HTTPCache: FetcherResponse.url should exist consistently (#105)

Previously, the `url` on the `FetcherResponse` returned from an
HTTPCache would be set properly if this was an actual fetch, but set to
'' if it were read from the cache.

This issue was introduced in
apollographql/apollo-server#1362 (as part of the
initial creation of RESTDataSource) as part of allowing for custom cache
keys.

Fixes #35.

.changeset/flat-roses-draw.md

@@ -0,0 +1,5 @@
+---
+'@apollo/datasource-rest': patch
+---
+
+The fetch Response now consistently has a non-empty `url` property; previously, `url` was an empty string if the response was read from the HTTP cache.

src/HTTPCache.ts

@@ -67,7 +67,10 @@ export class HTTPCache {
     const { policy: policyRaw, ttlOverride, body } = JSON.parse(entry);
 
     const policy = CachePolicy.fromObject(policyRaw);
-    // Remove url from the policy, because otherwise it would never match a request with a custom cache key
+    // Remove url from the policy, because otherwise it would never match a
+    // request with a custom cache key (ie, we want users to be able to tell us
+    // that two requests should be treated as the same even if the URL differs).
+    const urlFromPolicy = policy._url;
     policy._url = undefined;
 
     if (
@@ -79,7 +82,7 @@ export class HTTPCache {
     ) {
       const headers = policy.responseHeaders();
       return new Response(body, {
-        url: policy._url,
+        url: urlFromPolicy,
         status: policy._status,
         headers,
       });

src/__tests__/HTTPCache.test.ts

@@ -66,12 +66,14 @@ describe('HTTPCache', () => {
   it('returns a cached response when not expired', async () => {
     mockGetAdaLovelace({ 'cache-control': 'max-age=30' });
 
-    await httpCache.fetch(adaUrl);
+    const firstResponse = await httpCache.fetch(adaUrl);
+    expect(firstResponse.url).toBe(adaUrl.toString());
 
     jest.advanceTimersByTime(10000);
 
     const response = await httpCache.fetch(adaUrl);
 
+    expect(response.url).toBe(adaUrl.toString());
     expect(await response.json()).toEqual({ name: 'Ada Lovelace' });
     expect(response.headers.get('age')).toEqual('10');
   });