fix(fetch): optimize signals composing logic; (#6582)

lib/adapters/fetch.js

@@ -113,18 +113,13 @@ export default isFetchSupported && (async (config) => {
 
   responseType = responseType ? (responseType + '').toLowerCase() : 'text';
 
-  let [composedSignal, stopTimeout] = (signal || cancelToken || timeout) ?
-    composeSignals([signal, cancelToken], timeout) : [];
+  let composedSignal = composeSignals([signal, cancelToken && cancelToken.toAbortSignal()], timeout);
 
-  let finished, request;
+  let request;
 
-  const onFinish = () => {
-    !finished && setTimeout(() => {
-      composedSignal && composedSignal.unsubscribe();
-    });
-
-    finished = true;
-  }
+  const unsubscribe = composedSignal && composedSignal.unsubscribe && (() => {
+      composedSignal.unsubscribe();
+  });
 
   let requestContentLength;
 
@@ -161,7 +156,7 @@ export default isFetchSupported && (async (config) => {
 
     // Cloudflare Workers throws when credentials are defined
     // see https://github.com/cloudflare/workerd/issues/902
-    const isCredentialsSupported = "credentials" in Request.prototype; 
+    const isCredentialsSupported = "credentials" in Request.prototype;
     request = new Request(url, {
       ...fetchOptions,
       signal: composedSignal,
@@ -176,7 +171,7 @@ export default isFetchSupported && (async (config) => {
 
     const isStreamResponse = supportsResponseStream && (responseType === 'stream' || responseType === 'response');
 
-    if (supportsResponseStream && (onDownloadProgress || isStreamResponse)) {
+    if (supportsResponseStream && (onDownloadProgress || (isStreamResponse && unsubscribe))) {
       const options = {};
 
       ['status', 'statusText', 'headers'].forEach(prop => {
@@ -193,7 +188,7 @@ export default isFetchSupported && (async (config) => {
       response = new Response(
         trackStream(response.body, DEFAULT_CHUNK_SIZE, onProgress, () => {
           flush && flush();
-          isStreamResponse && onFinish();
+          unsubscribe && unsubscribe();
         }, encodeText),
         options
       );
@@ -203,9 +198,7 @@ export default isFetchSupported && (async (config) => {
 
     let responseData = await resolvers[utils.findKey(resolvers, responseType) || 'text'](response, config);
 
-    !isStreamResponse && onFinish();
-
-    stopTimeout && stopTimeout();
+    !isStreamResponse && unsubscribe && unsubscribe();
 
     return await new Promise((resolve, reject) => {
       settle(resolve, reject, {
@@ -218,7 +211,7 @@ export default isFetchSupported && (async (config) => {
       })
     })
   } catch (err) {
-    onFinish();
+    unsubscribe && unsubscribe();
 
     if (err && err.name === 'TypeError' && /fetch/i.test(err.message)) {
       throw Object.assign(