feat: support multiple fetch_factory instances (#579)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Refactor**
* Enhanced internal request handling by encapsulating dispatcher and
local storage within a singleton instance for improved reliability.

* **Tests**
* Added tests validating fetch operations with the new instance-based
design, including diagnostics and connection reuse verification.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: killagu

src/fetch.ts

@@ -61,20 +61,14 @@ export type FetchResponseDiagnosticsMessage = {
 };
 
 export class FetchFactory {
-  static #dispatcher: Dispatcher.ComposedDispatcher;
-  static #opaqueLocalStorage = new AsyncLocalStorage<FetchOpaque>();
+  #dispatcher?: Dispatcher.ComposedDispatcher;
+  #opaqueLocalStorage = new AsyncLocalStorage<FetchOpaque>();
 
-  static getDispatcher() {
-    return FetchFactory.#dispatcher ?? getGlobalDispatcher();
-  }
+  static #instance = new FetchFactory();
 
-  static setDispatcher(dispatcher: Agent) {
-    FetchFactory.#dispatcher = dispatcher;
-  }
-
-  static setClientOptions(clientOptions: ClientOptions) {
+  setClientOptions(clientOptions: ClientOptions) {
     let dispatcherOption: BaseAgentOptions = {
-      opaqueLocalStorage: FetchFactory.#opaqueLocalStorage,
+      opaqueLocalStorage: this.#opaqueLocalStorage,
     };
     let dispatcherClazz: new (options: BaseAgentOptions) => BaseAgent = BaseAgent;
     if (clientOptions?.lookup || clientOptions?.checkAddress) {
@@ -101,12 +95,20 @@ export class FetchFactory {
       } as HttpAgentOptions;
       dispatcherClazz = BaseAgent;
     }
-    FetchFactory.#dispatcher = new dispatcherClazz(dispatcherOption);
+    this.#dispatcher = new dispatcherClazz(dispatcherOption);
     initDiagnosticsChannel();
   }
 
-  static getDispatcherPoolStats() {
-    const agent = FetchFactory.getDispatcher();
+  getDispatcher() {
+    return this.#dispatcher ?? getGlobalDispatcher();
+  }
+
+  setDispatcher(dispatcher: Agent) {
+    this.#dispatcher = dispatcher;
+  }
+
+  getDispatcherPoolStats() {
+    const agent = this.getDispatcher();
     // origin => Pool Instance
     const clients: Map<string, WeakRef<Pool>> | undefined = Reflect.get(agent, undiciSymbols.kClients);
     const poolStatsMap: Record<string, PoolStat> = {};
@@ -131,10 +133,18 @@ export class FetchFactory {
     return poolStatsMap;
   }
 
-  static async fetch(input: RequestInfo, init?: UrllibRequestInit): Promise<Response> {
+  static setClientOptions(clientOptions: ClientOptions) {
+    FetchFactory.#instance.setClientOptions(clientOptions);
+  }
+
+  static getDispatcherPoolStats() {
+    return FetchFactory.#instance.getDispatcherPoolStats();
+  }
+
+  async fetch(input: RequestInfo, init?: UrllibRequestInit): Promise<Response> {
     const requestStartTime = performance.now();
     init = init ?? {};
-    init.dispatcher = init.dispatcher ?? FetchFactory.#dispatcher;
+    init.dispatcher = init.dispatcher ?? this.#dispatcher;
     const request = new Request(input, init);
     const requestId = globalId('HttpClientRequest');
     // https://developer.chrome.com/docs/devtools/network/reference/?utm_source=devtools#timing-explanation
@@ -219,7 +229,7 @@ export class FetchFactory {
       socketErrorRetries: 0,
     } as any as RawResponseWithMeta;
     try {
-      await FetchFactory.#opaqueLocalStorage.run(internalOpaque, async () => {
+      await this.#opaqueLocalStorage.run(internalOpaque, async () => {
         res = await UndiciFetch(request);
       });
     } catch (e: any) {
@@ -262,6 +272,18 @@ export class FetchFactory {
     } as ResponseDiagnosticsMessage);
     return res!;
   }
+
+  static getDispatcher() {
+    return FetchFactory.#instance.getDispatcher();
+  }
+
+  static setDispatcher(dispatcher: Agent) {
+    FetchFactory.#instance.setDispatcher(dispatcher);
+  }
+
+  static async fetch(input: RequestInfo, init?: UrllibRequestInit): Promise<Response> {
+    return FetchFactory.#instance.fetch(input, init);
+  }
 }
 
 export const fetch = FetchFactory.fetch;

test/fetch.test.ts

@@ -58,7 +58,6 @@ describe('fetch.test.ts', () => {
     await sleep(1);
     // again, keep alive
     response = await fetch(`${_url}html`);
-    // console.log(responseDiagnosticsMessage!.response.socket);
     assert(responseDiagnosticsMessage!.response.socket.handledRequests > 1);
     assert(responseDiagnosticsMessage!.response.socket.handledResponses > 1);
 
@@ -99,7 +98,6 @@ describe('fetch.test.ts', () => {
     assert(requestDiagnosticsMessage!.request);
     assert(responseDiagnosticsMessage!.request);
     assert(responseDiagnosticsMessage!.response);
-    // console.log(responseDiagnosticsMessage!.response.socket);
     assert(responseDiagnosticsMessage!.response.socket.localAddress);
     assert([ '127.0.0.1', '::1' ].includes(responseDiagnosticsMessage!.response.socket.localAddress));
 
@@ -120,4 +118,48 @@ describe('fetch.test.ts', () => {
       await fetch(request);
     }, /Cannot construct a Request with a Request object that has already been used/);
   });
+
+  it('fetch with new FetchFactory instance should work', async () => {
+    let requestDiagnosticsMessage: RequestDiagnosticsMessage;
+    let responseDiagnosticsMessage: ResponseDiagnosticsMessage;
+    let fetchDiagnosticsMessage: FetchDiagnosticsMessage;
+    let fetchResponseDiagnosticsMessage: FetchResponseDiagnosticsMessage;
+    diagnosticsChannel.subscribe('urllib:request', msg => {
+      requestDiagnosticsMessage = msg as RequestDiagnosticsMessage;
+    });
+    diagnosticsChannel.subscribe('urllib:response', msg => {
+      responseDiagnosticsMessage = msg as ResponseDiagnosticsMessage;
+    });
+    diagnosticsChannel.subscribe('urllib:fetch:request', msg => {
+      fetchDiagnosticsMessage = msg as FetchDiagnosticsMessage;
+    });
+    diagnosticsChannel.subscribe('urllib:fetch:response', msg => {
+      fetchResponseDiagnosticsMessage = msg as FetchResponseDiagnosticsMessage;
+    });
+    const factory = new FetchFactory();
+    factory.setClientOptions({});
+    let response = await factory.fetch(`${_url}html`);
+
+    assert(response);
+    assert(requestDiagnosticsMessage!.request);
+    assert(responseDiagnosticsMessage!.request);
+    assert(responseDiagnosticsMessage!.response);
+    assert(responseDiagnosticsMessage!.response.socket.localAddress);
+    assert([ '127.0.0.1', '::1' ].includes(responseDiagnosticsMessage!.response.socket.localAddress));
+
+    assert(fetchDiagnosticsMessage!.fetch);
+    assert(fetchResponseDiagnosticsMessage!.fetch);
+    assert(fetchResponseDiagnosticsMessage!.response);
+    assert(fetchResponseDiagnosticsMessage!.timingInfo);
+
+    await sleep(1);
+    // again, keep alive
+    response = await factory.fetch(`${_url}html`);
+    assert(responseDiagnosticsMessage!.response.socket.handledRequests > 1);
+    assert(responseDiagnosticsMessage!.response.socket.handledResponses > 1);
+
+    const stats = factory.getDispatcherPoolStats();
+    assert(stats);
+    assert(Object.keys(stats).length > 0);
+  });
 });