1#!/usr/bin/env python 2"""Small helper class to provide a small slice of a stream. 3 4This class reads ahead to detect if we are at the end of the stream. 5""" 6 7from apitools.base.py import exceptions 8 9 10# TODO(user): Consider replacing this with a StringIO. 11class BufferedStream(object): 12 13 """Buffers a stream, reading ahead to determine if we're at the end.""" 14 15 def __init__(self, stream, start, size): 16 self.__stream = stream 17 self.__start_pos = start 18 self.__buffer_pos = 0 19 self.__buffered_data = self.__stream.read(size) 20 self.__stream_at_end = len(self.__buffered_data) < size 21 self.__end_pos = self.__start_pos + len(self.__buffered_data) 22 23 def __str__(self): 24 return ('Buffered stream %s from position %s-%s with %s ' 25 'bytes remaining' % (self.__stream, self.__start_pos, 26 self.__end_pos, self._bytes_remaining)) 27 28 def __len__(self): 29 return len(self.__buffered_data) 30 31 @property 32 def stream_exhausted(self): 33 return self.__stream_at_end 34 35 @property 36 def stream_end_position(self): 37 return self.__end_pos 38 39 @property 40 def _bytes_remaining(self): 41 return len(self.__buffered_data) - self.__buffer_pos 42 43 def read(self, size=None): # pylint: disable=invalid-name 44 """Reads from the buffer.""" 45 if size is None or size < 0: 46 raise exceptions.NotYetImplementedError( 47 'Illegal read of size %s requested on BufferedStream. ' 48 'Wrapped stream %s is at position %s-%s, ' 49 '%s bytes remaining.' % 50 (size, self.__stream, self.__start_pos, self.__end_pos, 51 self._bytes_remaining)) 52 53 data = '' 54 if self._bytes_remaining: 55 size = min(size, self._bytes_remaining) 56 data = self.__buffered_data[ 57 self.__buffer_pos:self.__buffer_pos + size] 58 self.__buffer_pos += size 59 return data 60