//! A scoped, structured logging and diagnostics system. //! //! # Overview //! //! `tracing` is a framework for instrumenting Rust programs to collect //! structured, event-based diagnostic information. //! //! In asynchronous systems like Tokio, interpreting traditional log messages can //! often be quite challenging. Since individual tasks are multiplexed on the same //! thread, associated events and log lines are intermixed making it difficult to //! trace the logic flow. `tracing` expands upon logging-style diagnostics by //! allowing libraries and applications to record structured events with additional //! information about *temporality* and *causality* — unlike a log message, a span //! in `tracing` has a beginning and end time, may be entered and exited by the //! flow of execution, and may exist within a nested tree of similar spans. In //! addition, `tracing` spans are *structured*, with the ability to record typed //! data as well as textual messages. //! //! The `tracing` crate provides the APIs necessary for instrumenting libraries //! and applications to emit trace data. //! //! *Compiler support: [requires `rustc` 1.49+][msrv]* //! //! [msrv]: #supported-rust-versions //! # Core Concepts //! //! The core of `tracing`'s API is composed of _spans_, _events_ and //! _subscribers_. We'll cover these in turn. //! //! ## Spans //! //! To record the flow of execution through a program, `tracing` introduces the //! concept of [spans]. Unlike a log line that represents a _moment in //! time_, a span represents a _period of time_ with a beginning and an end. When a //! program begins executing in a context or performing a unit of work, it //! _enters_ that context's span, and when it stops executing in that context, //! it _exits_ the span. The span in which a thread is currently executing is //! referred to as that thread's _current_ span. //! //! For example: //! ``` //! use tracing::{span, Level}; //! # fn main() { //! let span = span!(Level::TRACE, "my_span"); //! // `enter` returns a RAII guard which, when dropped, exits the span. this //! // indicates that we are in the span for the current lexical scope. //! let _enter = span.enter(); //! // perform some work in the context of `my_span`... //! # } //!``` //! //! The [`span` module][span]'s documentation provides further details on how to //! use spans. //! //!
//!
//!  **Warning**: In asynchronous code that uses async/await syntax,
//!  `Span::enter` may produce incorrect traces if the returned drop
//!  guard is held across an await point. See
//!  [the method documentation][Span#in-asynchronous-code] for details.
//!
//! 
//! //! ## Events //! //! An [`Event`] represents a _moment_ in time. It signifies something that //! happened while a trace was being recorded. `Event`s are comparable to the log //! records emitted by unstructured logging code, but unlike a typical log line, //! an `Event` may occur within the context of a span. //! //! For example: //! ``` //! use tracing::{event, span, Level}; //! //! # fn main() { //! // records an event outside of any span context: //! event!(Level::INFO, "something happened"); //! //! let span = span!(Level::INFO, "my_span"); //! let _guard = span.enter(); //! //! // records an event within "my_span". //! event!(Level::DEBUG, "something happened inside my_span"); //! # } //!``` //! //! In general, events should be used to represent points in time _within_ a //! span — a request returned with a given status code, _n_ new items were //! taken from a queue, and so on. //! //! The [`Event` struct][`Event`] documentation provides further details on using //! events. //! //! ## Subscribers //! //! As `Span`s and `Event`s occur, they are recorded or aggregated by //! implementations of the [`Subscriber`] trait. `Subscriber`s are notified //! when an `Event` takes place and when a `Span` is entered or exited. These //! notifications are represented by the following `Subscriber` trait methods: //! //! + [`event`][Subscriber::event], called when an `Event` takes place, //! + [`enter`], called when execution enters a `Span`, //! + [`exit`], called when execution exits a `Span` //! //! In addition, subscribers may implement the [`enabled`] function to _filter_ //! the notifications they receive based on [metadata] describing each `Span` //! or `Event`. If a call to `Subscriber::enabled` returns `false` for a given //! set of metadata, that `Subscriber` will *not* be notified about the //! corresponding `Span` or `Event`. For performance reasons, if no currently //! active subscribers express interest in a given set of metadata by returning //! `true`, then the corresponding `Span` or `Event` will never be constructed. //! //! # Usage //! //! First, add this to your `Cargo.toml`: //! //! ```toml //! [dependencies] //! tracing = "0.1" //! ``` //! //! ## Recording Spans and Events //! //! Spans and events are recorded using macros. //! //! ### Spans //! //! The [`span!`] macro expands to a [`Span` struct][`Span`] which is used to //! record a span. The [`Span::enter`] method on that struct records that the //! span has been entered, and returns a [RAII] guard object, which will exit //! the span when dropped. //! //! For example: //! //! ```rust //! use tracing::{span, Level}; //! # fn main() { //! // Construct a new span named "my span" with trace log level. //! let span = span!(Level::TRACE, "my span"); //! //! // Enter the span, returning a guard object. //! let _enter = span.enter(); //! //! // Any trace events that occur before the guard is dropped will occur //! // within the span. //! //! // Dropping the guard will exit the span. //! # } //! ``` //! //! The [`#[instrument]`][instrument] attribute provides an easy way to //! add `tracing` spans to functions. A function annotated with `#[instrument]` //! will create and enter a span with that function's name every time the //! function is called, with arguments to that function will be recorded as //! fields using `fmt::Debug`. //! //! For example: //! ```ignore //! # // this doctest is ignored because we don't have a way to say //! # // that it should only be run with cfg(feature = "attributes") //! use tracing::{Level, event, instrument}; //! //! #[instrument] //! pub fn my_function(my_arg: usize) { //! // This event will be recorded inside a span named `my_function` with the //! // field `my_arg`. //! event!(Level::INFO, "inside my_function!"); //! // ... //! } //! # fn main() {} //! ``` //! //! For functions which don't have built-in tracing support and can't have //! the `#[instrument]` attribute applied (such as from an external crate), //! the [`Span` struct][`Span`] has a [`in_scope()` method][`in_scope`] //! which can be used to easily wrap synchonous code in a span. //! //! For example: //! ```rust //! use tracing::info_span; //! //! # fn doc() -> Result<(), ()> { //! # mod serde_json { //! # pub(crate) fn from_slice(buf: &[u8]) -> Result<(), ()> { Ok(()) } //! # } //! # let buf: [u8; 0] = []; //! let json = info_span!("json.parse").in_scope(|| serde_json::from_slice(&buf))?; //! # let _ = json; // suppress unused variable warning //! # Ok(()) //! # } //! ``` //! //! You can find more examples showing how to use this crate [here][examples]. //! //! [RAII]: https://github.com/rust-unofficial/patterns/blob/master/patterns/behavioural/RAII.md //! [examples]: https://github.com/tokio-rs/tracing/tree/master/examples //! //! ### Events //! //! [`Event`]s are recorded using the [`event!`] macro: //! //! ```rust //! # fn main() { //! use tracing::{event, Level}; //! event!(Level::INFO, "something has happened!"); //! # } //! ``` //! //! ## Using the Macros //! //! The [`span!`] and [`event!`] macros as well as the `#[instrument]` attribute //! use fairly similar syntax, with some exceptions. //! //! ### Configuring Attributes //! //! Both macros require a [`Level`] specifying the verbosity of the span or //! event. Optionally, the [target] and [parent span] may be overridden. If the //! target and parent span are not overridden, they will default to the //! module path where the macro was invoked and the current span (as determined //! by the subscriber), respectively. //! //! For example: //! //! ``` //! # use tracing::{span, event, Level}; //! # fn main() { //! span!(target: "app_spans", Level::TRACE, "my span"); //! event!(target: "app_events", Level::INFO, "something has happened!"); //! # } //! ``` //! ``` //! # use tracing::{span, event, Level}; //! # fn main() { //! let span = span!(Level::TRACE, "my span"); //! event!(parent: &span, Level::INFO, "something has happened!"); //! # } //! ``` //! //! The span macros also take a string literal after the level, to set the name //! of the span. //! //! ### Recording Fields //! //! Structured fields on spans and events are specified using the syntax //! `field_name = field_value`. Fields are separated by commas. //! //! ``` //! # use tracing::{event, Level}; //! # fn main() { //! // records an event with two fields: //! // - "answer", with the value 42 //! // - "question", with the value "life, the universe and everything" //! event!(Level::INFO, answer = 42, question = "life, the universe, and everything"); //! # } //! ``` //! //! As shorthand, local variables may be used as field values without an //! assignment, similar to [struct initializers]. For example: //! //! ``` //! # use tracing::{span, Level}; //! # fn main() { //! let user = "ferris"; //! //! span!(Level::TRACE, "login", user); //! // is equivalent to: //! span!(Level::TRACE, "login", user = user); //! # } //!``` //! //! Field names can include dots, but should not be terminated by them: //! ``` //! # use tracing::{span, Level}; //! # fn main() { //! let user = "ferris"; //! let email = "ferris@rust-lang.org"; //! span!(Level::TRACE, "login", user, user.email = email); //! # } //!``` //! //! Since field names can include dots, fields on local structs can be used //! using the local variable shorthand: //! ``` //! # use tracing::{span, Level}; //! # fn main() { //! # struct User { //! # name: &'static str, //! # email: &'static str, //! # } //! let user = User { //! name: "ferris", //! email: "ferris@rust-lang.org", //! }; //! // the span will have the fields `user.name = "ferris"` and //! // `user.email = "ferris@rust-lang.org"`. //! span!(Level::TRACE, "login", user.name, user.email); //! # } //!``` //! //! Fields with names that are not Rust identifiers, or with names that are Rust reserved words, //! may be created using quoted string literals. However, this may not be used with the local //! variable shorthand. //! ``` //! # use tracing::{span, Level}; //! # fn main() { //! // records an event with fields whose names are not Rust identifiers //! // - "guid:x-request-id", containing a `:`, with the value "abcdef" //! // - "type", which is a reserved word, with the value "request" //! span!(Level::TRACE, "api", "guid:x-request-id" = "abcdef", "type" = "request"); //! # } //!``` //! //! The `?` sigil is shorthand that specifies a field should be recorded using //! its [`fmt::Debug`] implementation: //! ``` //! # use tracing::{event, Level}; //! # fn main() { //! #[derive(Debug)] //! struct MyStruct { //! field: &'static str, //! } //! //! let my_struct = MyStruct { //! field: "Hello world!" //! }; //! //! // `my_struct` will be recorded using its `fmt::Debug` implementation. //! event!(Level::TRACE, greeting = ?my_struct); //! // is equivalent to: //! event!(Level::TRACE, greeting = tracing::field::debug(&my_struct)); //! # } //! ``` //! //! The `%` sigil operates similarly, but indicates that the value should be //! recorded using its [`fmt::Display`] implementation: //! ``` //! # use tracing::{event, Level}; //! # fn main() { //! # #[derive(Debug)] //! # struct MyStruct { //! # field: &'static str, //! # } //! # //! # let my_struct = MyStruct { //! # field: "Hello world!" //! # }; //! // `my_struct.field` will be recorded using its `fmt::Display` implementation. //! event!(Level::TRACE, greeting = %my_struct.field); //! // is equivalent to: //! event!(Level::TRACE, greeting = tracing::field::display(&my_struct.field)); //! # } //! ``` //! //! The `%` and `?` sigils may also be used with local variable shorthand: //! //! ``` //! # use tracing::{event, Level}; //! # fn main() { //! # #[derive(Debug)] //! # struct MyStruct { //! # field: &'static str, //! # } //! # //! # let my_struct = MyStruct { //! # field: "Hello world!" //! # }; //! // `my_struct.field` will be recorded using its `fmt::Display` implementation. //! event!(Level::TRACE, %my_struct.field); //! # } //! ``` //! //! Additionally, a span may declare fields with the special value [`Empty`], //! which indicates that that the value for that field does not currently exist //! but may be recorded later. For example: //! //! ``` //! use tracing::{trace_span, field}; //! //! // Create a span with two fields: `greeting`, with the value "hello world", and //! // `parting`, without a value. //! let span = trace_span!("my_span", greeting = "hello world", parting = field::Empty); //! //! // ... //! //! // Now, record a value for parting as well. //! span.record("parting", &"goodbye world!"); //! ``` //! //! Note that a span may have up to 32 fields. The following will not compile: //! //! ```rust,compile_fail //! # use tracing::Level; //! # fn main() { //! let bad_span = span!( //! Level::TRACE, //! "too many fields!", //! a = 1, b = 2, c = 3, d = 4, e = 5, f = 6, g = 7, h = 8, i = 9, //! j = 10, k = 11, l = 12, m = 13, n = 14, o = 15, p = 16, q = 17, //! r = 18, s = 19, t = 20, u = 21, v = 22, w = 23, x = 24, y = 25, //! z = 26, aa = 27, bb = 28, cc = 29, dd = 30, ee = 31, ff = 32, gg = 33 //! ); //! # } //! ``` //! //! Finally, events may also include human-readable messages, in the form of a //! [format string][fmt] and (optional) arguments, **after** the event's //! key-value fields. If a format string and arguments are provided, //! they will implicitly create a new field named `message` whose value is the //! provided set of format arguments. //! //! For example: //! //! ``` //! # use tracing::{event, Level}; //! # fn main() { //! let question = "the ultimate question of life, the universe, and everything"; //! let answer = 42; //! // records an event with the following fields: //! // - `question.answer` with the value 42, //! // - `question.tricky` with the value `true`, //! // - "message", with the value "the answer to the ultimate question of life, the //! // universe, and everything is 42." //! event!( //! Level::DEBUG, //! question.answer = answer, //! question.tricky = true, //! "the answer to {} is {}.", question, answer //! ); //! # } //! ``` //! //! Specifying a formatted message in this manner does not allocate by default. //! //! [struct initializers]: https://doc.rust-lang.org/book/ch05-01-defining-structs.html#using-the-field-init-shorthand-when-variables-and-fields-have-the-same-name //! [target]: Metadata::target //! [parent span]: span::Attributes::parent //! [determined contextually]: span::Attributes::is_contextual //! [`fmt::Debug`]: std::fmt::Debug //! [`fmt::Display`]: std::fmt::Display //! [fmt]: std::fmt#usage //! [`Empty`]: field::Empty //! //! ### Shorthand Macros //! //! `tracing` also offers a number of macros with preset verbosity levels. //! The [`trace!`], [`debug!`], [`info!`], [`warn!`], and [`error!`] behave //! similarly to the [`event!`] macro, but with the [`Level`] argument already //! specified, while the corresponding [`trace_span!`], [`debug_span!`], //! [`info_span!`], [`warn_span!`], and [`error_span!`] macros are the same, //! but for the [`span!`] macro. //! //! These are intended both as a shorthand, and for compatibility with the [`log`] //! crate (see the next section). //! //! [`span!`]: span! //! [`event!`]: event! //! [`trace!`]: trace! //! [`debug!`]: debug! //! [`info!`]: info! //! [`warn!`]: warn! //! [`error!`]: error! //! [`trace_span!`]: trace_span! //! [`debug_span!`]: debug_span! //! [`info_span!`]: info_span! //! [`warn_span!`]: warn_span! //! [`error_span!`]: error_span! //! //! ### For `log` Users //! //! Users of the [`log`] crate should note that `tracing` exposes a set of //! macros for creating `Event`s (`trace!`, `debug!`, `info!`, `warn!`, and //! `error!`) which may be invoked with the same syntax as the similarly-named //! macros from the `log` crate. Often, the process of converting a project to //! use `tracing` can begin with a simple drop-in replacement. //! //! Let's consider the `log` crate's yak-shaving example: //! //! ```rust,ignore //! use std::{error::Error, io}; //! use tracing::{debug, error, info, span, warn, Level}; //! //! // the `#[tracing::instrument]` attribute creates and enters a span //! // every time the instrumented function is called. The span is named after the //! // the function or method. Parameters passed to the function are recorded as fields. //! #[tracing::instrument] //! pub fn shave(yak: usize) -> Result<(), Box> { //! // this creates an event at the DEBUG level with two fields: //! // - `excitement`, with the key "excitement" and the value "yay!" //! // - `message`, with the key "message" and the value "hello! I'm gonna shave a yak." //! // //! // unlike other fields, `message`'s shorthand initialization is just the string itself. //! debug!(excitement = "yay!", "hello! I'm gonna shave a yak."); //! if yak == 3 { //! warn!("could not locate yak!"); //! // note that this is intended to demonstrate `tracing`'s features, not idiomatic //! // error handling! in a library or application, you should consider returning //! // a dedicated `YakError`. libraries like snafu or thiserror make this easy. //! return Err(io::Error::new(io::ErrorKind::Other, "shaving yak failed!").into()); //! } else { //! debug!("yak shaved successfully"); //! } //! Ok(()) //! } //! //! pub fn shave_all(yaks: usize) -> usize { //! // Constructs a new span named "shaving_yaks" at the TRACE level, //! // and a field whose key is "yaks". This is equivalent to writing: //! // //! // let span = span!(Level::TRACE, "shaving_yaks", yaks = yaks); //! // //! // local variables (`yaks`) can be used as field values //! // without an assignment, similar to struct initializers. //! let _span = span!(Level::TRACE, "shaving_yaks", yaks).entered(); //! //! info!("shaving yaks"); //! //! let mut yaks_shaved = 0; //! for yak in 1..=yaks { //! let res = shave(yak); //! debug!(yak, shaved = res.is_ok()); //! //! if let Err(ref error) = res { //! // Like spans, events can also use the field initialization shorthand. //! // In this instance, `yak` is the field being initalized. //! error!(yak, error = error.as_ref(), "failed to shave yak!"); //! } else { //! yaks_shaved += 1; //! } //! debug!(yaks_shaved); //! } //! //! yaks_shaved //! } //! ``` //! //! ## In libraries //! //! Libraries should link only to the `tracing` crate, and use the provided //! macros to record whatever information will be useful to downstream //! consumers. //! //! ## In executables //! //! In order to record trace events, executables have to use a `Subscriber` //! implementation compatible with `tracing`. A `Subscriber` implements a //! way of collecting trace data, such as by logging it to standard output. //! //! This library does not contain any `Subscriber` implementations; these are //! provided by [other crates](#related-crates). //! //! The simplest way to use a subscriber is to call the [`set_global_default`] //! function: //! //! ``` //! extern crate tracing; //! # pub struct FooSubscriber; //! # use tracing::{span::{Id, Attributes, Record}, Metadata}; //! # impl tracing::Subscriber for FooSubscriber { //! # fn new_span(&self, _: &Attributes) -> Id { Id::from_u64(0) } //! # fn record(&self, _: &Id, _: &Record) {} //! # fn event(&self, _: &tracing::Event) {} //! # fn record_follows_from(&self, _: &Id, _: &Id) {} //! # fn enabled(&self, _: &Metadata) -> bool { false } //! # fn enter(&self, _: &Id) {} //! # fn exit(&self, _: &Id) {} //! # } //! # impl FooSubscriber { //! # fn new() -> Self { FooSubscriber } //! # } //! # fn main() { //! //! let my_subscriber = FooSubscriber::new(); //! tracing::subscriber::set_global_default(my_subscriber) //! .expect("setting tracing default failed"); //! # } //! ``` //! //!
//!     Warning: In general, libraries should not call
//!     set_global_default()! Doing so will cause conflicts when
//!     executables that depend on the library try to set the default later.
//! 
//! //! This subscriber will be used as the default in all threads for the //! remainder of the duration of the program, similar to setting the logger //! in the `log` crate. //! //! In addition, the default subscriber can be set through using the //! [`with_default`] function. This follows the `tokio` pattern of using //! closures to represent executing code in a context that is exited at the end //! of the closure. For example: //! //! ```rust //! # pub struct FooSubscriber; //! # use tracing::{span::{Id, Attributes, Record}, Metadata}; //! # impl tracing::Subscriber for FooSubscriber { //! # fn new_span(&self, _: &Attributes) -> Id { Id::from_u64(0) } //! # fn record(&self, _: &Id, _: &Record) {} //! # fn event(&self, _: &tracing::Event) {} //! # fn record_follows_from(&self, _: &Id, _: &Id) {} //! # fn enabled(&self, _: &Metadata) -> bool { false } //! # fn enter(&self, _: &Id) {} //! # fn exit(&self, _: &Id) {} //! # } //! # impl FooSubscriber { //! # fn new() -> Self { FooSubscriber } //! # } //! # fn main() { //! //! let my_subscriber = FooSubscriber::new(); //! # #[cfg(feature = "std")] //! tracing::subscriber::with_default(my_subscriber, || { //! // Any trace events generated in this closure or by functions it calls //! // will be collected by `my_subscriber`. //! }) //! # } //! ``` //! //! This approach allows trace data to be collected by multiple subscribers //! within different contexts in the program. Note that the override only applies to the //! currently executing thread; other threads will not see the change from with_default. //! //! Any trace events generated outside the context of a subscriber will not be collected. //! //! Once a subscriber has been set, instrumentation points may be added to the //! executable using the `tracing` crate's macros. //! //! ## `log` Compatibility //! //! The [`log`] crate provides a simple, lightweight logging facade for Rust. //! While `tracing` builds upon `log`'s foundation with richer structured //! diagnostic data, `log`'s simplicity and ubiquity make it the "lowest common //! denominator" for text-based logging in Rust — a vast majority of Rust //! libraries and applications either emit or consume `log` records. Therefore, //! `tracing` provides multiple forms of interoperability with `log`: `tracing` //! instrumentation can emit `log` records, and a compatibility layer enables //! `tracing` [`Subscriber`]s to consume `log` records as `tracing` [`Event`]s. //! //! ### Emitting `log` Records //! //! This crate provides two feature flags, "log" and "log-always", which will //! cause [spans] and [events] to emit `log` records. When the "log" feature is //! enabled, if no `tracing` `Subscriber` is active, invoking an event macro or //! creating a span with fields will emit a `log` record. This is intended //! primarily for use in libraries which wish to emit diagnostics that can be //! consumed by applications using `tracing` *or* `log`, without paying the //! additional overhead of emitting both forms of diagnostics when `tracing` is //! in use. //! //! Enabling the "log-always" feature will cause `log` records to be emitted //! even if a `tracing` `Subscriber` _is_ set. This is intended to be used in //! applications where a `log` `Logger` is being used to record a textual log, //! and `tracing` is used only to record other forms of diagnostics (such as //! metrics, profiling, or distributed tracing data). Unlike the "log" feature, //! libraries generally should **not** enable the "log-always" feature, as doing //! so will prevent applications from being able to opt out of the `log` records. //! //! See [here][flags] for more details on this crate's feature flags. //! //! The generated `log` records' messages will be a string representation of the //! span or event's fields, and all additional information recorded by `log` //! (target, verbosity level, module path, file, and line number) will also be //! populated. Additionally, `log` records are also generated when spans are //! entered, exited, and closed. Since these additional span lifecycle logs have //! the potential to be very verbose, and don't include additional fields, they //! will always be emitted at the `Trace` level, rather than inheriting the //! level of the span that generated them. Furthermore, they are are categorized //! under a separate `log` target, "tracing::span" (and its sub-target, //! "tracing::span::active", for the logs on entering and exiting a span), which //! may be enabled or disabled separately from other `log` records emitted by //! `tracing`. //! //! ### Consuming `log` Records //! //! The [`tracing-log`] crate provides a compatibility layer which //! allows a `tracing` [`Subscriber`] to consume `log` records as though they //! were `tracing` [events]. This allows applications using `tracing` to record //! the logs emitted by dependencies using `log` as events within the context of //! the application's trace tree. See [that crate's documentation][log-tracer] //! for details. //! //! [log-tracer]: https://docs.rs/tracing-log/latest/tracing_log/#convert-log-records-to-tracing-events //! //! ## Related Crates //! //! In addition to `tracing` and `tracing-core`, the [`tokio-rs/tracing`] repository //! contains several additional crates designed to be used with the `tracing` ecosystem. //! This includes a collection of `Subscriber` implementations, as well as utility //! and adapter crates to assist in writing `Subscriber`s and instrumenting //! applications. //! //! In particular, the following crates are likely to be of interest: //! //! - [`tracing-futures`] provides a compatibility layer with the `futures` //! crate, allowing spans to be attached to `Future`s, `Stream`s, and `Executor`s. //! - [`tracing-subscriber`] provides `Subscriber` implementations and //! utilities for working with `Subscriber`s. This includes a [`FmtSubscriber`] //! `FmtSubscriber` for logging formatted trace data to stdout, with similar //! filtering and formatting to the [`env_logger`] crate. //! - [`tracing-log`] provides a compatibility layer with the [`log`] crate, //! allowing log messages to be recorded as `tracing` `Event`s within the //! trace tree. This is useful when a project using `tracing` have //! dependencies which use `log`. Note that if you're using //! `tracing-subscriber`'s `FmtSubscriber`, you don't need to depend on //! `tracing-log` directly. //! - [`tracing-appender`] provides utilities for outputting tracing data, //! including a file appender and non blocking writer. //! //! Additionally, there are also several third-party crates which are not //! maintained by the `tokio` project. These include: //! //! - [`tracing-timing`] implements inter-event timing metrics on top of `tracing`. //! It provides a subscriber that records the time elapsed between pairs of //! `tracing` events and generates histograms. //! - [`tracing-opentelemetry`] provides a subscriber for emitting traces to //! [OpenTelemetry]-compatible distributed tracing systems. //! - [`tracing-honeycomb`] Provides a layer that reports traces spanning multiple machines to [honeycomb.io]. Backed by [`tracing-distributed`]. //! - [`tracing-distributed`] Provides a generic implementation of a layer that reports traces spanning multiple machines to some backend. //! - [`tracing-actix-web`] provides `tracing` integration for the `actix-web` web framework. //! - [`tracing-actix`] provides `tracing` integration for the `actix` actor //! framework. //! - [`tracing-gelf`] implements a subscriber for exporting traces in Greylog //! GELF format. //! - [`tracing-coz`] provides integration with the [coz] causal profiler //! (Linux-only). //! - [`tracing-bunyan-formatter`] provides a layer implementation that reports events and spans //! in [bunyan] format, enriched with timing information. //! - [`tracing-wasm`] provides a `Subscriber`/`Layer` implementation that reports //! events and spans via browser `console.log` and [User Timing API (`window.performance`)]. //! - [`tide-tracing`] provides a [tide] middleware to trace all incoming requests and responses. //! - [`test-log`] takes care of initializing `tracing` for tests, based on //! environment variables with an `env_logger` compatible syntax. //! - [`tracing-unwrap`] provides convenience methods to report failed unwraps //! on `Result` or `Option` types to a `Subscriber`. //! - [`diesel-tracing`] provides integration with [`diesel`] database connections. //! - [`tracing-tracy`] provides a way to collect [Tracy] profiles in instrumented //! applications. //! - [`tracing-elastic-apm`] provides a layer for reporting traces to [Elastic APM]. //! - [`tracing-etw`] provides a layer for emitting Windows [ETW] events. //! - [`tracing-fluent-assertions`] provides a fluent assertions-style testing //! framework for validating the behavior of `tracing` spans. //! - [`sentry-tracing`] provides a layer for reporting events and traces to [Sentry]. //! - [`tracing-forest`] provides a subscriber that preserves contextual coherence by //! grouping together logs from the same spans during writing. //! - [`tracing-loki`] provides a layer for shipping logs to [Grafana Loki]. //! //! If you're the maintainer of a `tracing` ecosystem crate not listed above, //! please let us know! We'd love to add your project to the list! //! //! [`tracing-opentelemetry`]: https://crates.io/crates/tracing-opentelemetry //! [OpenTelemetry]: https://opentelemetry.io/ //! [`tracing-honeycomb`]: https://crates.io/crates/tracing-honeycomb //! [`tracing-distributed`]: https://crates.io/crates/tracing-distributed //! [honeycomb.io]: https://www.honeycomb.io/ //! [`tracing-actix-web`]: https://crates.io/crates/tracing-actix-web //! [`tracing-actix`]: https://crates.io/crates/tracing-actix //! [`tracing-gelf`]: https://crates.io/crates/tracing-gelf //! [`tracing-coz`]: https://crates.io/crates/tracing-coz //! [coz]: https://github.com/plasma-umass/coz //! [`tracing-bunyan-formatter`]: https://crates.io/crates/tracing-bunyan-formatter //! [bunyan]: https://github.com/trentm/node-bunyan //! [`tracing-wasm`]: https://docs.rs/tracing-wasm //! [User Timing API (`window.performance`)]: https://developer.mozilla.org/en-US/docs/Web/API/User_Timing_API //! [`tide-tracing`]: https://crates.io/crates/tide-tracing //! [tide]: https://crates.io/crates/tide //! [`test-log`]: https://crates.io/crates/test-log //! [`tracing-unwrap`]: https://docs.rs/tracing-unwrap //! [`diesel`]: https://crates.io/crates/diesel //! [`diesel-tracing`]: https://crates.io/crates/diesel-tracing //! [`tracing-tracy`]: https://crates.io/crates/tracing-tracy //! [Tracy]: https://github.com/wolfpld/tracy //! [`tracing-elastic-apm`]: https://crates.io/crates/tracing-elastic-apm //! [Elastic APM]: https://www.elastic.co/apm //! [`tracing-etw`]: https://github.com/microsoft/tracing-etw //! [ETW]: https://docs.microsoft.com/en-us/windows/win32/etw/about-event-tracing //! [`tracing-fluent-assertions`]: https://crates.io/crates/tracing-fluent-assertions //! [`sentry-tracing`]: https://crates.io/crates/sentry-tracing //! [Sentry]: https://sentry.io/welcome/ //! [`tracing-forest`]: https://crates.io/crates/tracing-forest //! [`tracing-loki`]: https://crates.io/crates/tracing-loki //! [Grafana Loki]: https://grafana.com/oss/loki/ //! //!
//!     Note: Some of these ecosystem crates are currently
//!     unreleased and/or in earlier stages of development. They may be less stable
//!     than tracing and tracing-core.
//! 
//! //! ## Crate Feature Flags //! //! The following crate [feature flags] are available: //! //! * A set of features controlling the [static verbosity level]. //! * `log`: causes trace instrumentation points to emit [`log`] records as well //! as trace events, if a default `tracing` subscriber has not been set. This //! is intended for use in libraries whose users may be using either `tracing` //! or `log`. //! * `log-always`: Emit `log` records from all `tracing` spans and events, even //! if a `tracing` subscriber has been set. This should be set only by //! applications which intend to collect traces and logs separately; if an //! adapter is used to convert `log` records into `tracing` events, this will //! cause duplicate events to occur. //! * `attributes`: Includes support for the `#[instrument]` attribute. //! This is on by default, but does bring in the `syn` crate as a dependency, //! which may add to the compile time of crates that do not already use it. //! * `std`: Depend on the Rust standard library (enabled by default). //! //! `no_std` users may disable this feature with `default-features = false`: //! //! ```toml //! [dependencies] //! tracing = { version = "0.1.35", default-features = false } //! ``` //! //!
//!     Note: tracing's no_std support
//!     requires liballoc.
//! 
//! //! ### Unstable Features //! //! These feature flags enable **unstable** features. The public API may break in 0.1.x //! releases. To enable these features, the `--cfg tracing_unstable` must be passed to //! `rustc` when compiling. //! //! The following unstable feature flags are currently available: //! //! * `valuable`: Enables support for recording [field values] using the //! [`valuable`] crate. //! //! #### Enabling Unstable Features //! //! The easiest way to set the `tracing_unstable` cfg is to use the `RUSTFLAGS` //! env variable when running `cargo` commands: //! //! ```shell //! RUSTFLAGS="--cfg tracing_unstable" cargo build //! ``` //! Alternatively, the following can be added to the `.cargo/config` file in a //! project to automatically enable the cfg flag for that project: //! //! ```toml //! [build] //! rustflags = ["--cfg", "tracing_unstable"] //! ``` //! //! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section //! [field values]: crate::field //! [`valuable`]: https://crates.io/crates/valuable //! //! ## Supported Rust Versions //! //! Tracing is built against the latest stable release. The minimum supported //! version is 1.49. 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. //! //! [`log`]: https://docs.rs/log/0.4.6/log/ //! [span]: mod@span //! [spans]: mod@span //! [`Span`]: span::Span //! [`in_scope`]: span::Span::in_scope //! [event]: Event //! [events]: Event //! [`Subscriber`]: subscriber::Subscriber //! [Subscriber::event]: subscriber::Subscriber::event //! [`enter`]: subscriber::Subscriber::enter //! [`exit`]: subscriber::Subscriber::exit //! [`enabled`]: subscriber::Subscriber::enabled //! [metadata]: Metadata //! [`field::display`]: field::display //! [`field::debug`]: field::debug //! [`set_global_default`]: subscriber::set_global_default //! [`with_default`]: subscriber::with_default //! [`tokio-rs/tracing`]: https://github.com/tokio-rs/tracing //! [`tracing-futures`]: https://crates.io/crates/tracing-futures //! [`tracing-subscriber`]: https://crates.io/crates/tracing-subscriber //! [`tracing-log`]: https://crates.io/crates/tracing-log //! [`tracing-timing`]: https://crates.io/crates/tracing-timing //! [`tracing-appender`]: https://crates.io/crates/tracing-appender //! [`env_logger`]: https://crates.io/crates/env_logger //! [`FmtSubscriber`]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/struct.Subscriber.html //! [static verbosity level]: level_filters#compile-time-filters //! [instrument]: https://docs.rs/tracing-attributes/latest/tracing_attributes/attr.instrument.html //! [flags]: #crate-feature-flags #![cfg_attr(not(feature = "std"), no_std)] #![cfg_attr(docsrs, feature(doc_cfg), deny(rustdoc::broken_intra_doc_links))] #![doc(html_root_url = "https://docs.rs/tracing/0.1.35")] #![doc( html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png", issue_tracker_base_url = "https://github.com/tokio-rs/tracing/issues/" )] #![warn( missing_debug_implementations, missing_docs, rust_2018_idioms, unreachable_pub, bad_style, const_err, dead_code, improper_ctypes, non_shorthand_field_patterns, no_mangle_generic_items, overflowing_literals, path_statements, patterns_in_fns_without_body, private_in_public, unconditional_recursion, unused, unused_allocation, unused_comparisons, unused_parens, while_true )] #[cfg(not(feature = "std"))] extern crate alloc; // Somehow this `use` statement is necessary for us to re-export the `core` // macros on Rust 1.26.0. I'm not sure how this makes it work, but it does. #[allow(unused_imports)] #[doc(hidden)] use tracing_core::*; #[doc(inline)] pub use self::instrument::Instrument; pub use self::{dispatcher::Dispatch, event::Event, field::Value, subscriber::Subscriber}; #[doc(hidden)] pub use self::span::Id; #[doc(hidden)] pub use tracing_core::{ callsite::{self, Callsite}, metadata, }; pub use tracing_core::{event, Level, Metadata}; #[doc(inline)] pub use self::span::Span; #[cfg(feature = "attributes")] #[cfg_attr(docsrs, doc(cfg(feature = "attributes")))] #[doc(inline)] pub use tracing_attributes::instrument; #[macro_use] mod macros; pub mod dispatcher; pub mod field; /// Attach a span to a `std::future::Future`. pub mod instrument; pub mod level_filters; pub mod span; pub(crate) mod stdlib; pub mod subscriber; #[doc(hidden)] pub mod __macro_support { pub use crate::callsite::Callsite; use crate::{subscriber::Interest, Metadata}; pub use core::concat; /// Callsite implementation used by macro-generated code. /// /// /!\ WARNING: This is *not* a stable API! /!\ /// This type, and all code contained in the `__macro_support` module, is /// a *private* API of `tracing`. It is exposed publicly because it is used /// by the `tracing` macros, but it is not part of the stable versioned API. /// Breaking changes to this module may occur in small-numbered versions /// without warning. pub use tracing_core::callsite::DefaultCallsite as MacroCallsite; /// /!\ WARNING: This is *not* a stable API! /!\ /// This function, and all code contained in the `__macro_support` module, is /// a *private* API of `tracing`. It is exposed publicly because it is used /// by the `tracing` macros, but it is not part of the stable versioned API. /// Breaking changes to this module may occur in small-numbered versions /// without warning. pub fn __is_enabled(meta: &Metadata<'static>, interest: Interest) -> bool { interest.is_always() || crate::dispatcher::get_default(|default| default.enabled(meta)) } /// /!\ WARNING: This is *not* a stable API! /!\ /// This function, and all code contained in the `__macro_support` module, is /// a *private* API of `tracing`. It is exposed publicly because it is used /// by the `tracing` macros, but it is not part of the stable versioned API. /// Breaking changes to this module may occur in small-numbered versions /// without warning. #[inline] #[cfg(feature = "log")] pub fn __disabled_span(meta: &'static Metadata<'static>) -> crate::Span { crate::Span::new_disabled(meta) } /// /!\ WARNING: This is *not* a stable API! /!\ /// This function, and all code contained in the `__macro_support` module, is /// a *private* API of `tracing`. It is exposed publicly because it is used /// by the `tracing` macros, but it is not part of the stable versioned API. /// Breaking changes to this module may occur in small-numbered versions /// without warning. #[inline] #[cfg(not(feature = "log"))] pub fn __disabled_span(_: &'static Metadata<'static>) -> crate::Span { crate::Span::none() } /// /!\ WARNING: This is *not* a stable API! /!\ /// This function, and all code contained in the `__macro_support` module, is /// a *private* API of `tracing`. It is exposed publicly because it is used /// by the `tracing` macros, but it is not part of the stable versioned API. /// Breaking changes to this module may occur in small-numbered versions /// without warning. #[cfg(feature = "log")] pub fn __tracing_log( meta: &Metadata<'static>, logger: &'static dyn log::Log, log_meta: log::Metadata<'_>, values: &tracing_core::field::ValueSet<'_>, ) { logger.log( &crate::log::Record::builder() .file(meta.file()) .module_path(meta.module_path()) .line(meta.line()) .metadata(log_meta) .args(format_args!( "{}", crate::log::LogValueSet { values, is_first: true } )) .build(), ); } } #[cfg(feature = "log")] #[doc(hidden)] pub mod log { use core::fmt; pub use log::*; use tracing_core::field::{Field, ValueSet, Visit}; /// Utility to format [`ValueSet`]s for logging. pub(crate) struct LogValueSet<'a> { pub(crate) values: &'a ValueSet<'a>, pub(crate) is_first: bool, } impl<'a> fmt::Display for LogValueSet<'a> { #[inline] fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { struct LogVisitor<'a, 'b> { f: &'a mut fmt::Formatter<'b>, is_first: bool, result: fmt::Result, } impl Visit for LogVisitor<'_, '_> { fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) { let res = if self.is_first { self.is_first = false; if field.name() == "message" { write!(self.f, "{:?}", value) } else { write!(self.f, "{}={:?}", field.name(), value) } } else { write!(self.f, " {}={:?}", field.name(), value) }; if let Err(err) = res { self.result = self.result.and(Err(err)); } } fn record_str(&mut self, field: &Field, value: &str) { if field.name() == "message" { self.record_debug(field, &format_args!("{}", value)) } else { self.record_debug(field, &value) } } } let mut visit = LogVisitor { f, is_first: self.is_first, result: Ok(()), }; self.values.record(&mut visit); visit.result } } } mod sealed { pub trait Sealed {} }