How to use logging library in Go?

In the development of the Go language, logging is a very important link. Through the log, important information such as the running status of the program, error messages, and performance bottlenecks can be recorded. There are many logging libraries to choose from in the Go language, such as log in the standard library, third-party libraries logrus, zap, etc. This article will introduce how to use the logging library in Go.

1. Log in Go standard library

The log package in Go standard library provides a simple logging method, which can be output to standard output, a file or other io.Writer instance. The log package has three output methods: Println, Printf, and Print. Among them, the Println and Printf methods will add a newline character at the end of the output statement, but the Print method will not. The following is an example of using log output to standard output:

package main

import (
    "log"
)

func main() {
    log.Println("hello world!")
}

The output results are as follows:

2021/05/25 22:12:57 hello world!

By default, the log output log will contain date and time information, which is a good feature . Timestamps and log prefixes can be turned off by setting log parameters. For example:

log.SetFlags(log.Flags() &^ (log.Ldate | log.Ltime))
log.SetPrefix("")

2. logrus

logrus is a popular third-party logging library with more features and flexibility. By using logrus, you can add fields to the log, record json format logs, flexible log level control, etc. The following is a simple logrus example:

package main

import (
    "github.com/sirupsen/logrus"
)

func main() {
    log := logrus.New()
    log.WithFields(logrus.Fields{
        "name": "john",
        "age":  30,
    }).Info("user information")
}

The output result is as follows:

{"age":30,"name":"john","level":"info","msg":"user information","time":"2021-05-25T22:33:38+08:00"}

In the above example, we added two fields, name and age, to the log through the WithFields method. Logrus also supports outputting different logs based on log levels, such as Debug, Info, Warning, Error, Fatal, and Panic levels. You can control the output log level by setting the global level of logrus. For example, the following example sets the output log level to Warning and above:

package main

import (
    "github.com/sirupsen/logrus"
)

func main() {
    log := logrus.New()
    log.SetLevel(logrus.WarnLevel)
    
    log.Debug("this is debug log")
    log.Warn("this is warning log")
    log.Error("this is error log")
}

The output results are as follows:

time="2021-05-25T22:44:34+08:00" level=warning msg="this is warning log"
time="2021-05-25T22:44:34+08:00" level=error msg="this is error log"

3. zap

zap is another popular The third-party log library has higher performance and more comprehensive features than logrus. zap is a type-safe logging library that supports structured logging and cached logging. The following is an example of using zap to output logs to a file:

package main

import (
    "go.uber.org/zap"
)

func main() {
    logger, _ := zap.NewProduction()
    defer logger.Sync()

    logger.Info("this is info log")
    logger.Warn("this is warning log")
    logger.Error("this is error log")
}

In the above example, we create a zap Logger instance through zap.NewProduction() and use the three methods Info, Warn and Error to output different level logs. Ensure that all cached log data is flushed to disk through the defer logger.Sync() statement.

Due to the flexibility of the zap library, it can be customized in many ways, such as setting the global log level, log output format, adding fields, changing the time format, etc. The following is an example of using zap to set the global log level:

package main

import (
    "go.uber.org/zap"
)

func main() {
    logger, _ := zap.NewProduction()
    defer logger.Sync()

    logger.Warn("this is warning log")
    logger.Error("this is error log")

    logger, _ = logger.WithOptions(zap.IncreaseLevel(zap.InfoLevel))

    logger.Info("this is info log")
}

In the above example, we first output two Warning and Error logs, and then raised the global log level to Info through the WithOptions method, and then Output an Info log.

Conclusion

Logging is an indispensable part of our development. The Go language provides a standard library log, and there are many third-party log libraries to choose from, such as logrus and zap. Each log library has different characteristics and is suitable for different scenarios. Depending on the actual application, we can use different log libraries and configuration methods to make our program more stable and maintainable.

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