![Tracing — Structured, application-level diagnostics][splash] [splash]: https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/splash.svg # tracing-appender Writers for logging events and spans [![Crates.io][crates-badge]][crates-url] [![Documentation][docs-badge]][docs-url] [![Documentation (master)][docs-master-badge]][docs-master-url] [![MIT licensed][mit-badge]][mit-url] [![Build Status][actions-badge]][actions-url] [![Discord chat][discord-badge]][discord-url] [Documentation][docs-url] | [Chat][discord-url] [crates-badge]: https://img.shields.io/crates/v/tracing-appender.svg [crates-url]: https://crates.io/crates/tracing-appender/0.2.2 [docs-badge]: https://docs.rs/tracing-appender/badge.svg [docs-url]: https://docs.rs/tracing-appender/0.2.2 [docs-master-badge]: https://img.shields.io/badge/docs-master-blue [docs-master-url]: https://tracing.rs/tracing-appender [mit-badge]: https://img.shields.io/badge/license-MIT-blue.svg [mit-url]: ../LICENSE [actions-badge]: https://github.com/tokio-rs/tracing/workflows/CI/badge.svg [actions-url]:https://github.com/tokio-rs/tracing/actions?query=workflow%3ACI [discord-badge]: https://img.shields.io/discord/500028886025895936?logo=discord&label=discord&logoColor=white [discord-url]: https://discord.gg/EeF3cQw ## Overview [`tracing`][tracing] is a framework for instrumenting Rust programs to collect structured, event-based diagnostic information. `tracing-appender` allows events and spans to be recorded in a non-blocking manner through a dedicated logging thread. It also provides a [`RollingFileAppender`][file_appender] that can be used with _or_ without the non-blocking writer. *Compiler support: [requires `rustc` 1.63+][msrv]* [msrv]: #supported-rust-versions ## Usage Add the following to your `Cargo.toml`: ```toml tracing-appender = "0.2" ``` This crate can be used in a few ways to record spans/events: - Using a [`RollingFileAppender`][file_appender] to write to a log file. This is a blocking operation. - Using *any* type implementing [`std::io::Write`][write] in a non-blocking fashion. - Using [`NonBlocking`][non_blocking] and [`RollingFileAppender`][file_appender] together to write to log files in a non-blocking fashion. ## Rolling File Appender ```rust fn main(){ let file_appender = tracing_appender::rolling::hourly("/some/directory", "prefix.log"); } ``` This creates an hourly rotating file appender that writes to `/some/directory/prefix.log.YYYY-MM-DD-HH`. [`Rotation::DAILY`] and [`Rotation::NEVER`] are the other available options. The file appender implements [`std::io::Write`][write]. To be used with [`tracing_subscriber::FmtSubscriber`][fmt_subscriber], it must be combined with a [`MakeWriter`][make_writer] implementation to be able to record tracing spans/event. The [rolling] module's documentation provides more detail on how to use this file appender. ## Non-Blocking Writer The example below demonstrates the construction of a `non_blocking` writer with an implementation of [`std::io::Writer`][write]. ```rust use std::io::Error; struct TestWriter; impl std::io::Write for TestWriter { fn write(&mut self, buf: &[u8]) -> std::io::Result { let buf_len = buf.len(); println!("{:?}", buf); Ok(buf_len) } fn flush(&mut self) -> std::io::Result<()> { Ok(()) } } fn main() { let (non_blocking, _guard) = tracing_appender::non_blocking(TestWriter); tracing_subscriber::fmt().with_writer(non_blocking).init(); } ``` **Note:** `_guard` is a [`WorkerGuard`][guard] which is returned by `tracing_appender::non_blocking` to ensure buffered logs are flushed to their output in the case of abrupt terminations of a process. See [`WorkerGuard`][guard] module for more details. The example below demonstrates the construction of a [`tracing_appender::non_blocking`][non_blocking] writer constructed with a [`std::io::Write`][write]: ```rust fn main() { let (non_blocking, _guard) = tracing_appender::non_blocking(std::io::stdout()); tracing_subscriber::fmt() .with_writer(non_blocking) .init(); } ``` The [non_blocking] module's documentation provides more detail on how to use `non_blocking`. ## Non-Blocking Rolling File Appender ```rust fn main() { let file_appender = tracing_appender::rolling::hourly("/some/directory", "prefix.log"); let (non_blocking, _guard) = tracing_appender::non_blocking(file_appender); tracing_subscriber::fmt() .with_writer(non_blocking) .init(); } ``` [tracing]: https://docs.rs/tracing/latest/tracing/ [make_writer]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/trait.MakeWriter.html [write]: https://doc.rust-lang.org/std/io/trait.Write.html [non_blocking]: https://docs.rs/tracing-appender/latest/tracing_appender/non_blocking/index.html [rolling]: https://docs.rs/tracing-appender/latest/tracing_appender/rolling/index.html [guard]: https://docs.rs/tracing-appender/latest/tracing_appender/non_blocking/struct.WorkerGuard.html [file_appender]: https://docs.rs/tracing-appender/latest/tracing_appender/rolling/struct.RollingFileAppender.html [fmt_subscriber]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/struct.Subscriber.html ## Supported Rust Versions `tracing-appender` is built against the latest stable release. The minimum supported version is 1.63. The current `tracing-appender` 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 1.69, the minimum supported version will not be increased past 1.66, 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. ## License This project is licensed under the [MIT license](../LICENSE). ### Contribution Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tokio by you, shall be licensed as MIT, without any additional terms or conditions.