类：ReadableStreamBYOBReader

【Class: ReadableStreamBYOBReader】

ReadableStreamBYOBReader 是字节导向 <ReadableStream> 的另一种消费方式（那些在创建 ReadableStream 时，其 underlyingSource.type 被设置为 'bytes' 的流）。

【The ReadableStreamBYOBReader is an alternative consumer for byte-oriented <ReadableStream>s (those that are created with underlyingSource.type set equal to 'bytes' when the ReadableStream was created).】

BYOB 是 “bring your own buffer”（自备缓冲区）的缩写。这是一种模式，它允许更高效地读取字节导向的数据，并避免不必要的复制。

【The BYOB is short for "bring your own buffer". This is a pattern that allows for more efficient reading of byte-oriented data that avoids extraneous copying.】

import {
  open,
} from 'node:fs/promises';

import {
  ReadableStream,
} from 'node:stream/web';

import { Buffer } from 'node:buffer';

class Source {
  type = 'bytes';
  autoAllocateChunkSize = 1024;

  async start(controller) {
    this.file = await open(new URL(import.meta.url));
    this.controller = controller;
  }

  async pull(controller) {
    const view = controller.byobRequest?.view;
    const {
      bytesRead,
    } = await this.file.read({
      buffer: view,
      offset: view.byteOffset,
      length: view.byteLength,
    });

    if (bytesRead === 0) {
      await this.file.close();
      this.controller.close();
    }
    controller.byobRequest.respond(bytesRead);
  }
}

const stream = new ReadableStream(new Source());

async function read(stream) {
  const reader = stream.getReader({ mode: 'byob' });

  const chunks = [];
  let result;
  do {
    result = await reader.read(Buffer.alloc(100));
    if (result.value !== undefined)
      chunks.push(Buffer.from(result.value));
  } while (!result.done);

  return Buffer.concat(chunks);
}

const data = await read(stream);
console.log(Buffer.from(data).toString()); 拷贝