log15

Package log15 provides an opinionated, simple toolkit for best-practice logging in Go (golang) that is both human and machine readable. It is modeled after the Go standard library's io and net/http packages and is an alternative to the standard library's log package.

Features

• A simple, easy-to-understand API
• Promotes structured logging by encouraging use of key/value pairs
• Child loggers which inherit and add their own private context
• Lazy evaluation of expensive operations
• Simple Handler interface allowing for construction of flexible, custom logging configurations with a tiny API.
• Color terminal support
• Built-in support for logging to files, streams, syslog, and the network
• Support for forking records to multiple handlers, buffering records for output, failing over from failed handler writes, + more

Versioning

The API of the master branch of log15 should always be considered unstable. Using a stable version of the log15 package is supported by gopkg.in. Include your dependency like so:

import log "gopkg.in/inconshreveable/log15.v2"

Examples

// all loggers can have key/value context
srvlog := log.New("module", "app/server")

// all log messages can have key/value context 
srvlog.Warn("abnormal conn rate", "rate", curRate, "low", lowRate, "high", highRate)

// child loggers with inherited context
connlog := srvlog.New("raddr", c.RemoteAddr())
connlog.Info("connection open")

// lazy evaluation
connlog.Debug("ping remote", "latency", log.Lazy(pingRemote))

// flexible configuration
srvlog.SetHandler(log.MultiHandler(
    log.StreamHandler(os.Stderr, log.LogfmtFormat()),
    log.LvlFilterHandler(
        log.LvlError,
        log.Must.FileHandler("errors.json", log.JsonFormat())))

FAQ

The varargs style is brittle and error prone! Can I have type safety please?

Yes. Use log.Ctx:

srvlog := log.New(log.Ctx{"module": "app/server"})
srvlog.Warn("abnormal conn rate", log.Ctx{"rate": curRate, "low": lowRate, "high": highRate})

License

Apache