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