Søren Rasmussen [email protected]
Oliver Gyldenberg Hjermitslev [email protected]

A tiny RPC framework, intended for calling Python functionality from Unity, using JSON signalling over ZMQ.

For an example of how to set up a Python RPC server and make a simple request from Python, refer to rpc_server.ipynb and rpc_client.ipynb.

Messaging is done via ZMQ (Request-Reply) using JSON encoded messages.

The structure of a call is as follows:

{
    rpc_tag: '__RPC_CALL__', #Marks this message as a RPC call
    handle: 'handle_name',   #Tells the server which function we're calling
    uid: 1234,               #A marker used to recognize the response to this call
    args: <args>,            #List of positional arguments
    kwargs: <kwargs>         #Dict of keyword arguments
}

JSON-unfriendly argument- and keyword argument types are converted to a JSON-friendly format for transmission and then back again. Conversion functions are rigistered in the the argument-encoder and -decoder dictionaries, pyunirpc.arg_encoders and pyunirpc.arg_decoders.

The argument encoder keeps track of special object types and the functions to convert them to JSON. By default, the only registered encoder is np.ndarray: ndarray2rpcarg, which handles Numpy arrays. Objects are encoded as dictionaries, holding the necessary data. An example for a Numpy array:

{
    'rpc_tag': '__RPC_VAL_NDARRAY__', #Unique tag for this type (ndarray in this case)
    'dtype': dtype,                   #Needed to re-create the array
    'shape': shape,                   #Needed to re-create the array
    'data': data_base64               #Base-64 endcoded raw data.
}

The argument decoder looks through (keyword-)arguments for dictionaries with a rpc_tag key which matches a key in the decoder dictionary and uses the corresponding function to transform the JSON dictionary to a Python object. By default, the only registered decoder is '__RPC_VAL_NDARRAY__': rpcarg2ndarray.

There are a few reserved tags, which cannot be used by custom encoder/decoders. These are:

__RPC_CALL__
__RPC_RESULT__
__RPC_ERROR__

The source includes the Unity project and a .unitypackage. In the Unity editor, import the .unitypackage (Assets->Import Package->Custom Package...)

This package includes a scene labelled "SampleScene" and a Test.cs script, which illustrates basic use of the plugin.

This sample scene illustrates communication between the Unity client and a python server running on localhost:6789

The REQ/RES structure, and thus the rpc tags, exist as separate classes which derive from a common PyUniType. All further distinction requires safe casting to e.g. PyUniCall, PyUniError, etc.

Deserializing the JSON with .JsonConstructor attempts, iteratively, to deserialize included PyUniValNdArrays to reduce manual conversions.

Data from PyUniValNdArrays can be collected as generic Array type using .GetData and casted. It is recommended to keep a reference to this data alive as long as necessary, as the conversion can be costly.