fix(Github): use x-ratelimit-remaining and 429 status code for rate limit detection

Signed-off-by: secustor <sebastian@poxhofer.at>

.changeset/sweet-ravens-glow.md

@@ -0,0 +1,6 @@
+---
+'@backstage/integration': minor
+'@backstage/backend-common': patch
+---
+
+Fix rate limit detection by looking for HTTP status code 429 and updating the header `x-ratelimit-remaining` to look for in case of a 403 code is returned

packages/backend-common/src/reading/GithubUrlReader.ts

@@ -149,10 +149,7 @@ export class GithubUrlReader implements UrlReader {
     // GitHub returns a 403 response with a couple of headers indicating rate
     // limit status. See more in the GitHub docs:
     // https://docs.github.com/en/rest/overview/resources-in-the-rest-api#rate-limiting
-    if (
-      response.status === 403 &&
-      response.headers.get('X-RateLimit-Remaining') === '0'
-    ) {
+    if (this.integration.isRateLimited(response)) {
       message += ' (rate limit exceeded)';
     }
 
@@ -350,10 +347,18 @@ export class GithubUrlReader implements UrlReader {
     const response = await fetch(urlAsString, init);
 
     if (!response.ok) {
-      const message = `Request failed for ${urlAsString}, ${response.status} ${response.statusText}`;
+      let message = `Request failed for ${urlAsString}, ${response.status} ${response.statusText}`;
       if (response.status === 404) {
         throw new NotFoundError(message);
       }
+
+      // GitHub returns a 403 response with a couple of headers indicating rate
+      // limit status. See more in the GitHub docs:
+      // https://docs.github.com/en/rest/overview/resources-in-the-rest-api#rate-limiting
+      if (this.integration.isRateLimited(response)) {
+        message += ' (rate limit exceeded)';
+      }
+
       throw new Error(message);
     }
 

packages/integration/src/github/GithubIntegration.test.ts

@@ -78,6 +78,31 @@ describe('GithubIntegration', () => {
       ),
     ).toBe('https://github.com/backstage/backstage/edit/master/README.md');
   });
+
+  describe('isRateLimited', () => {
+    const integration = new GithubIntegration({ host: 'h.com' });
+
+    it.each`
+      status | ratelimitRemaining | expected
+      ${404} | ${100}             | ${false}
+      ${429} | ${undefined}       | ${true}
+      ${429} | ${100}             | ${true}
+      ${403} | ${100}             | ${false}
+      ${403} | ${0}               | ${true}
+    `(
+      '(statusCode: $status, header: $ratelimitRemaining) === $expected',
+      ({ status, ratelimitRemaining, expected }) => {
+        const headers = new Headers({
+          'x-ratelimit-remaining': ratelimitRemaining,
+        });
+        const result = integration.isRateLimited({
+          status,
+          headers,
+        } as Response);
+        expect(expected).toBe(result);
+      },
+    );
+  });
 });
 
 describe('replaceGithubUrlType', () => {

packages/integration/src/github/GithubIntegration.ts

@@ -65,6 +65,14 @@ export class GithubIntegration implements ScmIntegration {
   resolveEditUrl(url: string): string {
     return replaceGithubUrlType(url, 'edit');
   }
+
+  isRateLimited(response: Response): boolean {
+    return (
+      response.status === 429 ||
+      (response.status === 403 &&
+        response.headers.get('x-ratelimit-remaining') === '0')
+    );
+  }
 }
 
 /**