🌱 Improve rate limit handling in roundtripper (#3237)

- Add rate limit testing and handling functionality
- Add tests for successful response and Retry-After header set scenarios

Signed-off-by: naveensrinivasan <172697+naveensrinivasan@users.noreply.github.com>

clients/githubrepo/roundtripper/rate_limit.go

@@ -42,7 +42,7 @@ type rateLimitTransport struct {
 	innerTransport http.RoundTripper
 }
 
-// Roundtrip handles caching and ratelimiting of responses from GitHub.
+// RoundTrip handles caching and rate-limiting of responses from GitHub.
 func (gh *rateLimitTransport) RoundTrip(r *http.Request) (*http.Response, error) {
 	resp, err := gh.innerTransport.RoundTrip(r)
 	if err != nil {

clients/githubrepo/roundtripper/rate_limit_test.go

@@ -0,0 +1,94 @@
+// Copyright 2023 OpenSSF Scorecard Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package roundtripper
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/ossf/scorecard/v4/log"
+)
+
+func TestRoundTrip(t *testing.T) {
+	t.Parallel()
+	var requestCount int
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Customize the response headers and body based on the test scenario
+		switch r.URL.Path {
+		case "/error":
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte("Internal Server Error")) // nolint: errcheck
+		case "/retry":
+			requestCount++
+			if requestCount == 2 {
+				// Second request: Return successful response
+				w.Header().Set("X-RateLimit-Remaining", "10")
+				w.WriteHeader(http.StatusOK)
+				w.Write([]byte("Success")) // nolint: errcheck
+			} else {
+				// First request: Return Retry-After header
+				w.Header().Set("Retry-After", "1")
+				w.WriteHeader(http.StatusTooManyRequests)
+				w.Write([]byte("Rate Limit Exceeded")) // nolint: errcheck
+			}
+		case "/success":
+			w.Header().Set("X-RateLimit-Remaining", "10")
+			w.WriteHeader(http.StatusOK)
+			w.Write([]byte("Success")) // nolint: errcheck
+		}
+	}))
+	t.Cleanup(func() {
+		defer ts.Close()
+	})
+
+	// Create the rateLimitTransport with the test server as the inner transport and a default logger
+	transport := &rateLimitTransport{
+		innerTransport: ts.Client().Transport,
+		logger:         log.NewLogger(log.DefaultLevel),
+	}
+
+	t.Run("Successful response", func(t *testing.T) {
+		req, err := http.NewRequest(http.MethodGet, ts.URL+"/success", nil)
+		if err != nil {
+			t.Fatalf("Failed to create request: %v", err)
+		}
+
+		resp, err := transport.RoundTrip(req)
+		if err != nil {
+			t.Errorf("Unexpected error: %v", err)
+		}
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Expected status code %d, got %d", http.StatusOK, resp.StatusCode)
+		}
+	})
+
+	t.Run("Retry-After header set", func(t *testing.T) {
+		req, err := http.NewRequest(http.MethodGet, ts.URL+"/retry", nil)
+		if err != nil {
+			t.Fatalf("Failed to create request: %v", err)
+		}
+
+		resp, err := transport.RoundTrip(req)
+		if err != nil {
+			t.Errorf("Unexpected error: %v", err)
+		}
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Expected status code %d, got %d", http.StatusOK, resp.StatusCode)
+		}
+		if requestCount != 2 {
+			t.Errorf("Expected 2 requests, got %d", requestCount)
+		}
+	})
+}