Add event hooks to execute code (like forwarding logs to an external service)

[ewoolsey]

Perhaps there is already a way to do this that I'm not aware of. Basically, what I would like to do is have a custom layer that can send off http requests to an external logging service like paper trail. As far as I can tell, the only way to accomplish this currently is to hack format_event to send the log through an mpsc channel to a tokio::task executes the async request. It would be very nice if there were a better way to do this. Event hooks. could be added to layers to solve this problem!

[davidbarsky]

tracing generally assumes that methods on layers are synchronous, and therefore, free to call from an async context without worrying about blocking. While you are technically correct about changing format_event to send logs through an MSPC channel to a Tokio task, we offer two, substantially more paved paths to tackle this issue:

• Implement your own MakeWriter that sends the formatted message over an MSPC channel. Note that tracing-appender is basically this, except it sends logs to a background thread, not a task.
• If MakeWriter isn't sufficient for whatever reason, writing your own layer is a decently lightweight option! For a guide, I'd take a look at this blog post: https://burgers.io/custom-logging-in-rust-using-tracing/.

That being said, I don't really recommend sending logs from within the application if you can avoid it—I think you're significantly better off writing logs to stdout/stderr and having some external logging daemon forward the logs to a service.

[ewoolsey]

Hey sorry I never replied to you on this. Appreciate the suggestions! They both seem good. Sending the logs directly I think is the only viable solution for me. I'd like to not lose the log level information when sending the logs to paper trail. I'll give the MakeWriter a shot first and see how that goes. Thanks!

[ewoolsey]

@davidbarsky So after some investigation I've come to the conclusion that there is no good way to do this sadly. To send my logs to the remote service I require both the formatted logs and the log level. It appears the only way to access to both of these is to hijack format_event method, which seems pretty hacky. I think this solution will work fine, even if not ideal.

I think the root cause for this difficulty is that format_event is actually doing 2 jobs, when it should probably only being doing one. It's both formatting the event and writing to the writer, so there is no easy way to inject logic in between those two steps.