<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _merge_prefix(self, size):
 """Replace the first entries in a deque of strings with a single string of up to size bytes. deque(['abcde', 'fghi', 'j']) Strings will be split as necessary to reach the desired size. deque(['abcdefg', 'hi', 'j']) deque(['abc', 'defg', 'hi', 'j']) deque(['abcdefghij']) """

        if len(self._buf) == 1 and len(self._buf[0]) <= size:
            return
        prefix = []
        remaining = size
        while self._buf and remaining > 0:
            chunk = self._buf.popleft()
            if len(chunk) > remaining:
                self._buf.appendleft(chunk[remaining:])
                chunk = chunk[:remaining]
            prefix.append(chunk)
            remaining -= len(chunk)
        if prefix:
            self._buf.appendleft(b''.join(prefix))
        if not self._buf:
            self._buf.appendleft(b'')