handle RateLimiter initialization errors (#8199)

Previously, an error occuring in NewRateLimiter would return a nil
reference – which would be de-referenced just after, making the server
crash.

app/ratelimit_test.go

@@ -25,6 +25,21 @@ func genRateLimitSettings(useAuth, useIP bool, header string) *model.RateLimitSe
 	}
 }
 
+func TestNewRateLimiterSuccess(t *testing.T) {
+	settings := genRateLimitSettings(false, false, "")
+	rateLimiter, err := NewRateLimiter(settings)
+	require.NotNil(t, rateLimiter)
+	require.NoError(t, err)
+}
+
+func TestNewRateLimiterFailure(t *testing.T) {
+	invalidSettings := genRateLimitSettings(false, false, "")
+	invalidSettings.MaxBurst = model.NewInt(-100)
+	rateLimiter, err := NewRateLimiter(invalidSettings)
+	require.Nil(t, rateLimiter)
+	require.Error(t, err)
+}
+
 func TestGenerateKey(t *testing.T) {
 	cases := []struct {
 		useAuth         bool
@@ -58,7 +73,7 @@ func TestGenerateKey(t *testing.T) {
 			req.Header.Set(tc.header, tc.headerResult)
 		}
 
-		rateLimiter := NewRateLimiter(genRateLimitSettings(tc.useAuth, tc.useIP, tc.header))
+		rateLimiter, _ := NewRateLimiter(genRateLimitSettings(tc.useAuth, tc.useIP, tc.header))
 
 		key := rateLimiter.GenerateKey(req)