Merge pull request #7676 from lunarway/feature/github-ratelimit

Detect GitHub rate limits in GithubUrlReader

.changeset/mean-glasses-play.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+Add "rate limit exceeded" to error from GithubUrlReader if that is the cause of a read failure

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

@@ -221,6 +221,32 @@ describe('GithubUrlReader', () => {
       ).rejects.toThrow(NotModifiedError);
     });
 
+    it('should throw Error with ratelimit exceeded if GitHub responds with 403 and rate limit is exceeded', async () => {
+      expect.assertions(1);
+
+      worker.use(
+        rest.get(
+          'https://ghe.github.com/api/v3/repos/backstage/mock/tree/contents/',
+          (_req, res, ctx) => {
+            return res(
+              ctx.status(403),
+              ctx.set('X-RateLimit-Remaining', '0'),
+              ctx.body(
+                '{"message": "API rate limit exceeded for xxx.xxx.xxx.xxx..."}',
+              ),
+            );
+          },
+        ),
+      );
+
+      await expect(
+        gheProcessor.readUrl(
+          'https://github.com/backstage/mock/tree/blob/main',
+          { etag: 'foo' },
+        ),
+      ).rejects.toThrow(/rate limit exceeded/);
+    });
+
     it('should return etag from the response', async () => {
       (mockCredentialsProvider.getCredentials as jest.Mock).mockResolvedValue({
         headers: {

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

@@ -126,10 +126,21 @@ export class GithubUrlReader implements UrlReader {
       };
     }
 
-    const message = `${url} could not be read as ${ghUrl}, ${response.status} ${response.statusText}`;
+    let message = `${url} could not be read as ${ghUrl}, ${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 (
+      response.status === 403 &&
+      response.headers.get('X-RateLimit-Remaining') === '0'
+    ) {
+      message += ' (rate limit exceeded)';
+    }
+
     throw new Error(message);
   }