tools/telemetry/third_party/gsutilz/gslib/file_part.py

   1 # -*- coding: utf-8 -*-
   2 # Copyright 2013 Google Inc. All Rights Reserved.
   3 #
   4 # Licensed under the Apache License, Version 2.0 (the "License");
   5 # you may not use this file except in compliance with the License.
   6 # You may obtain a copy of the License at
   7 #
   8 #     http://www.apache.org/licenses/LICENSE-2.0
   9 #
  10 # Unless required by applicable law or agreed to in writing, software
  11 # distributed under the License is distributed on an "AS IS" BASIS,
  12 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13 # See the License for the specific language governing permissions and
  14 # limitations under the License.
  15 """FilePart implementation for representing part of a file."""
  16
  17 from __future__ import absolute_import
  18
  19 import os
  20
  21
  22 class FilePart(file):
  23   """Subclass of the file API for representing part of a file.
  24
  25   This class behaves as a contiguous subset of a given file (e.g., this object
  26   will behave as though the desired part of the file was written to another
  27   file, and the second file was opened).
  28   """
  29
  30   # pylint: disable=super-init-not-called
  31   def __init__(self, filename, offset, length):
  32     """Initializes the FilePart.
  33
  34     Args:
  35       filename: The name of the existing file, of which this object represents
  36                 a part.
  37       offset: The position (in bytes) in the original file that corresponds to
  38               the first byte of the FilePart.
  39       length: The total number of bytes in the FilePart.
  40     """
  41     self._fp = open(filename, 'rb')
  42     self.length = length
  43     self._start = offset
  44     self._end = self._start + self.length
  45     self._fp.seek(self._start)
  46
  47   def __enter__(self):
  48     pass
  49
  50   # pylint: disable=redefined-builtin
  51   def __exit__(self, type, value, traceback):
  52     self.close()
  53
  54   def tell(self):
  55     return self._fp.tell() - self._start
  56
  57   def read(self, size=-1):
  58     if size < 0:
  59       size = self.length
  60     size = min(size, self._end - self._fp.tell())  # Only read to our EOF
  61     return self._fp.read(max(0, size))
  62
  63   def seek(self, offset, whence=os.SEEK_SET):
  64     if whence == os.SEEK_END:
  65       return self._fp.seek(offset + self._end)
  66     elif whence == os.SEEK_CUR:
  67       return self._fp.seek(offset, whence)
  68     else:
  69       return self._fp.seek(self._start + offset)
  70
  71   def close(self):
  72     self._fp.close()
  73
  74   def flush(self, size=None):
  75     raise NotImplementedError('flush is not implemented in FilePart.')
  76
  77   def fileno(self, size=None):
  78     raise NotImplementedError('fileno is not implemented in FilePart.')
  79
  80   def isatty(self, size=None):
  81     raise NotImplementedError('isatty is not implemented in FilePart.')
  82
  83   def next(self, size=None):
  84     raise NotImplementedError('next is not implemented in FilePart.')
  85
  86   def readline(self, size=None):
  87     raise NotImplementedError('readline is not implemented in FilePart.')
  88
  89   def readlines(self, size=None):
  90     raise NotImplementedError('readlines is not implemented in FilePart.')
  91
  92   def xreadlines(self, size=None):
  93     raise NotImplementedError('xreadlines is not implemented in FilePart.')
  94
  95   def truncate(self, size=None):
  96     raise NotImplementedError('truncate is not implemented in FilePart.')
  97
  98   def write(self, size=None):
  99     raise NotImplementedError('write is not implemented in FilePart.')
 100
 101   def writelines(self, size=None):
 102     raise NotImplementedError('writelines is not implemented in FilePart.')