Crate nanologger

Expand description

§nanologger

A minimal logger for Rust.

nanologger provides five leveled log macros (error!, warn!, info!, debug!, trace!) that write colored, formatted output to stderr. It supports optional timestamps, source locations, thread info, module filtering, file logging, and combined multi-output configurations.

§Quick start

use nanologger::{LoggerBuilder, LogLevel};

LoggerBuilder::new()
    .level(LogLevel::Trace)
    .timestamps(true)
    .init()
    .unwrap();

nanologger::error!("something went wrong: {}", "disk full");
nanologger::warn!("retries remaining: {}", 3);
nanologger::info!("server started on port {}", 8080);
nanologger::debug!("request payload: {:?}", vec![1, 2, 3]);
nanologger::trace!("entering function");

Or with defaults (Info level, stderr, no timestamps):

nanologger::init().unwrap();
nanologger::info!("hello");

§Log levels

LogLevel variants ordered by decreasing severity:

Level	Color	Tag
`Error`	Red bold	`[ERROR]`
`Warn`	Yellow bold	`[WARN]`
`Info`	Green bold	`[INFO]`
`Debug`	Blue bold	`[DEBUG]`
`Trace`	Magenta bold	`[TRACE]`

Messages below the configured level are silently discarded. Colors are automatically disabled when stderr is not a TTY.

§Output destinations

LogOutput controls where log messages go:

LogOutput::term — stderr with color support
LogOutput::writer — any impl Write + Send (files, buffers, etc.), plain text
LogOutput::test — via print!(), captured by Rust’s test harness

Multiple outputs can be added to a single logger, each with its own level filter:

use nanologger::{LogLevel, LogOutput, LoggerBuilder};
use std::fs::File;

let file = File::create("app.log").unwrap();

LoggerBuilder::new()
    .level(LogLevel::Trace)
    .add_output(LogOutput::term(LogLevel::Warn))          // terminal: Warn+
    .add_output(LogOutput::writer(LogLevel::Trace, file))  // file: everything
    .init()
    .unwrap();

§Optional features

Timestamps — .timestamps(true) prepends HH:MM:SS.mmm via nanotime
Source location — .source_location(true) appends [file:line] after the level tag
Thread info — .thread_info(true) shows (thread-name) or (ThreadId(N))
Module filtering — .module_allow() / .module_deny() for prefix-based filtering
Runtime level changes — set_level adjusts the global level after init
Env var — NANOLOGGER_LEVEL sets the default level (case-insensitive)

§`log` facade integration

Enable the log feature to use nanologger as a backend for the log crate:

[dependencies]
nanologger = { version = "0.1.0", features = ["log"] }

When initialized, nanologger registers itself via log::set_logger, so libraries using log::info!() etc. route through nanologger automatically.

§Colored message content

nanologger re-exports Colorize, style, and StyledString from nanocolor, so you can style log message content without an extra dependency:

use nanologger::{info, Colorize, style};

info!("listening on {}", "127.0.0.1:3000".cyan());

let v = style(format!("v{}.{}.{}", 0, 1, 0)).cyan().bold();
info!("running nanologger {}", v);

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.
trace: Logs a message at the Trace level.
warn: Logs a message at the Warn level.

Structs§

InitError: Error returned when attempting to initialize the logger more than once.
Logger: The global logger. Immutable after initialization. The global logger. Immutable after initialization.
LoggerBuilder: Builder for configuring and initializing the global Logger. Builder for configuring and initializing the global Logger.
ParseLevelError: Error returned when parsing an invalid log level string.
StyledString: A string with accumulated ANSI color and style information.

Enums§

LogLevel: Log severity levels, ordered from highest to lowest severity.
LogOutput: Represents a log output destination.

Traits§

Colorize

Functions§

init: Convenience function: initialize the global logger with default settings (level = Info).
matches_module_filter: Returns true if a message from module_path should be emitted given the allow and deny lists.
set_level: Changes the global log level at runtime.
style: Wraps any Display type in a StyledString for chainable styling.