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Golang / GoLang Production Patterns and Web Standards Interview Questions

What is the standard Go HTTP middleware signature and how do you chain multiple middleware?

Go middleware follows a consistent adapter pattern: a function that accepts an http.Handler and returns a new http.Handler that wraps it. The signature func(http.Handler) http.Handler is the community standard — used by virtually every Go HTTP library.

// The standard middleware type
type Middleware func(http.Handler) http.Handler

// Logging middleware
func loggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        start := time.Now()
        // Wrap ResponseWriter to capture status code
        lrw := &loggingResponseWriter{ResponseWriter: w, statusCode: http.StatusOK}
        next.ServeHTTP(lrw, r)  // call the next handler in the chain
        log.Printf("%s %s %d %v",
            r.Method, r.URL.Path, lrw.statusCode, time.Since(start))
    })
}

type loggingResponseWriter struct {
    http.ResponseWriter
    statusCode int
}
func (lrw *loggingResponseWriter) WriteHeader(code int) {
    lrw.statusCode = code
    lrw.ResponseWriter.WriteHeader(code)
}

// Auth middleware
func authMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := r.Header.Get("Authorization")
        if token == "" {
            http.Error(w, "unauthorized", http.StatusUnauthorized)
            return // short-circuit — next.ServeHTTP never called
        }
        next.ServeHTTP(w, r)
    })
}

// Recovery middleware — catch panics in handlers
func recoveryMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        defer func() {
            if rec := recover(); rec != nil {
                log.Printf("panic recovered: %v\n%s", rec, debug.Stack())
                http.Error(w, "internal server error", http.StatusInternalServerError)
            }
        }()
        next.ServeHTTP(w, r)
    })
}

// Chaining middleware — applied right-to-left (outermost runs first)
handler := recoveryMiddleware(loggingMiddleware(authMiddleware(mux)))
// Request order: recovery → logging → auth → mux → handler

// Cleaner chain helper
func Chain(h http.Handler, middlewares ...Middleware) http.Handler {
    for i := len(middlewares) - 1; i >= 0; i-- {
        h = middlewares[i](h)
    }
    return h
}
handler = Chain(mux, recoveryMiddleware, loggingMiddleware, authMiddleware)

What is the standard signature for a Go HTTP middleware function?
In the middleware chain 'recoveryMiddleware(loggingMiddleware(authMiddleware(mux)))', which middleware executes first?

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