log

A Rust library providing a lightweight logging facade.

• log
  documentation

A logging facade 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.

Minimum supported

rustc

This version is explicitly tested in CI and may be bumped in any release as needed. Maintaining compatibility with older compilers is a priority though, so the bar for bumping the minimum supported version is set very high. Any changes to the supported minimum version will be called out in the release notes.

Usage

In libraries

Libraries should link only to the

crate, and use the provided macros to log whatever information will be useful to downstream consumers:

In executables

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 options:

• Simple minimal loggers:
  • env_logger
  • colog
  • simple_logger
  • simplelog
  • pretty_env_logger
  • stderrlog
  • flexi_logger
  • call_logger
  • std-logger
  • structured-logger
  • clang_log
  • ftail
• Complex configurable frameworks:
  • log4rs
  • logforth
  • fern
  • spdlog-rs
• Adaptors for other facilities:
  • syslog
  • systemd-journal-logger
  • slog-stdlog
  • android_log
  • win_dbg_logger
  • db_logger
  • log-to-defmt
  • logcontrol-log
• For WebAssembly binaries:
  • console_log
• For dynamic libraries:
  • You may need to construct an FFI-safe wrapper over
    log
    to initialize in your libraries.
• Utilities:
  • log_err
  • log-reload
  • alterable_logger

Executables should choose a logger implementation and initialize it early in the runtime of the program. Logger implementations will typically include a function to do this. Any log messages generated before the logger is initialized will be ignored.

The executable itself may use the

crate to log as well.

Structured logging

If you enable the

feature, you can associate structured data with your log records: