asyncio.start_server example (!)

[cemox]

I will change the utime.sleep() to asyncio.sleep(). @pythoncoder and @jomas, thank you both for your comments.

I can listen to the radio channels pretty well now.

Now, I have another problem. I want to control my web radio from a remote web browser, my esp8266 board now works as a (AP) server and (STA) client now. For keeping things simple, I just want to change the radio channel by clicking a button. On the client side,

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reader, writer = await asyncio.open_connection(host, port)

hadles the incoming audio data pretty well. On the server side

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loop.create_task(asyncio.start_server(myWeb.serve, "0.0.0.0", 80))

does the job. All project runs in a asyncio loop. But when I click "Next Station" button on the web browser, it succesfully triggers "change channel function" (I confirmed that this function works), ESP8266 looses internet connection. So the work flow is like this:

1) system initiation
2) picks the firs radio station link
3) plays it
4) starts server, shows a button
5) pushing button triggers "change the channel" function (normallly works fine, tested)
6) cannot connect internet (!)

I suspect these two lines of code clash with each other, bu I cannot figure out how.

As a last resort, I will use two esp8266 boards, one will be responsible for the server side and the other for the client side.

[cemox]

Thank you Jomas, waiting for the blank lines solved both the server and the client side communication problems

At last it worked !

Putting a small delay right after

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writer.awrite(resp)

, solved the problem. The whole working code is :

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import uasyncio as asyncio
import utime

async def serve(reader, writer):
    t = utime.ticks_ms()
    resp = b"HTTP/1.0 200 OK\r\n\r\n" + "Ticks = {TICKS}\r\n".format(TICKS=t) 
    l = await reader.read(256)
    print(l)
    await writer.awrite(resp)
    utime.sleep(0.2)
    await writer.wait_closed()

loop = asyncio.get_event_loop()
loop.create_task(asyncio.start_server(serve, "0.0.0.0", 80))
try: 
    loop.run_forever()
except KeyboardInterrupt:
    print("closing")
    loop.close()

You really should have a look how the http protocol works.
In your code you read 256 bytes. Instead you should read lines until you hit a double blank line.
Then you should send your response. But this should better be html code not just text.
After you have send the response you can close the connection

A delay should not be needed if you follow the rules and certainly you should not use 'utime.sleep' because that will block asyncio.
Also better not use 'awrite' because it is legacy code.

[MasterOfGizmo]

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import uasyncio as asyncio
import utime

async def serve(reader, writer):
    t = utime.ticks_ms()
    resp = b"HTTP/1.0 200 OK\r\n\r\n" + "Ticks = {TICKS}\r\n".format(TICKS=t) 
    l = await reader.read(256)  # yield from may not work
    print(l)
    for _ in range(100):  # More RAM friendly than sending one huge string?
        await writer.awrite(resp)
    await writer.wait_closed()  # The close() call does nothing. This closes the socket.

try: 
    asyncio.run(asyncio.start_server(serve, "0.0.0.0", 80))
except KeyboardInterrupt:
    print("closing")
finally:
    asyncio.new_event_loop()  # Clear uasyncio stored state

This example does not close the servers listen port which in turn prevents it from being restarted after being stopped:

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Task exception wasn't retrieved
future: <Task> coro= <generator object 'start_server' at 3ffe72a0>
Traceback (most recent call last):
  File "uasyncio/core.py", line 1, in run_until_complete
  File "uasyncio/stream.py", line 1, in start_server
OSError: [Errno 112] EADDRINUSE

But where in this setup is the server socket accessible so it can be closed? This should happen in the finally clause. Calling loop.close() IMHO has nothing to do with closing the server socket itself. And in fact adding loop.close() doesn't fix this.

[pythoncoder]

I take your point. I guess it was written on the basis that the server would run forever, as is typical of a firmware solution. But there is nothing to stop you from writing your own start_server code based on the official one. And/or raising a ticket.

[MasterOfGizmo]

Thanks for the link. That code indeed tries to solve the same problem by allowing to re-use ports:

https://github.com/micropython/micropyt ... am.py#L138

But that doesn't seem to work.

I do have a completely different async server derived from tinyweb. I was just curious if this simpler approach here has an disadvantages.

Edit: The Server actually does close its socket when it receives a core.CancelledError (https://github.com/micropython/micropyt ... am.py#L115).

I think I just need to figure out how to send that signal into the server task.

[MasterOfGizmo]

I was hoping that something like this would do the trick:

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loop = asyncio.get_event_loop()
server_task = loop.create_task(asyncio.start_server(serve, "0.0.0.0", 80))
try: 
    loop.run_forever()
except KeyboardInterrupt:
    print("closing")
finally:
    server_task.cancel()

But it doesn't. Maybe because the entire loop processing has already stopped at that point and the cancel is never propagated into the server.

[pythoncoder]

That is correct. At that point uasyncio has shut down.

[MasterOfGizmo]

So how do i catch a Keyboard interrupt (or any other exception) without interrupting the loop?

[pythoncoder]

I suggest you read this discussion of exceptions.

tl;dr Trapping an exception which may occur anywhere in the program is easy if you want to stop the whole script. If you want the script to recover, it's difficult; I don't know a reliable way to do this. It's an unusual requirement: a given exception is usually confined to an individual coroutine. The purpose of a keyboard interrupt is usually to stop the program.

Maybe someone else can figure this out...