perf(ext/streams): fast path when consuming body of tee'd stream

cli/tests/unit/http_test.ts

@@ -2453,6 +2453,62 @@ Deno.test(
   },
 );
 
+Deno.test(
+  { permissions: { net: true } },
+  async function httpServerRequestResponseClone() {
+    const body = "deno".repeat(64 * 1024);
+    let httpConn: Deno.HttpConn;
+    const listener = Deno.listen({ port: 4501 });
+    const promise = (async () => {
+      const conn = await listener.accept();
+      listener.close();
+      httpConn = Deno.serveHttp(conn);
+      const reqEvent = await httpConn.nextRequest();
+      assert(reqEvent);
+      const { request, respondWith } = reqEvent;
+      const clone = request.clone();
+      const reader = clone.body!.getReader();
+
+      // get first chunk from branch2
+      const clonedChunks = [];
+      const { value, done } = await reader.read();
+      assert(!done);
+      clonedChunks.push(value);
+
+      // consume request after first chunk single read
+      // readAll should read correctly the rest of the body.
+      // firstChunk should be in the stream internal buffer
+      const body1 = await request.text();
+
+      while (true) {
+        const { value, done } = await reader.read();
+        if (done) break;
+        clonedChunks.push(value);
+      }
+      let offset = 0;
+      const body2 = new Uint8Array(body.length);
+      for (const chunk of clonedChunks) {
+        body2.set(chunk, offset);
+        offset += chunk.byteLength;
+      }
+
+      assertEquals(body1, body);
+      assertEquals(body1, new TextDecoder().decode(body2));
+      await respondWith(new Response(body));
+    })();
+
+    const response = await fetch("http://localhost:4501", {
+      body,
+      method: "POST",
+    });
+    const clone = response.clone();
+    assertEquals(await response.text(), await clone.text());
+
+    await promise;
+    httpConn!.close();
+  },
+);
+
 function chunkedBodyReader(h: Headers, r: BufReader): Deno.Reader {
   // Based on https://tools.ietf.org/html/rfc2616#section-19.4.6
   const tp = new TextProtoReader(r);

core/01_core.js

@@ -323,6 +323,7 @@
     close: (rid) => ops.op_close(rid),
     tryClose: (rid) => ops.op_try_close(rid),
     read: opAsync.bind(null, "op_read"),
+    readAll: opAsync.bind(null, "op_read_all"),
     write: opAsync.bind(null, "op_write"),
     writeAll: opAsync.bind(null, "op_write_all"),
     shutdown: opAsync.bind(null, "op_shutdown"),

ext/web/06_streams.js

@@ -652,6 +652,9 @@
   const RESOURCE_REGISTRY = new FinalizationRegistry((rid) => {
     core.tryClose(rid);
   });
+
+  const _readAll = Symbol("[[readAll]]");
+  const _original = Symbol("[[original]]");
   /**
    * Create a new ReadableStream object that is backed by a Resource that
    * implements `Resource::read_return`. This object contains enough metadata to
@@ -681,6 +684,17 @@
       async pull(controller) {
         const v = controller.byobRequest.view;
         try {
+          if (controller[_readAll] === true) {
+            // fast path for tee'd streams consuming body
+            const chunk = await core.readAll(rid);
+            if (chunk.byteLength > 0) {
+              controller.enqueue(chunk);
+            }
+            controller.close();
+            tryClose();
+            return;
+          }
+
           const bytesRead = await core.read(rid, v);
           if (bytesRead === 0) {
             tryClose();
@@ -809,8 +823,17 @@
     /** @type {Uint8Array[]} */
     const chunks = [];
     let totalLength = 0;
+
+    // tee'd stream
+    if (stream[_original]) {
+      // One of the branches is consuming the stream
+      // signal controller.pull that we can consume it in a single op
+      stream[_original][_controller][_readAll] = true;
+    }
+
     while (true) {
       const { value: chunk, done } = await reader.read();
+
       if (done) break;
 
       if (!ObjectPrototypeIsPrototypeOf(Uint8ArrayPrototype, chunk)) {
@@ -3029,6 +3052,10 @@
       pull2Algorithm,
       cancel2Algorithm,
     );
+
+    branch1[_original] = stream;
+    branch2[_original] = stream;
+
     forwardReaderError(reader);
     return [branch1, branch2];
   }