Crate tracing_subscriber
source · [−]Expand description
Utilities for implementing and composing tracing
subscribers.
tracing
is a framework for instrumenting Rust programs to collect
scoped, structured, and async-aware diagnostics. The Subscriber
trait
represents the functionality necessary to collect this trace data. This
crate contains tools for composing subscribers out of smaller units of
behaviour, and batteries-included implementations of common subscriber
functionality.
tracing-subscriber
is intended for use by both Subscriber
authors and
application authors using tracing
to instrument their applications.
Compiler support: requires rustc
1.49+
Layer
s and Filter
s
The most important component of the tracing-subscriber
API is the
Layer
trait, which provides a composable abstraction for building
Subscriber
s. Like the Subscriber
trait, a Layer
defines a
particular behavior for collecting trace data. Unlike Subscriber
s,
which implement a complete strategy for how trace data is collected,
Layer
s provide modular implementations of specific behaviors.
Therefore, they can be composed together to form a Subscriber
which is
capable of recording traces in a variety of ways. See the layer
module’s
documentation for details on using Layer
s.
In addition, the Filter
trait defines an interface for filtering what
spans and events are recorded by a particular layer. This allows different
Layer
s to handle separate subsets of the trace data emitted by a
program. See the documentation on per-layer filtering for more
information on using Filter
s.
Included Subscribers
The following Subscriber
s are provided for application authors:
fmt
- Formats and logs tracing data (requires thefmt
feature flag)
Feature Flags
std
: Enables APIs that depend on the on the Rust standard library (enabled by default).alloc
: Depend onliballoc
(enabled by “std”).env-filter
: Enables theEnvFilter
type, which implements filtering similar to theenv_logger
crate. Requires “std”.fmt
: Enables thefmt
module, which provides a subscriber implementation for printing formatted representations of trace events. Enabled by default. Requires “std”.ansi
: Enablesfmt
support for ANSI terminal colors. Enabled by default.registry
: enables theregistry
module. Enabled by default. Requires “std”.json
: Enablesfmt
support for JSON output. In JSON output, the ANSI feature does nothing. Requires “fmt” and “std”.local-time
: Enables local time formatting when using thetime
crate’s timestamp formatters with thefmt
subscriber.
Optional Dependencies
tracing-log
: Enables better formatting for events emitted bylog
macros in thefmt
subscriber. Enabled by default.time
: Enables support for using thetime
crate for timestamp formatting in thefmt
subscriber.smallvec
: Causes theEnvFilter
type to use thesmallvec
crate (rather thanVec
) as a performance optimization. Enabled by default.parking_lot
: Use theparking_lot
crate’sRwLock
implementation rather than the Rust standard library’s implementation.
no_std
Support
In embedded systems and other bare-metal applications, tracing
can be
used without requiring the Rust standard library, although some features are
disabled. Although most of the APIs provided by tracing-subscriber
, such
as fmt
and EnvFilter
, require the standard library, some
functionality, such as the Layer
trait, can still be used in
no_std
environments.
The dependency on the standard library is controlled by two crate feature
flags, “std”, which enables the dependency on libstd
, and “alloc”, which
enables the dependency on liballoc
(and is enabled by the “std”
feature). These features are enabled by default, but no_std
users can
disable them using:
tracing-subscriber = { version = "0.3", default-features = false }
Additional APIs are available when liballoc
is available. To enable
liballoc
but not std
, use:
tracing-subscriber = { version = "0.3", default-features = false, features = ["alloc"] }
Unstable Features
These feature flags enable unstable features. The public API may break in 0.1.x
releases. To enable these features, the --cfg tracing_unstable
must be passed to
rustc
when compiling.
The following unstable feature flags are currently available:
valuable
: Enables support for serializing values recorded using thevaluable
crate as structured JSON in theformat::Json
formatter.
Enabling Unstable Features
The easiest way to set the tracing_unstable
cfg is to use the RUSTFLAGS
env variable when running cargo
commands:
RUSTFLAGS="--cfg tracing_unstable" cargo build
Alternatively, the following can be added to the .cargo/config
file in a
project to automatically enable the cfg flag for that project:
[build]
rustflags = ["--cfg", "tracing_unstable"]
Supported Rust Versions
Tracing is built against the latest stable release. The minimum supported version is 1.49. The current Tracing version is not guaranteed to build on Rust versions earlier than the minimum supported version.
Tracing follows the same compiler support policies as the rest of the Tokio project. The current stable Rust compiler and the three most recent minor versions before it will always be supported. For example, if the current stable compiler version is 1.45, the minimum supported version will not be increased past 1.42, three minor versions prior. Increasing the minimum supported compiler version is not considered a semver breaking change as long as doing so complies with this policy.
Re-exports
Modules
Utilities for working with fields and field visitors.
A Subscriber
for formatting and logging tracing
data.
The Layer
trait, a composable abstraction for building Subscriber
s.
The tracing-subscriber
prelude.
Wrapper for a Layer
to allow it to be dynamically reloaded.
Extension traits and other utilities to make working with subscribers more ergonomic.
Structs
A shared, reusable store for spans.