Logging Exceptions through UseExceptionHandler

[woutervanranst]

It would seem reasonable to log errors in the exception handler, and configure it using the modified builder (as per #796 (comment)).

However, the context available in the UseExceptionHandler method has its services disposed.

Is this expected behavior, or how would I proceed to log the error with the logging infrastructure configured in the IHost.ConfigureLogging?

var _ = new CommandLineBuilder(rootCommand)
    .UseHost(_ => Host.CreateDefaultBuilder(), host =>
    {
        host
            .ConfigureAppConfiguration( ... )
            .ConfigureLogging( ... )
            .ConfigureServices( ... );
    })
    .UseDefaults()
    .UseExceptionHandler((e, context) =>
    {
            // throws 'System.ObjectDisposedException: 'Cannot access a disposed object. Object name: 'IServiceProvider'.'
            var logger = context.GetHost().Services.GetRequiredService<ILoggerFactory>(); 
            logger.LogError(e);
    })
    .Build();
    rootCommand.Invoke(args);

[jonsequitur]

@fredrikhr Any thoughts on this one?

[fredrikhr]

@woutervanranst
Looks like you're missing the call to UseHost?

[woutervanranst]

Let me have a look whether this is an actual error or a copy paste error. It comes from a working sample. Stay tuned

[woutervanranst]

@fredrikhr added the UseHost part to the snip (it was a copypaste error with excessive cutting)

Full code listing here: https://github.com/woutervanranst/Arius/blob/1dd2455ecc0fa0b91c87183e6ba2d8d6a31857fb/Arius/Arius.Cli/Program.cs

[fredrikhr]

@woutervanranst I see... Well in this case you are out of luck, since the ExecptionHandling middleware sits above the Hosting middleware (and so it should remain), which means the Host has been teared down at the point when the exception is caught.

Instead, create the handler to have a root-level try-catch that wraps the code you have as handler today.

[woutervanranst]

Is this what you mean?
What I'm trying to achieve is logging uncaught exceptions (which would be a useful feature for most applications IMHO). If I understood correctly, how would I obtain a reference to the logging infrastructure in the catch {} ?

try
{
    var _ = new CommandLineBuilder(rootCommand)
        .UseHost(_ => Host.CreateDefaultBuilder(), host =>
        {
            host
                .ConfigureAppConfiguration( ... )
                .ConfigureLogging( ... )
                .ConfigureServices( ... );
        })
        .UseDefaults()
        //.UseExceptionHandler() // commented out
        .Build();
        rootCommand.Invoke(args);
}
catch (Exception e)
{
    // handle the exception
    // var logger = context.GetHost().Services.GetRequiredService<ILoggerFactory>(); 
    // logger.LogError(e);
}

[fredrikhr]

no, more like this:

var parser = new CommandLineBuilder(new RootCommand { Handler = CommandHandler.Create(
    (IHost host, CancellationToken cancelToken) =>
    {
        // Forward to original Command Handler        
        try { return WhateverHandler_woutervanranst_UsedPreviously(host, cancelToken); }
        catch (Exception e)
        {
            host.Services.GetRequiredService<ILoggerFactory>();
            // Do some logging
        }
    })})
    .UseDefaults()
    .UseExceptionHandler()
    .UseHost( /* whatever stuff woutervanranst had here previously */ )
    .Build();
return parser.Invoke(args);


static partial int WhateverHandler_woutervanranst_UsedPreviously(IHost host, CancellationToken cancelToken);

UPDATE:
Huh, actually in that example above you probably wouldn't need UseExceptionHandler(), however, you might change the try-catch to just do the logging and then simply throw to propagte to the UseExceptionHandling middleware, i.e.:

try { /* ... */ }
catch (Exception e)
{ 
    // Do logging
    throw;
}

Hint, that could also be written as an always-false-returning exception filter if you want to prevent stack rewind