Improve disconnect vs reconnect reliability

[pblazej]

Resolves #757

• Adds cancellation to reconnect, making sure that it cannot continue after disconnect() and bring the room back to life
• ⚠️ Optionally, we can introduce a breaking .disconnecting state to prevent new tasks from being started (vs cancelling ongoing tasks - a little less elegant)
  • Theoretically it should not affect other state transitions, as disconnect() is basically "destructive" - the only valid path leads to .disconnected during cleanup(), however that's not statically enforced in any way
  • On the other hand, it does not provide any added value for other parts of the SDK, just covering this tiny time window

[github-actions]

⚠️ This PR does not contain any files in the .changes directory.

[saarva]

@pblazej this fixed some disconnect issues that we were seeing, do you know if it'll go into the main branch soon?

[pblazej]

@pblazej this fixed some disconnect issues that we were seeing, do you know if it'll go into the main branch soon?

Should be merged soon, the risk is moderate. We need to finalize the ongoing discussion about catching more edge cases (see the issue).

[hiroshihorie]

LGTM but If possible, I would rather avoid exposing the .disconnecting connection state for developer experience / simplicity. Removing/deprecating this would be hard in the future.

[pblazej]

LGTM but If possible, I would rather avoid exposing the .disconnecting connection state for developer experience / simplicity. Removing/deprecating this would be hard in the future.

• For the current (major) version - yes, that's a bit cumbersome to introduce it atm
• For the next version - why do we wanna remove that? I think it's a good addition to the (incomplete) state machine, without that you're basically unable to resolve the root cause of this one completely ⬆️ tl;dr now it looks complete (with all async state transitions)

@hiroshihorie I'm fine with reverting the state right now, if we're able to retest it.

[pblazej]

stateDiagram-v2
    [*] --> Disconnected

    Disconnected --> Connecting: start connection
    Connecting --> Connected: success
    Connecting --> Disconnected: failed/canceled

    Connected --> Disconnecting: user closes
    Disconnecting --> Disconnected: closed

    Connected --> Reconnecting: network loss / ICE restart
    Reconnecting --> Connected: recovered
    Reconnecting --> Disconnected: failed to reconnect
    Reconnecting --> Reconnecting: retrying

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