From 4ad2ad29f2d1592e738a2826f199ac66363616e3 Mon Sep 17 00:00:00 2001
From: Jakub Zych <jakub@keios.eu>
Date: Mon, 21 Sep 2026 19:42:41 +0200
Subject: [PATCH] fix(06-12): fail closed on invalid limiter definitions

---
 surf/limiter.go      | 30 ++++++++++++++++++++++++------
 surf/limiter_test.go | 14 ++++++++++++++
 2 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/surf/limiter.go b/surf/limiter.go
index 8369686..94ed9a5 100644
--- a/surf/limiter.go
+++ b/surf/limiter.go
@@ -2,6 +2,7 @@ package surf
 
 import (
 	"fmt"
+	"math"
 	"net/http"
 	"net/netip"
 	"strconv"
@@ -68,6 +69,16 @@ func (l *FixedWindowLimiter) RegisterBucket(pluginID, name string, b Bucket) err
 	if name == "" {
 		return fmt.Errorf("surf: plugin %q registered empty bucket", pluginID)
 	}
+	switch {
+	case l.store == nil:
+		return fmt.Errorf("surf: plugin %q bucket %q: limiter has no store", pluginID, name)
+	case b.Key == nil:
+		return fmt.Errorf("surf: plugin %q bucket %q has nil Key", pluginID, name)
+	case b.Max < 1:
+		return fmt.Errorf("surf: plugin %q bucket %q has Max < 1", pluginID, name)
+	case b.Decay <= 0:
+		return fmt.Errorf("surf: plugin %q bucket %q has non-positive Decay", pluginID, name)
+	}
 	l.mu.Lock()
 	defer l.mu.Unlock()
 	if existing, ok := l.owners[name]; ok {
@@ -82,16 +93,20 @@ func (l *FixedWindowLimiter) RegisterBucket(pluginID, name string, b Bucket) err
 // Middleware builds the throttle: factory body. param is either a
 // registered bucket name or a literal "N,M" pair (inline throttle).
 func (l *FixedWindowLimiter) Middleware(param string) pact.Middleware {
+	failClosed := func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusInternalServerError)
+		})
+	}
 	if l == nil {
-		return func(next http.Handler) http.Handler { return next }
+		return failClosed
 	}
 	b, err := l.resolve(param)
+	if err != nil || b.Key == nil || l.store == nil {
+		return failClosed
+	}
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if err != nil || b.Key == nil || l.store == nil {
-				next.ServeHTTP(w, r)
-				return
-			}
 			key := b.Key(r)
 			allowed, attempts, retryAfter := l.store.Attempt(key, b.Max, b.Decay)
 			if !allowed {
@@ -123,6 +138,9 @@ func (l *FixedWindowLimiter) ValidateThrottle(param string) error {
 	if l == nil {
 		return fmt.Errorf("surf: limiter is nil")
 	}
+	if l.store == nil {
+		return fmt.Errorf("surf: limiter has no store")
+	}
 	_, err := l.resolve(param)
 	return err
 }
@@ -142,7 +160,7 @@ func (l *FixedWindowLimiter) resolve(param string) (Bucket, error) {
 	}
 	n, errN := strconv.Atoi(strings.TrimSpace(nStr))
 	m, errM := strconv.Atoi(strings.TrimSpace(mStr))
-	if errN != nil || errM != nil || n < 1 || m < 1 {
+	if errN != nil || errM != nil || n < 1 || m < 1 || int64(m) > math.MaxInt64/int64(time.Minute) {
 		return Bucket{}, fmt.Errorf("surf: malformed throttle %q", param)
 	}
 	trusted := l.trusted
diff --git a/surf/limiter_test.go b/surf/limiter_test.go
index 02961ad..7990855 100644
--- a/surf/limiter_test.go
+++ b/surf/limiter_test.go
@@ -389,3 +389,17 @@ func stackThrottle(lim *FixedWindowLimiter, next http.Handler, names ...string)
 }
 
 var _ pact.Router = (*Router)(nil)
+
+func TestRegisterBucketRejectsInvalidDefinitions(t *testing.T) {
+	l := NewFixedWindowLimiter(NewMemoryStore(time.Minute), nil)
+	key := func(*http.Request) string { return "k" }
+	if err := l.RegisterBucket("p", "n", Bucket{Max: 1, Decay: 0, Key: key}); err == nil {
+		t.Fatal("zero decay accepted")
+	}
+	if err := l.RegisterBucket("p", "n", Bucket{Max: 1, Decay: time.Minute}); err == nil {
+		t.Fatal("nil key accepted")
+	}
+	if err := l.ValidateThrottle("1,9223372036854775807"); err == nil {
+		t.Fatal("overflowing minutes accepted")
+	}
+}