handleWriteComplete = function(err, written, buffer) {
                    totalWritten += written;

                    if (totalWritten >= buffer.length) {
                      resolve();
                    } else {
                      // We still have more to write...
                      fs.write(
                          fd, buffer, totalWritten,
                          buffer.length - totalWritten,
                          newEntry.offset + totalWritten, handleWriteComplete);
                    }
                  }
Write the Blob-convertible data to the buffer at the current seek
position.

Note: If overwriting existing data, the write must not cross preexisting
block boundaries (written data must be fully contained by the extent of a
previous write).