# documentação Django 2.0.8

# Código fonte para django.core.files.uploadhandler

    """
    Base file upload handler classes, and the built-in concrete subclasses
    """

    from io import BytesIO

    from django.conf import settings
    from django.core.files.uploadedfile import (
        InMemoryUploadedFile, TemporaryUploadedFile,
    )
    from django.utils.module_loading import import_string

    __all__ = [
        'UploadFileException', 'StopUpload', 'SkipFile', 'FileUploadHandler',
        'TemporaryFileUploadHandler', 'MemoryFileUploadHandler', 'load_handler',
        'StopFutureHandlers'
    ]

    class UploadFileException(Exception):
        """
        Any error having to do with uploading files.
        """
        pass

    class StopUpload(UploadFileException):
        """
        This exception is raised when an upload must abort.
        """
        def __init__(self, connection_reset=False):
            """
            If ``connection_reset`` is ``True``, Django knows will halt the upload
            without consuming the rest of the upload. This will cause the browser to
            show a "connection reset" error.
            """
            self.connection_reset = connection_reset

        def __str__(self):
            if self.connection_reset:
                return 'StopUpload: Halt current upload.'
            else:
                return 'StopUpload: Consume request data, then halt.'

    class SkipFile(UploadFileException):
        """
        This exception is raised by an upload handler that wants to skip a given file.
        """
        pass

    class StopFutureHandlers(UploadFileException):
        """
        Upload handers that have handled a file and do not want future handlers to
        run should raise this exception instead of returning None.
        """
        pass

    class FileUploadHandler:
        """
        Base class for streaming upload handlers.
        """
        chunk_size = 64 * 2 ** 10  # : The default chunk size is 64 KB.

        def __init__(self, request=None):
            self.file_name = None
            self.content_type = None
            self.content_length = None
            self.charset = None
            self.content_type_extra = None
            self.request = request

        def handle_raw_input(self, input_data, META, content_length, boundary, encoding=None):
            """
            Handle the raw input from the client.

            Parameters:

                :input_data:
                    An object that supports reading via .read().
                :META:
                    ``request.META``.
                :content_length:
                    The (integer) value of the Content-Length header from the
                    client.
                :boundary: The boundary from the Content-Type header. Be sure to
                    prepend two '--'.
            """
            pass

        def new_file(self, field_name, file_name, content_type, content_length, charset=None, content_type_extra=None):
            """
            Signal that a new file has been started.

            Warning: As with any data from the client, you should not trust
            content_length (and sometimes won't even get it).
            """
            self.field_name = field_name
            self.file_name = file_name
            self.content_type = content_type
            self.content_length = content_length
            self.charset = charset
            self.content_type_extra = content_type_extra

        def receive_data_chunk(self, raw_data, start):
            """
            Receive data from the streamed upload parser. ``start`` is the position
            in the file of the chunk.
            """
            raise NotImplementedError('subclasses of FileUploadHandler must provide a receive_data_chunk() method')

        def file_complete(self, file_size):
            """
            Signal that a file has completed. File size corresponds to the actual
            size accumulated by all the chunks.

            Subclasses should return a valid ``UploadedFile`` object.
            """
            raise NotImplementedError('subclasses of FileUploadHandler must provide a file_complete() method')

        def upload_complete(self):
            """
            Signal that the upload is complete. Subclasses should perform cleanup
            that is necessary for this handler.
            """
            pass

    class TemporaryFileUploadHandler(FileUploadHandler):
        """
        Upload handler that streams data into a temporary file.
        """
        def new_file(self, *args, **kwargs):
            """
            Create the file object to append to as data is coming in.
            """
            super().new_file(*args, **kwargs)
            self.file = TemporaryUploadedFile(self.file_name, self.content_type, 0, self.charset, self.content_type_extra)

        def receive_data_chunk(self, raw_data, start):
            self.file.write(raw_data)

        def file_complete(self, file_size):
            self.file.seek(0)
            self.file.size = file_size
            return self.file

    class MemoryFileUploadHandler(FileUploadHandler):
        """
        File upload handler to stream uploads into memory (used for small files).
        """

        def handle_raw_input(self, input_data, META, content_length, boundary, encoding=None):
            """
            Use the content_length to signal whether or not this handler should be
            used.
            """
            # Check the content-length header to see if we should
            # If the post is too large, we cannot use the Memory handler.
            if content_length > settings.FILE_UPLOAD_MAX_MEMORY_SIZE:
                self.activated = False
            else:
                self.activated = True

        def new_file(self, *args, **kwargs):
            super().new_file(*args, **kwargs)
            if self.activated:
                self.file = BytesIO()
                raise StopFutureHandlers()

        def receive_data_chunk(self, raw_data, start):
            """Add the data to the BytesIO file."""
            if self.activated:
                self.file.write(raw_data)
            else:
                return raw_data

        def file_complete(self, file_size):
            """Return a file object if this handler is activated."""
            if not self.activated:
                return

            self.file.seek(0)
            return InMemoryUploadedFile(
                file=self.file,
                field_name=self.field_name,
                name=self.file_name,
                content_type=self.content_type,
                size=file_size,
                charset=self.charset,
                content_type_extra=self.content_type_extra
            )

    def load_handler(path, *args, **kwargs):
        """
        Given a path to a handler, return an instance of that handler.

        E.g.::
            >>> from django.http import HttpRequest
            >>> request = HttpRequest()
            >>> load_handler('django.core.files.uploadhandler.TemporaryFileUploadHandler', request)
            <TemporaryFileUploadHandler object at 0x...>
        """
        return import_string(path)(*args, **kwargs)