Feature Description

Idempotency is a guarantee that enables the client to have safe retries if no response (or a 500 response) is received from the server, by using an "idempotency key" that is supplied by client to denote the initial request and its retry requests as a singular set of intention (instead of multiple intentions).

Production examples of idempotency:

• Stripe: Idempotency on all mutable requests
• Square
• Shopify

Additional Context (optional)

When the middleware received a request...

• ...without an idempotency key
  • It will just call the Next() handler and that's all.
• ...with an idempotency key, but such key does not exist/already expired
  • Lock the idempotency mutex lock with idempotency key as the key. The lock is typically a distributed redis lock. We should just provide an interface for outer libraries/users to implement.
    • After acquired lock, check the existence of idempotency key again in storage.
  • The middleware will call Next() handler, and
    • If returned non-nil error, return the error and skip idempotency saving.
  • Save the response status, body, and all headers specified in PersistResponseHeaders
  • Unlock the idempotency mutex lock with idempotency key as the key.
• ...with an idempotency key, and such key exists/not expired
  • Return the saved response (status, body, and all headers saved) for such key.

Code Snippet (optional)

package main

import (
	"log"
	"time"

	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/idempotency"
)

func main() {
	app := fiber.New()

	app.Use(idempotency.New(idempotency.Config{
		// LifeTime is the backtrack time window of the presence of an idempotency key. Default is 24h.
		LifeTime: time.Hour * 24,

		// KeyHeader is the header for looking up the idempotency key from. Default is "X-Idempotency-Key".
		KeyHeader: "X-Idempotency-Key",

		// Storage is the storage of idempotency responses. Default is a in-memory fiber.Storage.
		Storage: fiberstore.NewRedis(), // this is to just illustrate a storage that implements fiber.Storage

		// PersistResponseHeaders is a set of headers to persist. Default is nil.
		PersistResponseHeaders: []string{
			fiber.HeaderContentType,
			fiber.HeaderContentLength,
			fiber.HeaderSetCookie,
		},
	}))

	app.Post("/hello", func(ctx *fiber.Ctx) error {
		return ctx.SendString(time.Now().String())
	})

	log.Fatal(app.Listen(":3000"))
}

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my suggestion prior to opening this one.
• I understand that improperly formatted feature requests may be closed without explanation.