Parse the form data in the environ and return it as tuple in the form
``(stream, form, files)``. You should only call this method if the
transport method is `POST`, `PUT`, or `PATCH`.
If the mimetype of the data transmitted is `multipart/form-data` the
files multidict will be filled with `FileStorage` objects. If the
mimetype is unknown the input stream is wrapped and returned as first
argument, else the stream is empty.
This is a shortcut for the common usage of :class:`FormDataParser`.
Have a look at :ref:`dealing-with-request-data` for more details.
.. versionadded:: 0.5
The `max_form_memory_size`, `max_content_length` and
`cls` parameters were added.
.. versionadded:: 0.5.1
The optional `silent` flag was added.
:param environ: the WSGI environment to be used for parsing.
:param stream_factory: An optional callable that returns a new read and
writeable file descriptor. This callable works
the same as :meth:`~BaseResponse._get_file_stream`.
:param charset: The character set for URL and url encoded form data.
:param errors: The encoding error behavior.
:param max_form_memory_size: the maximum number of bytes to be accepted for
in-memory stored form data. If the data
exceeds the value specified an
:exc:`~exceptions.RequestEntityTooLarge`
exception is raised.
:param max_content_length: If this is provided and the transmitted data
is longer than this value an
:exc:`~exceptions.RequestEntityTooLarge`
exception is raised.
:param cls: an optional dict class to use. If this is not specified
or `None` the default :class:`MultiDict` is used.
:param silent: If set to False parsing errors will not be caught.
:return: A tuple in the form ``(stream, form, files)``.