FileWriter.Write will now always attempt to write the entire buffer, even if larger than max chunk size.

This is required to work with io.Copy, which returns an error if a write doesn't write the entire buffer but returns no error.

sync_file_writer.go

@@ -43,21 +43,31 @@ func encodePathAndMode(path string, mode os.FileMode) []byte {
 
 // Write writes the min of (len(buf), 64k).
 func (w *syncFileWriter) Write(buf []byte) (n int, err error) {
-	// Writes < 64k have a one-to-one mapping to chunks.
-	// If buffer is larger than the max, we'll return the max size and leave it up to the
-	// caller to handle correctly.
-	if len(buf) > wire.SyncMaxChunkSize {
-		buf = buf[:wire.SyncMaxChunkSize]
+	written := 0
+
+	// If buf > 64k we'll have to send multiple chunks.
+	// TODO Refactor this into something that can coalesce smaller writes into a single chukn.
+	for len(buf) > 0 {
+		// Writes < 64k have a one-to-one mapping to chunks.
+		// If buffer is larger than the max, we'll return the max size and leave it up to the
+		// caller to handle correctly.
+		partialBuf := buf
+		if len(partialBuf) > wire.SyncMaxChunkSize {
+			partialBuf = partialBuf[:wire.SyncMaxChunkSize]
+		}
+
+		if err := w.sender.SendOctetString(wire.StatusSyncData); err != nil {
+			return written, err
+		}
+		if err := w.sender.SendBytes(partialBuf); err != nil {
+			return written, err
+		}
+
+		written += len(partialBuf)
+		buf = buf[len(partialBuf):]
 	}
 
-	if err := w.sender.SendOctetString(wire.StatusSyncData); err != nil {
-		return 0, err
-	}
-	if err := w.sender.SendBytes(buf); err != nil {
-		return 0, err
-	}
-
-	return len(buf), nil
+	return written, nil
 }
 
 func (w *syncFileWriter) Close() error {

sync_file_writer_test.go

@@ -42,18 +42,26 @@ func TestFileWriterWriteLargeChunk(t *testing.T) {
 	var buf bytes.Buffer
 	writer := newSyncFileWriter(wire.NewSyncSender(&buf), MtimeOfClose)
 
+	// Send just enough data to get 2 chunks.
 	data := make([]byte, wire.SyncMaxChunkSize+1)
 	n, err := writer.Write(data)
 
 	assert.NoError(t, err)
-	assert.Equal(t, wire.SyncMaxChunkSize, n)
-	assert.Equal(t, 8 + wire.SyncMaxChunkSize, buf.Len())
+	assert.Equal(t, wire.SyncMaxChunkSize+1, n)
+	assert.Equal(t, 8 + 8 + wire.SyncMaxChunkSize+1, buf.Len())
 
-	expectedHeader := []byte("DATA0000")
+	// First header.
+	chunk := buf.Bytes()[:8+wire.SyncMaxChunkSize]
+	expectedHeader := []byte("DATA----")
 	binary.LittleEndian.PutUint32(expectedHeader[4:], wire.SyncMaxChunkSize)
-	assert.Equal(t, expectedHeader, buf.Bytes()[:8])
+	assert.Equal(t, expectedHeader, chunk[:8])
+	assert.Equal(t, data[:wire.SyncMaxChunkSize], chunk[8:])
 
-	assert.Equal(t, string(data[:wire.SyncMaxChunkSize]), buf.String()[8:])
+	// Second header.
+	chunk = buf.Bytes()[wire.SyncMaxChunkSize+8:wire.SyncMaxChunkSize+8+1]
+	expectedHeader = []byte("DATA\000\000\000\000")
+	binary.LittleEndian.PutUint32(expectedHeader[4:], 1)
+	assert.Equal(t, expectedHeader, chunk[:8])
 }
 
 func TestFileWriterCloseEmpty(t *testing.T) {