| #!/usr/bin/env python |
| """Small helper class to provide a small slice of a stream.""" |
| |
| from apitools.base.py import exceptions |
| |
| |
| class StreamSlice(object): |
| |
| """Provides a slice-like object for streams.""" |
| |
| def __init__(self, stream, max_bytes): |
| self.__stream = stream |
| self.__remaining_bytes = max_bytes |
| self.__max_bytes = max_bytes |
| |
| def __str__(self): |
| return 'Slice of stream %s with %s/%s bytes not yet read' % ( |
| self.__stream, self.__remaining_bytes, self.__max_bytes) |
| |
| def __len__(self): |
| return self.__max_bytes |
| |
| def __nonzero__(self): |
| # For 32-bit python2.x, len() cannot exceed a 32-bit number; avoid |
| # accidental len() calls from httplib in the form of "if this_object:". |
| return bool(self.__max_bytes) |
| |
| @property |
| def length(self): |
| # For 32-bit python2.x, len() cannot exceed a 32-bit number. |
| return self.__max_bytes |
| |
| def read(self, size=None): # pylint: disable=missing-docstring |
| """Read at most size bytes from this slice. |
| |
| Compared to other streams, there is one case where we may |
| unexpectedly raise an exception on read: if the underlying stream |
| is exhausted (i.e. returns no bytes on read), and the size of this |
| slice indicates we should still be able to read more bytes, we |
| raise exceptions.StreamExhausted. |
| |
| Args: |
| size: If provided, read no more than size bytes from the stream. |
| |
| Returns: |
| The bytes read from this slice. |
| |
| Raises: |
| exceptions.StreamExhausted |
| |
| """ |
| if size is not None: |
| read_size = min(size, self.__remaining_bytes) |
| else: |
| read_size = self.__remaining_bytes |
| data = self.__stream.read(read_size) |
| if read_size > 0 and not data: |
| raise exceptions.StreamExhausted( |
| 'Not enough bytes in stream; expected %d, exhausted ' |
| 'after %d' % ( |
| self.__max_bytes, |
| self.__max_bytes - self.__remaining_bytes)) |
| self.__remaining_bytes -= len(data) |
| return data |
