tracing_log/
lib.rs

1//! Adapters for connecting unstructured log records from the `log` crate into
2//! the `tracing` ecosystem.
3//!
4//! # Overview
5//!
6//! [`tracing`] is a framework for instrumenting Rust programs with context-aware,
7//! structured, event-based diagnostic information. This crate provides
8//! compatibility layers for using `tracing` alongside the logging facade provided
9//! by the [`log`] crate.
10//!
11//! This crate provides:
12//!
13//! - [`AsTrace`] and [`AsLog`] traits for converting between `tracing` and `log` types.
14//! - [`LogTracer`], a [`log::Log`] implementation that consumes [`log::Record`]s
15//!   and outputs them as [`tracing::Event`].
16//!
17//! *Compiler support: [requires `rustc` 1.56+][msrv]*
18//!
19//! [msrv]: #supported-rust-versions
20//!
21//! # Usage
22//!
23//! ## Convert log records to tracing `Event`s
24//!
25//! To convert [`log::Record`]s as [`tracing::Event`]s, set `LogTracer` as the default
26//! logger by calling its [`init`] or [`init_with_filter`] methods.
27//!
28//! ```rust
29//! # use std::error::Error;
30//! use tracing_log::LogTracer;
31//! use log;
32//!
33//! # fn main() -> Result<(), Box<Error>> {
34//! LogTracer::init()?;
35//!
36//! // will be available for Subscribers as a tracing Event
37//! log::trace!("an example trace log");
38//! # Ok(())
39//! # }
40//! ```
41//!
42//! This conversion does not convert unstructured data in log records (such as
43//! values passed as format arguments to the `log!` macro) to structured
44//! `tracing` fields. However, it *does* attach these new events to to the
45//! span that was currently executing when the record was logged. This is the
46//! primary use-case for this library: making it possible to locate the log
47//! records emitted by dependencies which use `log` within the context of a
48//! trace.
49//!
50//! ## Convert tracing `Event`s to logs
51//!
52//! Enabling the ["log" and "log-always" feature flags][flags] on the `tracing`
53//! crate will cause all `tracing` spans and events to emit `log::Record`s as
54//! they occur.
55//!
56//! ## Caution: Mixing both conversions
57//!
58//! Note that `log::Logger` implementations that convert log records to trace events
59//! should not be used with `Subscriber`s that convert trace events _back_ into
60//! `log` records, as doing so will result in the event recursing between the subscriber
61//! and the logger forever (or, in real life, probably overflowing the call stack).
62//!
63//! If the logging of trace events generated from log records produced by the
64//! `log` crate is desired, either the `log` crate should not be used to
65//! implement this logging, or an additional layer of filtering will be
66//! required to avoid infinitely converting between `Event` and `log::Record`.
67//!
68//! ## Feature Flags
69//!
70//! * `std`: enables features that require the Rust standard library (on by default)
71//! * `log-tracer`: enables the `LogTracer` type (on by default)
72//! * `interest-cache`: makes it possible to configure an interest cache for
73//!   logs emitted through the `log` crate (see [`Builder::with_interest_cache`]); requires `std`
74//!
75//! ## Supported Rust Versions
76//!
77//! Tracing is built against the latest stable release. The minimum supported
78//! version is 1.56. The current Tracing version is not guaranteed to build on
79//! Rust versions earlier than the minimum supported version.
80//!
81//! Tracing follows the same compiler support policies as the rest of the Tokio
82//! project. The current stable Rust compiler and the three most recent minor
83//! versions before it will always be supported. For example, if the current
84//! stable compiler version is 1.69, the minimum supported version will not be
85//! increased past 1.66, three minor versions prior. Increasing the minimum
86//! supported compiler version is not considered a semver breaking change as
87//! long as doing so complies with this policy.
88//!
89//! [`init`]: LogTracer::init
90//! [`init_with_filter`]: LogTracer::init_with_filter
91//! [`tracing`]: https://crates.io/crates/tracing
92//! [`tracing::Subscriber`]: https://docs.rs/tracing/latest/tracing/trait.Subscriber.html
93//! [`Subscriber`]: https://docs.rs/tracing/latest/tracing/trait.Subscriber.html
94//! [`tracing::Event`]: https://docs.rs/tracing/latest/tracing/struct.Event.html
95//! [flags]: https://docs.rs/tracing/latest/tracing/#crate-feature-flags
96//! [`Builder::with_interest_cache`]: log_tracer::Builder::with_interest_cache
97#![doc(
98    html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png",
99    issue_tracker_base_url = "https://github.com/tokio-rs/tracing/issues/"
100)]
101#![cfg_attr(docsrs, feature(doc_cfg), deny(rustdoc::broken_intra_doc_links))]
102#![warn(
103    missing_debug_implementations,
104    missing_docs,
105    rust_2018_idioms,
106    unreachable_pub,
107    bad_style,
108    dead_code,
109    improper_ctypes,
110    non_shorthand_field_patterns,
111    no_mangle_generic_items,
112    overflowing_literals,
113    path_statements,
114    patterns_in_fns_without_body,
115    private_in_public,
116    unconditional_recursion,
117    unused,
118    unused_allocation,
119    unused_comparisons,
120    unused_parens,
121    while_true
122)]
123use once_cell::sync::Lazy;
124
125use std::{fmt, io};
126
127use tracing_core::{
128    callsite::{self, Callsite},
129    dispatcher,
130    field::{self, Field, Visit},
131    identify_callsite,
132    metadata::{Kind, Level},
133    subscriber, Event, Metadata,
134};
135
136#[cfg(feature = "log-tracer")]
137#[cfg_attr(docsrs, doc(cfg(feature = "log-tracer")))]
138pub mod log_tracer;
139
140#[cfg(feature = "log-tracer")]
141#[cfg_attr(docsrs, doc(cfg(feature = "log-tracer")))]
142#[doc(inline)]
143pub use self::log_tracer::LogTracer;
144
145pub use log;
146
147#[cfg(all(feature = "interest-cache", feature = "log-tracer", feature = "std"))]
148mod interest_cache;
149
150#[cfg(all(feature = "interest-cache", feature = "log-tracer", feature = "std"))]
151#[cfg_attr(
152    docsrs,
153    doc(cfg(all(feature = "interest-cache", feature = "log-tracer", feature = "std")))
154)]
155pub use crate::interest_cache::InterestCacheConfig;
156
157/// Format a log record as a trace event in the current span.
158pub fn format_trace(record: &log::Record<'_>) -> io::Result<()> {
159    dispatch_record(record);
160    Ok(())
161}
162
163// XXX(eliza): this is factored out so that we don't have to deal with the pub
164// function `format_trace`'s `Result` return type...maybe we should get rid of
165// that in 0.2...
166pub(crate) fn dispatch_record(record: &log::Record<'_>) {
167    dispatcher::get_default(|dispatch| {
168        let filter_meta = record.as_trace();
169        if !dispatch.enabled(&filter_meta) {
170            return;
171        }
172
173        let (_, keys, meta) = loglevel_to_cs(record.level());
174
175        let log_module = record.module_path();
176        let log_file = record.file();
177        let log_line = record.line();
178
179        let module = log_module.as_ref().map(|s| s as &dyn field::Value);
180        let file = log_file.as_ref().map(|s| s as &dyn field::Value);
181        let line = log_line.as_ref().map(|s| s as &dyn field::Value);
182
183        dispatch.event(&Event::new(
184            meta,
185            &meta.fields().value_set(&[
186                (&keys.message, Some(record.args() as &dyn field::Value)),
187                (&keys.target, Some(&record.target())),
188                (&keys.module, module),
189                (&keys.file, file),
190                (&keys.line, line),
191            ]),
192        ));
193    });
194}
195
196/// Trait implemented for `tracing` types that can be converted to a `log`
197/// equivalent.
198pub trait AsLog: crate::sealed::Sealed {
199    /// The `log` type that this type can be converted into.
200    type Log;
201    /// Returns the `log` equivalent of `self`.
202    fn as_log(&self) -> Self::Log;
203}
204
205/// Trait implemented for `log` types that can be converted to a `tracing`
206/// equivalent.
207pub trait AsTrace: crate::sealed::Sealed {
208    /// The `tracing` type that this type can be converted into.
209    type Trace;
210    /// Returns the `tracing` equivalent of `self`.
211    fn as_trace(&self) -> Self::Trace;
212}
213
214impl<'a> crate::sealed::Sealed for Metadata<'a> {}
215
216impl<'a> AsLog for Metadata<'a> {
217    type Log = log::Metadata<'a>;
218    fn as_log(&self) -> Self::Log {
219        log::Metadata::builder()
220            .level(self.level().as_log())
221            .target(self.target())
222            .build()
223    }
224}
225impl<'a> crate::sealed::Sealed for log::Metadata<'a> {}
226
227impl<'a> AsTrace for log::Metadata<'a> {
228    type Trace = Metadata<'a>;
229    fn as_trace(&self) -> Self::Trace {
230        let cs_id = identify_callsite!(loglevel_to_cs(self.level()).0);
231        Metadata::new(
232            "log record",
233            self.target(),
234            self.level().as_trace(),
235            None,
236            None,
237            None,
238            field::FieldSet::new(FIELD_NAMES, cs_id),
239            Kind::EVENT,
240        )
241    }
242}
243
244struct Fields {
245    message: field::Field,
246    target: field::Field,
247    module: field::Field,
248    file: field::Field,
249    line: field::Field,
250}
251
252static FIELD_NAMES: &[&str] = &[
253    "message",
254    "log.target",
255    "log.module_path",
256    "log.file",
257    "log.line",
258];
259
260impl Fields {
261    fn new(cs: &'static dyn Callsite) -> Self {
262        let fieldset = cs.metadata().fields();
263        let message = fieldset.field("message").unwrap();
264        let target = fieldset.field("log.target").unwrap();
265        let module = fieldset.field("log.module_path").unwrap();
266        let file = fieldset.field("log.file").unwrap();
267        let line = fieldset.field("log.line").unwrap();
268        Fields {
269            message,
270            target,
271            module,
272            file,
273            line,
274        }
275    }
276}
277
278macro_rules! log_cs {
279    ($level:expr, $cs:ident, $meta:ident, $ty:ident) => {
280        struct $ty;
281        static $cs: $ty = $ty;
282        static $meta: Metadata<'static> = Metadata::new(
283            "log event",
284            "log",
285            $level,
286            ::core::option::Option::None,
287            ::core::option::Option::None,
288            ::core::option::Option::None,
289            field::FieldSet::new(FIELD_NAMES, identify_callsite!(&$cs)),
290            Kind::EVENT,
291        );
292
293        impl callsite::Callsite for $ty {
294            fn set_interest(&self, _: subscriber::Interest) {}
295            fn metadata(&self) -> &'static Metadata<'static> {
296                &$meta
297            }
298        }
299    };
300}
301
302log_cs!(
303    tracing_core::Level::TRACE,
304    TRACE_CS,
305    TRACE_META,
306    TraceCallsite
307);
308log_cs!(
309    tracing_core::Level::DEBUG,
310    DEBUG_CS,
311    DEBUG_META,
312    DebugCallsite
313);
314log_cs!(tracing_core::Level::INFO, INFO_CS, INFO_META, InfoCallsite);
315log_cs!(tracing_core::Level::WARN, WARN_CS, WARN_META, WarnCallsite);
316log_cs!(
317    tracing_core::Level::ERROR,
318    ERROR_CS,
319    ERROR_META,
320    ErrorCallsite
321);
322
323static TRACE_FIELDS: Lazy<Fields> = Lazy::new(|| Fields::new(&TRACE_CS));
324static DEBUG_FIELDS: Lazy<Fields> = Lazy::new(|| Fields::new(&DEBUG_CS));
325static INFO_FIELDS: Lazy<Fields> = Lazy::new(|| Fields::new(&INFO_CS));
326static WARN_FIELDS: Lazy<Fields> = Lazy::new(|| Fields::new(&WARN_CS));
327static ERROR_FIELDS: Lazy<Fields> = Lazy::new(|| Fields::new(&ERROR_CS));
328
329fn level_to_cs(level: Level) -> (&'static dyn Callsite, &'static Fields) {
330    match level {
331        Level::TRACE => (&TRACE_CS, &*TRACE_FIELDS),
332        Level::DEBUG => (&DEBUG_CS, &*DEBUG_FIELDS),
333        Level::INFO => (&INFO_CS, &*INFO_FIELDS),
334        Level::WARN => (&WARN_CS, &*WARN_FIELDS),
335        Level::ERROR => (&ERROR_CS, &*ERROR_FIELDS),
336    }
337}
338
339fn loglevel_to_cs(
340    level: log::Level,
341) -> (
342    &'static dyn Callsite,
343    &'static Fields,
344    &'static Metadata<'static>,
345) {
346    match level {
347        log::Level::Trace => (&TRACE_CS, &*TRACE_FIELDS, &TRACE_META),
348        log::Level::Debug => (&DEBUG_CS, &*DEBUG_FIELDS, &DEBUG_META),
349        log::Level::Info => (&INFO_CS, &*INFO_FIELDS, &INFO_META),
350        log::Level::Warn => (&WARN_CS, &*WARN_FIELDS, &WARN_META),
351        log::Level::Error => (&ERROR_CS, &*ERROR_FIELDS, &ERROR_META),
352    }
353}
354
355impl<'a> crate::sealed::Sealed for log::Record<'a> {}
356
357impl<'a> AsTrace for log::Record<'a> {
358    type Trace = Metadata<'a>;
359    fn as_trace(&self) -> Self::Trace {
360        let cs_id = identify_callsite!(loglevel_to_cs(self.level()).0);
361        Metadata::new(
362            "log record",
363            self.target(),
364            self.level().as_trace(),
365            self.file(),
366            self.line(),
367            self.module_path(),
368            field::FieldSet::new(FIELD_NAMES, cs_id),
369            Kind::EVENT,
370        )
371    }
372}
373
374impl crate::sealed::Sealed for tracing_core::Level {}
375
376impl AsLog for tracing_core::Level {
377    type Log = log::Level;
378    fn as_log(&self) -> log::Level {
379        match *self {
380            tracing_core::Level::ERROR => log::Level::Error,
381            tracing_core::Level::WARN => log::Level::Warn,
382            tracing_core::Level::INFO => log::Level::Info,
383            tracing_core::Level::DEBUG => log::Level::Debug,
384            tracing_core::Level::TRACE => log::Level::Trace,
385        }
386    }
387}
388
389impl crate::sealed::Sealed for log::Level {}
390
391impl AsTrace for log::Level {
392    type Trace = tracing_core::Level;
393    #[inline]
394    fn as_trace(&self) -> tracing_core::Level {
395        match self {
396            log::Level::Error => tracing_core::Level::ERROR,
397            log::Level::Warn => tracing_core::Level::WARN,
398            log::Level::Info => tracing_core::Level::INFO,
399            log::Level::Debug => tracing_core::Level::DEBUG,
400            log::Level::Trace => tracing_core::Level::TRACE,
401        }
402    }
403}
404
405impl crate::sealed::Sealed for log::LevelFilter {}
406
407impl AsTrace for log::LevelFilter {
408    type Trace = tracing_core::LevelFilter;
409    #[inline]
410    fn as_trace(&self) -> tracing_core::LevelFilter {
411        match self {
412            log::LevelFilter::Off => tracing_core::LevelFilter::OFF,
413            log::LevelFilter::Error => tracing_core::LevelFilter::ERROR,
414            log::LevelFilter::Warn => tracing_core::LevelFilter::WARN,
415            log::LevelFilter::Info => tracing_core::LevelFilter::INFO,
416            log::LevelFilter::Debug => tracing_core::LevelFilter::DEBUG,
417            log::LevelFilter::Trace => tracing_core::LevelFilter::TRACE,
418        }
419    }
420}
421
422impl crate::sealed::Sealed for tracing_core::LevelFilter {}
423
424impl AsLog for tracing_core::LevelFilter {
425    type Log = log::LevelFilter;
426    #[inline]
427    fn as_log(&self) -> Self::Log {
428        match *self {
429            tracing_core::LevelFilter::OFF => log::LevelFilter::Off,
430            tracing_core::LevelFilter::ERROR => log::LevelFilter::Error,
431            tracing_core::LevelFilter::WARN => log::LevelFilter::Warn,
432            tracing_core::LevelFilter::INFO => log::LevelFilter::Info,
433            tracing_core::LevelFilter::DEBUG => log::LevelFilter::Debug,
434            tracing_core::LevelFilter::TRACE => log::LevelFilter::Trace,
435        }
436    }
437}
438/// Extends log `Event`s to provide complete `Metadata`.
439///
440/// In `tracing-log`, an `Event` produced by a log (through [`AsTrace`]) has an hard coded
441/// "log" target and no `file`, `line`, or `module_path` attributes. This happens because `Event`
442/// requires its `Metadata` to be `'static`, while [`log::Record`]s provide them with a generic
443/// lifetime.
444///
445/// However, these values are stored in the `Event`'s fields and
446/// the [`normalized_metadata`] method allows to build a new `Metadata`
447/// that only lives as long as its source `Event`, but provides complete
448/// data.
449///
450/// It can typically be used by `Subscriber`s when processing an `Event`,
451/// to allow accessing its complete metadata in a consistent way,
452/// regardless of the source of its source.
453///
454/// [`normalized_metadata`]: NormalizeEvent#normalized_metadata
455pub trait NormalizeEvent<'a>: crate::sealed::Sealed {
456    /// If this `Event` comes from a `log`, this method provides a new
457    /// normalized `Metadata` which has all available attributes
458    /// from the original log, including `file`, `line`, `module_path`
459    /// and `target`.
460    /// Returns `None` is the `Event` is not issued from a `log`.
461    fn normalized_metadata(&'a self) -> Option<Metadata<'a>>;
462    /// Returns whether this `Event` represents a log (from the `log` crate)
463    fn is_log(&self) -> bool;
464}
465
466impl<'a> crate::sealed::Sealed for Event<'a> {}
467
468impl<'a> NormalizeEvent<'a> for Event<'a> {
469    fn normalized_metadata(&'a self) -> Option<Metadata<'a>> {
470        let original = self.metadata();
471        if self.is_log() {
472            let mut fields = LogVisitor::new_for(self, level_to_cs(*original.level()).1);
473            self.record(&mut fields);
474
475            Some(Metadata::new(
476                "log event",
477                fields.target.unwrap_or("log"),
478                *original.level(),
479                fields.file,
480                fields.line.map(|l| l as u32),
481                fields.module_path,
482                field::FieldSet::new(&["message"], original.callsite()),
483                Kind::EVENT,
484            ))
485        } else {
486            None
487        }
488    }
489
490    fn is_log(&self) -> bool {
491        self.metadata().callsite() == identify_callsite!(level_to_cs(*self.metadata().level()).0)
492    }
493}
494
495struct LogVisitor<'a> {
496    target: Option<&'a str>,
497    module_path: Option<&'a str>,
498    file: Option<&'a str>,
499    line: Option<u64>,
500    fields: &'static Fields,
501}
502
503impl<'a> LogVisitor<'a> {
504    // We don't actually _use_ the provided event argument; it is simply to
505    // ensure that the `LogVisitor` does not outlive the event whose fields it
506    // is visiting, so that the reference casts in `record_str` are safe.
507    fn new_for(_event: &'a Event<'a>, fields: &'static Fields) -> Self {
508        Self {
509            target: None,
510            module_path: None,
511            file: None,
512            line: None,
513            fields,
514        }
515    }
516}
517
518impl<'a> Visit for LogVisitor<'a> {
519    fn record_debug(&mut self, _field: &Field, _value: &dyn fmt::Debug) {}
520
521    fn record_u64(&mut self, field: &Field, value: u64) {
522        if field == &self.fields.line {
523            self.line = Some(value);
524        }
525    }
526
527    fn record_str(&mut self, field: &Field, value: &str) {
528        unsafe {
529            // The `Visit` API erases the string slice's lifetime. However, we
530            // know it is part of the `Event` struct with a lifetime of `'a`. If
531            // (and only if!) this `LogVisitor` was constructed with the same
532            // lifetime parameter `'a` as the event in question, it's safe to
533            // cast these string slices to the `'a` lifetime.
534            if field == &self.fields.file {
535                self.file = Some(&*(value as *const _));
536            } else if field == &self.fields.target {
537                self.target = Some(&*(value as *const _));
538            } else if field == &self.fields.module {
539                self.module_path = Some(&*(value as *const _));
540            }
541        }
542    }
543}
544
545mod sealed {
546    pub trait Sealed {}
547}
548
549#[cfg(test)]
550mod test {
551    use super::*;
552
553    fn test_callsite(level: log::Level) {
554        let record = log::Record::builder()
555            .args(format_args!("Error!"))
556            .level(level)
557            .target("myApp")
558            .file(Some("server.rs"))
559            .line(Some(144))
560            .module_path(Some("server"))
561            .build();
562
563        let meta = record.as_trace();
564        let (cs, _keys, _) = loglevel_to_cs(record.level());
565        let cs_meta = cs.metadata();
566        assert_eq!(
567            meta.callsite(),
568            cs_meta.callsite(),
569            "actual: {:#?}\nexpected: {:#?}",
570            meta,
571            cs_meta
572        );
573        assert_eq!(meta.level(), &level.as_trace());
574    }
575
576    #[test]
577    fn error_callsite_is_correct() {
578        test_callsite(log::Level::Error);
579    }
580
581    #[test]
582    fn warn_callsite_is_correct() {
583        test_callsite(log::Level::Warn);
584    }
585
586    #[test]
587    fn info_callsite_is_correct() {
588        test_callsite(log::Level::Info);
589    }
590
591    #[test]
592    fn debug_callsite_is_correct() {
593        test_callsite(log::Level::Debug);
594    }
595
596    #[test]
597    fn trace_callsite_is_correct() {
598        test_callsite(log::Level::Trace);
599    }
600}
tracing_log/lib.rs

tracing_log/
lib.rs
