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https://github.com/aphistic/gomol

Gomol is a library for structured, multiple-output logging for Go with extensible logging outputs
https://github.com/aphistic/gomol

go gomol logging structured-logging

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Gomol is a library for structured, multiple-output logging for Go with extensible logging outputs

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README 

        
gomol

=====



[![GoDoc](https://godoc.org/github.com/aphistic/gomol?status.svg)](https://godoc.org/github.com/aphistic/gomol)

[![Build Status](https://travis-ci.org/aphistic/gomol.svg?branch=master)](https://travis-ci.org/aphistic/gomol)

[![Code Coverage](https://img.shields.io/codecov/c/github/aphistic/gomol.svg)](http://codecov.io/github/aphistic/gomol?branch=master)

[![Go Report Card](https://goreportcard.com/badge/github.com/aphistic/gomol)](https://goreportcard.com/report/github.com/aphistic/gomol)



Gomol (Go Multi-Output Logger) is an MIT-licensed structured logging library for Go.  Gomol grew

from a desire to have a structured logging library that could write to any number of outputs

while also keeping a small in-band footprint.



Features

========



* Attach meta-data to each log message with attributes

* Multiple outputs at the same time

* Pluggable Logger interface

* Asynchronous logging so slow loggers won't slow down your application



Installation

============



Gomol can also be installed the standard way for Go:



    go get github.com/aphistic/gomol

    ...

    import "github.com/aphistic/gomol"



Vendoring is recommended!



Loggers

=======



Gomol has a growing list of supported logging formats.  The known loggers are listed

below.  If you have a logger you've written to support gomol and you'd like to add it

to this list please either submit a pull request with the updated document or let me

know and I can add it!



* **Console** - https://github.com/aphistic/gomol-console

* **Graylog Extended Log Format (GELF)** - https://github.com/aphistic/gomol-gelf

* **io.Writer** - https://github.com/aphistic/gomol-writer

* **JSON** - https://github.com/aphistic/gomol-json

* **Loggly** - https://github.com/aphistic/gomol-loggly



Other Usages

============



In addition to the loggers listed above, gomol can be used with other projects as well.



* **negroni-gomol** (https://github.com/aphistic/negroni-gomol) - Negroni logging middleware

	using gomol.



Examples

========



For brevity a lot of error checking has been omitted, be sure you do your checks!



This is a super basic example of adding a number of loggers and then logging a few messages:



```go

package main



import (

	"github.com/aphistic/gomol"

	gc "github.com/aphistic/gomol-console"

	gg "github.com/aphistic/gomol-gelf"

)



func main() {

	// Add a console logger

	consoleCfg := gc.NewConsoleLoggerConfig()

	consoleLogger, _ := gc.NewConsoleLogger(consoleCfg)

	// Set the template to display the full message, including

	// attributes.

	consoleLogger.SetTemplate(gc.NewTemplateFull())

	gomol.AddLogger(consoleLogger)



	// Add a GELF logger

	gelfCfg := gg.NewGelfLoggerConfig()

	gelfCfg.Hostname = "localhost"

	gelfCfg.Port = 12201

	gelfLogger, _ := gg.NewGelfLogger(gelfCfg)

	gomol.AddLogger(gelfLogger)



	// Set some global attrs that will be added to all

	// messages automatically

	gomol.SetAttr("facility", "gomol.example")

	gomol.SetAttr("another_attr", 1234)



	// Configure gomol to add the filename and line number that the

	// log was generated from, the internal sequence number to help

	// with ordering events if your log system doesn't support a

	// small enough sub-second resolution, and set the size of the

	// internal queue (default is 10k messages).

	cfg := gomol.NewConfig()

	cfg.FilenameAttr = "filename"

	cfg.LineNumberAttr = "line"

	cfg.SequenceAttr = "sequence"

	cfg.MaxQueueSize = 50000

	gomol.SetConfig(cfg)



	// Initialize the loggers

	gomol.InitLoggers()

	defer gomol.ShutdownLoggers()



	// Create a channel on which to receive internal (asynchronous)

	// logger errors. This is optional, but recommended in order to

	// determine when logging may be dropping messages.

	ch := make(chan error)



	go func() {

		// This consumer is expected to be efficient as writes to 

		// the channel are blocking. If this handler is slow, the

		// user should add a buffer to the channel, or manually

		// queue and batch errors for processing.



		for err := range ch {

			fmt.Printf("[Internal Error] %s\n", err.Error())

		}

	}()



	gomol.SetErrorChan(ch)



	// Log some debug messages with message-level attrs

	// that will be sent only with that message

	for idx := 1; idx <= 10; idx++ {

		gomol.Dbgm(gomol.NewAttrsFromMap(map[string]interface{}{

			"msg_attr1": 4321,

		}), "Test message %v", idx)

	}

}

```



Fallback Logger

===============



One feature gomol supports is the concept of a fallback logger.  In some cases a logger

may go unhealthy (a logger to a remote server, for example) and you want to log to a

different logger to ensure log messages are not lost.  The SetFallbackLogger method is

available for these such instances.



A fallback logger will be triggered if any of the primary loggers goes unhealthy even if

all others are fine. It's recommended the fallback logger not be added to the primary

loggers or you may see duplicate messages.  This does mean if multiple loggers are added

as primary loggers and just one is unhealthy the fallback logger logger will be triggered.



To add a fallback logger there are two options.  One is to use the default gomol instance

(`gomol.SetFallbackLogger()`) and the other is to use the method on a Base instance:



```go

import (

	"github.com/aphistic/gomol"

	"github.com/aphistic/gomol-console"

	"github.com/aphistic/gomol-json"

)



func main() {

	// Create a logger that logs over TCP using JSON

	jsonCfg := gomoljson.NewJSONLoggerConfig("tcp://192.0.2.125:4321")

	// Continue startup even if we can't connect initially

	jsonCfg.AllowDisconnectedInit = true

	jsonLogger, _ := gomoljson.NewJSONLogger(jsonCfg)

	gomol.AddLogger(jsonLogger)



	// Create a logger that logs to the console

	consoleCfg := gomolconsole.NewConsoleLoggerConfig()

	consoleLogger, _ := gomolconsole.NewConsoleLogger(consoleCfg)



	// Set the fallback logger to the console so if the

	// TCP JSON logger is unhealthy we still get logs

	// to stdout.

	_ = gomol.SetFallbackLogger(consoleLogger)



	gomol.InitLoggers()

	defer gomol.ShutdownLoggers()



	gomol.Debug("This is my message!")

}

```