use whatwg streams (#103)

* use whatwg streams
* could not use optional changing in v12
* could not use fs/promise in v12

Author: jimmywarting

Diff for: README.md

@@ -22,10 +22,8 @@ npm install fetch-blob
     - internal Buffer.from was replaced with TextEncoder/Decoder
     - internal buffers was replaced with Uint8Arrays
     - CommonJS was replaced with ESM
-    - The node stream returned by calling `blob.stream()` was replaced with a simple generator function that yields Uint8Array (Breaking change)
-      (Read "Differences from other blobs" for more info.)
-
-    All of this changes have made it dependency free of any core node modules, so it would be possible to just import it using http-import from a CDN without any bundling
+    - The node stream returned by calling `blob.stream()` was replaced with whatwg streams
+    - (Read "Differences from other blobs" for more info.)
 
 </details>
 
@@ -36,48 +34,12 @@ npm install fetch-blob
   - This blob version is more arbitrary, it can be constructed with blob parts that isn't a instance of itself
   it has to look and behave as a blob to be accepted as a blob part.
     - The benefit of this is that you can create other types of blobs that don't contain any internal data that has to be read in other ways, such as the `BlobDataItem` created in `from.js` that wraps a file path into a blob-like item and read lazily (nodejs plans to [implement this][fs-blobs] as well)
-  - The `blob.stream()` is the most noticeable differences. It returns a AsyncGeneratorFunction that yields Uint8Arrays
-
-  The reasoning behind `Blob.prototype.stream()` is that NodeJS readable stream
-  isn't spec compatible with whatwg streams and we didn't want to import the hole whatwg stream polyfill for node
-  or browserify NodeJS streams for the browsers and picking any flavor over the other. So we decided to opted out
-  of any stream and just implement the bear minium of what both streams have in common which is the asyncIterator
-  that both yields Uint8Array. this is the most isomorphic way with the use of `for-await-of` loops.
-  It would be redundant to convert anything to whatwg streams and than convert it back to
-  node streams since you work inside of Node.
-  It will probably stay like this until nodejs get native support for whatwg<sup>[1][https://github.com/nodejs/whatwg-stream]</sup> streams and whatwg stream add the node
-  equivalent for `Readable.from(iterable)`<sup>[2](https://github.com/whatwg/streams/issues/1018)</sup>
-
-  But for now if you really need a Node Stream then you can do so using this transformation
+  - The `blob.stream()` is the most noticeable differences. It returns a WHATWG stream now. to keep it as a node stream you would have to do:
+
   ```js
     import {Readable} from 'stream'
     const stream = Readable.from(blob.stream())
   ```
-  But if you don't need it to be a stream then you can just use the asyncIterator part of it that is isomorphic.
-  ```js
-    for await (const chunk of blob.stream()) {
-      console.log(chunk) // uInt8Array
-    }
-  ```
-  If you need to make some feature detection to fix this different behavior
-  ```js
-  if (Blob.prototype.stream?.constructor?.name === 'AsyncGeneratorFunction') {
-    // not spec compatible, monkey patch it...
-    // (Alternative you could extend the Blob and use super.stream())
-    let orig = Blob.prototype.stream
-    Blob.prototype.stream = function () {
-      const iterator = orig.call(this)
-      return new ReadableStream({
-        async pull (ctrl) {
-          const next = await iterator.next()
-          return next.done ? ctrl.close() : ctrl.enqueue(next.value)
-        }
-      })
-    }
-  }
-  ```
-  Possible feature whatwg version: `ReadableStream.from(iterator)`
-  It's also possible to delete this method and instead use `.slice()` and `.arrayBuffer()` since it has both a public and private stream method
 </details>
 
 ## Usage
@@ -100,12 +62,8 @@ const blob = new Blob(['hello, world'])
 await blob.text()
 await blob.arrayBuffer()
 for await (let chunk of  blob.stream()) { ... }
-
-// turn the async iterator into a node stream
-stream.Readable.from(blob.stream())
-
-// turn the async iterator into a whatwg stream (feature)
-globalThis.ReadableStream.from(blob.stream())
+blob.stream().getReader().read()
+blob.stream().getReader({mode: 'byob'}).read(view)
 ```
 
 ### Blob part backed up by filesystem

Diff for: from.js

@@ -1,10 +1,11 @@
-import {statSync, createReadStream} from 'fs';
-import {stat} from 'fs/promises';
+import {statSync, createReadStream, promises as fs} from 'fs';
 import {basename} from 'path';
 import File from './file.js';
 import Blob from './index.js';
 import {MessageChannel} from 'worker_threads';
 
+const {stat} = fs;
+
 const DOMException = globalThis.DOMException || (() => {
 	const port = new MessageChannel().port1
 	const ab = new ArrayBuffer(0)
@@ -86,12 +87,10 @@ class BlobDataItem {
 		if (mtimeMs > this.lastModified) {
 			throw new DOMException('The requested file could not be read, typically due to permission problems that have occurred after a reference to a file was acquired.', 'NotReadableError');
 		}
-		if (this.size) {
-			yield * createReadStream(this.#path, {
-				start: this.#start,
-				end: this.#start + this.size - 1
-			});
-		}
+		yield * createReadStream(this.#path, {
+			start: this.#start,
+			end: this.#start + this.size - 1
+		});
 	}
 
 	get [Symbol.toStringTag]() {

Diff for: index.js

@@ -1,7 +1,43 @@
+
+// TODO (jimmywarting): in the feature use conditional loading with top level await (requires 14.x)
+// Node has recently added whatwg stream into core, want to use that instead when it becomes avalible.
+
+import * as stream from 'web-streams-polyfill/dist/ponyfill.es2018.js'
+
+const ReadableStream = globalThis.ReadableStream || stream.ReadableStream
+const ByteLengthQueuingStrategy = globalThis.ByteLengthQueuingStrategy || stream.ReadableStream
+
+/** @typedef {import('buffer').Blob} NodeBlob} */
+
+// Fix buffer.Blob's missing stream implantation
+import('buffer').then(m => {
+	if (m.Blob && !m.Blob.prototype.stream) {
+		m.Blob.prototype.stream = function name(params) {
+			let position = 0;
+			const blob = this;
+			const stratergy = new ByteLengthQueuingStrategy({ highWaterMark: POOL_SIZE });
+
+			return new ReadableStream({
+				type: "bytes",
+				async pull(ctrl) {
+					const chunk = blob.slice(position, Math.min(blob.size, position + POOL_SIZE));
+					const buffer = await chunk.arrayBuffer();
+					position += buffer.byteLength;
+					ctrl.enqueue(new Uint8Array(buffer))
+
+					if (position === blob.size) {
+						ctrl.close()
+					}
+				}
+			}, stratergy)
+		}
+	}
+}, () => {})
+
 // 64 KiB (same size chrome slice theirs blob into Uint8array's)
 const POOL_SIZE = 65536;
 
-/** @param {(Blob | Uint8Array)[]} parts */
+/** @param {(Blob | NodeBlob | Uint8Array)[]} parts */
 async function * toIterator (parts, clone = true) {
 	for (let part of parts) {
 		if ('stream' in part) {
@@ -20,6 +56,7 @@ async function * toIterator (parts, clone = true) {
 				yield part;
 			}
 		} else {
+			/* c8 ignore start */
 			// For blobs that have arrayBuffer but no stream method (nodes buffer.Blob)
 			let position = 0;
 			while (position !== part.size) {
@@ -28,6 +65,7 @@ async function * toIterator (parts, clone = true) {
 				position += buffer.byteLength;
 				yield new Uint8Array(buffer);
 			}
+			/* c8 ignore end */
 		}
 	}
 }
@@ -116,6 +154,11 @@ export default class Blob {
 	 * @return {Promise<ArrayBuffer>}
 	 */
 	async arrayBuffer() {
+		// Easier way... Just a unnecessary overhead
+		// const view = new Uint8Array(this.size);
+		// await this.stream().getReader({mode: 'byob'}).read(view);
+		// return view.buffer;
+
 		const data = new Uint8Array(this.size);
 		let offset = 0;
 		for await (const chunk of toIterator(this.#parts, false)) {
@@ -126,14 +169,17 @@ export default class Blob {
 		return data.buffer;
 	}
 
-	/**
-	 * The Blob stream() implements partial support of the whatwg stream
-	 * by only being async iterable.
-	 *
-	 * @returns {AsyncGenerator<Uint8Array>}
-	 */
-	async * stream() {
-		yield * toIterator(this.#parts, true);
+	stream() {
+		const it = toIterator(this.#parts, true);
+		const stratergy = new ByteLengthQueuingStrategy({ highWaterMark: POOL_SIZE });
+
+		return new ReadableStream({
+			type: "bytes",
+			async pull(ctrl) {
+				const chunk = await it.next();
+				chunk.done ? ctrl.close() : ctrl.enqueue(chunk.value);
+			}
+		}, stratergy)
 	}
 
 	/**
@@ -157,6 +203,11 @@ export default class Blob {
 		let added = 0;
 
 		for (const part of parts) {
+			// don't add the overflow to new blobParts
+			if (added >= span) {
+				break;
+			}
+
 			const size = ArrayBuffer.isView(part) ? part.byteLength : part.size;
 			if (relativeStart && size <= relativeStart) {
 				// Skip the beginning and change the relative
@@ -174,11 +225,6 @@ export default class Blob {
 				}
 				blobParts.push(chunk);
 				relativeStart = 0; // All next sequential parts should start at 0
-
-				// don't add the overflow to new blobParts
-				if (added >= span) {
-					break;
-				}
 			}
 		}
 
@@ -195,7 +241,9 @@ export default class Blob {
 
 	static [Symbol.hasInstance](object) {
 		return (
-			typeof object?.constructor === 'function' &&
+			object &&
+			typeof object === 'object' &&
+			typeof object.constructor === 'function' &&
 			(
 				typeof object.stream === 'function' ||
 				typeof object.arrayBuffer === 'function'

Diff for: package.json

@@ -75,5 +75,8 @@
             "type": "paypal",
             "url": "https://paypal.me/jimmywarting"
         }
-    ]
+    ],
+    "dependencies": {
+        "web-streams-polyfill": "^3.0.3"
+    }
 }

Diff for: test.js

@@ -160,7 +160,7 @@ test('blob part backed up by filesystem', async t => {
 test('Reading after modified should fail', async t => {
 	const blob = blobFromSync('./LICENSE');
 	await new Promise(resolve => {
-		setTimeout(resolve, 100);
+		setTimeout(resolve, 500);
 	});
 	fs.closeSync(fs.openSync('./LICENSE', 'a'));
 	const error = await t.throwsAsync(blob.text());
@@ -174,7 +174,7 @@ test('Reading after modified should fail', async t => {
 	// The lastModifiedDate is deprecated and removed from spec
 	t.false('lastModifiedDate' in file);
 	const mod = file.lastModified - Date.now();
-	t.true(mod <= 0 && mod >= -100); // Close to tolerance: 0.100ms
+	t.true(mod <= 0 && mod >= -500); // Close to tolerance: 0.500ms
 });
 
 test('Reading file after modified should fail', async t => {
@@ -241,7 +241,7 @@ test('Parts are immutable', async t => {
 test('Blobs are immutable', async t => {
 	const buf = new Uint8Array([97]);
 	const blob = new Blob([buf]);
-	const chunk = await blob.stream().next();
+	const chunk = await blob.stream().getReader().read();
 	t.is(chunk.value[0], 97);
 	chunk.value[0] = 98;
 	t.is(await blob.text(), 'a');
@@ -344,3 +344,9 @@ test('new File() throws with too few args', t => {
 		message: 'Failed to construct \'File\': 2 arguments required, but only 0 present.'
 	});
 });
+
+test('can slice zero sized blobs', async t => {
+	const blob = new Blob();
+	const txt = await blob.slice(0, 0).text();
+	t.is(txt, '');
+});