Go Fiber Log Processing

Fiber Log

We can use logs to observe the behavior of the program, diagnose issues, or configure corresponding alerts. Defining a well-structured log can improve search efficiency and facilitate problem handling.

Fiber provides a default way to print logs to standard output. It also provides several global functions, such as log.Info, log.Errorf, and log.Warnw.

Log Levels

const (
    LevelTrace Level = iota
    LevelDebug
    LevelInfo
    LevelWarn
    LevelError
    LevelFatal
    LevelPanic
)

Custom Log

Fiber provides the AllLogger interface to adapt to various logging libraries.

type CommonLogger interface {
    Logger
    FormatLogger
    WithLogger
}

type AllLogger interface {
    CommonLogger
    ControlLogger
    WithLogger
}

Printing Logs

Note: Calling methods at a Fatal level will interrupt program execution after printing the log. Please use with caution. Directly printing logs at different levels will be input into the messageKey and are by default set to msg.

log.Info("Hello, World!")
log.Debug("Are you OK?")
log.Info("42 is the answer to life, the universe, and everything")
log.Warn("We are under attack!")
log.Error("Houston, we have a problem.")
log.Fatal("So Long, and Thanks for All the Fislog.")
log.Panic("The system is down.")

Formatting and printing logs at different levels, all methods end with f.

log.Debugf("Hello %s", "boy")
log.Infof("%d is the answer to life, the universe, and everything", 233)
log.Warnf("We are under attack %s!", "boss")
log.Errorf("%s, we have a problem.", "Master Shifu")
log.Fatalf("So Long, and Thanks for All the %s.", "banana")

Printing messages with keys and values. If the keys and values are not paired, KEYVALS UNPAIRED will be printed.

log.Debugw("", "Hello", "boy")
log.Infow("", "number", 233)
log.Warnw("", "job", "boss")
log.Errorw("", "name", "Master Shifu")
log.Fatalw("", "fruit", "banana")

Global Log

If you only want to use a simple log function in a project and print it globally at any time, we provide a global log.

import "github.com/gofiber/fiber/v2/log"

log.Info("info")
log.Warn("warn")

The above code uses the default log.DefaultLogger for standard output. You can also find adapters already implemented in the contrib folder, or use your own implemented Logger and set the global logger using log.SetLogger.

import (
    "log"
    fiberlog "github.com/gofiber/fiber/v2/log"
)

var _ log.AllLogger = (*customLogger)(nil)

type customLogger struct {
    stdlog *log.Logger
}

// ...
// Inject custom logger
fiberlog.SetLogger(customLogger)

Set Level

log.SetLevel sets the logs that are lower than this level and will not be output. The default log recorder is LevelTrace.

Please note that this method is not concurrency safe.

import "github.com/gofiber/fiber/v2/log"

log.SetLevel(log.LevelInfo)

Set Output

log.SetOutput sets the output destination for the logging. By default, the logger prints logs to the console.

var logger AllLogger = &defaultLogger{
    stdlog: log.New(os.Stderr, "", log.LstdFlags|log.Lshortfile|log.Lmicroseconds),
    depth:  4,
}

Set the output destination to a file.

// Output to the test.log file
f, err := os.OpenFile("test.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
if err != nil {
    return
}
log.SetOutput(f)

Set the output destination to both the console and a file.

// Output to the test.log file
file, _ := os.OpenFile("test.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
iw := io.MultiWriter(os.Stdout, file)
log.SetOutput(iw)

Bind Context

Set the context, and use the following method to return a CommonLogger instance bound to the specified context.

commonLogger := log.WithContext(ctx)
commonLogger.Info("info")

Note: This is the default logging library for the Fiber framework. Of course, you can choose other well-known Go open-source logging libraries.