Adjust log level based on http request parameter

[dominikwerder]

In a rest service I would like to enable debug/trace log output for some certain modules based on the http query.

I have tried to Instrument::instrument the async request handler with a span like this:

if query.log_level() == TRACE {
    tracing::span!(tracing::Level::TRACE, "span_my_crate_trace")
} else {
    tracing::Span::none()
}

and then configure the EnvFilter with

info,my_crate[span_my_crate_trace]=trace

This basically works, but it now also enables trace events from other crates while the span is entered (notably tokio runtime).

How can I achieve this to see only the trace events from my_crate based on the query parameter, but not see other trace events from e.g. tokio?

[mladedav]

I don't think you can do this with a single EnvFilter. What I think should work though is using two filters, the first one the same as you're currently using and another one with info,my_crate=trace.

This should make it so both filters are queried and if both enable the the event, only then is it emitted.

The main problem here is that you cannot set both the filters with a single env variable (or you have to parse it yourself).

I am not entirely sure though because the dynamic span filters are a bit magic so please do challenge this if it doesn't work for you.

Ideally, we would probably want to support this in a single filter, but there is no syntax for this right as far as I know.

[dominikwerder]

This works really well!

Especially because I can choose the name of the env var using with_env_var.

In the meantime, I also tried to implement that kind of filtering using dynamic_filter_fn because there I have access to the target. But it is a mystery to me how I can test in that filter fn whether my span_my_crate_trace is a "parent" of the event in question.

[mladedav]

The example seem to do exactly what you want where it checks for the current span's name. Or I maybe don't understand what you mean?

[dominikwerder]

Yes, I missed that I can access current_span.parent().

Thank you!