log

A lightweight logging wrapper for zerolog, providing convenience functions and sensible defaults for Interline and Transitland projects.

Note: This library is primarily intended for internal use across Interline/Transitland repositories—mainly for our convenience and to avoid having zerolog.Xyz scattered throughout our codebase and copy-pasting logging middlewares. It's published publicly for our convenience; external users should probably just use zerolog directly.

Features

• Simple printf-style logging functions (Infof, Debugf, Tracef, Errorf)
• Structured logging via zerolog's fluent API
• Pretty console output with colors (automatically disabled when piping/redirecting)
• JSON output mode for production environments
• Context-aware logging with request ID support
• HTTP middleware for request logging

Installation

go get github.com/interline-io/log

Usage

Basic Logging

package main

import "github.com/interline-io/log"

func main() {
    // Printf-style logging
    log.Infof("Processing %d items", 42)
    log.Debugf("Debug info: %s", "details")
    log.Errorf("Something went wrong: %v", err)
    log.Tracef("Verbose trace: %+v", obj)

    // Structured logging (zerolog style)
    log.Info().Str("user", "alice").Int("count", 5).Msg("User action")
    log.Error().Err(err).Str("op", "save").Msg("Operation failed")

    // Simple print (no timestamp, ignores log level)
    log.Print("Plain output: %s", "hello")
}

Context-Aware Logging

// Get logger from context
logger := log.For(ctx)
logger.Info().Msg("Using context logger")

// Add logger to context
ctx = log.WithLogger(ctx, customLogger)

HTTP Middleware

import "github.com/interline-io/log"

// Add request ID to each request
r.Use(log.RequestIDMiddleware)

// Add request ID to context logger
r.Use(log.RequestIDLoggingMiddleware)

// Log request duration and details
r.Use(log.LoggingMiddleware(1000, getUserNameFunc))

Configuration

Environment Variables

Variable	Description	Default
TL_LOG	Log level: TRACE, DEBUG, INFO, ERROR, FATAL	INFO
TL_LOG_JSON	Set to true for JSON output (no colors)	false

Examples

# Enable debug logging
TL_LOG=DEBUG ./myapp

# Enable trace logging (most verbose)
TL_LOG=TRACE ./myapp

# JSON output for production/log aggregation
TL_LOG_JSON=true ./myapp

Terminal Colors

Console output includes ANSI colors when writing to a terminal. Colors are automatically disabled when output is piped or redirected:

# Colors enabled (terminal)
./myapp

# Colors disabled (piped)
./myapp | tee output.log

# Colors disabled (redirected)
./myapp > output.log 2>&1

Log Levels

Level	Function	Use Case
TRACE	Tracef(), Trace()	Verbose debugging, performance tracing
DEBUG	Debugf(), Debug()	Development debugging
INFO	Infof(), Info()	General operational messages
ERROR	Errorf(), Error()	Error conditions

License

See LICENSE file.