Crate captains_log

Expand description

§captains-log

A light-weight logger for rust, implementation base on the crate log.

§Features

Allow customize log format and time format. Refer to LogFormat.
Supports multiple types of sink stacking, each with its own log level.
- LogConsole: Console output to stdout/stderr.
- LogRawFile: Support atomic appending from multi-process on linux
- LogBufFile: Write to log file with merged I/O and delay flush, and optional self-rotation.
- Syslog: (feature syslog)
  
  Write to local or remote syslog server, with timeout and auto reconnect.
- LogRingFile: (feature ringfile)
  
  For deadlock / race condition debugging, collect log to ring buffer in memory. See the doc of LogRingFile for how to use.
Log panic message by default.
Provide additional macros, for example: log_assert!(), logger_assert!() ..
Supports signal listening for log-rotate. Refer to Builder::signal()
Provides many preset recipes in recipe module for convenience.
Supports configure by environment
Fine-grain module-level control
API-level log handling
For test suits usage:
- Allow dynamic reconfigure logger setting in different test function.
  
  Refer to Unit test example.
- Provides an attribute macro #[logfn] to wrap test function.
  
  Refer to Best practice with rstest.
Provides a LogParser to work on your log files.

§Usage

Cargo.toml

[dependencies]
log = { version = "0.4", features = ["std", "kv_unstable"] }
captains_log = "0.8"

lib.rs or main.rs:


// By default, reexport the macros from log crate
#[macro_use]
extern crate captains_log;

§Fast setup examples

You can refer to various preset recipe in recipe module.

The following is setup two log files for different log-level:

#[macro_use]
extern crate captains_log;
use captains_log::recipe;

// You'll get /tmp/test.log with all logs, and /tmp/test.log.wf only with error logs.
let log_builder = recipe::split_error_file_logger("/tmp", "test", log::Level::Debug);
// Builder::build() is equivalent of setup_log().
log_builder.build();
// non-error msg will only appear in /tmp/test.log
debug!("Set a course to Sol system");
info!("Engage");
// will appear in both /tmp/test.log and /tmp/test.log.wf
error!("Engine over heat!");

Buffered sink with log rotation (See the definition of Rotation):

#[macro_use]
extern crate captains_log;
use captains_log::*;
// rotate when log file reaches 512M. Keep max 10 archiveed files, with recent 2 not compressed.
// All archived log is moved to "/tmp/rotation/old"
let rotation = Rotation::by_size(512 * 1024 * 1024, Some(10))
    .compress_exclude(2).archive_dir("/tmp/rotation/old");
let _ = recipe::buffered_rotated_file_logger("/tmp/rotation.log", Level::Debug, rotation).build();

§Configure by environment

There is a recipe env_logger() to configure a file logger or console logger from env. As simple as:

use captains_log::recipe;
let _ = recipe::env_logger("LOG_FILE", "LOG_LEVEL").build();

If you want to custom more, setup your config with env_or helper.

§Customize format example

use captains_log::*;

fn format_f(r: FormatRecord) -> String {
    let time = r.time();
    let level = r.level();
    let file = r.file();
    let line = r.line();
    let msg = r.msg();
    format!("{time}|{level}|{file}:{line}|{msg}\n").to_string()
}
let debug_format = LogFormat::new(
    "%Y%m%d %H:%M:%S%.6f",
    format_f,
);
let debug_file = LogRawFile::new(
    "/tmp", "test.log", log::Level::Trace, debug_format);
let config = Builder::default()
    .signal(signal_hook::consts::SIGINT)
    .add_sink(debug_file);
config.build();

§Fine-grain module-level control

Place LogFilter in Arc and share among coroutines. Log level can be changed on-the-fly.

There’re a set of macro “logger_XXX” to work with LogFilter.

use std::sync::Arc;
use captains_log::*;
log::set_max_level(log::LevelFilter::Debug);
let logger_io = Arc::new(LogFilter::new());
let logger_req = Arc::new(LogFilter::new());
logger_io.set_level(log::Level::Error);
logger_req.set_level(log::Level::Debug);
logger_debug!(logger_req, "Begin handle req ...");
logger_debug!(logger_io, "Issue io to disk ...");
logger_error!(logger_req, "Req invalid ...");

§API-level log handling

Request log can be track by customizable key (for example, “req_id”), which kept in LogFilterKV, and LogFilterKV is inherit from LogFilter. You need macro “logger_XXX” to work with it.

use captains_log::*;
fn debug_format_req_id_f(r: FormatRecord) -> String {
    let time = r.time();
    let level = r.level();
    let file = r.file();
    let line = r.line();
    let msg = r.msg();
    let req_id = r.key("req_id");
    format!("[{time}][{level}][{file}:{line}] {msg}{req_id}\n").to_string()
}
let builder = recipe::raw_file_logger_custom("/tmp/log_filter.log", log::Level::Debug,
    recipe::DEFAULT_TIME, debug_format_req_id_f);
builder.build().expect("setup_log");
let logger = LogFilterKV::new("req_id", format!("{:016x}", 123).to_string());
info!("API service started");
logger_debug!(logger, "Req / received");
logger_debug!(logger, "header xxx");
logger_info!(logger, "Req / 200 complete");

The log will be:

[2025-06-11 14:33:08.089090][DEBUG][request.rs:67] API service started
[2025-06-11 14:33:10.099092][DEBUG][request.rs:67] Req / received (000000000000007b)
[2025-06-11 14:33:10.099232][WARN][request.rs:68] header xxx (000000000000007b)
[2025-06-11 14:33:11.009092][DEBUG][request.rs:67] Req / 200 complete (000000000000007b)

§Unit test example

To setup different log config on different tests.

Make sure that you call Builder::test() in test cases. which enable dynamic log config and disable signal_hook.

use captains_log::*;

#[test]
fn test1() {
    recipe::raw_file_logger(
        "/tmp/test1.log", Level::Debug).test().build();
    info!("doing test1");
}

#[test]
fn test2() {
    recipe::raw_file_logger(
        "/tmp/test2.log", Level::Debug).test().build();
    info!("doing test2");
}

§Best practice with rstest

We provides proc macro logfn, the following example shows how to combine with rstest.

When you have large test suit, you want to know which logs belong to which test case.
Sometimes your test crashes, you want to find the responsible test case.
The time spend in each test.


use rstest::*;
use captains_log::*;

// A show case that setup() fixture will be called twice, before each test.
// In order make logs available.
#[fixture]
fn setup() {
    let builder = recipe::raw_file_logger("/tmp/log_rstest.log", log::Level::Debug).test();
    builder.build().expect("setup_log");
}

#[logfn]
#[rstest(file_size, case(0), case(1))]
fn test_rstest_foo(setup: (), file_size: usize) {
    info!("do something111");
}

#[logfn]
#[rstest]
fn test_rstest_bar(setup: ()) {
    info!("do something222");
}

// NOTE rstest must be at the bottom to make fixture effective
#[tokio::test]
#[logfn]
#[rstest]
async fn test_rstest_async(setup: ()) {
    info!("something333")
}

Notice: the order when combine tokio::test with rstest, #[rstest] attribute must be at the bottom to make setup fixture effective.

After running the test with:

cargo test – –test-threads=1

/tmp/log_rstest.log will have this content:

[2025-07-13 18:22:39.159642][INFO][test_rstest.rs:33] <<< test_rstest_async (setup = ()) enter <<<
[2025-07-13 18:22:39.160255][INFO][test_rstest.rs:37] something333
[2025-07-13 18:22:39.160567][INFO][test_rstest.rs:33] >>> test_rstest_async return () in 564.047µs >>>
[2025-07-13 18:22:39.161299][INFO][test_rstest.rs:26] <<< test_rstest_bar (setup = ()) enter <<<
[2025-07-13 18:22:39.161643][INFO][test_rstest.rs:29] do something222
[2025-07-13 18:22:39.161703][INFO][test_rstest.rs:26] >>> test_rstest_bar return () in 62.681µs >>>
[2025-07-13 18:22:39.162169][INFO][test_rstest.rs:20] <<< test_rstest_foo (setup = (), file_size = 0) enter <<<
[2025-07-13 18:22:39.162525][INFO][test_rstest.rs:23] do something111
[2025-07-13 18:22:39.162600][INFO][test_rstest.rs:20] >>> test_rstest_foo return () in 78.457µs >>>
[2025-07-13 18:22:39.163050][INFO][test_rstest.rs:20] <<< test_rstest_foo (setup = (), file_size = 1) enter <<<
[2025-07-13 18:22:39.163320][INFO][test_rstest.rs:23] do something111
[2025-07-13 18:22:39.163377][INFO][test_rstest.rs:20] >>> test_rstest_foo return () in 58.747µs >>>

Modules§

macros
parser
recipe: The recipe module contains some prelude functions that construct a Builder for convenience use.
signal_consts: Re-export from signal_hook::consts: The signal constants.

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_assert: Will log and panic when condition not met.
log_assert_eq: Will log and panic when condition not met.
log_debug_assert: On Debug build, will log and panic when condition not met. Skip the check on release build.
log_debug_assert_eq: On Debug build, will log and panic when condition not met. Skip the check on release build.
log_eprintln: log and println to stderr.
log_println: log and println to stdout.
logger_assert: Will log with log_filter and panic when condition not met.
logger_assert_eq: Will log with log_filter and panic when condition not met.
logger_debug: Similar to debug!(), but the first argument is LogFilter or LogFilterKV
logger_debug_assert: On debug build, will log with log_filter and panic when condition not met. Skip the check on release build.
logger_debug_assert_eq: On debug build, will log with log_filter and panic when condition not met. Skip the check on release build.
logger_error: Similar to error!(), but the first argument is LogFilter or LogFilterKV.
logger_info: Similar to info!(), but the first argument is LogFilter or LogFilterKV.
logger_trace: Similar to trace!(), but the first argument is LogFilter or LogFilterKV
logger_warn: Similar to warn!(), but the first argument is LogFilter or LogFilterKV.
trace: Logs a message at the trace level.
warn: Logs a message at the warn level.

Structs§

Builder: Global config to setup logger See crate::recipe for usage
ByAge
EnvVarDefault
FormatRecord
LogBufFile: Config for buffered file sink which merged I/O and delay flush. Optional log rotation can be configured.
LogConsole: Log config for output to console
LogFilter: A LogFilter supports concurrent control the log level. Use in combine with macros logger_XXX
LogFilterKV: LogFilter that carries one additional value into log format
LogFormat: Custom formatter which adds into a log sink
LogRawFile: Config for file sink that supports atomic append from multiprocess.
LogRingFileringfile: The LogRingFile sink is a way to minimize the cost of logging, for debugging deadlock or race condition, when the problem cannot be reproduce with ordinary log (because disk I/O will slow down the execution and prevent the bug to occur).
Rotation: Log rotation configuration.
Syslogsyslog: Config for syslog output, supports local and remote server.

Enums§

Age
ConsoleTarget
Facility
Level: Re-export log::Level: An enum representing the available verbosity levels of the logger.
LevelFilter: Re-export log::LevelFilter: An enum representing the available verbosity level filters of the logger.
SyslogAddrsyslog
SyslogProtosyslog
Upkeep

Traits§

SinkConfigTrait

Functions§

env_or: To config some logger setting with env.
setup_log: Initialize global logger from Builder

Type Aliases§

FormatFunc

Attribute Macros§

logfn: Provide an proc_macro #[logfn] which log the information: