Better error hanndling during client & server start, and during handshakes #4790
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For both `MapToolClient.start()`, if an `IOException` is thrown we now guarantee that the state will be `Closed`. This means the caller doesn't have to worry about cleaning up the client by calling `.close()` themselves on an object with some indeterminate state. Similar thing for `MapToolServer.start()` - its state will be set to `Stopped` if an `IOException` is thrown. `MapTool.startServer()` now relies on this by catching any `IOException` from the client. In this case it stops the server before propagating the exception. This makes sure both client and server are in a determinate state if `startServer()` fails. The change to `SocketServer.start()` is only to make it more clear what the state will be in case of a failure.
onComplete callbacks ow receive a flag indicating whether the handshake was successful. This allows us to bail early and to avoid proceeding with logic that assumes a successful connection. On the disconnect side, some logic was moved around to where it makes more sense, in particular expected disconnects resulting from `AppActions.DISCONNECT_FROM_SERVER`. Clients are now created after their respective servers if any. This isn't a huge deal, but is more intuitive and allows us a bit of an easier time in the client disconnect handler.
The parameters were never been filled because the server does not produce its version in the handshake message. This could be fixed, but comes with BC concerns so I just fixed the strings for now.
cwisniew
approved these changes
May 23, 2024
kwvanderlinde
deleted the
bugfix/4787-error-handling-for-server-and-client-starts
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Identify the Bug or Feature request
Improves on #4787
Description of the Change
I hope this will be the last in this series of PRs. This change fixes some edge cases during server start and client connect that can still leave the app in a bad state.
For server starts, some extra care is taken in the order of operations. We now always create the server first (if any) and then create the local client. And we always start the server first then start the local client. If the server fails to start with an
IOException, we can just propagate the exception since the caller handles that case. If the client fails to start, we make a point of stopping the already-started server before propagating the exception.The previous point also required some internal changes to servers and clients. Any
IOExceptionthrown in theirstart()methods will result in their states being set toStoppedandClosedrespectively. This avoids the possibility that such a client or server is mistakenly identified as still running.On the handshake side, the completion callbacks now receive a flag indicating whether the handshake was a success. Some of these callbacks have behaviour that should only trigger in success cases, while others have logic for both cases. An important case is that glass panes are hidden regardless of outcome, but a new glass pane is only installed if proceeding to the next step.
MapToolClientnow treats handshake failures as an unexpected disconnection.Possible Drawbacks
Should be none.
Documentation Notes
N/A
Release Notes
This change is