Update sample web-client

[AiyionPrime]

@einarmo I drafted an update of actix in the sample web-server in vorausrobotik@bc2ec95.

Currently this serves the webpage properly, but crashes upon connection through a websocket, as the rt.block_on calls are forbidden in the thread which handles async tasks.

WS: Ok(Text("connect opc.tcp://127.0.0.1:4855"))
thread 'actix-rt|system:0|arbiter:1' panicked at /home/aiyion/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.38.1/src/runtime/scheduler/multi_thread/mod.rs:86:9:
Cannot start a runtime from within a runtime. This happens because a function (like `block_on`) attempted to block the current thread while the thread is being used to drive asynchronous tasks.

spawning a thread appears to not be that easy either, as ctx is &mut which cannot be sent through threads.

Do you have an idea for a different approach?

The draft @antiblue referenced in #271 is older than your additions, I think.

[einarmo]

Hm. It's quite unpleasant isn't it, I don't see an easy way to fix this, though I don't see how this didn't happen before my changes as well, there has always been a blocking runtime.

It doesn't actually seem like any uses of block_on actually need the return value. A solution would be to use an unbounded_channel from tokio, since you can send messages on that without blocking, that way you could offload all the actual asynchronous processing to an event loop on a separate tokio task.

[einarmo]

That will require even more changes though, I can see, you'd need some way to communicate back with the actor... I don't know enough about actix to know the best way to do this.

[AiyionPrime]

That's a bummer, but thanks for the fast replies :)

@locka99 Do you have any suggestions how we go on with this sample?

[AiyionPrime]

DataNotifications did still work in 0.11.
Starting a bisect.

[AiyionPrime]

43afb6a was the first commit where this sample stopped working, as the response as element.value.value does not exist since then anymore, but its capitalized variant does. element.value.Value One drawback is that it does not hold the plain value, but {"Type":6,"Body":755}.

If that change would not have stopped the example, the async change of the client would have, as the subscription to e.g. ns=2;s=v1 does not work for the same (unknown) reasons as the regular client
like discussed in #324.

@locka99 Is dropping the sample temporarily an option?
Until someone fixes it?

In the current state its not helping that much, I'm afraid.

[AiyionPrime]

If it was, I drafted its temporary removal in #368.