This article will show how to use Rust's tracing_subscriber crate for certain use cases.

What is logging

Example Rust program:

#[instrument]
pub extern "C" fn divide(a: c_int, b: c_int) -> c_int {
    tracing::trace!("dividing {a} by {b}");

    if b == 0 {
        tracing::error!("Cannot divide by zero");
        tracing::debug!("a: {a}, b: {b}");
        return 0;
    }

    let result = a / b;

    tracing::info!("{a}/{b}={result}");
    result
}

Logging generated by this program:

2024-02-28T22:19:07.883953Z TRACE divide{a=10 b=2}: tracing_rust: dividing 10 by 2
2024-02-28T22:19:07.884076Z  INFO divide{a=10 b=2}: tracing_rust: 10/2=5

2024-02-28T22:19:07.884318Z TRACE divide{a=10 b=1}: tracing_rust: dividing 10 by 1
2024-02-28T22:19:07.884369Z  INFO divide{a=10 b=1}: tracing_rust: 10/1=10

2024-02-28T22:19:07.884467Z TRACE divide{a=10 b=0}: tracing_rust: dividing 10 by 0
2024-02-28T22:19:07.884525Z ERROR divide{a=10 b=0}: tracing_rust: Cannot divide by zero
2024-02-28T22:19:07.884582Z DEBUG divide{a=10 b=0}: tracing_rust: a: 10, b: 0

What is tracing_subscriber

https://docs.rs/tracing-subscriber/latest/tracing_subscriber/

When it comes to generating/collecting logging from your Rust program, you want to use these 2 crates:

1. tracing
2. Use this crate to generate logging (like ERROR, INFO, DEBUG loggings)
3. tracing-subscriber
4. Use this crate to collect and print out the generated logging from tracing

The usage of tracing is pretty straightforward, so this article focus on configuring and using tracing-subscriber

TODO

As of writing, the prerelease version tracing GitHub repo has some significant changes over the latest release. I don’t want to waste time on current version only for it to be changed soon