[🐛 Bug]: [dotnet] [bidi] Event handlers are blocked logically

[nvborisenko]

Description

Currently all events came from remote end are processed ordered and synchronously. It is good approach following well-known experience by users, according "classic events".

The following code represents self-blocking situation: e.Context.NavigateAsync("https://www.selenium.dev") wants to execute a method which depends on another event handler (e.ContinueAsync()). It is logical dead lock.

Reproducible Code

using var driver = new FirefoxDriver(new FirefoxOptions { UseWebSocketUrl = true });

await using var bidi = await driver.AsBiDiAsync();

var context = new BrowsingContext(bidi, driver.CurrentWindowHandle);

Console.WriteLine(await bidi.StatusAsync());

await bidi.Network.InterceptRequestAsync(async e =>
{
    await e.ContinueAsync();
});

await context.NavigateAsync("https://www.selenium.dev", new() { Wait = ReadinessState.Complete });

await bidi.BrowsingContext.OnContextCreatedAsync(async e => await e.Context.NavigateAsync("https://www.selenium.dev"));

Debugging Logs

23:15:07.621 TRACE WebSocketTransport: BiDi SND --> {"id":31,"method":"browsingContext.navigate","params":{"context":"cb5faabc-d9fd-448a-8697-6a3ec7710473","url":"https://www.selenium.dev"}}
23:15:07.686 TRACE WebSocketTransport: BiDi RCV <-- {"type":"event","method":"network.beforeRequestSent","params":{"context":"cb5faabc-d9fd-448a-8697-6a3ec7710473","isBlocked":true,"navigation":"8be3d577-078f-49ee-8527-bd54ae120d64","redirectCount":0,"request":{"request":"83-00fe42f3-e49a-4f10-8fcc-db6d26b81b4b","url":"https://www.selenium.dev/","method":"GET","bodySize":0,"headersSize":0,"headers":[{"name":"Host","value":{"type":"string","value":"www.selenium.dev"}},{"name":"User-Agent","value":{"type":"string","value":"Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:146.0) Gecko/20100101 Firefox/146.0"}},{"name":"Accept","value":{"type":"string","value":"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"}},{"name":"Accept-Language","value":{"type":"string","value":"en-US,en;q=0.5"}},{"name":"Accept-Encoding","value":{"type":"string","value":"gzip, deflate, br, zstd"}},{"name":"Connection","value":{"type":"string","value":"keep-alive"}},{"name":"Upgrade-Insecure-Requests","value":{"type":"string","value":"1"}},{"name":"Sec-Fetch-Dest","value":{"type":"string","value":"document"}},{"name":"Sec-Fetch-Mode","value":{"type":"string","value":"navigate"}},{"name":"Sec-Fetch-Site","value":{"type":"string","value":"none"}},{"name":"Sec-Fetch-User","value":{"type":"string","value":"?1"}}],"cookies":[],"destination":"document","initiatorType":null,"timings":{"timeOrigin":0,"requestTime":1766088907679.986,"redirectStart":0,"redirectEnd":0,"fetchStart":0,"dnsStart":0,"dnsEnd":0,"connectStart":0,"connectEnd":0,"tlsStart":0,"tlsEnd":0,"requestStart":0,"responseStart":0,"responseEnd":0}},"timestamp":1766088907685,"intercepts":["ecf8ca39-ca52-4823-bb4f-4d4aa87c5c2c"],"initiator":{"type":"other"}}}
23:15:37.645 ERROR Broker: Unhandled error processing BiDi event handler: System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at OpenQA.Selenium.BiDi.Broker.ExecuteCommandAsync[TCommand,TResult](TCommand command, CommandOptions options, JsonTypeInfo`1 jsonCommandTypeInfo, JsonTypeInfo`1 jsonResultTypeInfo)
   at OpenQA.Selenium.BiDi.BrowsingContext.BrowsingContextModule.NavigateAsync(BrowsingContext context, String url, NavigateOptions options)
   at Program.<>c.<<<Main>$>b__0_1>d.MoveNext() in E:\Temp\ConsoleApp79\ConsoleApp79\Program.cs:line 26
--- End of stack trace from previous location ---
   at OpenQA.Selenium.BiDi.AsyncEventHandler`1.InvokeAsync(EventArgs args)
   at OpenQA.Selenium.BiDi.Broker.ProcessEventsAwaiterAsync()
23:15:37.645 TRACE WebSocketTransport: BiDi SND --> {"id":32,"method":"network.continueRequest","params":{"request":"83-00fe42f3-e49a-4f10-8fcc-db6d26b81b4b"}}
23:15:37.647 TRACE WebSocketTransport: BiDi RCV <-- {"type":"success","id":32,"result":{}}
23:15:37.673 TRACE WebSocketTransport: BiDi RCV <-- {"type":"success","id":31,"result":{"navigation":"8be3d577-078f-49ee-8527-bd54ae120d64","url":"https://www.selenium.dev/"}}
23:15:37.674 ERROR Broker: Unhandled error occured while processing remote message: System.InvalidOperationException: An attempt was made to transition a task to a final state when it had already completed.
   at System.Threading.Tasks.TaskCompletionSource`1.SetException(Exception exception)
   at OpenQA.Selenium.BiDi.Broker.ProcessReceivedMessage(Byte[] data)
   at OpenQA.Selenium.BiDi.Broker.ReceiveMessagesAsync(CancellationToken cancellationToken)

[selenium-ci]

@nvborisenko, thank you for creating this issue. We will troubleshoot it as soon as we can.

Selenium Triage Team: remember to follow the Triage Guide

[nvborisenko]

This is very good question how to dispatch events... We can implement any approach, but which one is expected? Currently all events are dispatched one by one, synchronously.

How to improve:

1. async dispatching by default

Dispatch asynchronously like fire and forget (but not forget entirely, wait all handlers when disposing)

2. user knows

User is able to specify how his handler can be executed: simultaneously or concurrently?

Like:

bidi.Network.OnBeforeRequestSend(Console.WriteLine, new() { RunAsynchronously = true });

[nvborisenko]

Personally I am trying to understand when event's order may be so important, given that our future implementation will BeginInvoke() event handler most likely ordered?