Export RateLimiter type (#43)

So users pass *http.RateLimiter (or save in their server struct) and use
the new .OnLimit() feature from #42.

httprate.go

@@ -12,7 +12,7 @@ func Limit(requestLimit int, windowLength time.Duration, options ...Option) func
 }
 
 type KeyFunc func(r *http.Request) (string, error)
-type Option func(rl *rateLimiter)
+type Option func(rl *RateLimiter)
 
 // Set custom response headers. If empty, the header is omitted.
 type ResponseHeaders struct {
@@ -72,7 +72,7 @@ func KeyByEndpoint(r *http.Request) (string, error) {
 }
 
 func WithKeyFuncs(keyFuncs ...KeyFunc) Option {
-	return func(rl *rateLimiter) {
+	return func(rl *RateLimiter) {
 		if len(keyFuncs) > 0 {
 			rl.keyFn = composedKeyFunc(keyFuncs...)
 		}
@@ -88,31 +88,31 @@ func WithKeyByRealIP() Option {
 }
 
 func WithLimitHandler(h http.HandlerFunc) Option {
-	return func(rl *rateLimiter) {
+	return func(rl *RateLimiter) {
 		rl.onRateLimited = h
 	}
 }
 
 func WithErrorHandler(h func(http.ResponseWriter, *http.Request, error)) Option {
-	return func(rl *rateLimiter) {
+	return func(rl *RateLimiter) {
 		rl.onError = h
 	}
 }
 
 func WithLimitCounter(c LimitCounter) Option {
-	return func(rl *rateLimiter) {
+	return func(rl *RateLimiter) {
 		rl.limitCounter = c
 	}
 }
 
 func WithResponseHeaders(headers ResponseHeaders) Option {
-	return func(rl *rateLimiter) {
+	return func(rl *RateLimiter) {
 		rl.headers = headers
 	}
 }
 
 func WithNoop() Option {
-	return func(rl *rateLimiter) {}
+	return func(rl *RateLimiter) {}
 }
 
 func composedKeyFunc(keyFuncs ...KeyFunc) KeyFunc {

limiter.go

@@ -15,8 +15,8 @@ type LimitCounter interface {
 	Get(key string, currentWindow, previousWindow time.Time) (int, int, error)
 }
 
-func NewRateLimiter(requestLimit int, windowLength time.Duration, options ...Option) *rateLimiter {
-	rl := &rateLimiter{
+func NewRateLimiter(requestLimit int, windowLength time.Duration, options ...Option) *RateLimiter {
+	rl := &RateLimiter{
 		requestLimit: requestLimit,
 		windowLength: windowLength,
 		headers: ResponseHeaders{
@@ -55,7 +55,7 @@ func NewRateLimiter(requestLimit int, windowLength time.Duration, options ...Opt
 	return rl
 }
 
-type rateLimiter struct {
+type RateLimiter struct {
 	requestLimit  int
 	windowLength  time.Duration
 	keyFn         KeyFunc
@@ -70,7 +70,7 @@ type rateLimiter struct {
 // and automatically sends HTTP response. The caller should halt further request processing.
 // If the limit is not reached, it increments the request count and returns false, allowing
 // the request to proceed.
-func (l *rateLimiter) OnLimit(w http.ResponseWriter, r *http.Request, key string) bool {
+func (l *RateLimiter) OnLimit(w http.ResponseWriter, r *http.Request, key string) bool {
 	currentWindow := time.Now().UTC().Truncate(l.windowLength)
 	ctx := r.Context()
 
@@ -116,15 +116,15 @@ func (l *rateLimiter) OnLimit(w http.ResponseWriter, r *http.Request, key string
 	return false
 }
 
-func (l *rateLimiter) Counter() LimitCounter {
+func (l *RateLimiter) Counter() LimitCounter {
 	return l.limitCounter
 }
 
-func (l *rateLimiter) Status(key string) (bool, float64, error) {
+func (l *RateLimiter) Status(key string) (bool, float64, error) {
 	return l.calculateRate(key, l.requestLimit)
 }
 
-func (l *rateLimiter) Handler(next http.Handler) http.Handler {
+func (l *RateLimiter) Handler(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		key, err := l.keyFn(r)
 		if err != nil {
@@ -140,7 +140,7 @@ func (l *rateLimiter) Handler(next http.Handler) http.Handler {
 	})
 }
 
-func (l *rateLimiter) calculateRate(key string, requestLimit int) (bool, float64, error) {
+func (l *RateLimiter) calculateRate(key string, requestLimit int) (bool, float64, error) {
 	now := time.Now().UTC()
 	currentWindow := now.Truncate(l.windowLength)
 	previousWindow := currentWindow.Add(-l.windowLength)