Operate on blob parts (byte sequence) (#44)

* operate on blob parts

* jsdoc

* specify parts type

* Back to 100% (discovered a small bug)

index.js

@@ -1,106 +1,170 @@
-// Based on https://github.com/tmpvar/jsdom/blob/aa85b2abf07766ff7bf5c1f6daafb3726f2f2db5/lib/jsdom/living/blob.js
-// (MIT licensed)
-
-const {Readable: ReadableStream} = require('stream');
+const {Readable} = require('stream');
 
+/**
+ * @type {WeakMap<Blob, {type: string, size: number, parts: (Blob | Buffer)[] }>}
+ */
 const wm = new WeakMap();
 
+async function * read(parts) {
+ for (const part of parts) {
+ if ('stream' in part) {
+ yield * part.stream();
+ } else {
+ yield part;
+ }
+ }
+}
+
+/**
+ * @template T
+ * @param {T} object
+ * @returns {T is Blob}
+ */
+const isBlob = object => {
+ return (
+ typeof object === 'object' &&
+ typeof object.stream === 'function' &&
+ typeof object.constructor === 'function' &&
+ /^(Blob|File)$/.test(object[Symbol.toStringTag])
+ );
+};
+
 class Blob {
+ /**
+ * The Blob() constructor returns a new Blob object. The content
+ * of the blob consists of the concatenation of the values given
+ * in the parameter array.
+ *
+ * @param {(ArrayBufferLike | ArrayBufferView | Blob | Buffer | string)[]} blobParts
+ * @param {{ type?: string }} [options]
+ */
  constructor(blobParts = [], options = {type: ''}) {
- const buffers = [];
  let size = 0;
 
- blobParts.forEach(element => {
+ const parts = blobParts.map(element => {
  let buffer;
- if (element instanceof Buffer) {
+ if (Buffer.isBuffer(element)) {
  buffer = element;
  } else if (ArrayBuffer.isView(element)) {
  buffer = Buffer.from(element.buffer, element.byteOffset, element.byteLength);
  } else if (element instanceof ArrayBuffer) {
  buffer = Buffer.from(element);
- } else if (element instanceof Blob) {
- buffer = wm.get(element).buffer;
+ } else if (isBlob(element)) {
+ buffer = element;
  } else {
  buffer = Buffer.from(typeof element === 'string' ? element : String(element));
  }
 
- size += buffer.length;
- buffers.push(buffer);
+ size += buffer.length || buffer.size || 0;
+ return buffer;
  });
 
- const buffer = Buffer.concat(buffers, size);
-
  const type = options.type === undefined ? '' : String(options.type).toLowerCase();
 
  wm.set(this, {
  type: /[^\u0020-\u007E]/.test(type) ? '' : type,
  size,
- buffer
+ parts
  });
  }
 
+ /**
+ * The Blob interface's size property returns the
+ * size of the Blob in bytes.
+ */
  get size() {
  return wm.get(this).size;
  }
 
+ /**
+ * The type property of a Blob object returns the MIME type of the file.
+ */
  get type() {
  return wm.get(this).type;
  }
 
- text() {
- return Promise.resolve(wm.get(this).buffer.toString());
+ /**
+ * The text() method in the Blob interface returns a Promise
+ * that resolves with a string containing the contents of
+ * the blob, interpreted as UTF-8.
+ *
+ * @return {Promise<string>}
+ */
+ async text() {
+ return Buffer.from(await this.arrayBuffer()).toString();
  }
 
- arrayBuffer() {
- const buf = wm.get(this).buffer;
- const ab = buf.buffer.slice(buf.byteOffset, buf.byteOffset + buf.byteLength);
- return Promise.resolve(ab);
- }
+ /**
+ * The arrayBuffer() method in the Blob interface returns a
+ * Promise that resolves with the contents of the blob as
+ * binary data contained in an ArrayBuffer.
+ *
+ * @return {Promise<ArrayBuffer>}
+ */
+ async arrayBuffer() {
+ const data = new Uint8Array(this.size);
+ let offset = 0;
+ for await (const chunk of this.stream()) {
+ data.set(chunk, offset);
+ offset += chunk.length;
+ }
 
- stream() {
- const readable = new ReadableStream();
- readable._read = () => { };
- readable.push(wm.get(this).buffer);
- readable.push(null);
- return readable;
+ return data.buffer;
  }
 
- toString() {
- return '[object Blob]';
+ /**
+ * The Blob interface's stream() method is difference from native
+ * and uses node streams instead of whatwg streams.
+ *
+ * @returns {Readable} Node readable stream
+ */
+ stream() {
+ return Readable.from(read(wm.get(this).parts));
  }
 
- slice(...args) {
+ /**
+ * The Blob interface's slice() method creates and returns a
+ * new Blob object which contains data from a subset of the
+ * blob on which it's called.
+ *
+ * @param {number} [start]
+ * @param {number} [end]
+ * @param {string} [contentType]
+ */
+ slice(start = 0, end = this.size, type = '') {
  const {size} = this;
 
- const start = args[0];
- const end = args[1];
- let relativeStart;
- let relativeEnd;
+ let relativeStart = start < 0 ? Math.max(size + start, 0) : Math.min(start, size);
+ let relativeEnd = end < 0 ? Math.max(size + end, 0) : Math.min(end, size);
 
- if (start === undefined) {
- relativeStart = 0; //
- } else if (start < 0) {
- relativeStart = Math.max(size + start, 0); //
- } else {
- relativeStart = Math.min(start, size);
+ const span = Math.max(relativeEnd - relativeStart, 0);
+ const parts = wm.get(this).parts.values();
+ const blobParts = [];
+ let added = 0;
+
+ for (const part of parts) {
+ const size = ArrayBuffer.isView(part) ? part.byteLength : part.size;
+ if (relativeStart && size <= relativeStart) {
+ // Skip the beginning and change the relative
+ // start & end position as we skip the unwanted parts
+ relativeStart -= size;
+ relativeEnd -= size;
+ } else {
+ const chunk = part.slice(relativeStart, Math.min(size, relativeEnd));
+ blobParts.push(chunk);
+ added += size;
+ relativeStart = 0; // All next sequental parts should start at 0
+
+ // don't add the overflow to new blobParts
+ if (added >= span) {
+ break;
+ }
+ }
  }
 
- if (end === undefined) {
- relativeEnd = size; //
- } else if (end < 0) {
- relativeEnd = Math.max(size + end, 0); //
- } else {
- relativeEnd = Math.min(end, size);
- }
+ const blob = new Blob([], {type});
+ Object.assign(wm.get(blob), {size: span, parts: blobParts});
 
- const span = Math.max(relativeEnd - relativeStart, 0);
- const slicedBuffer = wm.get(this).buffer.slice(
- relativeStart,
- relativeStart + span
- );
- const blob = new Blob([], {type: args[2]});
- const _ = wm.get(blob);
- _.buffer = slicedBuffer;
  return blob;
  }
 }

package.json

@@ -19,7 +19,7 @@
  "node-fetch"
  ],
  "engines": {
- "node": ">=6"
+ "node": "^10.17.0"
  },
  "author": "David Frank",
  "license": "MIT",

test.js

@@ -113,6 +113,11 @@ test('Blob slice(0, -1)', async t => {
  t.is(await blob.text(), 'abcdefg');
 });
 
+test('throw away unwanted parts', async t => {
+ const blob = new Blob(['a', 'b', 'c']).slice(1, 2);
+ t.is(await blob.text(), 'b');
+});
+
 test('Blob works with node-fetch Response.blob()', async t => {
  const data = 'a=1';
  const type = 'text/plain';