80 lines
2.4 KiB
Python
80 lines
2.4 KiB
Python
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"""Small helper class to provide a small slice of a stream.
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This class reads ahead to detect if we are at the end of the stream.
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"""
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class BufferedStream(object):
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"""Buffers a stream, reading ahead to determine if we're at the end.
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:type stream: readable file-like object
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:param stream: the stream to be buffered
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:type start: integer
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:param start: the starting point in the stream
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:type size: integer
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:param size: the size of the buffer
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"""
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def __init__(self, stream, start, size):
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self._stream = stream
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self._start_pos = start
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self._buffer_pos = 0
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self._buffered_data = self._stream.read(size)
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self._stream_at_end = len(self._buffered_data) < size
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self._end_pos = self._start_pos + len(self._buffered_data)
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def __repr__(self):
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return ('Buffered stream %s from position %s-%s with %s '
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'bytes remaining' % (self._stream, self._start_pos,
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self._end_pos, self._bytes_remaining))
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def __len__(self):
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return len(self._buffered_data)
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@property
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def stream_exhausted(self):
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"""Does the stream have bytes remaining beyond the buffer
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:rtype: boolean
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"""
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return self._stream_at_end
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@property
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def stream_end_position(self):
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"""Point to which stream was read into the buffer
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:rtype: integer
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"""
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return self._end_pos
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@property
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def _bytes_remaining(self):
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"""Bytes remaining to be read from the buffer
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:rtype: integer
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"""
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return len(self._buffered_data) - self._buffer_pos
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def read(self, size=None):
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"""Read bytes from the buffer.
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:type size: integer or None
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:param size: How many bytes to read (defaults to all remaining bytes).
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"""
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if size is None or size < 0:
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raise ValueError(
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'Illegal read of size %s requested on BufferedStream. '
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'Wrapped stream %s is at position %s-%s, '
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'%s bytes remaining.' %
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(size, self._stream, self._start_pos, self._end_pos,
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self._bytes_remaining))
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if not self._bytes_remaining:
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return b''
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size = min(size, self._bytes_remaining)
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data = self._buffered_data[self._buffer_pos:self._buffer_pos + size]
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self._buffer_pos += size
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return data
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