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| -rw-r--r-- | vendor/tracing-subscriber/src/layer/mod.rs | 1798 |
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diff --git a/vendor/tracing-subscriber/src/layer/mod.rs b/vendor/tracing-subscriber/src/layer/mod.rs deleted file mode 100644 index 24b853323..000000000 --- a/vendor/tracing-subscriber/src/layer/mod.rs +++ /dev/null @@ -1,1798 +0,0 @@ -//! The [`Layer`] trait, a composable abstraction for building [`Subscriber`]s. -//! -//! The [`Subscriber`] trait in `tracing-core` represents the _complete_ set of -//! functionality required to consume `tracing` instrumentation. This means that -//! a single `Subscriber` instance is a self-contained implementation of a -//! complete strategy for collecting traces; but it _also_ means that the -//! `Subscriber` trait cannot easily be composed with other `Subscriber`s. -//! -//! In particular, [`Subscriber`]s are responsible for generating [span IDs] and -//! assigning them to spans. Since these IDs must uniquely identify a span -//! within the context of the current trace, this means that there may only be -//! a single `Subscriber` for a given thread at any point in time — -//! otherwise, there would be no authoritative source of span IDs. -//! -//! On the other hand, the majority of the [`Subscriber`] trait's functionality -//! is composable: any number of subscribers may _observe_ events, span entry -//! and exit, and so on, provided that there is a single authoritative source of -//! span IDs. The [`Layer`] trait represents this composable subset of the -//! [`Subscriber`] behavior; it can _observe_ events and spans, but does not -//! assign IDs. -//! -//! # Composing Layers -//! -//! Since a [`Layer`] does not implement a complete strategy for collecting -//! traces, it must be composed with a `Subscriber` in order to be used. The -//! [`Layer`] trait is generic over a type parameter (called `S` in the trait -//! definition), representing the types of `Subscriber` they can be composed -//! with. Thus, a [`Layer`] may be implemented that will only compose with a -//! particular `Subscriber` implementation, or additional trait bounds may be -//! added to constrain what types implementing `Subscriber` a `Layer` can wrap. -//! -//! `Layer`s may be added to a `Subscriber` by using the [`SubscriberExt::with`] -//! method, which is provided by `tracing-subscriber`'s [prelude]. This method -//! returns a [`Layered`] struct that implements `Subscriber` by composing the -//! `Layer` with the `Subscriber`. -//! -//! For example: -//! ```rust -//! use tracing_subscriber::Layer; -//! use tracing_subscriber::prelude::*; -//! use tracing::Subscriber; -//! -//! pub struct MyLayer { -//! // ... -//! } -//! -//! impl<S: Subscriber> Layer<S> for MyLayer { -//! // ... -//! } -//! -//! pub struct MySubscriber { -//! // ... -//! } -//! -//! # use tracing_core::{span::{Id, Attributes, Record}, Metadata, Event}; -//! impl Subscriber for MySubscriber { -//! // ... -//! # fn new_span(&self, _: &Attributes) -> Id { Id::from_u64(1) } -//! # fn record(&self, _: &Id, _: &Record) {} -//! # fn event(&self, _: &Event) {} -//! # fn record_follows_from(&self, _: &Id, _: &Id) {} -//! # fn enabled(&self, _: &Metadata) -> bool { false } -//! # fn enter(&self, _: &Id) {} -//! # fn exit(&self, _: &Id) {} -//! } -//! # impl MyLayer { -//! # fn new() -> Self { Self {} } -//! # } -//! # impl MySubscriber { -//! # fn new() -> Self { Self { }} -//! # } -//! -//! let subscriber = MySubscriber::new() -//! .with(MyLayer::new()); -//! -//! tracing::subscriber::set_global_default(subscriber); -//! ``` -//! -//! Multiple `Layer`s may be composed in the same manner: -//! ```rust -//! # use tracing_subscriber::{Layer, layer::SubscriberExt}; -//! # use tracing::Subscriber; -//! pub struct MyOtherLayer { -//! // ... -//! } -//! -//! impl<S: Subscriber> Layer<S> for MyOtherLayer { -//! // ... -//! } -//! -//! pub struct MyThirdLayer { -//! // ... -//! } -//! -//! impl<S: Subscriber> Layer<S> for MyThirdLayer { -//! // ... -//! } -//! # pub struct MyLayer {} -//! # impl<S: Subscriber> Layer<S> for MyLayer {} -//! # pub struct MySubscriber { } -//! # use tracing_core::{span::{Id, Attributes, Record}, Metadata, Event}; -//! # impl Subscriber for MySubscriber { -//! # fn new_span(&self, _: &Attributes) -> Id { Id::from_u64(1) } -//! # fn record(&self, _: &Id, _: &Record) {} -//! # fn event(&self, _: &Event) {} -//! # fn record_follows_from(&self, _: &Id, _: &Id) {} -//! # fn enabled(&self, _: &Metadata) -> bool { false } -//! # fn enter(&self, _: &Id) {} -//! # fn exit(&self, _: &Id) {} -//! } -//! # impl MyLayer { -//! # fn new() -> Self { Self {} } -//! # } -//! # impl MyOtherLayer { -//! # fn new() -> Self { Self {} } -//! # } -//! # impl MyThirdLayer { -//! # fn new() -> Self { Self {} } -//! # } -//! # impl MySubscriber { -//! # fn new() -> Self { Self { }} -//! # } -//! -//! let subscriber = MySubscriber::new() -//! .with(MyLayer::new()) -//! .with(MyOtherLayer::new()) -//! .with(MyThirdLayer::new()); -//! -//! tracing::subscriber::set_global_default(subscriber); -//! ``` -//! -//! The [`Layer::with_subscriber`] constructs the [`Layered`] type from a -//! [`Layer`] and [`Subscriber`], and is called by [`SubscriberExt::with`]. In -//! general, it is more idiomatic to use [`SubscriberExt::with`], and treat -//! [`Layer::with_subscriber`] as an implementation detail, as `with_subscriber` -//! calls must be nested, leading to less clear code for the reader. -//! -//! ## Runtime Configuration With `Layer`s -//! -//! In some cases, a particular [`Layer`] may be enabled or disabled based on -//! runtime configuration. This can introduce challenges, because the type of a -//! layered [`Subscriber`] depends on which layers are added to it: if an `if` -//! or `match` expression adds some [`Layer`] implementation in one branch, -//! and other layers in another, the [`Subscriber`] values returned by those -//! branches will have different types. For example, the following _will not_ -//! work: -//! -//! ```compile_fail -//! # fn docs() -> Result<(), Box<dyn std::error::Error + 'static>> { -//! # struct Config { -//! # is_prod: bool, -//! # path: &'static str, -//! # } -//! # let cfg = Config { is_prod: false, path: "debug.log" }; -//! use std::fs::File; -//! use tracing_subscriber::{Registry, prelude::*}; -//! -//! let stdout_log = tracing_subscriber::fmt::layer().pretty(); -//! let subscriber = Registry::default().with(stdout_log); -//! -//! // The compile error will occur here because the if and else -//! // branches have different (and therefore incompatible) types. -//! let subscriber = if cfg.is_prod { -//! let file = File::create(cfg.path)?; -//! let layer = tracing_subscriber::fmt::layer() -//! .json() -//! .with_writer(Arc::new(file)); -//! layer.with(subscriber) -//! } else { -//! layer -//! }; -//! -//! tracing::subscriber::set_global_default(subscriber) -//! .expect("Unable to set global subscriber"); -//! # Ok(()) } -//! ``` -//! -//! However, a [`Layer`] wrapped in an [`Option`] [also implements the `Layer` -//! trait][option-impl]. This allows individual layers to be enabled or disabled at -//! runtime while always producing a [`Subscriber`] of the same type. For -//! example: -//! -//! ``` -//! # fn docs() -> Result<(), Box<dyn std::error::Error + 'static>> { -//! # struct Config { -//! # is_prod: bool, -//! # path: &'static str, -//! # } -//! # let cfg = Config { is_prod: false, path: "debug.log" }; -//! use std::fs::File; -//! use tracing_subscriber::{Registry, prelude::*}; -//! -//! let stdout_log = tracing_subscriber::fmt::layer().pretty(); -//! let subscriber = Registry::default().with(stdout_log); -//! -//! // if `cfg.is_prod` is true, also log JSON-formatted logs to a file. -//! let json_log = if cfg.is_prod { -//! let file = File::create(cfg.path)?; -//! let json_log = tracing_subscriber::fmt::layer() -//! .json() -//! .with_writer(file); -//! Some(json_log) -//! } else { -//! None -//! }; -//! -//! // If `cfg.is_prod` is false, then `json` will be `None`, and this layer -//! // will do nothing. However, the subscriber will still have the same type -//! // regardless of whether the `Option`'s value is `None` or `Some`. -//! let subscriber = subscriber.with(json_log); -//! -//! tracing::subscriber::set_global_default(subscriber) -//! .expect("Unable to set global subscriber"); -//! # Ok(()) } -//! ``` -//! -//! If a [`Layer`] may be one of several different types, note that [`Box<dyn -//! Layer<S> + Send + Sync>` implements `Layer`][box-impl]. -//! This may be used to erase the type of a [`Layer`]. -//! -//! For example, a function that configures a [`Layer`] to log to one of -//! several outputs might return a `Box<dyn Layer<S> + Send + Sync + 'static>`: -//! ``` -//! use tracing_subscriber::{ -//! Layer, -//! registry::LookupSpan, -//! prelude::*, -//! }; -//! use std::{path::PathBuf, fs::File, io}; -//! -//! /// Configures whether logs are emitted to a file, to stdout, or to stderr. -//! pub enum LogConfig { -//! File(PathBuf), -//! Stdout, -//! Stderr, -//! } -//! -//! impl LogConfig { -//! pub fn layer<S>(self) -> Box<dyn Layer<S> + Send + Sync + 'static> -//! where -//! S: tracing_core::Subscriber, -//! for<'a> S: LookupSpan<'a>, -//! { -//! // Shared configuration regardless of where logs are output to. -//! let fmt = tracing_subscriber::fmt::layer() -//! .with_target(true) -//! .with_thread_names(true); -//! -//! // Configure the writer based on the desired log target: -//! match self { -//! LogConfig::File(path) => { -//! let file = File::create(path).expect("failed to create log file"); -//! Box::new(fmt.with_writer(file)) -//! }, -//! LogConfig::Stdout => Box::new(fmt.with_writer(io::stdout)), -//! LogConfig::Stderr => Box::new(fmt.with_writer(io::stderr)), -//! } -//! } -//! } -//! -//! let config = LogConfig::Stdout; -//! tracing_subscriber::registry() -//! .with(config.layer()) -//! .init(); -//! ``` -//! -//! The [`Layer::boxed`] method is provided to make boxing a `Layer` -//! more convenient, but [`Box::new`] may be used as well. -//! -//! When the number of `Layer`s varies at runtime, note that a -//! [`Vec<L> where L: Layer` also implements `Layer`][vec-impl]. This -//! can be used to add a variable number of `Layer`s to a `Subscriber`: -//! -//! ``` -//! use tracing_subscriber::{Layer, prelude::*}; -//! struct MyLayer { -//! // ... -//! } -//! # impl MyLayer { fn new() -> Self { Self {} }} -//! -//! impl<S: tracing_core::Subscriber> Layer<S> for MyLayer { -//! // ... -//! } -//! -//! /// Returns how many layers we need -//! fn how_many_layers() -> usize { -//! // ... -//! # 3 -//! } -//! -//! // Create a variable-length `Vec` of layers -//! let mut layers = Vec::new(); -//! for _ in 0..how_many_layers() { -//! layers.push(MyLayer::new()); -//! } -//! -//! tracing_subscriber::registry() -//! .with(layers) -//! .init(); -//! ``` -//! -//! If a variable number of `Layer` is needed and those `Layer`s have -//! different types, a `Vec` of [boxed `Layer` trait objects][box-impl] may -//! be used. For example: -//! -//! ``` -//! use tracing_subscriber::{filter::LevelFilter, Layer, prelude::*}; -//! use std::fs::File; -//! # fn main() -> Result<(), Box<dyn std::error::Error>> { -//! struct Config { -//! enable_log_file: bool, -//! enable_stdout: bool, -//! enable_stderr: bool, -//! // ... -//! } -//! # impl Config { -//! # fn from_config_file()-> Result<Self, Box<dyn std::error::Error>> { -//! # // don't enable the log file so that the example doesn't actually create it -//! # Ok(Self { enable_log_file: false, enable_stdout: true, enable_stderr: true }) -//! # } -//! # } -//! -//! let cfg = Config::from_config_file()?; -//! -//! // Based on our dynamically loaded config file, create any number of layers: -//! let mut layers = Vec::new(); -//! -//! if cfg.enable_log_file { -//! let file = File::create("myapp.log")?; -//! let layer = tracing_subscriber::fmt::layer() -//! .with_thread_names(true) -//! .with_target(true) -//! .json() -//! .with_writer(file) -//! // Box the layer as a type-erased trait object, so that it can -//! // be pushed to the `Vec`. -//! .boxed(); -//! layers.push(layer); -//! } -//! -//! if cfg.enable_stdout { -//! let layer = tracing_subscriber::fmt::layer() -//! .pretty() -//! .with_filter(LevelFilter::INFO) -//! // Box the layer as a type-erased trait object, so that it can -//! // be pushed to the `Vec`. -//! .boxed(); -//! layers.push(layer); -//! } -//! -//! if cfg.enable_stdout { -//! let layer = tracing_subscriber::fmt::layer() -//! .with_target(false) -//! .with_filter(LevelFilter::WARN) -//! // Box the layer as a type-erased trait object, so that it can -//! // be pushed to the `Vec`. -//! .boxed(); -//! layers.push(layer); -//! } -//! -//! tracing_subscriber::registry() -//! .with(layers) -//! .init(); -//!# Ok(()) } -//! ``` -//! -//! Finally, if the number of layers _changes_ at runtime, a `Vec` of -//! subscribers can be used alongside the [`reload`](crate::reload) module to -//! add or remove subscribers dynamically at runtime. -//! -//! [option-impl]: Layer#impl-Layer<S>-for-Option<L> -//! [box-impl]: Layer#impl-Layer%3CS%3E-for-Box%3Cdyn%20Layer%3CS%3E%20+%20Send%20+%20Sync%3E -//! [vec-impl]: Layer#impl-Layer<S>-for-Vec<L> -//! [prelude]: crate::prelude -//! -//! # Recording Traces -//! -//! The [`Layer`] trait defines a set of methods for consuming notifications from -//! tracing instrumentation, which are generally equivalent to the similarly -//! named methods on [`Subscriber`]. Unlike [`Subscriber`], the methods on -//! `Layer` are additionally passed a [`Context`] type, which exposes additional -//! information provided by the wrapped subscriber (such as [the current span]) -//! to the layer. -//! -//! # Filtering with `Layer`s -//! -//! As well as strategies for handling trace events, the `Layer` trait may also -//! be used to represent composable _filters_. This allows the determination of -//! what spans and events should be recorded to be decoupled from _how_ they are -//! recorded: a filtering layer can be applied to other layers or -//! subscribers. `Layer`s can be used to implement _global filtering_, where a -//! `Layer` provides a filtering strategy for the entire subscriber. -//! Additionally, individual recording `Layer`s or sets of `Layer`s may be -//! combined with _per-layer filters_ that control what spans and events are -//! recorded by those layers. -//! -//! ## Global Filtering -//! -//! A `Layer` that implements a filtering strategy should override the -//! [`register_callsite`] and/or [`enabled`] methods. It may also choose to implement -//! methods such as [`on_enter`], if it wishes to filter trace events based on -//! the current span context. -//! -//! Note that the [`Layer::register_callsite`] and [`Layer::enabled`] methods -//! determine whether a span or event is enabled *globally*. Thus, they should -//! **not** be used to indicate whether an individual layer wishes to record a -//! particular span or event. Instead, if a layer is only interested in a subset -//! of trace data, but does *not* wish to disable other spans and events for the -//! rest of the layer stack should ignore those spans and events in its -//! notification methods. -//! -//! The filtering methods on a stack of `Layer`s are evaluated in a top-down -//! order, starting with the outermost `Layer` and ending with the wrapped -//! [`Subscriber`]. If any layer returns `false` from its [`enabled`] method, or -//! [`Interest::never()`] from its [`register_callsite`] method, filter -//! evaluation will short-circuit and the span or event will be disabled. -//! -//! ### Enabling Interest -//! -//! Whenever an tracing event (or span) is emitted, it goes through a number of -//! steps to determine how and how much it should be processed. The earlier an -//! event is disabled, the less work has to be done to process the event, so -//! `Layer`s that implement filtering should attempt to disable unwanted -//! events as early as possible. In order, each event checks: -//! -//! - [`register_callsite`], once per callsite (roughly: once per time that -//! `event!` or `span!` is written in the source code; this is cached at the -//! callsite). See [`Subscriber::register_callsite`] and -//! [`tracing_core::callsite`] for a summary of how this behaves. -//! - [`enabled`], once per emitted event (roughly: once per time that `event!` -//! or `span!` is *executed*), and only if `register_callsite` regesters an -//! [`Interest::sometimes`]. This is the main customization point to globally -//! filter events based on their [`Metadata`]. If an event can be disabled -//! based only on [`Metadata`], it should be, as this allows the construction -//! of the actual `Event`/`Span` to be skipped. -//! - For events only (and not spans), [`event_enabled`] is called just before -//! processing the event. This gives layers one last chance to say that -//! an event should be filtered out, now that the event's fields are known. -//! -//! ## Per-Layer Filtering -//! -//! **Note**: per-layer filtering APIs currently require the [`"registry"` crate -//! feature flag][feat] to be enabled. -//! -//! Sometimes, it may be desirable for one `Layer` to record a particular subset -//! of spans and events, while a different subset of spans and events are -//! recorded by other `Layer`s. For example: -//! -//! - A layer that records metrics may wish to observe only events including -//! particular tracked values, while a logging layer ignores those events. -//! - If recording a distributed trace is expensive, it might be desirable to -//! only send spans with `INFO` and lower verbosity to the distributed tracing -//! system, while logging more verbose spans to a file. -//! - Spans and events with a particular target might be recorded differently -//! from others, such as by generating an HTTP access log from a span that -//! tracks the lifetime of an HTTP request. -//! -//! The [`Filter`] trait is used to control what spans and events are -//! observed by an individual `Layer`, while still allowing other `Layer`s to -//! potentially record them. The [`Layer::with_filter`] method combines a -//! `Layer` with a [`Filter`], returning a [`Filtered`] layer. -//! -//! This crate's [`filter`] module provides a number of types which implement -//! the [`Filter`] trait, such as [`LevelFilter`], [`Targets`], and -//! [`FilterFn`]. These [`Filter`]s provide ready-made implementations of -//! common forms of filtering. For custom filtering policies, the [`FilterFn`] -//! and [`DynFilterFn`] types allow implementing a [`Filter`] with a closure or -//! function pointer. In addition, when more control is required, the [`Filter`] -//! trait may also be implemented for user-defined types. -//! -//! <pre class="compile_fail" style="white-space:normal;font:inherit;"> -//! <strong>Warning</strong>: Currently, the <a href="../struct.Registry.html"> -//! <code>Registry</code></a> type defined in this crate is the only root -//! <code>Subscriber</code> capable of supporting <code>Layer</code>s with -//! per-layer filters. In the future, new APIs will be added to allow other -//! root <code>Subscriber</code>s to support per-layer filters. -//! </pre> -//! -//! For example, to generate an HTTP access log based on spans with -//! the `http_access` target, while logging other spans and events to -//! standard out, a [`Filter`] can be added to the access log layer: -//! -//! ``` -//! use tracing_subscriber::{filter, prelude::*}; -//! -//! // Generates an HTTP access log. -//! let access_log = // ... -//! # filter::LevelFilter::INFO; -//! -//! // Add a filter to the access log layer so that it only observes -//! // spans and events with the `http_access` target. -//! let access_log = access_log.with_filter(filter::filter_fn(|metadata| { -//! // Returns `true` if and only if the span or event's target is -//! // "http_access". -//! metadata.target() == "http_access" -//! })); -//! -//! // A general-purpose logging layer. -//! let fmt_layer = tracing_subscriber::fmt::layer(); -//! -//! // Build a subscriber that combines the access log and stdout log -//! // layers. -//! tracing_subscriber::registry() -//! .with(fmt_layer) -//! .with(access_log) -//! .init(); -//! ``` -//! -//! Multiple layers can have their own, separate per-layer filters. A span or -//! event will be recorded if it is enabled by _any_ per-layer filter, but it -//! will be skipped by the layers whose filters did not enable it. Building on -//! the previous example: -//! -//! ``` -//! use tracing_subscriber::{filter::{filter_fn, LevelFilter}, prelude::*}; -//! -//! let access_log = // ... -//! # LevelFilter::INFO; -//! let fmt_layer = tracing_subscriber::fmt::layer(); -//! -//! tracing_subscriber::registry() -//! // Add the filter for the "http_access" target to the access -//! // log layer, like before. -//! .with(access_log.with_filter(filter_fn(|metadata| { -//! metadata.target() == "http_access" -//! }))) -//! // Add a filter for spans and events with the INFO level -//! // and below to the logging layer. -//! .with(fmt_layer.with_filter(LevelFilter::INFO)) -//! .init(); -//! -//! // Neither layer will observe this event -//! tracing::debug!(does_anyone_care = false, "a tree fell in the forest"); -//! -//! // This event will be observed by the logging layer, but not -//! // by the access log layer. -//! tracing::warn!(dose_roentgen = %3.8, "not great, but not terrible"); -//! -//! // This event will be observed only by the access log layer. -//! tracing::trace!(target: "http_access", "HTTP request started"); -//! -//! // Both layers will observe this event. -//! tracing::error!(target: "http_access", "HTTP request failed with a very bad error!"); -//! ``` -//! -//! A per-layer filter can be applied to multiple [`Layer`]s at a time, by -//! combining them into a [`Layered`] layer using [`Layer::and_then`], and then -//! calling [`Layer::with_filter`] on the resulting [`Layered`] layer. -//! -//! Consider the following: -//! - `layer_a` and `layer_b`, which should only receive spans and events at -//! the [`INFO`] [level] and above. -//! - A third layer, `layer_c`, which should receive spans and events at -//! the [`DEBUG`] [level] as well. -//! The layers and filters would be composed thusly: -//! -//! ``` -//! use tracing_subscriber::{filter::LevelFilter, prelude::*}; -//! -//! let layer_a = // ... -//! # LevelFilter::INFO; -//! let layer_b = // ... -//! # LevelFilter::INFO; -//! let layer_c = // ... -//! # LevelFilter::INFO; -//! -//! let info_layers = layer_a -//! // Combine `layer_a` and `layer_b` into a `Layered` layer: -//! .and_then(layer_b) -//! // ...and then add an `INFO` `LevelFilter` to that layer: -//! .with_filter(LevelFilter::INFO); -//! -//! tracing_subscriber::registry() -//! // Add `layer_c` with a `DEBUG` filter. -//! .with(layer_c.with_filter(LevelFilter::DEBUG)) -//! .with(info_layers) -//! .init(); -//!``` -//! -//! If a [`Filtered`] [`Layer`] is combined with another [`Layer`] -//! [`Layer::and_then`], and a filter is added to the [`Layered`] layer, that -//! layer will be filtered by *both* the inner filter and the outer filter. -//! Only spans and events that are enabled by *both* filters will be -//! observed by that layer. This can be used to implement complex filtering -//! trees. -//! -//! As an example, consider the following constraints: -//! - Suppose that a particular [target] is used to indicate events that -//! should be counted as part of a metrics system, which should be only -//! observed by a layer that collects metrics. -//! - A log of high-priority events ([`INFO`] and above) should be logged -//! to stdout, while more verbose events should be logged to a debugging log file. -//! - Metrics-focused events should *not* be included in either log output. -//! -//! In that case, it is possible to apply a filter to both logging layers to -//! exclude the metrics events, while additionally adding a [`LevelFilter`] -//! to the stdout log: -//! -//! ``` -//! # // wrap this in a function so we don't actually create `debug.log` when -//! # // running the doctests.. -//! # fn docs() -> Result<(), Box<dyn std::error::Error + 'static>> { -//! use tracing_subscriber::{filter, prelude::*}; -//! use std::{fs::File, sync::Arc}; -//! -//! // A layer that logs events to stdout using the human-readable "pretty" -//! // format. -//! let stdout_log = tracing_subscriber::fmt::layer() -//! .pretty(); -//! -//! // A layer that logs events to a file. -//! let file = File::create("debug.log")?; -//! let debug_log = tracing_subscriber::fmt::layer() -//! .with_writer(Arc::new(file)); -//! -//! // A layer that collects metrics using specific events. -//! let metrics_layer = /* ... */ filter::LevelFilter::INFO; -//! -//! tracing_subscriber::registry() -//! .with( -//! stdout_log -//! // Add an `INFO` filter to the stdout logging layer -//! .with_filter(filter::LevelFilter::INFO) -//! // Combine the filtered `stdout_log` layer with the -//! // `debug_log` layer, producing a new `Layered` layer. -//! .and_then(debug_log) -//! // Add a filter to *both* layers that rejects spans and -//! // events whose targets start with `metrics`. -//! .with_filter(filter::filter_fn(|metadata| { -//! !metadata.target().starts_with("metrics") -//! })) -//! ) -//! .with( -//! // Add a filter to the metrics label that *only* enables -//! // events whose targets start with `metrics`. -//! metrics_layer.with_filter(filter::filter_fn(|metadata| { -//! metadata.target().starts_with("metrics") -//! })) -//! ) -//! .init(); -//! -//! // This event will *only* be recorded by the metrics layer. -//! tracing::info!(target: "metrics::cool_stuff_count", value = 42); -//! -//! // This event will only be seen by the debug log file layer: -//! tracing::debug!("this is a message, and part of a system of messages"); -//! -//! // This event will be seen by both the stdout log layer *and* -//! // the debug log file layer, but not by the metrics layer. -//! tracing::warn!("the message is a warning about danger!"); -//! # Ok(()) } -//! ``` -//! -//! [`Subscriber`]: tracing_core::subscriber::Subscriber -//! [span IDs]: tracing_core::span::Id -//! [the current span]: Context::current_span -//! [`register_callsite`]: Layer::register_callsite -//! [`enabled`]: Layer::enabled -//! [`event_enabled`]: Layer::event_enabled -//! [`on_enter`]: Layer::on_enter -//! [`Layer::register_callsite`]: Layer::register_callsite -//! [`Layer::enabled`]: Layer::enabled -//! [`Interest::never()`]: tracing_core::subscriber::Interest::never() -//! [`Filtered`]: crate::filter::Filtered -//! [`filter`]: crate::filter -//! [`Targets`]: crate::filter::Targets -//! [`FilterFn`]: crate::filter::FilterFn -//! [`DynFilterFn`]: crate::filter::DynFilterFn -//! [level]: tracing_core::Level -//! [`INFO`]: tracing_core::Level::INFO -//! [`DEBUG`]: tracing_core::Level::DEBUG -//! [target]: tracing_core::Metadata::target -//! [`LevelFilter`]: crate::filter::LevelFilter -//! [feat]: crate#feature-flags -use crate::filter; - -use tracing_core::{ - metadata::Metadata, - span, - subscriber::{Interest, Subscriber}, - Event, LevelFilter, -}; - -use core::any::TypeId; - -feature! { - #![feature = "alloc"] - use alloc::boxed::Box; - use core::ops::{Deref, DerefMut}; -} - -mod context; -mod layered; -pub use self::{context::*, layered::*}; - -// The `tests` module is `pub(crate)` because it contains test utilities used by -// other modules. -#[cfg(test)] -pub(crate) mod tests; - -/// A composable handler for `tracing` events. -/// -/// A `Layer` implements a behavior for recording or collecting traces that can -/// be composed together with other `Layer`s to build a [`Subscriber`]. See the -/// [module-level documentation](crate::layer) for details. -/// -/// [`Subscriber`]: tracing_core::Subscriber -#[cfg_attr(docsrs, doc(notable_trait))] -pub trait Layer<S> -where - S: Subscriber, - Self: 'static, -{ - /// Performs late initialization when attaching a `Layer` to a - /// [`Subscriber`]. - /// - /// This is a callback that is called when the `Layer` is added to a - /// [`Subscriber`] (e.g. in [`Layer::with_subscriber`] and - /// [`SubscriberExt::with`]). Since this can only occur before the - /// [`Subscriber`] has been set as the default, both the `Layer` and - /// [`Subscriber`] are passed to this method _mutably_. This gives the - /// `Layer` the opportunity to set any of its own fields with values - /// recieved by method calls on the [`Subscriber`]. - /// - /// For example, [`Filtered`] layers implement `on_layer` to call the - /// [`Subscriber`]'s [`register_filter`] method, and store the returned - /// [`FilterId`] as a field. - /// - /// **Note** In most cases, `Layer` implementations will not need to - /// implement this method. However, in cases where a type implementing - /// `Layer` wraps one or more other types that implement `Layer`, like the - /// [`Layered`] and [`Filtered`] types in this crate, that type MUST ensure - /// that the inner `Layer`s' `on_layer` methods are called. Otherwise, - /// functionality that relies on `on_layer`, such as [per-layer filtering], - /// may not work correctly. - /// - /// [`Filtered`]: crate::filter::Filtered - /// [`register_filter`]: crate::registry::LookupSpan::register_filter - /// [per-layer filtering]: #per-layer-filtering - /// [`FilterId`]: crate::filter::FilterId - fn on_layer(&mut self, subscriber: &mut S) { - let _ = subscriber; - } - - /// Registers a new callsite with this layer, returning whether or not - /// the layer is interested in being notified about the callsite, similarly - /// to [`Subscriber::register_callsite`]. - /// - /// By default, this returns [`Interest::always()`] if [`self.enabled`] returns - /// true, or [`Interest::never()`] if it returns false. - /// - /// <pre class="ignore" style="white-space:normal;font:inherit;"> - /// <strong>Note</strong>: This method (and <a href="#method.enabled"> - /// <code>Layer::enabled</code></a>) determine whether a span or event is - /// globally enabled, <em>not</em> whether the individual layer will be - /// notified about that span or event. This is intended to be used - /// by layers that implement filtering for the entire stack. Layers which do - /// not wish to be notified about certain spans or events but do not wish to - /// globally disable them should ignore those spans or events in their - /// <a href="#method.on_event"><code>on_event</code></a>, - /// <a href="#method.on_enter"><code>on_enter</code></a>, - /// <a href="#method.on_exit"><code>on_exit</code></a>, and other notification - /// methods. - /// </pre> - /// - /// See [the trait-level documentation] for more information on filtering - /// with `Layer`s. - /// - /// Layers may also implement this method to perform any behaviour that - /// should be run once per callsite. If the layer wishes to use - /// `register_callsite` for per-callsite behaviour, but does not want to - /// globally enable or disable those callsites, it should always return - /// [`Interest::always()`]. - /// - /// [`Interest`]: tracing_core::Interest - /// [`Subscriber::register_callsite`]: tracing_core::Subscriber::register_callsite() - /// [`Interest::never()`]: tracing_core::subscriber::Interest::never() - /// [`Interest::always()`]: tracing_core::subscriber::Interest::always() - /// [`self.enabled`]: Layer::enabled() - /// [`Layer::enabled`]: Layer::enabled() - /// [`on_event`]: Layer::on_event() - /// [`on_enter`]: Layer::on_enter() - /// [`on_exit`]: Layer::on_exit() - /// [the trait-level documentation]: #filtering-with-layers - fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { - if self.enabled(metadata, Context::none()) { - Interest::always() - } else { - Interest::never() - } - } - - /// Returns `true` if this layer is interested in a span or event with the - /// given `metadata` in the current [`Context`], similarly to - /// [`Subscriber::enabled`]. - /// - /// By default, this always returns `true`, allowing the wrapped subscriber - /// to choose to disable the span. - /// - /// <pre class="ignore" style="white-space:normal;font:inherit;"> - /// <strong>Note</strong>: This method (and <a href="#method.register_callsite"> - /// <code>Layer::register_callsite</code></a>) determine whether a span or event is - /// globally enabled, <em>not</em> whether the individual layer will be - /// notified about that span or event. This is intended to be used - /// by layers that implement filtering for the entire stack. Layers which do - /// not wish to be notified about certain spans or events but do not wish to - /// globally disable them should ignore those spans or events in their - /// <a href="#method.on_event"><code>on_event</code></a>, - /// <a href="#method.on_enter"><code>on_enter</code></a>, - /// <a href="#method.on_exit"><code>on_exit</code></a>, and other notification - /// methods. - /// </pre> - /// - /// - /// See [the trait-level documentation] for more information on filtering - /// with `Layer`s. - /// - /// [`Interest`]: tracing_core::Interest - /// [`Subscriber::enabled`]: tracing_core::Subscriber::enabled() - /// [`Layer::register_callsite`]: Layer::register_callsite() - /// [`on_event`]: Layer::on_event() - /// [`on_enter`]: Layer::on_enter() - /// [`on_exit`]: Layer::on_exit() - /// [the trait-level documentation]: #filtering-with-layers - fn enabled(&self, metadata: &Metadata<'_>, ctx: Context<'_, S>) -> bool { - let _ = (metadata, ctx); - true - } - - /// Notifies this layer that a new span was constructed with the given - /// `Attributes` and `Id`. - fn on_new_span(&self, attrs: &span::Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) { - let _ = (attrs, id, ctx); - } - - // TODO(eliza): do we want this to be a public API? If we end up moving - // filtering layers to a separate trait, we may no longer want `Layer`s to - // be able to participate in max level hinting... - #[doc(hidden)] - fn max_level_hint(&self) -> Option<LevelFilter> { - None - } - - /// Notifies this layer that a span with the given `Id` recorded the given - /// `values`. - // Note: it's unclear to me why we'd need the current span in `record` (the - // only thing the `Context` type currently provides), but passing it in anyway - // seems like a good future-proofing measure as it may grow other methods later... - fn on_record(&self, _span: &span::Id, _values: &span::Record<'_>, _ctx: Context<'_, S>) {} - - /// Notifies this layer that a span with the ID `span` recorded that it - /// follows from the span with the ID `follows`. - // Note: it's unclear to me why we'd need the current span in `record` (the - // only thing the `Context` type currently provides), but passing it in anyway - // seems like a good future-proofing measure as it may grow other methods later... - fn on_follows_from(&self, _span: &span::Id, _follows: &span::Id, _ctx: Context<'_, S>) {} - - /// Called before [`on_event`], to determine if `on_event` should be called. - /// - /// <div class="example-wrap" style="display:inline-block"> - /// <pre class="ignore" style="white-space:normal;font:inherit;"> - /// - /// **Note**: This method determines whether an event is globally enabled, - /// *not* whether the individual `Layer` will be notified about the - /// event. This is intended to be used by `Layer`s that implement - /// filtering for the entire stack. `Layer`s which do not wish to be - /// notified about certain events but do not wish to globally disable them - /// should ignore those events in their [on_event][Self::on_event]. - /// - /// </pre></div> - /// - /// See [the trait-level documentation] for more information on filtering - /// with `Layer`s. - /// - /// [`on_event`]: Self::on_event - /// [`Interest`]: tracing_core::Interest - /// [the trait-level documentation]: #filtering-with-layers - #[inline] // collapse this to a constant please mrs optimizer - fn event_enabled(&self, _event: &Event<'_>, _ctx: Context<'_, S>) -> bool { - true - } - - /// Notifies this layer that an event has occurred. - fn on_event(&self, _event: &Event<'_>, _ctx: Context<'_, S>) {} - - /// Notifies this layer that a span with the given ID was entered. - fn on_enter(&self, _id: &span::Id, _ctx: Context<'_, S>) {} - - /// Notifies this layer that the span with the given ID was exited. - fn on_exit(&self, _id: &span::Id, _ctx: Context<'_, S>) {} - - /// Notifies this layer that the span with the given ID has been closed. - fn on_close(&self, _id: span::Id, _ctx: Context<'_, S>) {} - - /// Notifies this layer that a span ID has been cloned, and that the - /// subscriber returned a different ID. - fn on_id_change(&self, _old: &span::Id, _new: &span::Id, _ctx: Context<'_, S>) {} - - /// Composes this layer around the given `Layer`, returning a `Layered` - /// struct implementing `Layer`. - /// - /// The returned `Layer` will call the methods on this `Layer` and then - /// those of the new `Layer`, before calling the methods on the subscriber - /// it wraps. For example: - /// - /// ```rust - /// # use tracing_subscriber::layer::Layer; - /// # use tracing_core::Subscriber; - /// pub struct FooLayer { - /// // ... - /// } - /// - /// pub struct BarLayer { - /// // ... - /// } - /// - /// pub struct MySubscriber { - /// // ... - /// } - /// - /// impl<S: Subscriber> Layer<S> for FooLayer { - /// // ... - /// } - /// - /// impl<S: Subscriber> Layer<S> for BarLayer { - /// // ... - /// } - /// - /// # impl FooLayer { - /// # fn new() -> Self { Self {} } - /// # } - /// # impl BarLayer { - /// # fn new() -> Self { Self { }} - /// # } - /// # impl MySubscriber { - /// # fn new() -> Self { Self { }} - /// # } - /// # use tracing_core::{span::{Id, Attributes, Record}, Metadata, Event}; - /// # impl tracing_core::Subscriber for MySubscriber { - /// # fn new_span(&self, _: &Attributes) -> Id { Id::from_u64(1) } - /// # fn record(&self, _: &Id, _: &Record) {} - /// # fn event(&self, _: &Event) {} - /// # fn record_follows_from(&self, _: &Id, _: &Id) {} - /// # fn enabled(&self, _: &Metadata) -> bool { false } - /// # fn enter(&self, _: &Id) {} - /// # fn exit(&self, _: &Id) {} - /// # } - /// let subscriber = FooLayer::new() - /// .and_then(BarLayer::new()) - /// .with_subscriber(MySubscriber::new()); - /// ``` - /// - /// Multiple layers may be composed in this manner: - /// - /// ```rust - /// # use tracing_subscriber::layer::Layer; - /// # use tracing_core::Subscriber; - /// # pub struct FooLayer {} - /// # pub struct BarLayer {} - /// # pub struct MySubscriber {} - /// # impl<S: Subscriber> Layer<S> for FooLayer {} - /// # impl<S: Subscriber> Layer<S> for BarLayer {} - /// # impl FooLayer { - /// # fn new() -> Self { Self {} } - /// # } - /// # impl BarLayer { - /// # fn new() -> Self { Self { }} - /// # } - /// # impl MySubscriber { - /// # fn new() -> Self { Self { }} - /// # } - /// # use tracing_core::{span::{Id, Attributes, Record}, Metadata, Event}; - /// # impl tracing_core::Subscriber for MySubscriber { - /// # fn new_span(&self, _: &Attributes) -> Id { Id::from_u64(1) } - /// # fn record(&self, _: &Id, _: &Record) {} - /// # fn event(&self, _: &Event) {} - /// # fn record_follows_from(&self, _: &Id, _: &Id) {} - /// # fn enabled(&self, _: &Metadata) -> bool { false } - /// # fn enter(&self, _: &Id) {} - /// # fn exit(&self, _: &Id) {} - /// # } - /// pub struct BazLayer { - /// // ... - /// } - /// - /// impl<S: Subscriber> Layer<S> for BazLayer { - /// // ... - /// } - /// # impl BazLayer { fn new() -> Self { BazLayer {} } } - /// - /// let subscriber = FooLayer::new() - /// .and_then(BarLayer::new()) - /// .and_then(BazLayer::new()) - /// .with_subscriber(MySubscriber::new()); - /// ``` - fn and_then<L>(self, layer: L) -> Layered<L, Self, S> - where - L: Layer<S>, - Self: Sized, - { - let inner_has_layer_filter = filter::layer_has_plf(&self); - Layered::new(layer, self, inner_has_layer_filter) - } - - /// Composes this `Layer` with the given [`Subscriber`], returning a - /// `Layered` struct that implements [`Subscriber`]. - /// - /// The returned `Layered` subscriber will call the methods on this `Layer` - /// and then those of the wrapped subscriber. - /// - /// For example: - /// ```rust - /// # use tracing_subscriber::layer::Layer; - /// # use tracing_core::Subscriber; - /// pub struct FooLayer { - /// // ... - /// } - /// - /// pub struct MySubscriber { - /// // ... - /// } - /// - /// impl<S: Subscriber> Layer<S> for FooLayer { - /// // ... - /// } - /// - /// # impl FooLayer { - /// # fn new() -> Self { Self {} } - /// # } - /// # impl MySubscriber { - /// # fn new() -> Self { Self { }} - /// # } - /// # use tracing_core::{span::{Id, Attributes, Record}, Metadata}; - /// # impl tracing_core::Subscriber for MySubscriber { - /// # fn new_span(&self, _: &Attributes) -> Id { Id::from_u64(0) } - /// # fn record(&self, _: &Id, _: &Record) {} - /// # fn event(&self, _: &tracing_core::Event) {} - /// # fn record_follows_from(&self, _: &Id, _: &Id) {} - /// # fn enabled(&self, _: &Metadata) -> bool { false } - /// # fn enter(&self, _: &Id) {} - /// # fn exit(&self, _: &Id) {} - /// # } - /// let subscriber = FooLayer::new() - /// .with_subscriber(MySubscriber::new()); - ///``` - /// - /// [`Subscriber`]: tracing_core::Subscriber - fn with_subscriber(mut self, mut inner: S) -> Layered<Self, S> - where - Self: Sized, - { - let inner_has_layer_filter = filter::subscriber_has_plf(&inner); - self.on_layer(&mut inner); - Layered::new(self, inner, inner_has_layer_filter) - } - - /// Combines `self` with a [`Filter`], returning a [`Filtered`] layer. - /// - /// The [`Filter`] will control which spans and events are enabled for - /// this layer. See [the trait-level documentation][plf] for details on - /// per-layer filtering. - /// - /// [`Filtered`]: crate::filter::Filtered - /// [plf]: crate::layer#per-layer-filtering - #[cfg(all(feature = "registry", feature = "std"))] - #[cfg_attr(docsrs, doc(cfg(all(feature = "registry", feature = "std"))))] - fn with_filter<F>(self, filter: F) -> filter::Filtered<Self, F, S> - where - Self: Sized, - F: Filter<S>, - { - filter::Filtered::new(self, filter) - } - - /// Erases the type of this [`Layer`], returning a [`Box`]ed `dyn - /// Layer` trait object. - /// - /// This can be used when a function returns a `Layer` which may be of - /// one of several types, or when a `Layer` subscriber has a very long type - /// signature. - /// - /// # Examples - /// - /// The following example will *not* compile, because the value assigned to - /// `log_layer` may have one of several different types: - /// - /// ```compile_fail - /// # fn main() -> Result<(), Box<dyn std::error::Error>> { - /// use tracing_subscriber::{Layer, filter::LevelFilter, prelude::*}; - /// use std::{path::PathBuf, fs::File, io}; - /// - /// /// Configures whether logs are emitted to a file, to stdout, or to stderr. - /// pub enum LogConfig { - /// File(PathBuf), - /// Stdout, - /// Stderr, - /// } - /// - /// let config = // ... - /// # LogConfig::Stdout; - /// - /// // Depending on the config, construct a layer of one of several types. - /// let log_layer = match config { - /// // If logging to a file, use a maximally-verbose configuration. - /// LogConfig::File(path) => { - /// let file = File::create(path)?; - /// tracing_subscriber::fmt::layer() - /// .with_thread_ids(true) - /// .with_thread_names(true) - /// // Selecting the JSON logging format changes the layer's - /// // type. - /// .json() - /// .with_span_list(true) - /// // Setting the writer to use our log file changes the - /// // layer's type again. - /// .with_writer(file) - /// }, - /// - /// // If logging to stdout, use a pretty, human-readable configuration. - /// LogConfig::Stdout => tracing_subscriber::fmt::layer() - /// // Selecting the "pretty" logging format changes the - /// // layer's type! - /// .pretty() - /// .with_writer(io::stdout) - /// // Add a filter based on the RUST_LOG environment variable; - /// // this changes the type too! - /// .and_then(tracing_subscriber::EnvFilter::from_default_env()), - /// - /// // If logging to stdout, only log errors and warnings. - /// LogConfig::Stderr => tracing_subscriber::fmt::layer() - /// // Changing the writer changes the layer's type - /// .with_writer(io::stderr) - /// // Only log the `WARN` and `ERROR` levels. Adding a filter - /// // changes the layer's type to `Filtered<LevelFilter, ...>`. - /// .with_filter(LevelFilter::WARN), - /// }; - /// - /// tracing_subscriber::registry() - /// .with(log_layer) - /// .init(); - /// # Ok(()) } - /// ``` - /// - /// However, adding a call to `.boxed()` after each match arm erases the - /// layer's type, so this code *does* compile: - /// - /// ``` - /// # fn main() -> Result<(), Box<dyn std::error::Error>> { - /// # use tracing_subscriber::{Layer, filter::LevelFilter, prelude::*}; - /// # use std::{path::PathBuf, fs::File, io}; - /// # pub enum LogConfig { - /// # File(PathBuf), - /// # Stdout, - /// # Stderr, - /// # } - /// # let config = LogConfig::Stdout; - /// let log_layer = match config { - /// LogConfig::File(path) => { - /// let file = File::create(path)?; - /// tracing_subscriber::fmt::layer() - /// .with_thread_ids(true) - /// .with_thread_names(true) - /// .json() - /// .with_span_list(true) - /// .with_writer(file) - /// // Erase the type by boxing the layer - /// .boxed() - /// }, - /// - /// LogConfig::Stdout => tracing_subscriber::fmt::layer() - /// .pretty() - /// .with_writer(io::stdout) - /// .and_then(tracing_subscriber::EnvFilter::from_default_env()) - /// // Erase the type by boxing the layer - /// .boxed(), - /// - /// LogConfig::Stderr => tracing_subscriber::fmt::layer() - /// .with_writer(io::stderr) - /// .with_filter(LevelFilter::WARN) - /// // Erase the type by boxing the layer - /// .boxed(), - /// }; - /// - /// tracing_subscriber::registry() - /// .with(log_layer) - /// .init(); - /// # Ok(()) } - /// ``` - #[cfg(any(feature = "alloc", feature = "std"))] - #[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))] - fn boxed(self) -> Box<dyn Layer<S> + Send + Sync + 'static> - where - Self: Sized, - Self: Layer<S> + Send + Sync + 'static, - S: Subscriber, - { - Box::new(self) - } - - #[doc(hidden)] - unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { - if id == TypeId::of::<Self>() { - Some(self as *const _ as *const ()) - } else { - None - } - } -} - -feature! { - #![all(feature = "registry", feature = "std")] - - /// A per-[`Layer`] filter that determines whether a span or event is enabled - /// for an individual layer. - /// - /// See [the module-level documentation][plf] for details on using [`Filter`]s. - /// - /// [plf]: crate::layer#per-layer-filtering - #[cfg_attr(docsrs, doc(notable_trait))] - pub trait Filter<S> { - /// Returns `true` if this layer is interested in a span or event with the - /// given [`Metadata`] in the current [`Context`], similarly to - /// [`Subscriber::enabled`]. - /// - /// If this returns `false`, the span or event will be disabled _for the - /// wrapped [`Layer`]_. Unlike [`Layer::enabled`], the span or event will - /// still be recorded if any _other_ layers choose to enable it. However, - /// the layer [filtered] by this filter will skip recording that span or - /// event. - /// - /// If all layers indicate that they do not wish to see this span or event, - /// it will be disabled. - /// - /// [`metadata`]: tracing_core::Metadata - /// [`Subscriber::enabled`]: tracing_core::Subscriber::enabled - /// [filtered]: crate::filter::Filtered - fn enabled(&self, meta: &Metadata<'_>, cx: &Context<'_, S>) -> bool; - - /// Returns an [`Interest`] indicating whether this layer will [always], - /// [sometimes], or [never] be interested in the given [`Metadata`]. - /// - /// When a given callsite will [always] or [never] be enabled, the results - /// of evaluating the filter may be cached for improved performance. - /// Therefore, if a filter is capable of determining that it will always or - /// never enable a particular callsite, providing an implementation of this - /// function is recommended. - /// - /// <pre class="ignore" style="white-space:normal;font:inherit;"> - /// <strong>Note</strong>: If a <code>Filter</code> will perform - /// <em>dynamic filtering</em> that depends on the current context in which - /// a span or event was observered (e.g. only enabling an event when it - /// occurs within a particular span), it <strong>must</strong> return - /// <code>Interest::sometimes()</code> from this method. If it returns - /// <code>Interest::always()</code> or <code>Interest::never()</code>, the - /// <code>enabled</code> method may not be called when a particular instance - /// of that span or event is recorded. - /// </pre> - /// - /// This method is broadly similar to [`Subscriber::register_callsite`]; - /// however, since the returned value represents only the interest of - /// *this* layer, the resulting behavior is somewhat different. - /// - /// If a [`Subscriber`] returns [`Interest::always()`][always] or - /// [`Interest::never()`][never] for a given [`Metadata`], its [`enabled`] - /// method is then *guaranteed* to never be called for that callsite. On the - /// other hand, when a `Filter` returns [`Interest::always()`][always] or - /// [`Interest::never()`][never] for a callsite, _other_ [`Layer`]s may have - /// differing interests in that callsite. If this is the case, the callsite - /// will recieve [`Interest::sometimes()`][sometimes], and the [`enabled`] - /// method will still be called for that callsite when it records a span or - /// event. - /// - /// Returning [`Interest::always()`][always] or [`Interest::never()`][never] from - /// `Filter::callsite_enabled` will permanently enable or disable a - /// callsite (without requiring subsequent calls to [`enabled`]) if and only - /// if the following is true: - /// - /// - all [`Layer`]s that comprise the subscriber include `Filter`s - /// (this includes a tree of [`Layered`] layers that share the same - /// `Filter`) - /// - all those `Filter`s return the same [`Interest`]. - /// - /// For example, if a [`Subscriber`] consists of two [`Filtered`] layers, - /// and both of those layers return [`Interest::never()`][never], that - /// callsite *will* never be enabled, and the [`enabled`] methods of those - /// [`Filter`]s will not be called. - /// - /// ## Default Implementation - /// - /// The default implementation of this method assumes that the - /// `Filter`'s [`enabled`] method _may_ perform dynamic filtering, and - /// returns [`Interest::sometimes()`][sometimes], to ensure that [`enabled`] - /// is called to determine whether a particular _instance_ of the callsite - /// is enabled in the current context. If this is *not* the case, and the - /// `Filter`'s [`enabled`] method will always return the same result - /// for a particular [`Metadata`], this method can be overridden as - /// follows: - /// - /// ``` - /// use tracing_subscriber::layer; - /// use tracing_core::{Metadata, subscriber::Interest}; - /// - /// struct MyFilter { - /// // ... - /// } - /// - /// impl MyFilter { - /// // The actual logic for determining whether a `Metadata` is enabled - /// // must be factored out from the `enabled` method, so that it can be - /// // called without a `Context` (which is not provided to the - /// // `callsite_enabled` method). - /// fn is_enabled(&self, metadata: &Metadata<'_>) -> bool { - /// // ... - /// # drop(metadata); true - /// } - /// } - /// - /// impl<S> layer::Filter<S> for MyFilter { - /// fn enabled(&self, metadata: &Metadata<'_>, _: &layer::Context<'_, S>) -> bool { - /// // Even though we are implementing `callsite_enabled`, we must still provide a - /// // working implementation of `enabled`, as returning `Interest::always()` or - /// // `Interest::never()` will *allow* caching, but will not *guarantee* it. - /// // Other filters may still return `Interest::sometimes()`, so we may be - /// // asked again in `enabled`. - /// self.is_enabled(metadata) - /// } - /// - /// fn callsite_enabled(&self, metadata: &'static Metadata<'static>) -> Interest { - /// // The result of `self.enabled(metadata, ...)` will always be - /// // the same for any given `Metadata`, so we can convert it into - /// // an `Interest`: - /// if self.is_enabled(metadata) { - /// Interest::always() - /// } else { - /// Interest::never() - /// } - /// } - /// } - /// ``` - /// - /// [`Metadata`]: tracing_core::Metadata - /// [`Interest`]: tracing_core::Interest - /// [always]: tracing_core::Interest::always - /// [sometimes]: tracing_core::Interest::sometimes - /// [never]: tracing_core::Interest::never - /// [`Subscriber::register_callsite`]: tracing_core::Subscriber::register_callsite - /// [`Subscriber`]: tracing_core::Subscriber - /// [`enabled`]: Filter::enabled - /// [`Filtered`]: crate::filter::Filtered - fn callsite_enabled(&self, meta: &'static Metadata<'static>) -> Interest { - let _ = meta; - Interest::sometimes() - } - - /// Returns an optional hint of the highest [verbosity level][level] that - /// this `Filter` will enable. - /// - /// If this method returns a [`LevelFilter`], it will be used as a hint to - /// determine the most verbose level that will be enabled. This will allow - /// spans and events which are more verbose than that level to be skipped - /// more efficiently. An implementation of this method is optional, but - /// strongly encouraged. - /// - /// If the maximum level the `Filter` will enable can change over the - /// course of its lifetime, it is free to return a different value from - /// multiple invocations of this method. However, note that changes in the - /// maximum level will **only** be reflected after the callsite [`Interest`] - /// cache is rebuilt, by calling the - /// [`tracing_core::callsite::rebuild_interest_cache`][rebuild] function. - /// Therefore, if the `Filter will change the value returned by this - /// method, it is responsible for ensuring that - /// [`rebuild_interest_cache`][rebuild] is called after the value of the max - /// level changes. - /// - /// ## Default Implementation - /// - /// By default, this method returns `None`, indicating that the maximum - /// level is unknown. - /// - /// [level]: tracing_core::metadata::Level - /// [`LevelFilter`]: crate::filter::LevelFilter - /// [`Interest`]: tracing_core::subscriber::Interest - /// [rebuild]: tracing_core::callsite::rebuild_interest_cache - fn max_level_hint(&self) -> Option<LevelFilter> { - None - } - - /// Notifies this filter that a new span was constructed with the given - /// `Attributes` and `Id`. - /// - /// By default, this method does nothing. `Filter` implementations that - /// need to be notified when new spans are created can override this - /// method. - fn on_new_span(&self, attrs: &span::Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) { - let _ = (attrs, id, ctx); - } - - - /// Notifies this filter that a span with the given `Id` recorded the given - /// `values`. - /// - /// By default, this method does nothing. `Filter` implementations that - /// need to be notified when new spans are created can override this - /// method. - fn on_record(&self, id: &span::Id, values: &span::Record<'_>, ctx: Context<'_, S>) { - let _ = (id, values, ctx); - } - - /// Notifies this filter that a span with the given ID was entered. - /// - /// By default, this method does nothing. `Filter` implementations that - /// need to be notified when a span is entered can override this method. - fn on_enter(&self, id: &span::Id, ctx: Context<'_, S>) { - let _ = (id, ctx); - } - - /// Notifies this filter that a span with the given ID was exited. - /// - /// By default, this method does nothing. `Filter` implementations that - /// need to be notified when a span is exited can override this method. - fn on_exit(&self, id: &span::Id, ctx: Context<'_, S>) { - let _ = (id, ctx); - } - - /// Notifies this filter that a span with the given ID has been closed. - /// - /// By default, this method does nothing. `Filter` implementations that - /// need to be notified when a span is closed can override this method. - fn on_close(&self, id: span::Id, ctx: Context<'_, S>) { - let _ = (id, ctx); - } - } -} - -/// Extension trait adding a `with(Layer)` combinator to `Subscriber`s. -pub trait SubscriberExt: Subscriber + crate::sealed::Sealed { - /// Wraps `self` with the provided `layer`. - fn with<L>(self, layer: L) -> Layered<L, Self> - where - L: Layer<Self>, - Self: Sized, - { - layer.with_subscriber(self) - } -} - -/// A layer that does nothing. -#[derive(Clone, Debug, Default)] -pub struct Identity { - _p: (), -} - -// === impl Layer === - -impl<L, S> Layer<S> for Option<L> -where - L: Layer<S>, - S: Subscriber, -{ - fn on_layer(&mut self, subscriber: &mut S) { - if let Some(ref mut layer) = self { - layer.on_layer(subscriber) - } - } - - #[inline] - fn on_new_span(&self, attrs: &span::Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_new_span(attrs, id, ctx) - } - } - - #[inline] - fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { - match self { - Some(ref inner) => inner.register_callsite(metadata), - None => Interest::always(), - } - } - - #[inline] - fn enabled(&self, metadata: &Metadata<'_>, ctx: Context<'_, S>) -> bool { - match self { - Some(ref inner) => inner.enabled(metadata, ctx), - None => true, - } - } - - #[inline] - fn max_level_hint(&self) -> Option<LevelFilter> { - match self { - Some(ref inner) => inner.max_level_hint(), - None => { - // There is no inner layer, so this layer will - // never enable anything. - Some(LevelFilter::OFF) - } - } - } - - #[inline] - fn on_record(&self, span: &span::Id, values: &span::Record<'_>, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_record(span, values, ctx); - } - } - - #[inline] - fn on_follows_from(&self, span: &span::Id, follows: &span::Id, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_follows_from(span, follows, ctx); - } - } - - #[inline] - fn event_enabled(&self, event: &Event<'_>, ctx: Context<'_, S>) -> bool { - match self { - Some(ref inner) => inner.event_enabled(event, ctx), - None => true, - } - } - - #[inline] - fn on_event(&self, event: &Event<'_>, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_event(event, ctx); - } - } - - #[inline] - fn on_enter(&self, id: &span::Id, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_enter(id, ctx); - } - } - - #[inline] - fn on_exit(&self, id: &span::Id, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_exit(id, ctx); - } - } - - #[inline] - fn on_close(&self, id: span::Id, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_close(id, ctx); - } - } - - #[inline] - fn on_id_change(&self, old: &span::Id, new: &span::Id, ctx: Context<'_, S>) { - if let Some(ref inner) = self { - inner.on_id_change(old, new, ctx) - } - } - - #[doc(hidden)] - #[inline] - unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { - if id == TypeId::of::<Self>() { - Some(self as *const _ as *const ()) - } else { - self.as_ref().and_then(|inner| inner.downcast_raw(id)) - } - } -} - -feature! { - #![any(feature = "std", feature = "alloc")] - #[cfg(not(feature = "std"))] - use alloc::vec::Vec; - - macro_rules! layer_impl_body { - () => { - #[inline] - fn on_layer(&mut self, subscriber: &mut S) { - self.deref_mut().on_layer(subscriber); - } - - #[inline] - fn on_new_span(&self, attrs: &span::Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) { - self.deref().on_new_span(attrs, id, ctx) - } - - #[inline] - fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { - self.deref().register_callsite(metadata) - } - - #[inline] - fn enabled(&self, metadata: &Metadata<'_>, ctx: Context<'_, S>) -> bool { - self.deref().enabled(metadata, ctx) - } - - #[inline] - fn max_level_hint(&self) -> Option<LevelFilter> { - self.deref().max_level_hint() - } - - #[inline] - fn on_record(&self, span: &span::Id, values: &span::Record<'_>, ctx: Context<'_, S>) { - self.deref().on_record(span, values, ctx) - } - - #[inline] - fn on_follows_from(&self, span: &span::Id, follows: &span::Id, ctx: Context<'_, S>) { - self.deref().on_follows_from(span, follows, ctx) - } - - #[inline] - fn event_enabled(&self, event: &Event<'_>, ctx: Context<'_, S>) -> bool { - self.deref().event_enabled(event, ctx) - } - - #[inline] - fn on_event(&self, event: &Event<'_>, ctx: Context<'_, S>) { - self.deref().on_event(event, ctx) - } - - #[inline] - fn on_enter(&self, id: &span::Id, ctx: Context<'_, S>) { - self.deref().on_enter(id, ctx) - } - - #[inline] - fn on_exit(&self, id: &span::Id, ctx: Context<'_, S>) { - self.deref().on_exit(id, ctx) - } - - #[inline] - fn on_close(&self, id: span::Id, ctx: Context<'_, S>) { - self.deref().on_close(id, ctx) - } - - #[inline] - fn on_id_change(&self, old: &span::Id, new: &span::Id, ctx: Context<'_, S>) { - self.deref().on_id_change(old, new, ctx) - } - - #[doc(hidden)] - #[inline] - unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { - self.deref().downcast_raw(id) - } - }; - } - - impl<L, S> Layer<S> for Box<L> - where - L: Layer<S>, - S: Subscriber, - { - layer_impl_body! {} - } - - impl<S> Layer<S> for Box<dyn Layer<S> + Send + Sync> - where - S: Subscriber, - { - layer_impl_body! {} - } - - - - impl<S, L> Layer<S> for Vec<L> - where - L: Layer<S>, - S: Subscriber, - { - - fn on_layer(&mut self, subscriber: &mut S) { - for l in self { - l.on_layer(subscriber); - } - } - - fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest { - // Return highest level of interest. - let mut interest = Interest::never(); - for l in self { - let new_interest = l.register_callsite(metadata); - if (interest.is_sometimes() && new_interest.is_always()) - || (interest.is_never() && !new_interest.is_never()) - { - interest = new_interest; - } - } - - interest - } - - fn enabled(&self, metadata: &Metadata<'_>, ctx: Context<'_, S>) -> bool { - self.iter().all(|l| l.enabled(metadata, ctx.clone())) - } - - fn event_enabled(&self, event: &Event<'_>, ctx: Context<'_, S>) -> bool { - self.iter().all(|l| l.event_enabled(event, ctx.clone())) - } - - fn on_new_span(&self, attrs: &span::Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) { - for l in self { - l.on_new_span(attrs, id, ctx.clone()); - } - } - - fn max_level_hint(&self) -> Option<LevelFilter> { - // Default to `OFF` if there are no inner layers. - let mut max_level = LevelFilter::OFF; - for l in self { - // NOTE(eliza): this is slightly subtle: if *any* layer - // returns `None`, we have to return `None`, assuming there is - // no max level hint, since that particular layer cannot - // provide a hint. - let hint = l.max_level_hint()?; - max_level = core::cmp::max(hint, max_level); - } - Some(max_level) - } - - fn on_record(&self, span: &span::Id, values: &span::Record<'_>, ctx: Context<'_, S>) { - for l in self { - l.on_record(span, values, ctx.clone()) - } - } - - fn on_follows_from(&self, span: &span::Id, follows: &span::Id, ctx: Context<'_, S>) { - for l in self { - l.on_follows_from(span, follows, ctx.clone()); - } - } - - fn on_event(&self, event: &Event<'_>, ctx: Context<'_, S>) { - for l in self { - l.on_event(event, ctx.clone()); - } - } - - fn on_enter(&self, id: &span::Id, ctx: Context<'_, S>) { - for l in self { - l.on_enter(id, ctx.clone()); - } - } - - fn on_exit(&self, id: &span::Id, ctx: Context<'_, S>) { - for l in self { - l.on_exit(id, ctx.clone()); - } - } - - fn on_close(&self, id: span::Id, ctx: Context<'_, S>) { - for l in self { - l.on_close(id.clone(), ctx.clone()); - } - } - - #[doc(hidden)] - unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { - // If downcasting to `Self`, return a pointer to `self`. - if id == TypeId::of::<Self>() { - return Some(self as *const _ as *const ()); - } - - // Someone is looking for per-layer filters. But, this `Vec` - // might contain layers with per-layer filters *and* - // layers without filters. It should only be treated as a - // per-layer-filtered layer if *all* its layers have - // per-layer filters. - // XXX(eliza): it's a bummer we have to do this linear search every - // time. It would be nice if this could be cached, but that would - // require replacing the `Vec` impl with an impl for a newtype... - if filter::is_plf_downcast_marker(id) && self.iter().any(|s| s.downcast_raw(id).is_none()) { - return None; - } - - // Otherwise, return the first child of `self` that downcaasts to - // the selected type, if any. - // XXX(eliza): hope this is reasonable lol - self.iter().find_map(|l| l.downcast_raw(id)) - } - } -} - -// === impl SubscriberExt === - -impl<S: Subscriber> crate::sealed::Sealed for S {} -impl<S: Subscriber> SubscriberExt for S {} - -// === impl Identity === - -impl<S: Subscriber> Layer<S> for Identity {} - -impl Identity { - /// Returns a new `Identity` layer. - pub fn new() -> Self { - Self { _p: () } - } -} |