[Python] Create Python examples of HTTP POST Arrow client/server supporting multipart/form-data request

[ianmcook]

Describe the enhancement requested

Contribute Python client and server examples to the HTTP POST multipart examples in the arrow-experiments repo. This should demonstrate a client sending a POST request to a server with a multipart request body (Content-Type: multipart/form-data) containing JSON data (Content-Type: application/json) and Arrow IPC stream data (Content-Type: application/vnd.apache.arrow.stream).

Component(s)

Python

[ianmcook]

A challenge with this approach is that the part boundaries must not occur in the data, as described here: https://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.2

So to support all possible sequences of bytes that might occur in Arrow IPC stream data, the client would need to be able to dynamically choose a viable boundary sequence by checking that it is not contained in the IPC stream bytes to be sent in the request.

On the other hand, maybe it's sufficient for the client to simply use a part boundary that is highly unlikely to occur in the IPC stream bytes.

[ianmcook]

apache/arrow-experiments#33 established a good practice for creating a random byte string with enough entropy to make the probability of a collision negligible.

[github-actions]

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