tracing-error

Utilities for enriching error handling with [tracing] diagnostic information.

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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 1.42+

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:

```rust 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.

```rust use tracing_error::prelude::*;

std::fs::readtostring("myfile.txt").incurrentspan()?; ```

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]:

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

fn printextractedspantraces(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.

```rust use std::error::Error;

fn printnaivespantraces(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 [SpanTrace]s. For example:

```rust use tracingerror::ErrorLayer; use tracingsubscriber::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.

Supported Rust Versions

Tracing is built against the latest stable release. The minimum supported version is 1.42. The current Tracing version is not guaranteed to build on Rust versions earlier than the minimum supported version.

Tracing follows the same compiler support policies as the rest of the Tokio project. The current stable Rust compiler and the three most recent minor versions before it will always be supported. For example, if the current stable compiler version is 1.45, the minimum supported version will not be increased past 1.42, three minor versions prior. Increasing the minimum supported compiler version is not considered a semver breaking change as long as doing so complies with this policy.

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.