Package: trio-protocol
# trio-protocolThis implements the `asyncio.Transport` interface and foundational asyncio classes such as `asyncio.Task` on top of [`trio`](https://github.com/python-trio/trio), to aid porting `asyncio` libraries. The idea is to allow `trio` to run an [`asyncio.Protocol`](https://docs.python.org/3/library/asyncio-protocol.html#protocols), making it possible for a single code base to run on both frameworks.It is **not a goal** of `trio-protocol` to let you run `asyncio` code on `trio` without any changes. If you need this, look at [`asyncio-trio`](https://github.com/python-trio/trio-asyncio).#### What is and is not currently supportedThis is an early version. You can use it to support some basic `asyncio` servers. However, it lacks:- Support for clients (only servers have been tested)- A test suite.- Robust experience running it in production.- Likely, implementations for useful/necessary methods that asyncio code is using in the wild, and should be added.## UsageLet's say you want to run the [`asyncio-len-prefixed-string-protocol.py` from the python3-samples repository](https://github.com/eliben/python3-samples/blob/master/async/asyncio-len-prefixed-string-protocol.py) on top of `trio`.If you follow the link, you see that the module first implements subclass of `asyncio.Protocol`, which it then subclasses further. Ultimately, the protocol as implemented reads strings from the client, prefixed by length, and sends back an `"ok"` message.At the bottom of the file, you'll find the following code to start the server:```pythonloop = asyncio.get_event_loop()coro = loop.create_server(MyStringReceiver, '127.0.0.1', 5566)server = loop.run_until_complete(coro)print('serving on {}'.format(server.sockets[0].getsockname()))try:loop.run_forever()except KeyboardInterrupt:print("exit")finally:server.close()loop.close()```This creates an `asyncio` server running on port `5566`. Every connection to that port will be served by the `MyStringReceiver` protocol. Specifically, `loop.create_server()` will setup the server's socket (since it is an `async` function, it will not do anything until awaited, which in this case we do via `loop.run_until_complete`). Whenever someone connects to the server, asyncio will schedule a task to handle the connection. We run `loop.run_forever()` to have the loop be active and process these tasks.Now let's run this on `trio` instead. Replace this section of the code with:```pythonimport triofrom trio_protocol import run_servertrio.run(run_server, MyStringReceiver, '127.0.0.1', 5566)```And that would work! The code is a bit shorter than the original, partly because setting up trio is just less verbose, and partly because we do less: We do not handle `KeyboardInterrupt` cleanly, and we do not print a message once we are ready to accept connections. Instead, `trio_protocol.run_server` is a shortcut that does everything for us: It opens a nursery, starts a server, and runs the `asyncio.Protocol` on that server.If we want to copy the original code more exactly, I can do this:```pythonimport triofrom trio_protocol import create_serverasync def run_server():async with trio.open_nursery() as nursery:server = await create_server(nursery, MyStringReceiver, '127.0.0.1', 5566)print('serving on {}'.format(server.sockets[0].getsockname()))try:trio.run(run_server)except KeyboardInterrupt:print("exit")``````trio_protocol.create_server``` will start listening on the socket. It will return a `trio_protocol.Server` object that is intended to mirror `asyncio.Server`. You are then free to run your own code, with the server running in the background, similar to the `asyncio` version.>>> Note: To test this server, you can use:>>> `python -c "import struct; print((b'%shello world' % struct.pack('<L', 12)).decode('ascii'))" | nc localhost 5566`### What if the protocol needs access to the loopIf the protocol uses the `asyncio` loop, for example to start background tasks, you can use `trio_protocol.Loop` which is a loop-like class that supports some of the commonly used methods such as `call_later` or `create_task`. Most protocols are written to accept a `loop` argument, so you would do:```pythonimport functoolsimport triofrom trio_protocol import Loop, run_serverasync def run_server():async with trio.open_nursery() as nursery:loop = Loop(nursery)protocol_factory = functools.partial(MyProtocol, loop=loop)await create_server(nursery, protocol_factory, '127.0.0.1', 5566)trio.run(run_server)```Background task the protocol want to spawn now run within the nursery given to `trio_protocol.Loop`.Note: It is strictly a requirement that the protocol class you want to run uses an explicit loop. Most `asyncio` interfaces are written in such a way that when an explicit loop is not passed, the current global loop will be used automatically. This won't work, because you would end up using the `asyncio` loop.