Fetch: Support BYOB reading for Response.body

ReadableByteStream is a variant of ReadableStream specialized for
bytes[1]. Given the performance benefits, this CL adds BYOB support
for Fetch by making Response.body a byte stream to allow for reading
with a bring-your-own-buffer(BYOB) reader.

The corresponding spec PR for this was landed at whatwg/fetch#1593.
Tests for reading from Blob with a BYOB reader were factored out, as
support for that will be implemented in follow-up CLs.

[1] https://streams.spec.whatwg.org/#readable-byte-stream

Bug: 1243329
Change-Id: I381b9f2272a7f1202fa748ae5c039ca0a998de00

Author: nidhijaju

FileAPI/blob/Blob-stream-BYOB.any.js

@@ -0,0 +1,46 @@
+// META: title=Blob Stream BYOB
+// META: script=../support/Blob.js
+// META: script=/common/gc.js
+'use strict';
+
+// Helper function that triggers garbage collection while reading a chunk
+// if perform_gc is true.
+async function read_and_gc(reader, perform_gc) {
+  // Passing Uint8Array for byte streams; non-byte streams will simply ignore it
+  const read_promise = reader.read(new Uint8Array(64));
+  if (perform_gc) {
+    await garbageCollect();
+  }
+  return read_promise;
+}
+
+// Takes in a ReadableStream and reads from it until it is done, returning
+// an array that contains the results of each read operation. If perform_gc
+// is true, garbage collection is triggered while reading every chunk.
+async function read_all_chunks(stream, { perform_gc = false, mode } = {}) {
+  assert_true(stream instanceof ReadableStream);
+  assert_true('getReader' in stream);
+  const reader = stream.getReader({ mode });
+
+  assert_true('read' in reader);
+  let read_value = await read_and_gc(reader, perform_gc);
+
+  let out = [];
+  let i = 0;
+  while (!read_value.done) {
+    for (let val of read_value.value) {
+      out[i++] = val;
+    }
+    read_value = await read_and_gc(reader, perform_gc);
+  }
+  return out;
+}
+
+promise_test(async () => {
+  const input_arr = [8, 241, 48, 123, 151];
+  const typed_arr = new Uint8Array(input_arr);
+  let blob = new Blob([typed_arr]);
+  const stream = blob.stream();
+  const chunks = await read_all_chunks(stream, { mode: "byob" });
+  assert_array_equals(chunks, input_arr);
+}, "Reading Blob.stream() with BYOB reader")

FileAPI/blob/Blob-stream.any.js

@@ -71,13 +71,4 @@ promise_test(async() => {
   const chunks = await read_all_chunks(stream, { perform_gc: true });
   assert_array_equals(chunks, input_arr);
 }, "Blob.stream() garbage collection of blob shouldn't break stream" +
-      "consumption")
-
-promise_test(async () => {
-  const input_arr = [8, 241, 48, 123, 151];
-  const typed_arr = new Uint8Array(input_arr);
-  let blob = new Blob([typed_arr]);
-  const stream = blob.stream();
-  const chunks = await read_all_chunks(stream, { mode: "byob" });
-  assert_array_equals(chunks, input_arr);
-}, "Reading Blob.stream() with BYOB reader")
+"consumption")

fetch/api/response/response-consume-byob-blob.any.js

@@ -0,0 +1,11 @@
+// META: global=window,worker
+// META: title=Response consume BYOB blob
+// META: script=../resources/utils.js
+
+var textData = JSON.stringify("This is response's body");
+var blob = new Blob([textData], { "type": "text/plain" });
+
+promise_test(function (test) {
+  var response = new Response(blob);
+  return validateStreamFromString(response.body.getReader({ mode: "byob" }), textData);
+}, `Read blob response's body as readableStream with mode="byob"}`);

fetch/api/response/response-consume-stream.any.js

@@ -20,12 +20,12 @@ var blob = new Blob([textData], { "type" : "text/plain" });
 var urlSearchParamsData = "name=value";
 var urlSearchParams = new URLSearchParams(urlSearchParamsData);
 
-for (const mode of [undefined, "byob"]) {
-    promise_test(function(test) {
-        var response = new Response(blob);
-        return validateStreamFromString(response.body.getReader({ mode }), textData);
-    }, `Read blob response's body as readableStream with mode=${mode}`);
+promise_test(function (test) {
+  var response = new Response(blob);
+  return validateStreamFromString(response.body.getReader(), textData);
+}, "Read blob response's body as readableStream");
 
+for (const mode of [undefined, "byob"]) {
     promise_test(function(test) {
         var response = new Response(textData);
         return validateStreamFromString(response.body.getReader({ mode }), textData);