Add support for AbortController signal passed via context

src/__tests__/restLink.ts

@@ -4207,4 +4207,76 @@ describe('Playing nice with others', () => {
       authors: { message: 'Your query was bad and you should feel bad!' },
     });
   });
+
+  it('should fulfill fetch when an AbortController signal is passed but never aborted', done => {
+    fetchMock.get('/api/posts', posts);
+    const link = new RestLink({ uri: '/api' });
+
+    const query = gql`
+      query {
+        people @rest(type: "[Post]", path: "/posts") {
+          title
+        }
+      }
+    `;
+
+    const controller = new AbortController();
+    const reqPromise = toPromise<Result>(
+      execute(link, {
+        operationName: 'abortQuery',
+        query,
+        context: { fetchOptions: { signal: controller.signal } },
+      }),
+    );
+
+    const timeout = setTimeout(() => {
+      done('timeout should never run');
+    }, 100);
+
+    return reqPromise.then(res => {
+      clearTimeout(timeout);
+      expect(res.data).toEqual({
+        people: [
+          { title: 'Love apollo', __typename: 'Post' },
+          { title: 'Respect apollo', __typename: 'Post' },
+        ],
+      });
+      done();
+    });
+  });
+
+  it('should cancel fetch when an AbortController signal is passed and aborted', done => {
+    fetchMock.get('/api/posts', posts);
+    const link = new RestLink({ uri: '/api' });
+
+    const query = gql`
+      query {
+        people @rest(ftype: "[Post]", path: "/posts") {
+          title
+        }
+      }
+    `;
+
+    const controller = new AbortController();
+    const reqPromise = toPromise<Result>(
+      execute(link, {
+        operationName: 'abortQuery',
+        query,
+        context: { fetchOptions: { signal: controller.signal } },
+      }),
+    );
+    controller.abort();
+
+    let reqData = null;
+    const timeout = setTimeout(() => {
+      expect(reqData).toBeNull();
+      done();
+    }, 100);
+
+    return reqPromise.then(res => {
+      clearTimeout(timeout);
+      reqData = res.data;
+      done('fetch request should not resolve');
+    });
+  });
 });

src/restLink.ts

@@ -814,6 +814,11 @@ interface LinkChainContext {
 
   /** An array of the responses from each fetched URL, useful for accessing headers in earlier links */
   restResponses?: Response[];
+
+  /** Overrides some fetch options arguments passed to the fetch call */
+  fetchOptions?: {
+    signal?: AbortSignal;
+  };
 }
 
 /** Context passed via graphql() to our resolver */
@@ -840,6 +845,8 @@ interface RequestContext {
 
   /** An array of the responses from each fetched URL */
   responses: Response[];
+
+  signal?: AbortSignal;
 }
 
 const addTypeToNode = (node, typename) => {
@@ -924,6 +931,7 @@ const resolver: Resolver = async (
     fieldNameNormalizer: linkLevelNameNormalizer,
     fieldNameDenormalizer: linkLevelNameDenormalizer,
     serializers,
+    signal,
     responseTransformer,
   } = context;
 
@@ -1060,6 +1068,7 @@ const resolver: Resolver = async (
     // Only set credentials if they're non-null as some browsers throw an exception:
     // https://github.com/apollographql/apollo-link-rest/issues/121#issuecomment-396049677
     ...(credentials ? { credentials } : {}),
+    ...(signal ? { signal } : {}),
   };
   const requestUrl = `${endpointOption.uri}${pathWithParams}`;
 
@@ -1332,6 +1341,8 @@ export class RestLink extends ApolloLink {
 
     const credentials: RequestCredentials =
       context.credentials || this.credentials;
+    const signal: AbortSignal | undefined =
+      context.fetchOptions != null ? context.fetchOptions.signal : undefined;
 
     const queryWithTypename = addTypenameToDocument(query);
 
@@ -1355,6 +1366,7 @@ export class RestLink extends ApolloLink {
       fragmentDefinitions,
       typePatcher: this.typePatcher,
       serializers: this.serializers,
+      signal,
       responses: [],
       responseTransformer: this.responseTransformer,
     };