RPyC:无法保存图像文件

Question

我正在开发使用平板扫描仪的Django应用程序。为了保持与扫描仪的连接，使用了RPyC。(连接到扫描仪需要很长时间，所以我想多次重复使用该连接。)

连接到扫描仪并保持服务运行似乎很好。我可以打电话给扫描仪，它马上就会有反应。但是我无法保存PIL图像文件，请参阅下面的错误。如果没有RPyC，就能够保存PIL图像文件。

Traceback (most recent call last):
  File "/usr/lib/python3.6/code.py", line 91, in runcode
    exec(code, self.locals)
  File "<console>", line 1, in <module>
  File "/home/user/Projects/django-project/project/appname/models.py", line 55, in scan_preview
    image_file.save(file_path)
  File "/home/user/Envs/project/lib/python3.6/site-packages/rpyc/core/netref.py", line 166, in __getattr__
    return syncreq(self, consts.HANDLE_GETATTR, name)
  File "/home/user/Envs/project/lib/python3.6/site-packages/rpyc/core/netref.py", line 76, in syncreq
    return conn.sync_request(handler, proxy, *args)
  File "/home/user/Envs/project/lib/python3.6/site-packages/rpyc/core/protocol.py", line 469, in sync_request
    return self.async_request(handler, *args, timeout=timeout).value
  File "/home/user/Envs/project/lib/python3.6/site-packages/rpyc/core/async_.py", line 102, in value
    raise self._obj
AttributeError: cannot access 'save'

看起来RPyC想要保存这个图像，我不明白为什么。在保存映像之前关闭连接将导致有关流正在关闭的错误。

我想要的是RPyC在返回PIL映像文件后停止干扰我。，我希望它返回PIL映像，而不是流mambo巨无霸。(对于RPyC，我不知道正确的术语。)

scanner_service.py

import rpyc
import sane


class Scanner(object):
    """
    The Scanner class is used to interact with flatbed scanners.
    """

    def __init__(self):
        sane.init()
        self.device_name = None
        self.error_message = None
        self.device = self.get_device()

    def get_device(self):
        """
        Return the first detected scanner and set the name.

        @return: sane.SaneDev
        """
        devices = sane.get_devices()
        print('Available devices:', devices)

        # Empty list means no scanner is connect or the connected scanner is
        # already being used
        if not devices:
            self.error_message = 'Scanner disconnect or already being used.'
            return None

        # open the first scanner you see
        try:
            device = sane.open(devices[0][0])
        except Exception as e:
            self.error_message = e
            print(e)
            return None

        brand = devices[0][1]
        model = devices[0][2]
        self.device_name = "{brand}_{model}".format(
            brand=brand,
            model=model
        )

        print("Device name:", self.device_name)

        # set to color scanning mode, this is not always the default mode
        device.mode = 'color'

        return device

    def print_options(self):
        """Print the device's options. Useful for development."""
        for opt in self.device.get_options():
            print(opt, '\n')

    def scan_image(self, dpi):
        """
        Scan an image.

        @param dpi: integer
        @return: PIL image
        """
        self.device.resolution = dpi
        self.device.start()
        image = self.device.snap()

        return image

    def scan_roi(
            self,
            top_left_x, top_left_y,
            bottom_right_x, bottom_right_y,
            dpi=2400
    ):
        """
        Scan a Region of Interest.

        The ROI is selected by giving two x/y coordinates, one for the top left
        and one for the bottom right. This creates a square that the scanner
        will scan.
        To create a ROI measure the amount of millimeters starting at the top
        left corner of the document.
        http://www.sane-project.org/html/doc014.html

        @param top_left_x: integer
        @param top_left_y: integer
        @param bottom_right_x: integer
        @param bottom_right_y: integer
        @param dpi: integer
        @return: PIL image
        """
        self.device.resolution = dpi

        # top left x/y
        self.device.tl_x = top_left_x
        self.device.tl_y = top_left_y

        # bottom right x/y
        self.device.br_x = bottom_right_x
        self.device.br_y = bottom_right_y

        self.device.start()
        image = self.device.snap()

        return image


class ScannerService(rpyc.Service):
    """
    Run the scanner as a service.

    Multiple clients can connect to the Scanner Service to use the flatbed
    scanner without having to wait for sane to setup a connection.
    """

    def __init__(self):
        self.scanner = Scanner()

    def on_connect(self, conn):
        pass

    def on_disconnect(self, conn):
        pass

    def exposed_get_device_name(self):
        """
        Return the name of the scanner

        @return: string
        """
        return self.scanner.device_name

    def exposed_scan_image(self, dpi):
        """
        Scan an image.

        @param dpi: integer
        @return: PIL image
        """
        image = self.scanner.scan_image(dpi)
        return image

    def exposed_scan_roi(
            self,
            top_left_x, top_left_y,
            bottom_right_x, bottom_right_y,
            dpi=2400
    ):
        """
        Scan a Region of Interest.

        @param top_left_x: integer
        @param top_left_y: integer
        @param bottom_right_x: integer
        @param bottom_right_y: integer
        @param dpi: integer
        @return: PIL image
       """
        image = self.scanner.scan_roi(
            top_left_x, top_left_y,
            bottom_right_x, bottom_right_y,
            dpi
        )
        return image


if __name__ == "__main__":
    from rpyc.utils.server import ThreadedServer
    t = ThreadedServer(ScannerService(), port=18861)
    t.start()

utils.py

class ScannerServiceConnection(object):
    """Connect to and interact with the scanner service."""

    def __init__(self):
        self.connection = self.get_connection()

    @staticmethod
    def get_connection():
        """
        Connect to the scanner service

        @return: ScannerService object
        """
        connection = rpyc.connect("localhost", 18861)
        return connection

    def get_device_name(self):
        """
        Return the name of the scanner

        @return: string
        """
        return self.connection.root.exposed_get_device_name()

    def scan_image(self, dpi):
        """
        Scan an image.

        @param dpi: integer
        @return: PIL image
        """
        image = self.connection.exposed_scan_image(dpi)
        return image

    def scan_roi(
            self,
            top_left_x, top_left_y,
            bottom_right_x, bottom_right_y,
            dpi=2400
    ):
        """
        Scan a Region of Interest.

        @param top_left_x: integer
        @param top_left_y: integer
        @param bottom_right_x: integer
        @param bottom_right_y: integer
        @param dpi: integer
        @return: PIL image
       """
        image = self.connection.root.exposed_scan_roi(
            top_left_x, top_left_y,
            bottom_right_x, bottom_right_y,
            dpi
        )
        return image

Answer 1

我找到了我问题的答案，耶！

我所要做的就是将访问策略更改为以下内容。现在可以访问PIL映像上的保存方法。

我不知道这是不是正确的方法。如果没有，请告诉我。

if __name__ == "__main__":
    from rpyc.utils.server import ThreadedServer
    t = ThreadedServer(
        ScannerService(), port=18861,
        protocol_config={'allow_public_attrs': True}
    )
    t.start()