🚀 feat: Add Load-Shedding Middleware

docs/whats_new.md

@@ -31,6 +31,7 @@ Here's a quick overview of the changes in Fiber `v3`:
   - [Filesystem](#filesystem)
   - [Monitor](#monitor)
   - [Healthcheck](#healthcheck)
+  - [Load shedding](#loadshedding)
 - [📋 Migration guide](#-migration-guide)
 
 ## Drop for old Go versions
@@ -810,6 +811,15 @@ The Healthcheck middleware has been enhanced to support more than two routes, wi
 
 Refer to the [healthcheck middleware migration guide](./middleware/healthcheck.md) or the [general migration guide](#-migration-guide) to review the changes.
 
+### Load shedding
+We've added **Load Shedding Middleware**.It ensures system stability under high load by enforcing timeouts on request processing. This mechanism allows the application to shed excessive load gracefully and maintain responsiveness.
+
+**Functionality**
+- **Timeout Enforcement**: Automatically terminates requests exceeding a specified processing time.
+- **Custom Response**: Uses a configurable load-shedding handler to define the response for shed requests.
+- **Request Exclusion**: Allows certain requests to bypass load-shedding logic through an exclusion filter.
+
+This middleware is designed to enhance server resilience and improve the user experience during periods of high traffic.
 ## 📋 Migration guide
 
 - [🚀 App](#-app-1)
@@ -1361,6 +1371,34 @@ app.Get(healthcheck.DefaultStartupEndpoint, healthcheck.NewHealthChecker(healthc
 app.Get("/live", healthcheck.NewHealthChecker())
 ```
 
+#### Load shedding
+This middleware uses `context.WithTimeout` to manage the lifecycle of requests. If a request exceeds the specified timeout, the custom load-shedding handler is triggered, ensuring the system remains stable under stress.
+
+**Key Parameters**
+
+`timeout` (`time.Duration`): The maximum time a request is allowed to process. Requests exceeding this time are terminated.
+
+`loadSheddingHandler` (`fiber.Handler`): A custom handler that executes when a request exceeds the timeout. Typically used to return a `503 Service Unavailable` response or a custom message.
+
+`exclude` (`func(fiber.Ctx) bool`): A filter function to exclude specific requests from being subjected to the load-shedding logic (optional).
+
+**Usage Example**
+
+```go
+import "github.com/gofiber/fiber/v3/middleware/loadshedding
+
+app.Use(loadshedding.New(
+    10*time.Second, // Timeout duration
+    func(c fiber.Ctx) error { // Load shedding response
+        return c.Status(fiber.StatusServiceUnavailable).
+            SendString("Service overloaded, try again later.")
+    },
+    func(c fiber.Ctx) bool { // Exclude health checks
+        return c.Path() == "/health"
+    },
+))
+```
+
 #### Monitor
 
 Since v3 the Monitor middleware has been moved to the [Contrib package](https://github.com/gofiber/contrib/tree/main/monitor)

middleware/loadshedding/loadshedding.go

@@ -0,0 +1,45 @@
+package loadshedding
+
+import (
+	"context"
+	"time"
+
+	"github.com/gofiber/fiber/v3"
+)
+
+// New creates a middleware handler enforces a timeout on request processing to manage server load.
+// If a request exceeds the specified timeout, a custom load-shedding handler is executed.
+func New(timeout time.Duration, loadSheddingHandler fiber.Handler, exclude func(fiber.Ctx) bool) fiber.Handler {
+	return func(c fiber.Ctx) error {
+		// Skip load-shedding logic for requests matching the exclusion criteria
+		if exclude != nil && exclude(c) {
+			return c.Next()
+		}
+
+		// Create a context with a timeout for the current request
+		ctx, cancel := context.WithTimeout(c.Context(), timeout)
+		defer cancel()
+
+		// Set the new context with a timeout
+		c.SetContext(ctx)
+
+		// Process the request and capture any error
+		err := c.Next()
+
+		// Create a channel to signal when request processing completes
+		done := make(chan error, 1)
+
+		// Send the result of the request processing to the channel
+		go func() {
+			done <- err
+		}()
+
+		// Handle either request completion or timeout
+		select {
+		case <-ctx.Done(): // Triggered if the timeout expires
+			return loadSheddingHandler(c)
+		case err := <-done: // Triggered if request processing completes
+			return err
+		}
+	}
+}

middleware/loadshedding/loadshedding_test.go

@@ -0,0 +1,92 @@
+package loadshedding_test
+
+import (
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/gofiber/fiber/v3"
+	"github.com/gofiber/fiber/v3/middleware/loadshedding"
+	"github.com/stretchr/testify/require"
+)
+
+// Helper handlers
+func successHandler(c fiber.Ctx) error {
+	return c.SendString("Request processed successfully!")
+}
+
+func timeoutHandler(c fiber.Ctx) error {
+	time.Sleep(2 * time.Second) // Simulate a long-running request
+	return c.SendString("This should not appear")
+}
+
+func loadSheddingHandler(c fiber.Ctx) error {
+	return c.Status(fiber.StatusServiceUnavailable).SendString("Service Overloaded")
+}
+
+func excludedHandler(c fiber.Ctx) error {
+	return c.SendString("Excluded route")
+}
+
+// go test -run Test_LoadSheddingExcluded
+func Test_LoadSheddingExcluded(t *testing.T) {
+	t.Parallel()
+	app := fiber.New()
+
+	// Middleware with exclusion
+	app.Use(loadshedding.New(
+		1*time.Second,
+		loadSheddingHandler,
+		func(c fiber.Ctx) bool { return c.Path() == "/excluded" },
+	))
+	app.Get("/", successHandler)
+	app.Get("/excluded", excludedHandler)
+
+	// Test excluded route
+	resp, err := app.Test(httptest.NewRequest(fiber.MethodGet, "/excluded", nil))
+	require.NoError(t, err)
+	require.Equal(t, fiber.StatusOK, resp.StatusCode)
+}
+
+// go test -run Test_LoadSheddingTimeout
+func Test_LoadSheddingTimeout(t *testing.T) {
+	t.Parallel()
+	app := fiber.New()
+
+	// Middleware with a 1-second timeout
+	app.Use(loadshedding.New(
+		1*time.Second, // Middleware timeout
+		loadSheddingHandler,
+		nil,
+	))
+	app.Get("/", timeoutHandler)
+
+	// Create a custom request
+	req := httptest.NewRequest(fiber.MethodGet, "/", nil)
+
+	// Test timeout behavior
+	resp, err := app.Test(req, fiber.TestConfig{
+		Timeout: 3 * time.Second, // Ensure the test timeout exceeds middleware timeout
+	})
+	require.NoError(t, err)
+	require.Equal(t, fiber.StatusServiceUnavailable, resp.StatusCode)
+}
+
+// go test -run Test_LoadSheddingSuccessfulRequest
+func Test_LoadSheddingSuccessfulRequest(t *testing.T) {
+	t.Parallel()
+	app := fiber.New()
+
+	// Middleware with sufficient time for request to complete
+	app.Use(loadshedding.New(
+		2*time.Second,
+		loadSheddingHandler,
+		nil,
+	))
+	app.Get("/", successHandler)
+
+	// Test successful request
+	resp, err := app.Test(httptest.NewRequest(fiber.MethodGet, "/", nil))
+	require.NoError(t, err)
+	require.Equal(t, fiber.StatusOK, resp.StatusCode)
+}