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. If you want to rely on a stable API,
you must vendor the library.
Importing
import log "github.com/inconshreveable/log15"
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()))))
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 theLoggerinterface to retrieve the current handler - 93404652ee366648fa622b64d1e2b67d75a3094a -
RecordfieldCallchanged tostack.Callwith switch togithub.com/go-stack/stack - a5e7613673c73281f58e15a87d2cf0cf111e8152 - Restored
syslog.Priorityargument to theSyslogXxxhandler constructors
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})
Regenerating the CONTRIBUTORS file
go get -u github.com/kevinburke/write_mailmap
write_mailmap > CONTRIBUTORS
License
Apache