How to do it...

These steps cover the writing and running of your application:

1. From your Terminal/console application, create a new directory called ~/projects/go-programming-cookbook/chapter4/structured and navigate to this directory.
2. Run the following command:

$ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter4/structured

You should see a file called go.mod that contains the following:

module github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter4/structured    

3. Copy tests from ~/projects/go-programming-cookbook-original/chapter4/structured, or use this as an exercise to write some of your own code!
4. Create a file called logrus.go with the following content:

        package structured

        import "github.com/sirupsen/logrus"

        // Hook will implement the logrus
        // hook interface
        type Hook struct {
            id string
        }

        // Fire will trigger whenever you log
        func (hook *Hook) Fire(entry *logrus.Entry) error {
            entry.Data["id"] = hook.id
            return nil
        }

        // Levels is what levels this hook will fire on
        func (hook *Hook) Levels() []logrus.Level {
            return logrus.AllLevels
        }

        // Logrus demonstrates some basic logrus functionality
        func Logrus() {
            // we're emitting in json format
            logrus.SetFormatter(&logrus.TextFormatter{})
            logrus.SetLevel(logrus.InfoLevel)
            logrus.AddHook(&Hook{"123"})

            fields := logrus.Fields{}
            fields["success"] = true
            fields["complex_struct"] = struct {
                Event string
                When string
            }{"Something happened", "Just now"}

            x := logrus.WithFields(fields)
            x.Warn("warning!")
            x.Error("error!")
        }

5. Create a file called apex.go with the following content:

        package structured

        import (
            "errors"
            "os"

            "github.com/apex/log"
            "github.com/apex/log/handlers/text"
        )

        // ThrowError throws an error that we'll trace
        func ThrowError() error {
            err := errors.New("a crazy failure")
            log.WithField("id", "123").Trace("ThrowError").Stop(&err)
            return err
        }

        // CustomHandler splits to two streams
        type CustomHandler struct {
            id string
            handler log.Handler
        }

        // HandleLog adds a hook and does the emitting
        func (h *CustomHandler) HandleLog(e *log.Entry) error {
            e.WithField("id", h.id)
            return h.handler.HandleLog(e)
        }

        // Apex has a number of useful tricks
        func Apex() {
            log.SetHandler(&CustomHandler{"123", text.New(os.Stdout)})
            err := ThrowError()

            //With error convenience function
            log.WithError(err).Error("an error occurred")
        }

6. Create a new directory named example and navigate to it.
7. Create a main.go file with the following content:

        package main

        import (
            "fmt"

            "github.com/PacktPublishing/
             Go-Programming-Cookbook-Second-Edition/
             chapter4/structured"
        )

        func main() {
            fmt.Println("Logrus:")
            structured.Logrus()

            fmt.Println()
            fmt.Println("Apex:")
            structured.Apex()
        }

8. Run go run main.go.
9. You may also run the following commands:

$ go build
$ ./example

You should now see the following output:

$ go run main.go
Logrus:
WARN[0000] warning! complex_struct={Something happened Just now} 
id=123 success=true
ERRO[0000] error! complex_struct={Something happened Just now} 
id=123 success=true

Apex:
INFO[0000] ThrowError id=123
ERROR[0000] ThrowError duration=133ns error=a crazy failure 
id=123
ERROR[0000] an error occurred error=a crazy failure

10. The go.mod file should be updated and the go.sum file should now be present in the top-level recipe directory.
11. If you copied or wrote your own tests, then go up one directory and run go test. Ensure that all the tests pass.