"""
Defines utility methods for working with gzip streams.
"""

import zlib

# Window size for decompressing GZIP streams.
# This results in ZLIB automatically detecting the GZIP headers.
# http://stackoverflow.com/questions/3122145/zlib-error-error-3-while-decompressing-incorrect-header-check/22310760#22310760
ZLIB_GZIP_WINDOW = zlib.MAX_WBITS | 32

def calculate_size_handler():
  """ Returns an object and a SocketReader handler. The handler will gunzip the data it receives,
      adding the size found to the object.
  """
  uncompressed_size_info = {
    'size': 0
  }
 
  decompressor = zlib.decompressobj(ZLIB_GZIP_WINDOW)

  def fn(buf):
    uncompressed_size_info['size'] += len(decompressor.decompress(buf))

  return uncompressed_size_info, fn