1#!/usr/bin/env python 2# 3# Copyright 2015 Google Inc. 4# 5# Licensed under the Apache License, Version 2.0 (the "License"); 6# you may not use this file except in compliance with the License. 7# You may obtain a copy of the License at 8# 9# http://www.apache.org/licenses/LICENSE-2.0 10# 11# Unless required by applicable law or agreed to in writing, software 12# distributed under the License is distributed on an "AS IS" BASIS, 13# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14# See the License for the specific language governing permissions and 15# limitations under the License. 16 17"""Small helper class to provide a small slice of a stream.""" 18 19from apitools.base.py import exceptions 20 21 22class StreamSlice(object): 23 24 """Provides a slice-like object for streams.""" 25 26 def __init__(self, stream, max_bytes): 27 self.__stream = stream 28 self.__remaining_bytes = max_bytes 29 self.__max_bytes = max_bytes 30 31 def __str__(self): 32 return 'Slice of stream %s with %s/%s bytes not yet read' % ( 33 self.__stream, self.__remaining_bytes, self.__max_bytes) 34 35 def __len__(self): 36 return self.__max_bytes 37 38 def __nonzero__(self): 39 # For 32-bit python2.x, len() cannot exceed a 32-bit number; avoid 40 # accidental len() calls from httplib in the form of "if this_object:". 41 return bool(self.__max_bytes) 42 43 @property 44 def length(self): 45 # For 32-bit python2.x, len() cannot exceed a 32-bit number. 46 return self.__max_bytes 47 48 def read(self, size=None): # pylint: disable=missing-docstring 49 """Read at most size bytes from this slice. 50 51 Compared to other streams, there is one case where we may 52 unexpectedly raise an exception on read: if the underlying stream 53 is exhausted (i.e. returns no bytes on read), and the size of this 54 slice indicates we should still be able to read more bytes, we 55 raise exceptions.StreamExhausted. 56 57 Args: 58 size: If provided, read no more than size bytes from the stream. 59 60 Returns: 61 The bytes read from this slice. 62 63 Raises: 64 exceptions.StreamExhausted 65 66 """ 67 if size is not None: 68 read_size = min(size, self.__remaining_bytes) 69 else: 70 read_size = self.__remaining_bytes 71 data = self.__stream.read(read_size) 72 if read_size > 0 and not data: 73 raise exceptions.StreamExhausted( 74 'Not enough bytes in stream; expected %d, exhausted ' 75 'after %d' % ( 76 self.__max_bytes, 77 self.__max_bytes - self.__remaining_bytes)) 78 self.__remaining_bytes -= len(data) 79 return data 80