Middleware

Middleware provides a way to execute code before and after HTTP requests.

Overview

Middleware functions follow the standard Go HTTP middleware pattern:

func(next http.Handler) http.Handler

They can be chained together and applied globally to all routes or to specific route groups.

Middleware Order

The order of middleware matters. Middleware is executed in the order they are added:

1. Global middleware (added via mux.Use()) is executed first
2. Group middleware is executed next
3. Route-specific middleware is executed last
4. Your handler is executed at the end

mux.Use(middleware1, middleware2)           // Global: 1, 2
api := mux.Group("/api", middleware3)       // Group: 1, 2, 3
api.GET("/users", handler, middleware4)     // Route: 1, 2, 3, 4, handler

Middleware added with Use only affects handlers and groups registered after the call; it does not apply to routes or groups defined earlier.

Creating Custom Middleware

You can create your own middleware functions following the standard pattern:

func authMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Check authentication
        token := r.Header.Get("Authorization")
        if token == "" {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        
        // Validate token (implement your logic here)
        if !isValidToken(token) {
            http.Error(w, "Invalid token", http.StatusUnauthorized)
            return
        }
        
        // Call the next handler
        next.ServeHTTP(w, r)
    })
}

func rateLimitMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Implement rate limiting logic
        if isRateLimited(r) {
            http.Error(w, "Rate limit exceeded", http.StatusTooManyRequests)
            return
        }
        
        next.ServeHTTP(w, r)
    })
}