python/util/file_object_adapter.py

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""FileObjectAdapter class.

Used in conjunction with PythonOutputStream/PythonInputStream to allow a C++
OutputStream/InputStream to interact with a Python file-like object.
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import google_type_annotations
from __future__ import print_function

import io
from typing import BinaryIO

from tink.python.cc.clif import python_file_object_adapter


class FileObjectAdapter(python_file_object_adapter.PythonFileObjectAdapter):
  """Adapts a Python file object for use in C++."""

  def __init__(self, file_object: BinaryIO):
    # Required to fix CLIF "Value invalidated due to capture by std::unique_ptr"
    super(FileObjectAdapter, self).__init__()
    self._file_object = file_object

  def write(self, data: bytes) -> int:
    """Writes to underlying file object and returns number of bytes written."""
    try:
      written = self._file_object.write(data)
      return 0 if written is None else written
    except io.BlockingIOError as e:
      return e.characters_written

  def close(self) -> None:
    self._file_object.close()

  def read(self, size: int) -> bytes:
    """Reads at most 'size' bytes from the underlying file object.

    Args:
      size: A non-negative integer, maximum number of bytes to read.

    Returns:
      Bytes that were read. An empty bytes object is returned if no bytes are
      available at the moment.

    Raises:
      EOFError if the file object is already at EOF.
    """
    if size < 0:
      raise ValueError('size must be non-negative')

    try:
      data = self._file_object.read(size)
      if data is None:
        return b''
      elif not data and size > 0:
        raise EOFError('EOF')
      return data
    except io.BlockingIOError:
      return b''