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README.md

go-gelf - GELF Library and Writer for Go

GELF (Graylog Extended Log Format) is an application-level logging protocol that avoids many of the shortcomings of syslog. While it can be run over any stream or datagram transport protocol, it has special support (chunking) to allow long messages to be split over multiple datagrams.

Versions

In order to enable versionning of this package with Go, this project is using GoPkg.in. The default branch of this project will be v1 for some time to prevent breaking clients. We encourage all project to change their imports to the new GoPkg.in URIs as soon as possible.

To see up to date code, make sure to switch to the master branch.

v1.0.0

This implementation currently supports only UDP as a transport protocol. TCP and TLS are unsupported.

The library provides an API that applications can use to log messages directly to a Graylog server and an io.Writer that can be used to redirect the standard library's log messages (os.Stdout) to a Graylog server.

Installing

go-gelf is go get-able:

go get gopkg.in/Graylog2/go-gelf.v1/gelf

or

go get github.com/Graylog2/go-gelf/gelf

This will get you version 1.0.0, with only UDP support and legacy API. Newer versions are available through GoPkg.in:

go get gopkg.in/Graylog2/go-gelf.v2/gelf

Usage

The easiest way to integrate graylog logging into your go app is by having your main function (or even init) call log.SetOutput(). By using an io.MultiWriter, we can log to both stdout and graylog - giving us both centralized and local logs. (Redundancy is nice).

package main

import (
	"flag"
	"gopkg.in/Graylog2/go-gelf.v1/gelf"
	"io"
	"log"
	"os"
)

func main() {
	var graylogAddr string

	flag.StringVar(&graylogAddr, "graylog", "", "graylog server addr")
	flag.Parse()

	if graylogAddr != "" {
		gelfWriter, err := gelf.NewWriter(graylogAddr)
		if err != nil {
			log.Fatalf("gelf.NewWriter: %s", err)
		}
		// log to both stderr and graylog2
		log.SetOutput(io.MultiWriter(os.Stderr, gelfWriter))
		log.Printf("logging to stderr & graylog2@'%s'", graylogAddr)
	}

	// From here on out, any calls to log.Print* functions
	// will appear on stdout, and be sent over UDP to the
	// specified Graylog2 server.

	log.Printf("Hello gray World")

	// ...
}

The above program can be invoked as:

go run test.go -graylog=localhost:12201

When using UDP messages may be dropped or re-ordered. However, Graylog server availability will not impact application performance; there is a small, fixed overhead per log call regardless of whether the target server is reachable or not.

To Do

  • WriteMessage example

License

go-gelf is offered under the MIT license, see LICENSE for details.