add rate limiting, CSRF, newsletter, auto-checker, /uses and /projects pages

internal/ratelimit/ratelimit.go

@@ -0,0 +1,91 @@
+// Package ratelimit provides a simple in-memory per-IP sliding-window rate limiter.
+package ratelimit
+
+import (
+	"net"
+	"net/http"
+	"sync"
+	"time"
+)
+
+// Limiter tracks request counts per IP within a sliding window.
+type Limiter struct {
+	mu      sync.Mutex
+	entries map[string][]time.Time
+	window  time.Duration
+	max     int
+}
+
+// New creates a Limiter that allows at most max requests per window per IP.
+func New(window time.Duration, max int) *Limiter {
+	l := &Limiter{
+		entries: make(map[string][]time.Time),
+		window:  window,
+		max:     max,
+	}
+	go l.cleanup()
+	return l
+}
+
+// Allow returns true if the IP is within its rate limit, recording the attempt.
+func (l *Limiter) Allow(ip string) bool {
+	now := time.Now()
+	cutoff := now.Add(-l.window)
+
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	times := l.entries[ip]
+	recent := times[:0]
+	for _, t := range times {
+		if t.After(cutoff) {
+			recent = append(recent, t)
+		}
+	}
+
+	if len(recent) >= l.max {
+		l.entries[ip] = recent
+		return false
+	}
+
+	l.entries[ip] = append(recent, now)
+	return true
+}
+
+// Middleware wraps a handler, rejecting over-limit requests with 429.
+func (l *Limiter) Middleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ip, _, err := net.SplitHostPort(r.RemoteAddr)
+		if err != nil {
+			ip = r.RemoteAddr
+		}
+		if !l.Allow(ip) {
+			http.Error(w, "Too many requests. Please wait and try again.", http.StatusTooManyRequests)
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}
+
+// cleanup periodically removes expired entries to prevent unbounded growth.
+func (l *Limiter) cleanup() {
+	for {
+		time.Sleep(5 * time.Minute)
+		cutoff := time.Now().Add(-l.window)
+		l.mu.Lock()
+		for ip, times := range l.entries {
+			recent := times[:0]
+			for _, t := range times {
+				if t.After(cutoff) {
+					recent = append(recent, t)
+				}
+			}
+			if len(recent) == 0 {
+				delete(l.entries, ip)
+			} else {
+				l.entries[ip] = recent
+			}
+		}
+		l.mu.Unlock()
+	}
+}