[Mono.Android] Make HTTP connection attempt cancellable (#472) #519
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The `HttpURLConnection.ConnectAsync` API doesn't accept a `CancellationToken` instance and, thus, cannot be easily cancelled in a graceful manner. This limitation resulted in using the `Task.WhenAny` to make sure the connection attempt is aborted whenever the calling task is cancelled. This, however, led to a problem of unobserved exceptions should the cancellation occur before the connection attempt was successful. This commit wraps the synchronous `HttpURLConnection.Connect` call in a task that is passed the cancellation token, so that it can be gracefully cancelled when needed. The cancellation is done by registering a handler for when token is about to expire as Task.Run will check if cancellation was requested only before it runs the passed code, the rest is the code's responsibility. Since `URLConnection.Connect()` is asynchronous we abort it by calling `Disconnect()` on the instance which is a brutal but effective way to interrupt the connection attempt. Additionally, the diff makes sure to properly configure a few tasks for `await` Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=51804
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The
HttpURLConnection.ConnectAsyncAPI doesn't accept aCancellationTokeninstance and, thus, cannot be easily cancelled in a graceful manner. This
limitation resulted in using the
Task.WhenAnyto make sure the connectionattempt is aborted whenever the calling task is cancelled. This, however, led to
a problem of unobserved exceptions should the cancellation occur before the
connection attempt was successful.
This commit wraps the synchronous
HttpURLConnection.Connectcall in a taskthat is passed the cancellation token, so that it can be gracefully cancelled
when needed. The cancellation is done by registering a handler for when token is
about to expire as Task.Run will check if cancellation was requested only before
it runs the passed code, the rest is the code's responsibility.
Since
URLConnection.Connect()is asynchronous we abort it by callingDisconnect()on the instance which is a brutal but effective way to interruptthe connection attempt.
Additionally, the diff makes sure to properly configure a few tasks for
awaitFixes https://bugzilla.xamarin.com/show_bug.cgi?id=51804