w.buf.WriteTo(w.file); err != nil {
 			return err
 		}
 	}

pkg/writers/buffered_file_writer/bufferedfilewriter_test.go

@@ -650,11 +650,19 @@ func TestBufferedFileWriter_ReadFrom(t *testing.T) {
 			expectedSize:   1 << 20,
 		},
 		{
-			name:           "Input greater than threshold",
+			name:           "Input slightly greater than threshold",
 			input:          string(make([]byte, defaultThreshold+1)),
 			expectedOutput: string(make([]byte, defaultThreshold+1)),
 			expectedSize:   defaultThreshold + 1,
 		},
+		// Test to ensure that anytime the buffer exceeds the threshold, the data is written to a file
+		// and the buffer is cleared.
+		{
+			name:           "Input much greater than threshold",
+			input:          string(make([]byte, (2*defaultThreshold)+largeBufferSize+1)),
+			expectedOutput: string(make([]byte, (2*defaultThreshold)+largeBufferSize+1)),
+			expectedSize:   (2 * defaultThreshold) + largeBufferSize + 1,
+		},
 	}
 
 	for _, tc := range tests {
@@ -668,6 +676,10 @@ func TestBufferedFileWriter_ReadFrom(t *testing.T) {
 			size, err := writer.ReadFrom(reader)
 			assert.NoError(t, err)
 
+			if writer.buf != nil && writer.file != nil {
+				assert.Len(t, writer.buf.Bytes(), 0)
+			}
+
 			err = writer.CloseForWriting()
 			assert.NoError(t, err)