Skip the creation of a transform stream in fetch (#3093)

lib/web/fetch/index.js

@@ -1080,23 +1080,17 @@ function fetchFinale (fetchParams, response) {
   if (internalResponse.body == null) {
     processResponseEndOfBody()
   } else {
+    // mcollina: all the following steps of the specs are skipped.
+    // The internal transform stream is not needed.
+    //
     // 1. Let transformStream be a new TransformStream.
     // 2. Let identityTransformAlgorithm be an algorithm which, given chunk, enqueues chunk in transformStream.
     // 3. Set up transformStream with transformAlgorithm set to identityTransformAlgorithm and flushAlgorithm
     //    set to processResponseEndOfBody.
-    const transformStream = new TransformStream({
-      start () { },
-      transform (chunk, controller) {
-        controller.enqueue(chunk)
-      },
-      flush: processResponseEndOfBody
-    })
-
     // 4. Set internalResponse’s body’s stream to the result of internalResponse’s body’s stream piped through transformStream.
-    internalResponse.body.stream.pipeThrough(transformStream)
 
     const byteStream = new ReadableStream({
-      readableStream: transformStream.readable,
+      readableStream: internalResponse.body.stream,
       async start () {
         this._bodyReader = this.readableStream.getReader()
       },
@@ -1105,7 +1099,12 @@ function fetchFinale (fetchParams, response) {
           const { done, value } = await this._bodyReader.read()
 
           if (done) {
-            queueMicrotask(() => readableStreamClose(controller))
+            queueMicrotask(() => {
+              readableStreamClose(controller)
+
+              // Added to in lieu of steps 1-4 of the spec
+              processResponseEndOfBody()
+            })
             break
           }