![obligatory xkcd](http://imgs.xkcd.com/comics/standards.png) # log15 [![godoc reference](https://godoc.org/github.com/inconshreveable/log15?status.png)](https://godoc.org/github.com/inconshreveable/log15) [![Build Status](https://travis-ci.org/inconshreveable/log15.svg?branch=master)](https://travis-ci.org/inconshreveable/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`](http://golang.org/pkg/io/) and [`net/http`](http://golang.org/pkg/net/http/) packages and is an alternative to the standard library's [`log`](http://golang.org/pkg/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. If you want to rely on a stable API, you must vendor the library. ## Importing ```go import log "github.com/inconshreveable/log15" ``` ## Examples ```go // 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())))) ``` Will result in output that looks like this: ``` WARN[06-17|21:58:10] abnormal conn rate module=app/server rate=0.500 low=0.100 high=0.800 INFO[06-17|21:58:10] connection open module=app/server raddr=10.0.0.1 ``` ## Breaking API Changes The following commits broke API stability. This reference is intended to help you understand the consequences of updating to a newer version of log15. - 57a084d014d4150152b19e4e531399a7145d1540 - Added a `Get()` method to the `Logger` interface to retrieve the current handler - 93404652ee366648fa622b64d1e2b67d75a3094a - `Record` field `Call` changed to `stack.Call` with switch to `github.com/go-stack/stack` - a5e7613673c73281f58e15a87d2cf0cf111e8152 - Restored `syslog.Priority` argument to the `SyslogXxx` handler constructors ## FAQ ### The varargs style is brittle and error prone! Can I have type safety please? Yes. Use `log.Ctx`: ```go srvlog := log.New(log.Ctx{"module": "app/server"}) srvlog.Warn("abnormal conn rate", log.Ctx{"rate": curRate, "low": lowRate, "high": highRate}) ``` ### Regenerating the CONTRIBUTORS file ``` go get -u github.com/kevinburke/write_mailmap write_mailmap > CONTRIBUTORS ``` ## License Apache