[Python] Enable Flight servers to be implemented in pure Python

[asfimport]

While it will be straightforward to offer a Flight client to Python users, enabling servers to be written in Python will require a glue class to invoke methods on a provided server implementation, coercing to and from various Python objects and Arrow wrapper classes

Reporter: Wes McKinney / @wesm
Assignee: David Li / @lidavidm

PRs and other links:

• GitHub Pull Request #3566
• GitHub Pull Request #3712

_{Note: This issue was originally created as ARROW-3162. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
The likely way to accomplish this will be to create an implementation of arrow::flight::FlightServerBase in libarrow_python that takes the Python class implementing specific callback functions having a certain API. Opaque data from the server API will be passed to Python as pyarrow.Buffer objects or PyBytes as appropriate

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 3566
#3566

[asfimport]

David Li / @lidavidm:
Not quite done yet - there will be another PR or two to sort things out fully.

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 3712
#3712