Yet another Go logging library.

Optimized for convenience, typing, compatibility.

Features:

• Built on top of slog (introduced in Go 1.21, see Go blog)
  • All handlers and utils can be wrapped with a *slog.Logger or other logger frontends, for logging compatibility with projects that do not use proto-log/log.Logger.
• Extended Logger interface:
  • Trace, TraceContext:
  • Crit, CritContext: without os.Exit, instead attach a PostHandlerMod to follow-up crit logs with your preferred crit handling.
  • Context to access the default context
  • WithContext to make a logger clone and attach a new default context
• Handler Unwrap pattern, to find handler-wrappers easily
• A set of HandlerMod to adjust log-handlers of (sub-)loggers at runtime:
  • ContextMod to adjust the default context
  • LevelMod to adjust the log-level
  • CapturingMod to capture logging
  • PostProcessMod to post-process log records (e.g. handle special log levels)
• A set of slog.Handler implementations:
  • DiscardHandler
  • JSONHandler
  • LogfmtHandler: for human-readable but Loki-compatible logging.
  • TerminalHandler:
    • Like logfmt, but stylish, with automatic source-filepath and field padding.
    • Looks for TerminalString() string on types for custom formatting.
    • uint64, *big.Int and *uint256.Int are logged with _ thousand-separators.
• TestLogger: minimal test log-handling stack on top of T.Output() (introduced in Go 1.23)
  • Can be customized with additional HandlerMod
  • Logger.Crit / Logger.CritContext are followed up with T.FailNow()
• FormatOption to configure formatting of handlers:
  • Option to exclude time, for logging in Go Example output to be stable
  • Option to resolve file-paths of source-file data to relative paths
  • Option to color output of TerminalHandler
• No dependencies

See: Log example tests

Some other log libraries influenced this:

• log15 v1 (obligatory xkcd):
  • Originally introduced in go-ethereum.
  • Pushed forward Go structured log fields, sub-logger contexts.
  • Influenced terminal log-formatting in go-ethereum / optimism / others (see notice in format.go).
• Logging was adapted in optimism:
  • Optimism introduced initial log-capturer (forked now).
  • First version of handler-wrapping idea for composition.
  • MIT, see LICENSE entry.
• slog was introduced in Go 1.21.
  • Go finally got standard modern structured logging.
  • Introduced into go-ethereum.
  • Reduced code, adopted standard log-level values and utils.

MIT License, see LICENSE file.