lib: allow byob reader for 'blob.stream()'

Fixes: #47993
PR-URL: #49713
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/blob.js

@@ -321,6 +321,7 @@ class Blob {
 
     const reader = this[kHandle].getReader();
     return new lazyReadableStream({
+      type: 'bytes',
       start(c) {
         // There really should only be one read at a time so using an
         // array here is purely defensive.
@@ -340,6 +341,9 @@ class Blob {
             if (status === 0) {
               // EOS
               c.close();
+              // This is to signal the end for byob readers
+              // see https://streams.spec.whatwg.org/#example-rbs-pull
+              c.byobRequest?.respond(0);
               const pending = this.pendingPulls.shift();
               pending.resolve();
               return;
@@ -353,13 +357,15 @@ class Blob {
               pending.reject(error);
               return;
             }
-            if (buffer !== undefined) {
+            // ReadableByteStreamController.enqueue errors if we submit a 0-length
+            // buffer. We need to check for that here.
+            if (buffer !== undefined && buffer.byteLength !== 0) {
               c.enqueue(new Uint8Array(buffer));
             }
             // We keep reading until we either reach EOS, some error, or we
             // hit the flow rate of the stream (c.desiredSize).
             queueMicrotask(() => {
-              if (c.desiredSize <= 0) {
+              if (c.desiredSize < 0) {
                 // A manual backpressure check.
                 if (this.pendingPulls.length !== 0) {
                   // A case of waiting pull finished (= not yet canceled)

test/parallel/test-blob.js

@@ -331,12 +331,54 @@ assert.throws(() => new Blob({}), {
   const b = new Blob(Array(10).fill('hello'));
   const stream = b.stream();
   const reader = stream.getReader();
-  assert.strictEqual(stream[kState].controller.desiredSize, 1);
+  assert.strictEqual(stream[kState].controller.desiredSize, 0);
   const { value, done } = await reader.read();
   assert.strictEqual(value.byteLength, 5);
   assert(!done);
   setTimeout(() => {
-    assert.strictEqual(stream[kState].controller.desiredSize, 0);
+    // The blob stream is now a byte stream hence after the first read,
+    // it should pull in the next 'hello' which is 5 bytes hence -5.
+    assert.strictEqual(stream[kState].controller.desiredSize, -5);
+  }, 0);
+})().then(common.mustCall());
+
+(async () => {
+  const blob = new Blob(['hello', 'world']);
+  const stream = blob.stream();
+  const reader = stream.getReader({ mode: 'byob' });
+  const decoder = new TextDecoder();
+  const chunks = [];
+  while (true) {
+    const { value, done } = await reader.read(new Uint8Array(100));
+    if (done) break;
+    chunks.push(decoder.decode(value, { stream: true }));
+  }
+  assert.strictEqual(chunks.join(''), 'helloworld');
+})().then(common.mustCall());
+
+(async () => {
+  const b = new Blob(Array(10).fill('hello'));
+  const stream = b.stream();
+  const reader = stream.getReader({ mode: 'byob' });
+  assert.strictEqual(stream[kState].controller.desiredSize, 0);
+  const { value, done } = await reader.read(new Uint8Array(100));
+  assert.strictEqual(value.byteLength, 5);
+  assert(!done);
+  setTimeout(() => {
+    assert.strictEqual(stream[kState].controller.desiredSize, -5);
+  }, 0);
+})().then(common.mustCall());
+
+(async () => {
+  const b = new Blob(Array(10).fill('hello'));
+  const stream = b.stream();
+  const reader = stream.getReader({ mode: 'byob' });
+  assert.strictEqual(stream[kState].controller.desiredSize, 0);
+  const { value, done } = await reader.read(new Uint8Array(2));
+  assert.strictEqual(value.byteLength, 2);
+  assert(!done);
+  setTimeout(() => {
+    assert.strictEqual(stream[kState].controller.desiredSize, -3);
   }, 0);
 })().then(common.mustCall());
 

test/wpt/status/FileAPI/blob.json

@@ -44,12 +44,5 @@
   },
   "Blob-slice.any.js": {
     "skip": "Depends on File API"
-  },
-  "Blob-stream.any.js": {
-    "fail": {
-      "expected": [
-        "Reading Blob.stream() with BYOB reader"
-      ]
-    }
   }
 }