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PROTOCOL.md

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Protocol between AD plugin and worker program

  • The AD plugin provides a unix socket to talk to the workers
  • Every message is a JSON in which the root element is an object.
  • The frame data is passed in shared memory

Handshake

  • Once a worker connects to the AD plugin socket, it will send a message to indicate its name, e.g.: {"class_name" : "gauss_fit"} If the server doesn't expect that type of worker, it will send an error message and close the connection. If the server expects that worker, it will send a message indicating the name of the shared memory file (which will be present in /dev/shm), e.g. {"ok": true, "shm_name": "shm_file1", "vars": {}}, this message can also contain a set of values for the plugin parameters inside key "vars"

Updating parameters

  • The worker can update AD parameters by sending a message with a "vars" object, e.g. {"vars": {"sModel": "model1", "iVersion": 1, "dTemperature": 25.0}}
  • The name of each parameters should indicate its type in the first letter, 'i' for integer, 'd' for double or 's' for string.
  • The AD plugin can update worker parameters by sending the same type of message

Sending frames

  • The AD plugin will tell the worker to process a frame by sending a message like this: {"frame_dims": (1024, 768), "data_type": "uint8", "frame_loc": 0, "ts": 41810261.4522744}
  • "data_type" indicates the data type, first part indicates if is signed integer(int), unsigned integer(uint) or float(float), then follows a number indicating bits of data type
  • "frame_loc" indicates the offset in bytes from the frame data from the start of shared memory
  • "ts" indicates the timestamp associated to the frame

Receiving frames

  • The worker will notify the AD plugin of a frame by sending a message like this: {"push_frame": true, "frame_dims": (1024, 768), "data_type": "uint8"}

if data_type or frame_dims is missing, it will be assumed to be the same as input frame

  • Given that the same shared memory region is used for the output frame, the worker can produce only frames of the same size or less than the input frame.
  • If the worker doesn't want the frame to be pushed, it will have the field "push_frame" set to false, this also let the AD plugin know that frame can be released, e.g. {"push_frame": false}
  • The message can contain the field "vars" to update parameters
  • The message can contain the field "attrs" to associate attributes to the frame
  • New attributes can only be integer, double or string