catch errors from AsyncIterable

src/__tests__/http-test.ts

@@ -2356,6 +2356,86 @@ function runTests(server: Server) {
         '{"errors":[{"message":"I did something wrong"}]}',
       );
     });
+
+    it('catches first error thrown from custom execute function that returns an AsyncIterable', async () => {
+      const app = server();
+
+      app.get(
+        urlString(),
+        graphqlHTTP(() => ({
+          schema: TestSchema,
+          customExecuteFn() {
+            return {
+              [Symbol.asyncIterator]: () => ({
+                next: () => Promise.reject(new Error('I did something wrong')),
+              }),
+            };
+          },
+        })),
+      );
+
+      const response = await app.request().get(urlString({ query: '{test}' }));
+      expect(response.status).to.equal(400);
+      expect(response.text).to.equal(
+        '{"errors":[{"message":"I did something wrong"}]}',
+      );
+    });
+
+    it('catches subsequent errors thrown from custom execute function that returns an AsyncIterable', async () => {
+      const app = server();
+
+      app.get(
+        urlString(),
+        graphqlHTTP(() => ({
+          schema: TestSchema,
+          async *customExecuteFn() {
+            await new Promise((r) => {
+              setTimeout(r, 1);
+            });
+            yield {
+              data: {
+                test2: 'Modification',
+              },
+              hasNext: true,
+            };
+            throw new Error('I did something wrong');
+          },
+        })),
+      );
+
+      const response = await app
+        .request()
+        .get(urlString({ query: '{test}' }))
+        .parse((res, cb) => {
+          res.on('data', (data) => {
+            res.text = `${res.text || ''}${data.toString('utf8') as string}`;
+          });
+          res.on('end', (err) => {
+            cb(err, null);
+          });
+        });
+
+      expect(response.status).to.equal(200);
+      expect(response.text).to.equal(
+        [
+          '',
+          '---',
+          'Content-Type: application/json; charset=utf-8',
+          'Content-Length: 48',
+          '',
+          '{"data":{"test2":"Modification"},"hasNext":true}',
+          '',
+          '---',
+          'Content-Type: application/json; charset=utf-8',
+          'Content-Length: 64',
+          '',
+          '{"errors":[{"message":"I did something wrong"}],"hasNext":false}',
+          '',
+          '-----',
+          '',
+        ].join('\r\n'),
+      );
+    });
   });
 
   describe('Custom parse function', () => {

src/__tests__/isAsyncIterable-test.ts

@@ -0,0 +1,20 @@
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import { isAsyncIterable } from '../isAsyncIterable';
+
+describe('isAsyncIterable', () => {
+  it('returns false for null', () => {
+    expect(isAsyncIterable(null)).to.equal(false);
+  });
+  it('returns false for non-object', () => {
+    expect(isAsyncIterable(1)).to.equal(false);
+  });
+  it('returns true for async generator function', () => {
+    // istanbul ignore next: test function
+    // eslint-disable-next-line @typescript-eslint/no-empty-function
+    const myGen = async function* () {};
+    const result = myGen();
+    expect(isAsyncIterable(result)).to.equal(true);
+  });
+});

src/index.ts

@@ -275,7 +275,7 @@ export function graphqlHTTP(options: Options): Middleware {
       // https://graphql.github.io/graphql-spec/#sec-Response-Format
       if (optionsData.extensions) {
         extensionsFn = (payload: AsyncExecutionResult) => {
-          /* istanbul ignore next condition not reachable, required for flow */
+          /* istanbul ignore else: condition not reachable, required for typescript */
           if (optionsData.extensions) {
             return optionsData.extensions({
               document: documentAST,
@@ -285,6 +285,8 @@ export function graphqlHTTP(options: Options): Middleware {
               context,
             });
           }
+          /* istanbul ignore next: condition not reachable, required for typescript */
+          return undefined;
         };
       }
 
@@ -362,23 +364,25 @@ export function graphqlHTTP(options: Options): Middleware {
           fieldResolver,
           typeResolver,
         });
+
+        if (isAsyncIterable(executeResult)) {
+          // Get first payload from AsyncIterator. http status will reflect status
+          // of this payload.
+          const asyncIterator = getAsyncIterator<ExecutionResult>(
+            executeResult,
+          );
+          const { value } = await asyncIterator.next();
+          result = value;
+        } else {
+          result = executeResult;
+        }
       } catch (contextError: unknown) {
         // Return 400: Bad Request if any execution context errors exist.
         throw httpError(400, 'GraphQL execution context error.', {
           graphqlErrors: [contextError],
         });
       }
 
-      if (isAsyncIterable(executeResult)) {
-        // Get first payload from AsyncIterator. http status will reflect status
-        // of this payload.
-        const asyncIterator = getAsyncIterator<ExecutionResult>(executeResult);
-        const { value } = await asyncIterator.next();
-        result = value;
-      } else {
-        result = executeResult;
-      }
-
       if (extensionsFn) {
         const extensions = await extensionsFn(result);
 
@@ -412,9 +416,12 @@ export function graphqlHTTP(options: Options): Middleware {
           undefined,
           error,
         );
-        result = { data: undefined, errors: [graphqlError] };
+        executeResult = result = { data: undefined, errors: [graphqlError] };
       } else {
-        result = { data: undefined, errors: error.graphqlErrors };
+        executeResult = result = {
+          data: undefined,
+          errors: error.graphqlErrors,
+        };
       }
     }
 
@@ -436,22 +443,41 @@ export function graphqlHTTP(options: Options): Middleware {
     if (isAsyncIterable(executeResult)) {
       response.setHeader('Content-Type', 'multipart/mixed; boundary="-"');
       sendPartialResponse(pretty, response, formattedResult);
-      for await (let payload of executeResult) {
-        // Collect and apply any metadata extensions if a function was provided.
-        // https://graphql.github.io/graphql-spec/#sec-Response-Format
-        if (extensionsFn) {
-          const extensions = await extensionsFn(payload);
-
-          if (extensions != null) {
-            payload = { ...payload, extensions };
+      try {
+        for await (let payload of executeResult) {
+          // Collect and apply any metadata extensions if a function was provided.
+          // https://graphql.github.io/graphql-spec/#sec-Response-Format
+          if (extensionsFn) {
+            const extensions = await extensionsFn(payload);
+
+            if (extensions != null) {
+              payload = { ...payload, extensions };
+            }
           }
+          const formattedPayload: FormattedExecutionPatchResult = {
+            // first payload is already consumed, all subsequent payloads typed as ExecutionPatchResult
+            ...(payload as ExecutionPatchResult),
+            errors: payload.errors?.map(formatErrorFn),
+          };
+          sendPartialResponse(pretty, response, formattedPayload);
         }
-        const formattedPayload: FormattedExecutionPatchResult = {
-          // first payload is already consumed, all subsequent payloads typed as ExecutionPatchResult
-          ...(payload as ExecutionPatchResult),
-          errors: payload.errors?.map(formatErrorFn),
-        };
-        sendPartialResponse(pretty, response, formattedPayload);
+      } catch (rawError: unknown) {
+        /* istanbul ignore next: Thrown by underlying library. */
+        const error =
+          rawError instanceof Error ? rawError : new Error(String(rawError));
+        const graphqlError = new GraphQLError(
+          error.message,
+          undefined,
+          undefined,
+          undefined,
+          undefined,
+          error,
+        );
+        sendPartialResponse(pretty, response, {
+          data: undefined,
+          errors: [formatErrorFn(graphqlError)],
+          hasNext: false,
+        });
       }
       response.write('\r\n-----\r\n');
       response.end();

src/isAsyncIterable.ts

@@ -1,6 +1,5 @@
 export function isAsyncIterable<T>(
   maybeAsyncIterable: any,
-  // eslint-disable-next-line no-undef
 ): maybeAsyncIterable is AsyncIterable<T> {
   if (maybeAsyncIterable == null || typeof maybeAsyncIterable !== 'object') {
     return false;