glogger

glogger is a Go package that provides a logger that can be used to write log messages to an output destination, such as the standard output or a file. It has various levels of log severity (e.g. debug, info, warning, error, fatal) and supports two formats: inline-string and JSON.

Installation

To install glogger, run:

go get github.com/psyb0t/glogger

Usage

The global variables output, logFormat, and logLevel control the output destination, format, and minimum severity level of log messages, respectively. You can set these variables using the functions SetOutput, SetLogFormat, and SetLogLevel.

To create a new logger, use the New function and pass in a Caller struct that contains the caller information (e.g. service, package, receiver, function). The Logger interface provides methods for logging messages at different severity levels: Debug, Info, Warn, Error, and Fatal.

The Err, RequestID, TraceID, SpanID, and Data methods can be used to add extra data to the log entry. The Err method sets the error field in the log entry to the given value. The RequestID, TraceID, and SpanID methods set the corresponding fields in the log entry to the given values. The Data method adds a data field to the log entry as key => val.

Example

package main

import (
	"errors"
	"fmt"
	"os"

	"github.com/psyb0t/glogger"
)

func main() {
	f, err := os.OpenFile("app.log", os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
	if err != nil {
		panic(fmt.Sprintf("error opening file: %v", err))
	}
	defer f.Close()

	// Set the output writer where log messages will be written.
	glogger.SetOutput(f)

	// Set the log format to JSON.
	glogger.SetLogFormat(glogger.LogFormatJSON)

	// Set the log level to "Info" or higher.
	glogger.SetLogLevel(glogger.LogLevelInfo)

	// Create a logger instance.
	logger := glogger.New(glogger.Caller{Service: "my-service", Package: "main", Function: "main"})

	// Log messages at different severity levels with various extra data.
	logger.RequestID("abc123").Debug("hello world")
	logger.TraceID("zzzsss").Info("hello world")
	logger.TraceID("zzzsss").SpanID("123456").Warn("hello world")
	logger.Err(errors.New("something bad happened")).Error("hello world")
	logger.Data("key", "value").Fatal("hello world")
}

The log file app.log will contain the following messages:

{"service":"my-service","package":"main","function":"main","time":"2023-01-04T00:50:04+02:00","level":"INFO","message":"hello world","requestID":"abc123","traceID":"zzzsss"}
{"service":"my-service","package":"main","function":"main","time":"2023-01-04T00:50:04+02:00","level":"WARN","message":"hello world","traceID":"zzzsss","spanID":"123456"}
{"service":"my-service","package":"main","function":"main","time":"2023-01-04T00:50:04+02:00","level":"ERROR","message":"hello world","error":"something bad happened"}
{"service":"my-service","package":"main","function":"main","time":"2023-01-04T00:50:04+02:00","level":"FATAL","message":"hello world","data":{"key":"value"}}