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- from io import BytesIO
- class CallbackFileWrapper(object):
- """
- Small wrapper around a fp object which will tee everything read into a
- buffer, and when that file is closed it will execute a callback with the
- contents of that buffer.
- All attributes are proxied to the underlying file object.
- This class uses members with a double underscore (__) leading prefix so as
- not to accidentally shadow an attribute.
- """
- def __init__(self, fp, callback):
- self.__buf = BytesIO()
- self.__fp = fp
- self.__callback = callback
- def __getattr__(self, name):
- # The vaguaries of garbage collection means that self.__fp is
- # not always set. By using __getattribute__ and the private
- # name[0] allows looking up the attribute value and raising an
- # AttributeError when it doesn't exist. This stop thigns from
- # infinitely recursing calls to getattr in the case where
- # self.__fp hasn't been set.
- #
- # [0] https://docs.python.org/2/reference/expressions.html#atom-identifiers
- fp = self.__getattribute__('_CallbackFileWrapper__fp')
- return getattr(fp, name)
- def __is_fp_closed(self):
- try:
- return self.__fp.fp is None
- except AttributeError:
- pass
- try:
- return self.__fp.closed
- except AttributeError:
- pass
- # We just don't cache it then.
- # TODO: Add some logging here...
- return False
- def read(self, amt=None):
- data = self.__fp.read(amt)
- self.__buf.write(data)
- if self.__is_fp_closed():
- if self.__callback:
- self.__callback(self.__buf.getvalue())
- # We assign this to None here, because otherwise we can get into
- # really tricky problems where the CPython interpreter dead locks
- # because the callback is holding a reference to something which
- # has a __del__ method. Setting this to None breaks the cycle
- # and allows the garbage collector to do it's thing normally.
- self.__callback = None
- return data
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