Introduction

Middleware is a software pattern that allows you to intercept and modify the processing of messages in a chain. It is a powerful tool for customizing the behavior of a system and adding additional functionality, such as logging, retries, deadlettering, backoffs, and tracing.

In the KP library, every feature is implemented as a middleware. This means that you can add or remove features by adding or removing middlewares from the middleware chain.

Adding Middleware to the KP Library

The KP library provides a way to add middlewares to the middleware chain through the AddMiddleware

This method takes a middleware as an argument and returns a new MessageProcessor with the middleware added to the chain. Here is an example of how to use the AddMiddleware method:

Example

package main

import (
	"context"
	"fmt"
	"time"

	v2 "github.com/honestbank/kp/v2"
	"github.com/honestbank/kp/v2/middlewares/measurement"
	"github.com/honestbank/kp/v2/middlewares/tracing"
	"go.opentelemetry.io/otel"
)

type UserLoggedInEvent struct {
	UserID string
}

func main() {
	retryCount := 10
	kp := v2.New[UserLoggedInEvent]("user-logged-in", getConfig()).
		WithRetryOrPanic("send-login-notification-retries", retryCount).
		WithDeadletterOrPanic("send-login-notification-failures")
	kp.AddMiddleware(measurement.NewMeasurementMiddleware("/path/to/push-gateway", "application-name"))
	tp := otel.GetTracerProvider() // you'll need to set the tracer provider as well
	kp.AddMiddleware(tracing.NewTracingMiddleware(tp))
	err := kp.Process(processUserLoggedInEvent)
	if err != nil {
		panic(err) // do better error handling
	}
}

func processUserLoggedInEvent(ctx context.Context, message UserLoggedInEvent) error {
	// here, you can focus on your business logic.
	fmt.Printf("processing %v\n", message)
	time.Sleep(time.Millisecond * 200) // simulate long running process
	return nil                         // or error
}

func getConfig() any {
	return nil // return your config
}

Notes

Middlewares are executed in the order they are added to the chain. It is important to consider the order in which middlewares are added.
The KP library provides several built-in middlewares for common features, such as consuming messages, retries, deadletters, backoffs, and tracing. You can also write custom middlewares to meet your specific

Adding Middleware to the KP Library​

Example​

Notes​

Adding Middleware to the KP Library

Example

Notes