Idempotency

The Idempotency middleware helps build fault-tolerant APIs. Duplicate requests—such as retries after network issues—won't trigger the same action twice on the server.

Refer to IETF RFC 7231 §4.2.2 for definitions of safe and idempotent HTTP methods.

HTTP Method Categories

• Safe Methods (do not modify server state): GET, HEAD, OPTIONS, TRACE
• Idempotent Methods (identical requests have the same effect as a single one): all safe methods plus PUT and DELETE

According to the RFC, safe methods never change server state, while idempotent methods may change state but remain safe to repeat.

Signatures

func New(config ...Config) fiber.Handler
func IsFromCache(c fiber.Ctx) bool
func WasPutToCache(c fiber.Ctx) bool

Examples

Import the middleware package:

import (
    "github.com/gofiber/fiber/v3"
    "github.com/gofiber/fiber/v3/middleware/idempotency"
)

Once your Fiber app is initialized, configure the middleware:

Default Config (Skip Safe Methods)

By default, the Next function skips middleware for safe methods only:

app.Use(idempotency.New())

Skip Idempotent Methods Instead

Skip all idempotent methods (including PUT and DELETE) by overriding Next:

app.Use(idempotency.New(idempotency.Config{
    Next: func(c fiber.Ctx) bool {
        // Skip middleware for idempotent methods (safe + PUT, DELETE)
        return fiber.IsMethodIdempotent(c.Method())
    },
}))

Custom Config

app.Use(idempotency.New(idempotency.Config{
    Lifetime: 42 * time.Minute,
    // ...
}))

Config

Property	Type	Description	Default
Next	func(fiber.Ctx) bool	Function to skip this middleware when it returns true; use IsMethodSafe or IsMethodIdempotent.	func(c fiber.Ctx) bool { return fiber.IsMethodSafe(c.Method()) }
Lifetime	time.Duration	Maximum lifetime of an idempotency key.	30 * time.Minute
KeyHeader	string	Header name containing the idempotency key.	"X-Idempotency-Key"
KeyHeaderValidate	func(string) error	Function to validate idempotency header syntax (e.g., UUID).	UUID length check (36 characters)
KeepResponseHeaders	[]string	List of headers to preserve from original response.	nil (keep all headers)
Lock	Locker	Locks an idempotency key to prevent race conditions.	In-memory locker
Storage	fiber.Storage	Stores response data by idempotency key.	In-memory storage

Default Config Values

var ConfigDefault = Config{
    Next: func(c fiber.Ctx) bool {
        // Skip middleware for safe methods per RFC 7231 §4.2.2
        return fiber.IsMethodSafe(c.Method())
    },

    Lifetime: 30 * time.Minute,

    KeyHeader: "X-Idempotency-Key",
    KeyHeaderValidate: func(k string) error {
        if l, wl := len(k), 36; l != wl { // UUID length is 36 chars
            return fmt.Errorf("%w: invalid length: %d != %d", ErrInvalidIdempotencyKey, l, wl)
        }

        return nil
    },

    KeepResponseHeaders: nil,

    Lock: nil, // Set in configDefault so we don't allocate data here.

    Storage: nil, // Set in configDefault so we don't allocate data here.
}