Chain go design pattern language Of Responsibility (Chain of Responsibility)

ChainOfResponsibility.go

package ChainOfResponsibility

import (
	"fmt"
	"io"
	"strings"
)

type ChainLogger interface {
	Next(string)
}

type FirstLogger struct {
	NextChain ChainLogger
}

func (f *FirstLogger) Next(s string) {
	fmt.Printf("First logger: %s\n", s)

	if f.NextChain != nil {
		f.NextChain.Next(s)
	}
}

type SecondLogger struct {
	NextChain ChainLogger
}

func (se *SecondLogger) Next(s string) {
	if strings.Contains(strings.ToLower(s), "hello") {
		fmt.Printf("Second logger: %s\n", s)

		if se.NextChain != nil {
			se.NextChain.Next(s)
		}
		return
	}
	fmt.Printf("Finishing in second logging\n\n")
}

type WriterLogger struct {
	NextChain ChainLogger
	Writer    io.Writer
}

func (w *WriterLogger) Next(s string) {
	if w.Writer != nil {
		w.Writer.Write([]byte("WriterLogger: " + s))
	}
	if w.NextChain != nil {
		w.NextChain.Next(s)
	}
}

　　

ChainOfResponsibility_test.go

package ChainOfResponsibility

import (
	"fmt"
	"strings"
	"testing"
)

type myTestWriter struct {
	receivedMessage *string
}

func (m *myTestWriter) Write(p []byte) (int, error) {
	if m.receivedMessage == nil {
		m.receivedMessage = new(string)
	}
	tempMessage := fmt.Sprintf("%p%s", m.receivedMessage, p)
	m.receivedMessage = &tempMessage
	return len(p), nil
}

func (m *myTestWriter) Next(s string) {
	m.Write([]byte(s))
}

func TestCreateDefaultChain(t *testing.T) {
	myWriter := myTestWriter{}

	writerLogger := WriterLogger{Writer: &myWriter}
	second := SecondLogger{NextChain: &writerLogger}
	chain := FirstLogger{NextChain: &second}

	t.Run("3 loggers, 2 of them writes to console, second only if it founds"+
		"the world 'hello', third writes to some variable if second found 'hello'",
		func(t *testing.T) {
			chain.Next("message that breaks the chain\n")

			if myWriter.receivedMessage != nil {
				t.Error("Last link should not receive any message")
			}

			chain.Next("Hello\n")
			if *myWriter.receivedMessage == "" ||
				!strings.Contains(*myWriter.receivedMessage, "Hello") {
				t.Fatal("Last link did not received expected message")
			}
		})
}