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//! A `Subscriber` for formatting and logging `tracing` data. //! //! ## Overview //! //! [`tracing`] is a framework for instrumenting Rust programs with context-aware, //! structured, event-based diagnostic information. This crate provides an //! implementation of the [`Subscriber`] trait that records `tracing`'s `Event`s //! and `Span`s by formatting them as text and logging them to stdout. //! //! ## Usage //! //! First, add this to your `Cargo.toml` file: //! //! ```toml //! [dependencies] //! tracing-subscriber = "0.2" //! ``` //! //! *Compiler support: requires rustc 1.39+* //! //! Add the following to your executable to initialize the default subscriber: //! ```rust //! use tracing_subscriber; //! //! tracing_subscriber::fmt::init(); //! ``` //! //! ## Filtering Events with Environment Variables //! //! The default subscriber installed by `init` enables you to filter events //! at runtime using environment variables (using the [`EnvFilter`]). //! //! The filter syntax is a superset of the [`env_logger`] syntax. //! //! For example: //! - Setting `RUST_LOG=debug` enables all `Span`s and `Event`s //! set to the log level `DEBUG` or higher //! - Setting `RUST_LOG=my_crate=trace` enables `Span`s and `Event`s //! in `my_crate` at all log levels //! //! **Note**: This should **not** be called by libraries. Libraries should use //! [`tracing`] to publish `tracing` `Event`s. //! //! ## Configuration //! //! You can configure a subscriber instead of using the defaults with //! the following functions: //! //! ### Subscriber //! //! The [`FmtSubscriber`] formats and records `tracing` events as line-oriented logs. //! You can create one by calling: //! //! ```rust //! use tracing_subscriber::FmtSubscriber; //! //! let subscriber = FmtSubscriber::builder() //! // ... add configuration //! .finish(); //! ``` //! //! You can find the configuration methods for [`FmtSubscriber`] in [`fmt::SubscriberBuilder`]. //! //! ### Filters //! //! If you want to filter the `tracing` `Events` based on environment //! variables, you can use the [`EnvFilter`] as follows: //! //! ```rust //! use tracing_subscriber::EnvFilter; //! //! let filter = EnvFilter::from_default_env(); //! ``` //! //! As mentioned above, the [`EnvFilter`] allows `Span`s and `Event`s to //! be filtered at runtime by setting the `RUST_LOG` environment variable. //! //! You can find the other available [`filter`]s in the documentation. //! //! ### Using Your Subscriber //! //! Finally, once you have configured your `Subscriber`, you need to //! configure your executable to use it. //! //! A subscriber can be installed globally using: //! ```rust //! use tracing; //! use tracing_subscriber::FmtSubscriber; //! //! let subscriber = FmtSubscriber::new(); //! //! tracing::subscriber::set_global_default(subscriber) //! .map_err(|_err| eprintln!("Unable to set global default subscriber")); //! // Note this will only fail if you try to set the global default //! // subscriber multiple times //! ``` //! //! ### Composing Layers //! //! Composing an [`EnvFilter`] `Layer` and a [format `Layer`](../fmt/struct.Layer.html): //! //! ```rust //! use tracing_subscriber::{fmt, Layer, registry::Registry, EnvFilter}; //! //! let fmt_layer = fmt::Layer::builder() //! .with_target(false) //! .finish(); //! //! let subscriber = EnvFilter::try_from_default_env() //! .or_else(|_| EnvFilter::try_new("info")) //! .unwrap() //! .and_then(fmt_layer) //! .with_subscriber(Registry::default()); //! //! tracing::subscriber::set_global_default(subscriber).unwrap(); //! ``` //! //! [`EnvFilter`]: ../filter/struct.EnvFilter.html //! [`env_logger`]: https://docs.rs/env_logger/ //! [`filter`]: ../filter/index.html //! [`fmt::SubscriberBuilder`]: ./struct.SubscriberBuilder.html //! [`FmtSubscriber`]: ./struct.Subscriber.html //! [`Subscriber`]: //! https://docs.rs/tracing/latest/tracing/trait.Subscriber.html //! [`tracing`]: https://crates.io/crates/tracing use std::{any::TypeId, error::Error, io}; use tracing_core::{span, subscriber::Interest, Event, Metadata}; mod fmt_layer; pub mod format; pub mod time; pub mod writer; pub use fmt_layer::{FmtContext, FormattedFields, Layer, LayerBuilder}; use crate::layer::Layer as _; use crate::{filter::LevelFilter, layer, registry::Registry}; #[doc(inline)] pub use self::{ format::{FormatEvent, FormatFields}, writer::MakeWriter, }; /// A `Subscriber` that logs formatted representations of `tracing` events. /// /// This consists of an inner `Formatter` wrapped in a layer that performs filtering. #[derive(Debug)] pub struct Subscriber< N = format::DefaultFields, E = format::Format<format::Full>, F = LevelFilter, W = fn() -> io::Stdout, > { inner: layer::Layered<F, Formatter<N, E, W>>, } /// A `Subscriber` that logs formatted representations of `tracing` events. /// This type only logs formatted events; it does not perform any filtering. pub type Formatter< N = format::DefaultFields, E = format::Format<format::Full>, W = fn() -> io::Stdout, > = layer::Layered<fmt_layer::Layer<Registry, N, E, W>, Registry>; /// Configures and constructs `Subscriber`s. #[derive(Debug)] pub struct SubscriberBuilder< N = format::DefaultFields, E = format::Format<format::Full>, F = LevelFilter, W = fn() -> io::Stdout, > { filter: F, inner: LayerBuilder<Registry, N, E, W>, } impl Subscriber { /// The maximum [verbosity level] that is enabled by a `Subscriber` by /// default. /// /// This can be overridden with the [`SubscriberBuilder::with_max_level`] method. /// /// [verbosity level]: https://docs.rs/tracing-core/0.1.5/tracing_core/struct.Level.html /// [`SubscriberBuilder::with_max_level`]: struct.SubscriberBuilder.html#method.with_max_level pub const DEFAULT_MAX_LEVEL: LevelFilter = LevelFilter::INFO; /// Returns a new `SubscriberBuilder` for configuring a format subscriber. pub fn builder() -> SubscriberBuilder { SubscriberBuilder::default() } /// Returns a new format subscriber with the default configuration. pub fn new() -> Self { Default::default() } } impl Default for Subscriber { fn default() -> Self { SubscriberBuilder::default().finish() } } // === impl Subscriber === impl<N, E, F, W> tracing_core::Subscriber for Subscriber<N, E, F, W> where N: for<'writer> FormatFields<'writer> + 'static, E: FormatEvent<Registry, N> + 'static, F: layer::Layer<Formatter<N, E, W>> + 'static, W: MakeWriter + 'static, layer::Layered<F, Formatter<N, E, W>>: tracing_core::Subscriber, fmt_layer::Layer<Registry, N, E, W>: layer::Layer<Registry>, { #[inline] fn register_callsite(&self, meta: &'static Metadata<'static>) -> Interest { self.inner.register_callsite(meta) } #[inline] fn enabled(&self, meta: &Metadata<'_>) -> bool { self.inner.enabled(meta) } #[inline] fn new_span(&self, attrs: &span::Attributes<'_>) -> span::Id { self.inner.new_span(attrs) } #[inline] fn record(&self, span: &span::Id, values: &span::Record<'_>) { self.inner.record(span, values) } #[inline] fn record_follows_from(&self, span: &span::Id, follows: &span::Id) { self.inner.record_follows_from(span, follows) } #[inline] fn event(&self, event: &Event<'_>) { self.inner.event(event); } #[inline] fn enter(&self, id: &span::Id) { // TODO: add on_enter hook self.inner.enter(id); } #[inline] fn exit(&self, id: &span::Id) { self.inner.exit(id); } #[inline] fn current_span(&self) -> span::Current { self.inner.current_span() } #[inline] fn clone_span(&self, id: &span::Id) -> span::Id { self.inner.clone_span(id) } #[inline] fn try_close(&self, id: span::Id) -> bool { self.inner.try_close(id) } unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> { if id == TypeId::of::<Self>() { Some(self as *const Self as *const ()) } else { self.inner.downcast_raw(id) } } } #[cfg(feature = "registry")] #[cfg_attr(docsrs, doc(cfg(feature = "registry")))] impl<N, E, F, W> crate::registry::LookupMetadata for Subscriber<N, E, F, W> where layer::Layered<F, Formatter<N, E, W>>: crate::registry::LookupMetadata, { #[inline] fn metadata(&self, id: &span::Id) -> Option<&'static Metadata<'static>> { self.inner.metadata(id) } } // ===== impl SubscriberBuilder ===== impl Default for SubscriberBuilder { fn default() -> Self { SubscriberBuilder { filter: Subscriber::DEFAULT_MAX_LEVEL, inner: Default::default(), } } } impl<N, E, F, W> SubscriberBuilder<N, E, F, W> where N: for<'writer> FormatFields<'writer> + 'static, E: FormatEvent<Registry, N> + 'static, W: MakeWriter + 'static, F: layer::Layer<Formatter<N, E, W>> + Send + Sync + 'static, fmt_layer::Layer<Registry, N, E, W>: layer::Layer<Registry> + Send + Sync + 'static, { /// Finish the builder, returning a new `FmtSubscriber`. pub fn finish(self) -> Subscriber<N, E, F, W> { let subscriber = self.inner.finish().with_subscriber(Registry::default()); Subscriber { inner: self.filter.with_subscriber(subscriber), } } /// Install this Subscriber as the global default if one is /// not already set. /// /// If the `tracing-log` feature is enabled, this will also install /// the LogTracer to convert `Log` records into `tracing` `Event`s. /// /// # Errors /// Returns an Error if the initialization was unsuccessful, likely /// because a global subscriber was already installed by another /// call to `try_init`. pub fn try_init(self) -> Result<(), Box<dyn Error + Send + Sync + 'static>> { #[cfg(feature = "tracing-log")] tracing_log::LogTracer::init().map_err(Box::new)?; tracing_core::dispatcher::set_global_default(tracing_core::dispatcher::Dispatch::new( self.finish(), ))?; Ok(()) } /// Install this Subscriber as the global default. /// /// If the `tracing-log` feature is enabled, this will also install /// the LogTracer to convert `Log` records into `tracing` `Event`s. /// /// # Panics /// Panics if the initialization was unsuccessful, likely because a /// global subscriber was already installed by another call to `try_init`. pub fn init(self) { self.try_init() .expect("Unable to install global subscriber") } } impl<N, L, T, F, W> SubscriberBuilder<N, format::Format<L, T>, F, W> where N: for<'writer> FormatFields<'writer> + 'static, { /// Use the given [`timer`] for log message timestamps. /// /// See [`time`] for the provided timer implementations. /// /// Note that using the `chrono` feature flag enables the /// additional time formatters [`ChronoUtc`] and [`ChronoLocal`]. /// /// [`time`]: ./time/index.html /// [`timer`]: ./time/trait.FormatTime.html /// [`ChronoUtc`]: ./time/struct.ChronoUtc.html /// [`ChronoLocal`]: ./time/struct.ChronoLocal.html pub fn with_timer<T2>(self, timer: T2) -> SubscriberBuilder<N, format::Format<L, T2>, F, W> { SubscriberBuilder { filter: self.filter, inner: self.inner.with_timer(timer), } } /// Do not emit timestamps with log messages. pub fn without_time(self) -> SubscriberBuilder<N, format::Format<L, ()>, F, W> { SubscriberBuilder { filter: self.filter, inner: self.inner.without_time(), } } /// Enable ANSI encoding for formatted events. #[cfg(feature = "ansi")] #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))] pub fn with_ansi(self, ansi: bool) -> SubscriberBuilder<N, format::Format<L, T>, F, W> { SubscriberBuilder { filter: self.filter, inner: self.inner.with_ansi(ansi), } } /// Sets whether or not an event's target is displayed. pub fn with_target( self, display_target: bool, ) -> SubscriberBuilder<N, format::Format<L, T>, F, W> { SubscriberBuilder { filter: self.filter, inner: self.inner.with_target(display_target), } } /// Sets the subscriber being built to use a less verbose formatter. /// /// See [`format::Compact`]. pub fn compact(self) -> SubscriberBuilder<N, format::Format<format::Compact, T>, F, W> where N: for<'writer> FormatFields<'writer> + 'static, { SubscriberBuilder { filter: self.filter, inner: self.inner.compact(), } } /// Sets the subscriber being built to use a JSON formatter. /// /// See [`format::Json`] #[cfg(feature = "json")] #[cfg_attr(docsrs, doc(cfg(feature = "json")))] pub fn json( self, ) -> SubscriberBuilder<format::JsonFields, format::Format<format::Json, T>, F, W> where N: for<'writer> FormatFields<'writer> + 'static, { SubscriberBuilder { filter: self.filter, inner: self.inner.json(), } } } #[cfg(feature = "env-filter")] #[cfg_attr(docsrs, doc(cfg(feature = "env-filter")))] impl<N, E, W> SubscriberBuilder<N, E, crate::EnvFilter, W> where Formatter<N, E, W>: tracing_core::Subscriber + 'static, { /// Configures the subscriber being built to allow filter reloading at /// runtime. pub fn with_filter_reloading( self, ) -> SubscriberBuilder<N, E, crate::reload::Layer<crate::EnvFilter, Formatter<N, E, W>>, W> { let (filter, _) = crate::reload::Layer::new(self.filter); SubscriberBuilder { filter, inner: self.inner, } } } #[cfg(feature = "env-filter")] #[cfg_attr(docsrs, doc(cfg(feature = "env-filter")))] impl<N, E, W> SubscriberBuilder<N, E, crate::reload::Layer<crate::EnvFilter, Formatter<N, E, W>>, W> where Formatter<N, E, W>: tracing_core::Subscriber + 'static, { /// Returns a `Handle` that may be used to reload the constructed subscriber's /// filter. pub fn reload_handle(&self) -> crate::reload::Handle<crate::EnvFilter, Formatter<N, E, W>> { self.filter.handle() } } impl<N, E, F, W> SubscriberBuilder<N, E, F, W> { /// Sets the Visitor that the subscriber being built will use to record /// fields. /// /// For example: /// ```rust /// use tracing_subscriber::fmt::{Subscriber, format}; /// use tracing_subscriber::prelude::*; /// /// let formatter = /// // Construct a custom formatter for `Debug` fields /// format::debug_fn(|writer, field, value| write!(writer, "{}: {:?}", field, value)) /// // Use the `tracing_subscriber::MakeFmtExt` trait to wrap the /// // formatter so that a delimiter is added between fields. /// .delimited(", "); /// /// let subscriber = Subscriber::builder() /// .fmt_fields(formatter) /// .finish(); /// # drop(subscriber) /// ``` pub fn fmt_fields<N2>(self, fmt_fields: N2) -> SubscriberBuilder<N2, E, F, W> where N2: for<'writer> FormatFields<'writer> + 'static, { SubscriberBuilder { filter: self.filter, inner: self.inner.fmt_fields(fmt_fields), } } /// Sets the [`EnvFilter`] that the subscriber will use to determine if /// a span or event is enabled. /// /// Note that this method requires the "env-filter" feature flag to be enabled. /// /// If a filter was previously set, or a maximum level was set by the /// [`with_max_level`] method, that value is replaced by the new filter. /// /// # Examples /// /// Setting a filter based on the value of the `RUST_LOG` environment /// variable: /// ```rust /// use tracing_subscriber::{FmtSubscriber, EnvFilter}; /// /// let subscriber = FmtSubscriber::builder() /// .with_env_filter(EnvFilter::from_default_env()) /// .finish(); /// ``` /// /// Setting a filter based on a pre-set filter directive string: /// ```rust /// use tracing_subscriber::FmtSubscriber; /// /// # fn main() -> Result<(), Box<dyn std::error::Error>> { /// let subscriber = FmtSubscriber::builder() /// .with_env_filter("my_crate=info,my_crate::my_mod=debug,[my_span]=trace") /// .finish(); /// # Ok(()) } /// ``` /// /// Adding additional directives to a filter constructed from an env var: /// ```rust /// use tracing_subscriber::{ /// FmtSubscriber, /// filter::{EnvFilter, LevelFilter}, /// }; /// /// # fn filter() -> Result<(), Box<dyn std::error::Error>> { /// let filter = EnvFilter::try_from_env("MY_CUSTOM_FILTER_ENV_VAR")? /// // Set the base level when not matched by other directives to WARN. /// .add_directive(LevelFilter::WARN.into()) /// // Set the max level for `my_crate::my_mod` to DEBUG, overriding /// // any directives parsed from the env variable. /// .add_directive("my_crate::my_mod=debug".parse()?); /// /// let subscriber = FmtSubscriber::builder() /// .with_env_filter(filter) /// .finish(); /// # Ok(())} /// ``` /// [`EnvFilter`]: ../filter/struct.EnvFilter.html /// [`with_max_level`]: #method.with_max_level #[cfg(feature = "env-filter")] #[cfg_attr(docsrs, doc(cfg(feature = "env-filter")))] pub fn with_env_filter( self, filter: impl Into<crate::EnvFilter>, ) -> SubscriberBuilder<N, E, crate::EnvFilter, W> where Formatter<N, E, W>: tracing_core::Subscriber + 'static, { let filter = filter.into(); SubscriberBuilder { filter, inner: self.inner, } } /// Sets the maximum [verbosity level] that will be enabled by the /// subscriber. /// /// If the max level has already been set, or a [`EnvFilter`] was added by /// [`with_filter`], this replaces that configuration with the new /// maximum level. /// /// # Examples /// /// Enable up to the `DEBUG` verbosity level: /// ```rust /// use tracing_subscriber::FmtSubscriber; /// use tracing::Level; /// /// let subscriber = FmtSubscriber::builder() /// .with_max_level(Level::DEBUG) /// .finish(); /// ``` /// This subscriber won't record any spans or events! /// ```rust /// use tracing_subscriber::{ /// FmtSubscriber, /// filter::LevelFilter, /// }; /// /// let subscriber = FmtSubscriber::builder() /// .with_max_level(LevelFilter::OFF) /// .finish(); /// ``` /// [verbosity level]: https://docs.rs/tracing-core/0.1.5/tracing_core/struct.Level.html /// [`EnvFilter`]: ../filter/struct.EnvFilter.html /// [`with_filter`]: #method.with_filter pub fn with_max_level( self, filter: impl Into<LevelFilter>, ) -> SubscriberBuilder<N, E, LevelFilter, W> { let filter = filter.into(); SubscriberBuilder { filter, inner: self.inner, } } /// Sets the function that the subscriber being built should use to format /// events that occur. pub fn event_format<E2>(self, fmt_event: E2) -> SubscriberBuilder<N, E2, F, W> where E2: FormatEvent<Registry, N> + 'static, N: for<'writer> FormatFields<'writer> + 'static, W: MakeWriter + 'static, { SubscriberBuilder { filter: self.filter, inner: self.inner.event_format(fmt_event), } } /// Sets whether or not spans inherit their parents' field values (disabled /// by default). #[deprecated(since = "0.2.0", note = "this no longer does anything")] pub fn inherit_fields(self, inherit_fields: bool) -> Self { let _ = inherit_fields; self } /// Sets the function that the subscriber being built should use to format /// events that occur. #[deprecated(since = "0.2.0", note = "renamed to `event_format`.")] pub fn on_event<E2>(self, fmt_event: E2) -> SubscriberBuilder<N, E2, F, W> where E2: FormatEvent<Registry, N> + 'static, N: for<'writer> FormatFields<'writer> + 'static, W: MakeWriter + 'static, { self.event_format(fmt_event) } /// Sets the [`MakeWriter`] that the subscriber being built will use to write events. /// /// # Examples /// /// Using `stderr` rather than `stdout`: /// /// ```rust /// use std::io; /// /// let subscriber = tracing_subscriber::fmt::Subscriber::builder() /// .with_writer(io::stderr) /// .finish(); /// ``` /// /// [`MakeWriter`]: trait.MakeWriter.html pub fn with_writer<W2>(self, make_writer: W2) -> SubscriberBuilder<N, E, F, W2> where W2: MakeWriter + 'static, { SubscriberBuilder { filter: self.filter, inner: self.inner.with_writer(make_writer), } } } /// Install a global tracing subscriber that listens for events and /// filters based on the value of the [`RUST_LOG` environment variable], /// if one is not already set. /// /// If the `tracing-log` feature is enabled, this will also install /// the [`LogTracer`] to convert `log` records into `tracing` `Event`s. /// /// /// # Errors /// Returns an Error if the initialization was unsuccessful, /// likely because a global subscriber was already installed by another /// call to `try_init`. /// /// [`LogTracer`]: /// https://docs.rs/tracing-log/0.1.0/tracing_log/struct.LogTracer.html /// [`RUST_LOG` environment variable]: /// ../filter/struct.EnvFilter.html#associatedconstant.DEFAULT_ENV pub fn try_init() -> Result<(), Box<dyn Error + Send + Sync + 'static>> { let builder = Subscriber::builder(); #[cfg(feature = "env-filter")] let builder = builder.with_env_filter(crate::EnvFilter::from_default_env()); builder.try_init() } /// Install a global tracing subscriber that listens for events and /// filters based on the value of the [`RUST_LOG` environment variable]. /// /// If the `tracing-log` feature is enabled, this will also install /// the LogTracer to convert `Log` records into `tracing` `Event`s. /// /// # Panics /// Panics if the initialization was unsuccessful, likely because a /// global subscriber was already installed by another call to `try_init`. /// /// [`RUST_LOG` environment variable]: /// ../filter/struct.EnvFilter.html#associatedconstant.DEFAULT_ENV pub fn init() { try_init().expect("Unable to install global subscriber") } #[cfg(test)] mod test { use crate::{ filter::LevelFilter, fmt::{ format::{self, Format}, time, writer::MakeWriter, Subscriber, }, }; use std::{ io, sync::{Mutex, MutexGuard, TryLockError}, }; use tracing_core::dispatcher::Dispatch; pub(crate) struct MockWriter<'a> { buf: &'a Mutex<Vec<u8>>, } impl<'a> MockWriter<'a> { pub(crate) fn new(buf: &'a Mutex<Vec<u8>>) -> Self { Self { buf } } pub(crate) fn map_error<Guard>(err: TryLockError<Guard>) -> io::Error { match err { TryLockError::WouldBlock => io::Error::from(io::ErrorKind::WouldBlock), TryLockError::Poisoned(_) => io::Error::from(io::ErrorKind::Other), } } pub(crate) fn buf(&self) -> io::Result<MutexGuard<'a, Vec<u8>>> { self.buf.try_lock().map_err(Self::map_error) } } impl<'a> io::Write for MockWriter<'a> { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { self.buf()?.write(buf) } fn flush(&mut self) -> io::Result<()> { self.buf()?.flush() } } pub(crate) struct MockMakeWriter<'a> { buf: &'a Mutex<Vec<u8>>, } impl<'a> MockMakeWriter<'a> { pub(crate) fn new(buf: &'a Mutex<Vec<u8>>) -> Self { Self { buf } } } impl<'a> MakeWriter for MockMakeWriter<'a> { type Writer = MockWriter<'a>; fn make_writer(&self) -> Self::Writer { MockWriter::new(self.buf) } } #[test] fn impls() { let f = Format::default().with_timer(time::Uptime::default()); let subscriber = Subscriber::builder().event_format(f).finish(); let _dispatch = Dispatch::new(subscriber); let f = format::Format::default(); let subscriber = Subscriber::builder().event_format(f).finish(); let _dispatch = Dispatch::new(subscriber); let f = format::Format::default().compact(); let subscriber = Subscriber::builder().event_format(f).finish(); let _dispatch = Dispatch::new(subscriber); } #[test] fn subscriber_downcasts() { let subscriber = Subscriber::builder().finish(); let dispatch = Dispatch::new(subscriber); assert!(dispatch.downcast_ref::<Subscriber>().is_some()); } #[test] fn subscriber_downcasts_to_parts() { let subscriber = Subscriber::new(); let dispatch = Dispatch::new(subscriber); assert!(dispatch.downcast_ref::<format::DefaultFields>().is_some()); assert!(dispatch.downcast_ref::<LevelFilter>().is_some()); assert!(dispatch.downcast_ref::<format::Format>().is_some()) } #[test] fn is_lookup_meta() { fn assert_lookup_meta<T: crate::registry::LookupMetadata>(_: T) {} let subscriber = Subscriber::new(); assert_lookup_meta(subscriber) } }