feat(core): Reimplement fetch source as async generator

.changeset/real-donkeys-act.md

@@ -0,0 +1,5 @@
+---
+'@urql/core': patch
+---
+
+Replace fetch source implementation with async generator implementation, based on Wonka's `fromAsyncIterable`.

exchanges/multipart-fetch/src/multipartFetchExchange.test.ts

@@ -1,5 +1,6 @@
-import { Client, OperationResult, makeOperation } from '@urql/core';
-import { empty, fromValue, pipe, Source, subscribe, toPromise } from 'wonka';
+import { Client, OperationResult } from '@urql/core';
+import { empty, fromValue, pipe, Source, toPromise } from 'wonka';
+
 import {
   vi,
   expect,
@@ -23,9 +24,6 @@ import {
 const fetch = (global as any).fetch as Mock;
 const abort = vi.fn();
 
-const abortError = new Error();
-abortError.name = 'AbortError';
-
 beforeAll(() => {
   (global as any).AbortController = function AbortController() {
     this.signal = undefined;
@@ -177,52 +175,3 @@ describe('on error', () => {
     expect(data.data).toEqual(JSON.parse(response).data);
   });
 });
-
-describe('on teardown', () => {
-  const fail = () => {
-    expect(true).toEqual(false);
-  };
-
-  it('does not start the outgoing request on immediate teardowns', () => {
-    fetch.mockRejectedValueOnce(abortError);
-
-    const { unsubscribe } = pipe(
-      fromValue(queryOperation),
-      multipartFetchExchange(exchangeArgs),
-      subscribe(fail)
-    );
-
-    unsubscribe();
-    expect(fetch).toHaveBeenCalledTimes(0);
-    expect(abort).toHaveBeenCalledTimes(1);
-  });
-
-  it('aborts the outgoing request', async () => {
-    fetch.mockRejectedValueOnce(abortError);
-
-    const { unsubscribe } = pipe(
-      fromValue(queryOperation),
-      multipartFetchExchange(exchangeArgs),
-      subscribe(fail)
-    );
-
-    await Promise.resolve();
-
-    unsubscribe();
-    expect(fetch).toHaveBeenCalledTimes(1);
-    expect(abort).toHaveBeenCalledTimes(1);
-  });
-
-  it('does not call the query', () => {
-    pipe(
-      fromValue(
-        makeOperation('teardown', queryOperation, queryOperation.context)
-      ),
-      multipartFetchExchange(exchangeArgs),
-      subscribe(fail)
-    );
-
-    expect(fetch).toHaveBeenCalledTimes(0);
-    expect(abort).toHaveBeenCalledTimes(0);
-  });
-});

packages/core/src/exchanges/fetch.test.ts

@@ -143,8 +143,9 @@ describe('on teardown', () => {
   const fail = () => {
     expect(true).toEqual(false);
   };
+
   it('does not start the outgoing request on immediate teardowns', () => {
-    fetch.mockRejectedValueOnce(abortError);
+    fetch.mockResolvedValue(new Response('text', { status: 200 }));
 
     const { unsubscribe } = pipe(
       fromValue(queryOperation),
@@ -154,11 +155,11 @@ describe('on teardown', () => {
 
     unsubscribe();
     expect(fetch).toHaveBeenCalledTimes(0);
-    expect(abort).toHaveBeenCalledTimes(1);
+    expect(abort).toHaveBeenCalledTimes(0);
   });
 
   it('aborts the outgoing request', async () => {
-    fetch.mockRejectedValueOnce(abortError);
+    fetch.mockResolvedValue(new Response('text', { status: 200 }));
 
     const { unsubscribe } = pipe(
       fromValue(queryOperation),
@@ -169,11 +170,16 @@ describe('on teardown', () => {
     await Promise.resolve();
 
     unsubscribe();
+
+    // NOTE: We can only observe the async iterator's final run after a macro tick
+    await new Promise(resolve => setTimeout(resolve));
     expect(fetch).toHaveBeenCalledTimes(1);
-    expect(abort).toHaveBeenCalledTimes(1);
+    expect(abort).toHaveBeenCalled();
   });
 
   it('does not call the query', () => {
+    fetch.mockResolvedValue(new Response('text', { status: 200 }));
+
     pipe(
       fromValue(
         makeOperation('teardown', queryOperation, queryOperation.context)

packages/core/src/internal/fetchSource.test.ts

@@ -19,9 +19,6 @@ import { makeOperation } from '../utils';
 const fetch = (global as any).fetch as Mock;
 const abort = vi.fn();
 
-const abortError = new Error();
-abortError.name = 'AbortError';
-
 beforeAll(() => {
   (global as any).AbortController = function AbortController() {
     this.signal = undefined;
@@ -165,7 +162,7 @@ describe('on teardown', () => {
   };
 
   it('does not start the outgoing request on immediate teardowns', () => {
-    fetch.mockRejectedValue(abortError);
+    fetch.mockResolvedValue(new Response('text', { status: 200 }));
 
     const { unsubscribe } = pipe(
       makeFetchSource(queryOperation, 'https://test.com/graphql', {}),
@@ -174,20 +171,22 @@ describe('on teardown', () => {
 
     unsubscribe();
     expect(fetch).toHaveBeenCalledTimes(0);
-    expect(abort).toHaveBeenCalledTimes(1);
+    expect(abort).toHaveBeenCalledTimes(0);
   });
 
   it('aborts the outgoing request', async () => {
-    fetch.mockRejectedValue(abortError);
+    fetch.mockResolvedValue(new Response('text', { status: 200 }));
 
     const { unsubscribe } = pipe(
       makeFetchSource(queryOperation, 'https://test.com/graphql', {}),
       subscribe(fail)
     );
 
     await Promise.resolve();
-
     unsubscribe();
+
+    // NOTE: We can only observe the async iterator's final run after a macro tick
+    await new Promise(resolve => setTimeout(resolve));
     expect(fetch).toHaveBeenCalledTimes(1);
     expect(abort).toHaveBeenCalledTimes(1);
   });