rename rate/ to Foxnouns.RateLimiter/ for consistency

Foxnouns.RateLimiter/rate_limiter.go

@@ -0,0 +1,139 @@
+package main
+
+import (
+	"encoding/hex"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/go-chi/httprate"
+)
+
+func userOrIp(r *http.Request, userId *string) (string, error) {
+	if userId != nil {
+		return *userId, nil
+	}
+
+	return httprate.KeyByRealIP(r)
+}
+
+type Limiter struct {
+	bucketRateLimiters map[bucketKey]*httprate.RateLimiter
+	globalRateLimiters map[string]*httprate.RateLimiter
+
+	bucketMu *sync.Mutex
+	globalMu *sync.Mutex
+}
+
+type LimitData struct {
+	Global    bool
+	Bucket    string
+	Remaining int
+	Reset     int
+}
+
+type bucketKey struct {
+	user, bucket string
+}
+
+func NewLimiter() *Limiter {
+	return &Limiter{
+		bucketRateLimiters: make(map[bucketKey]*httprate.RateLimiter),
+		globalRateLimiters: make(map[string]*httprate.RateLimiter),
+
+		bucketMu: new(sync.Mutex),
+		globalMu: new(sync.Mutex),
+	}
+}
+
+// TryLimit handles rate limiting for a request.
+// If this function returns true, a rate limit was hit, and the request should be aborted with a 429 status.
+func (l *Limiter) TryLimit(w http.ResponseWriter, r *http.Request, userID *string, template string) (bool, error) {
+	user, err := userOrIp(r, userID)
+	if err != nil {
+		return false, fmt.Errorf("getting user or IP: %w", err)
+	}
+
+	// Check the globalLimiter rate limit for this user
+	globalLimiter := l.globalLimiter(user)
+	if globalLimiter.OnLimit(w, r, "") {
+		w.Header().Add("X-RateLimit-Global", "true")
+		return true, nil
+	}
+
+	bucket := requestBucket(r.Method, template)
+	w.Header().Add("X-RateLimit-Bucket", bucket)
+
+	bucketLimiter := l.bucketLimiter(user, r.Method, bucket)
+	if bucketLimiter.OnLimit(w, r, "") {
+		return true, nil
+	}
+
+	return false, nil
+}
+
+func getReset(w http.ResponseWriter) int64 {
+	header := w.Header().Get("X-RateLimit-Reset")
+	if header == "" {
+		return 0
+	}
+
+	i, err := strconv.ParseInt(header, 10, 64)
+	if err != nil {
+		return 0
+	}
+
+	return i
+}
+
+func requestBucket(method, template string) string {
+	return hex.EncodeToString([]byte(method + "-" + template))
+}
+
+func (l *Limiter) globalLimiter(user string) *httprate.RateLimiter {
+	l.globalMu.Lock()
+	defer l.globalMu.Unlock()
+
+	limiter, ok := l.globalRateLimiters[user]
+	if ok {
+		return limiter
+	}
+
+	limiter = httprate.NewRateLimiter(20, time.Second)
+	l.globalRateLimiters[user] = limiter
+	return limiter
+}
+
+func (l *Limiter) bucketLimiter(user, method, bucket string) *httprate.RateLimiter {
+	l.bucketMu.Lock()
+	defer l.bucketMu.Unlock()
+
+	limiter, ok := l.bucketRateLimiters[bucketKey{user, bucket}]
+	if ok {
+		return limiter
+	}
+
+	requestLimit, windowLength := requestLimitFor(method)
+
+	limiter = httprate.NewRateLimiter(requestLimit, windowLength)
+	l.bucketRateLimiters[bucketKey{user, bucket}] = limiter
+	return limiter
+}
+
+// returns the request limit and window length for the given method.
+// methods that change state have lower rate limits
+func requestLimitFor(method string) (int, time.Duration) {
+	switch strings.ToUpper(method) {
+	case "PATCH", "POST":
+		return 3, time.Second
+	case "DELETE":
+		return 2, 5 * time.Second
+	case "GET":
+		return 10, time.Second
+	default:
+		return 5, time.Second
+	}
+}