300 lines
10 KiB
Plaintext
300 lines
10 KiB
Plaintext
|
---
|
|||
|
|
source: tests/output.rs
|
|||
|
|
expression: "get_stdout(path, &[\"log\"])"
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
log Module log rusty-man
|
|||
|
|
|
|||
|
|
DESCRIPTION
|
|||
|
|
A lightweight logging facade.
|
|||
|
|
|
|||
|
|
The `log` crate provides a single logging API that abstracts over the actual logging
|
|||
|
|
implementation. Libraries can use the logging API provided by this crate, and the consumer of
|
|||
|
|
those libraries can choose the logging implementation that is most suitable for its use case.
|
|||
|
|
|
|||
|
|
If no logging implementation is selected, the facade falls back to a “noop” implementation
|
|||
|
|
that ignores all log messages. The overhead in this case is very small - just an integer load,
|
|||
|
|
comparison and jump.
|
|||
|
|
|
|||
|
|
A log request consists of a *target*, a *level*, and a *body*. A target is a string which
|
|||
|
|
defaults to the module path of the location of the log request, though that default may be
|
|||
|
|
overridden. Logger implementations typically use the target to filter requests based on some
|
|||
|
|
user configuration.
|
|||
|
|
|
|||
|
|
# Use
|
|||
|
|
|
|||
|
|
The basic use of the log crate is through the five logging macros: `error!`, `warn!`, `info!`,
|
|||
|
|
`debug!` and `trace!` where `error!` represents the highest-priority log messages and `trace!`
|
|||
|
|
the lowest. The log messages are filtered by configuring the log level to exclude messages
|
|||
|
|
with a lower priority. Each of these macros accept format strings similarly to
|
|||
|
|
[`println!`][1].
|
|||
|
|
|
|||
|
|
## In libraries
|
|||
|
|
|
|||
|
|
Libraries should link only to the `log` crate, and use the provided macros to log whatever
|
|||
|
|
information will be useful to downstream consumers.
|
|||
|
|
|
|||
|
|
### Examples
|
|||
|
|
|
|||
|
|
ⓘ
|
|||
|
|
`use log::{info, warn};
|
|||
|
|
pub fn shave_the_yak(yak: &mut Yak) {
|
|||
|
|
info!(target: "yak_events", "Commencing yak shaving for {:?}", yak);
|
|||
|
|
loop {
|
|||
|
|
match find_a_razor() {
|
|||
|
|
Ok(razor) => {
|
|||
|
|
info!("Razor located: {}", razor);
|
|||
|
|
yak.shave(razor);
|
|||
|
|
break;
|
|||
|
|
}
|
|||
|
|
Err(err) => {
|
|||
|
|
warn!("Unable to locate a razor: {}, retrying", err);
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
}`
|
|||
|
|
|
|||
|
|
|
|||
|
|
## In executables
|
|||
|
|
|
|||
|
|
Executables should choose a logging implementation and initialize it early in the runtime of
|
|||
|
|
the program. Logging implementations will typically include a function to do this. Any log
|
|||
|
|
messages generated before the implementation is initialized will be ignored.
|
|||
|
|
|
|||
|
|
The executable itself may use the `log` crate to log as well.
|
|||
|
|
|
|||
|
|
### Warning
|
|||
|
|
|
|||
|
|
The logging system may only be initialized once.
|
|||
|
|
|
|||
|
|
# Available logging implementations
|
|||
|
|
|
|||
|
|
In order to produce log output executables have to use a logger implementation compatible with
|
|||
|
|
the facade. There are many available implementations to choose from, here are some of the most
|
|||
|
|
popular ones:
|
|||
|
|
|
|||
|
|
* Simple minimal loggers:
|
|||
|
|
|
|||
|
|
* [env_logger][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/env_logger/*/env_logger/
|
|||
|
|
* [simple_logger][1]
|
|||
|
|
|
|||
|
|
[1] https://github.com/borntyping/rust-simple_logger
|
|||
|
|
* [simplelog][1]
|
|||
|
|
|
|||
|
|
[1] https://github.com/drakulix/simplelog.rs
|
|||
|
|
* [pretty_env_logger][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/pretty_env_logger/*/pretty_env_logger/
|
|||
|
|
* [stderrlog][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/stderrlog/*/stderrlog/
|
|||
|
|
* [flexi_logger][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/flexi_logger/*/flexi_logger/
|
|||
|
|
* Complex configurable frameworks:
|
|||
|
|
|
|||
|
|
* [log4rs][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/log4rs/*/log4rs/
|
|||
|
|
* [fern][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/fern/*/fern/
|
|||
|
|
* Adaptors for other facilities:
|
|||
|
|
|
|||
|
|
* [syslog][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/syslog/*/syslog/
|
|||
|
|
* [slog-stdlog][1]
|
|||
|
|
|
|||
|
|
[1] https://docs.rs/slog-stdlog/*/slog_stdlog/
|
|||
|
|
|
|||
|
|
|
|||
|
|
# Implementing a Logger
|
|||
|
|
|
|||
|
|
Loggers implement the `Log` trait. Here’s a very basic example that simply logs all messages
|
|||
|
|
at the `Error`, `Warn` or `Info` levels to stdout:
|
|||
|
|
|
|||
|
|
ⓘ
|
|||
|
|
`use log::{Record, Level, Metadata};
|
|||
|
|
struct SimpleLogger;
|
|||
|
|
impl log::Log for SimpleLogger {
|
|||
|
|
fn enabled(&self, metadata: &Metadata) -> bool {
|
|||
|
|
metadata.level() <= Level::Info
|
|||
|
|
}
|
|||
|
|
fn log(&self, record: &Record) {
|
|||
|
|
if self.enabled(record.metadata()) {
|
|||
|
|
println!("{} - {}", record.level(), record.args());
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
fn flush(&self) {}
|
|||
|
|
}
|
|||
|
|
`
|
|||
|
|
|
|||
|
|
Loggers are installed by calling the `set_logger` function. The maximum log level also needs
|
|||
|
|
to be adjusted via the `set_max_level` function. The logging facade uses this as an
|
|||
|
|
optimization to improve performance of log messages at levels that are disabled. It’s
|
|||
|
|
important to set it, as it defaults to `Off`, so no log messages will ever be captured! In the
|
|||
|
|
case of our example logger, we’ll want to set the maximum log level to `Info`, since we ignore
|
|||
|
|
any `Debug` or `Trace` level log messages. A logging implementation should provide a function
|
|||
|
|
that wraps a call to `set_logger` and `set_max_level`, handling initialization of the logger:
|
|||
|
|
|
|||
|
|
ⓘ
|
|||
|
|
`use log::{SetLoggerError, LevelFilter};
|
|||
|
|
static LOGGER: SimpleLogger = SimpleLogger;
|
|||
|
|
pub fn init() -> Result<(), SetLoggerError> {
|
|||
|
|
log::set_logger(&LOGGER)
|
|||
|
|
.map(|()| log::set_max_level(LevelFilter::Info))
|
|||
|
|
}`
|
|||
|
|
|
|||
|
|
Implementations that adjust their configurations at runtime should take care to adjust the
|
|||
|
|
maximum log level as well.
|
|||
|
|
|
|||
|
|
# Use with `std`
|
|||
|
|
|
|||
|
|
`set_logger` requires you to provide a `&'static Log`, which can be hard to obtain if your
|
|||
|
|
logger depends on some runtime configuration. The `set_boxed_logger` function is available
|
|||
|
|
with the `std` Cargo feature. It is identical to `set_logger` except that it takes a
|
|||
|
|
`Box<Log>` rather than a `&'static Log`:
|
|||
|
|
|
|||
|
|
ⓘ
|
|||
|
|
`pub fn init() -> Result<(), SetLoggerError> {
|
|||
|
|
log::set_boxed_logger(Box::new(SimpleLogger))
|
|||
|
|
.map(|()| log::set_max_level(LevelFilter::Info))
|
|||
|
|
}`
|
|||
|
|
|
|||
|
|
|
|||
|
|
# Compile time filters
|
|||
|
|
|
|||
|
|
Log levels can be statically disabled at compile time via Cargo features. Log invocations at
|
|||
|
|
disabled levels will be skipped and will not even be present in the resulting binary. This
|
|||
|
|
level is configured separately for release and debug builds. The features are:
|
|||
|
|
|
|||
|
|
* `max_level_off`
|
|||
|
|
* `max_level_error`
|
|||
|
|
* `max_level_warn`
|
|||
|
|
* `max_level_info`
|
|||
|
|
* `max_level_debug`
|
|||
|
|
* `max_level_trace`
|
|||
|
|
* `release_max_level_off`
|
|||
|
|
* `release_max_level_error`
|
|||
|
|
* `release_max_level_warn`
|
|||
|
|
* `release_max_level_info`
|
|||
|
|
* `release_max_level_debug`
|
|||
|
|
* `release_max_level_trace`
|
|||
|
|
|
|||
|
|
These features control the value of the `STATIC_MAX_LEVEL` constant. The logging macros check
|
|||
|
|
this value before logging a message. By default, no levels are disabled.
|
|||
|
|
|
|||
|
|
Libraries should avoid using the max level features because they’re global and can’t be
|
|||
|
|
changed once they’re set.
|
|||
|
|
|
|||
|
|
For example, a crate can disable trace level logs in debug builds and trace, debug, and info
|
|||
|
|
level logs in release builds with the following configuration:
|
|||
|
|
|
|||
|
|
`[dependencies]
|
|||
|
|
log = { version = "0.4", features = ["max_level_debug", "release_max_level_warn"] }`
|
|||
|
|
|
|||
|
|
|
|||
|
|
# Crate Feature Flags
|
|||
|
|
|
|||
|
|
The following crate feature flags are available in addition to the filters. They are
|
|||
|
|
configured in your `Cargo.toml`.
|
|||
|
|
|
|||
|
|
* `std` allows use of `std` crate instead of the default `core`. Enables using `std::error`
|
|||
|
|
and `set_boxed_logger` functionality.
|
|||
|
|
* `serde` enables support for serialization and deserialization of `Level` and `LevelFilter`.
|
|||
|
|
`[dependencies]
|
|||
|
|
log = { version = "0.4", features = ["std", "serde"] }`
|
|||
|
|
|
|||
|
|
|
|||
|
|
# Version compatibility
|
|||
|
|
|
|||
|
|
The 0.3 and 0.4 versions of the `log` crate are almost entirely compatible. Log messages made
|
|||
|
|
using `log` 0.3 will forward transparently to a logger implementation using `log` 0.4. Log
|
|||
|
|
messages made using `log` 0.4 will forward to a logger implementation using `log` 0.3, but the
|
|||
|
|
module path and file name information associated with the message will unfortunately be lost.
|
|||
|
|
|
|||
|
|
[1] https://doc.rust-lang.org/stable/std/macro.println.html
|
|||
|
|
|
|||
|
|
MACROS
|
|||
|
|
debug
|
|||
|
|
Logs a message at the debug level.
|
|||
|
|
|
|||
|
|
error
|
|||
|
|
Logs a message at the error level.
|
|||
|
|
|
|||
|
|
info
|
|||
|
|
Logs a message at the info level.
|
|||
|
|
|
|||
|
|
log
|
|||
|
|
The standard logging macro.
|
|||
|
|
|
|||
|
|
log_enabled
|
|||
|
|
Determines if a message logged at the specified level in that module will be logged.
|
|||
|
|
|
|||
|
|
trace
|
|||
|
|
Logs a message at the trace level.
|
|||
|
|
|
|||
|
|
warn
|
|||
|
|
Logs a message at the warn level.
|
|||
|
|
|
|||
|
|
STRUCTS
|
|||
|
|
Metadata
|
|||
|
|
Metadata about a log message.
|
|||
|
|
|
|||
|
|
MetadataBuilder
|
|||
|
|
Builder for `Metadata`.
|
|||
|
|
|
|||
|
|
ParseLevelError
|
|||
|
|
The type returned by [`from_str`][1] when the string doesn’t match any of the log
|
|||
|
|
levels.
|
|||
|
|
|
|||
|
|
[1] https://doc.rust-lang.org/std/str/trait.FromStr.html#tymethod.from_str
|
|||
|
|
|
|||
|
|
Record
|
|||
|
|
The “payload” of a log message.
|
|||
|
|
|
|||
|
|
RecordBuilder
|
|||
|
|
Builder for `Record`.
|
|||
|
|
|
|||
|
|
SetLoggerError
|
|||
|
|
The type returned by `set_logger` if `set_logger` has already been called.
|
|||
|
|
|
|||
|
|
ENUMS
|
|||
|
|
Level
|
|||
|
|
An enum representing the available verbosity levels of the logger.
|
|||
|
|
|
|||
|
|
LevelFilter
|
|||
|
|
An enum representing the available verbosity level filters of the logger.
|
|||
|
|
|
|||
|
|
CONSTANTS
|
|||
|
|
STATIC_MAX_LEVEL
|
|||
|
|
The statically resolved maximum log level.
|
|||
|
|
|
|||
|
|
TRAITS
|
|||
|
|
Log
|
|||
|
|
A trait encapsulating the operations required of a logger.
|
|||
|
|
|
|||
|
|
FUNCTIONS
|
|||
|
|
logger
|
|||
|
|
Returns a reference to the logger.
|
|||
|
|
|
|||
|
|
max_level
|
|||
|
|
Returns the current maximum log level.
|
|||
|
|
|
|||
|
|
set_boxed_logger
|
|||
|
|
Sets the global logger to a `Box<Log>`.
|
|||
|
|
|
|||
|
|
set_logger
|
|||
|
|
Sets the global logger to a `&'static Log`.
|
|||
|
|
|
|||
|
|
set_logger_racy⚠
|
|||
|
|
A thread-unsafe version of `set_logger`.
|
|||
|
|
|
|||
|
|
set_max_level
|
|||
|
|
Sets the global maximum log level.
|
|||
|
|
|
|||
|
|
|