tracing-error

tracing-error

Utilities for enriching error handling with tracing diagnostic information.

Documentation (release) | Documentation (master) | Chat

Overview

tracing is a framework for instrumenting Rust programs to collect scoped, structured, and async-aware diagnostics. This crate provides integrations between tracing instrumentation and Rust error handling. It enables enriching error types with diagnostic information from tracing span contexts, formatting those contexts when errors are displayed, and automatically generate tracing events when errors occur.

The crate provides the following:

• SpanTrace, a captured trace of the current tracing span context

• ErrorLayer, a subscriber layer which enables capturing SpanTraces

Note: This crate is currently experimental.

Compiler support: requires rustc 1.39+

Usage

tracing-error provides the SpanTrace type, which captures the current tracing span context when it is constructed and allows it to be displayed at a later time.

For example:

use std::{fmt, error::Error};
use tracing_error::SpanTrace;

#[derive(Debug)]
pub struct MyError {
    context: SpanTrace,
    // ...
}

impl fmt::Display for MyError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // ... format other parts of the error ...

        self.context.fmt(f)?;

        // ... format other error context information, cause chain, etc ...
        # Ok(())
    }
}

impl Error for MyError {}

impl MyError {
    pub fn new() -> Self {
        Self {
            context: SpanTrace::capture(),
            // ... other error information ...
        }
    }
}

This crate also provides TracedError, for attaching a SpanTrace to an existing error. The easiest way to wrap errors in TracedError is to either use the InstrumentResult and InstrumentError traits or the From/Into traits.

use tracing_error::prelude::*;

std::fs::read_to_string("myfile.txt").in_current_span()?;

Once an error has been wrapped with with a TracedError, the SpanTrace can be extracted one of three ways: either via TracedError's Display/Debug implementations, or via the ExtractSpanTrace trait.

For example, here is how one might print the errors but specialize the printing when the error is a placeholder for a wrapping SpanTrace:

use std::error::Error;
use tracing_error::ExtractSpanTrace as _;

fn print_extracted_spantraces(error: &(dyn Error + 'static)) {
    let mut error = Some(error);
    let mut ind = 0;

    eprintln!("Error:");

    while let Some(err) = error {
        if let Some(spantrace) = err.span_trace() {
            eprintln!("found a spantrace:\n{}", spantrace);
        } else {
            eprintln!("{:>4}: {}", ind, err);
        }

        error = err.source();
        ind += 1;
    }
}

Whereas here, we can still display the content of the SpanTraces without any special casing by simply printing all errors in our error chain.

use std::error::Error;

fn print_naive_spantraces(error: &(dyn Error + 'static)) {
    let mut error = Some(error);
    let mut ind = 0;

    eprintln!("Error:");

    while let Some(err) = error {
        eprintln!("{:>4}: {}", ind, err);
        error = err.source();
        ind += 1;
    }
}

Applications that wish to use tracing-error-enabled errors should construct an ErrorLayer and add it to their Subscriber in order to enable capturing SpanTraces. For example:

use tracing_error::ErrorLayer;
use tracing_subscriber::prelude::*;

fn main() {
    let subscriber = tracing_subscriber::Registry::default()
        // any number of other subscriber layers may be added before or
        // after the `ErrorLayer`...
        .with(ErrorLayer::default());

    // set the subscriber as the default for the application
    tracing::subscriber::set_global_default(subscriber);
}

Feature Flags

• traced-error - Enables the TracedError type and related traits
  • InstrumentResult and InstrumentError extension traits, which provide an in_current_span() method for bundling errors with a SpanTrace.
  • ExtractSpanTrace extension trait, for extracting SpanTraces from behind dyn Error trait objects.

Related Crates

In addition to this repository, here are also several third-party crates which are not maintained by the tokio project. These include:

• color-spantrace provides a formatter for rendering SpanTrace in the style of color-backtrace
• color-eyre provides a customized version of eyre::Report for capturing span traces and backtraces with new errors and pretty printing them in error reports.

License

This project is licensed under the MIT license.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tracing by you, shall be licensed as MIT, without any additional terms or conditions.