如何将Dart Html客户端Web套接字响应从Blob转换为Uint8List? [英] How to convert a Dart Html client web socket response from Blob to Uint8List?

问题描述

我已经实现了自己的二进制消息协议，用于从Dart客户端到Java服务器的简单请求/响应对象.这些在Dart中编码为Uint8List，在Java的远程服务器上编码为ByteBuffer.往返行程适用于[dart:io]中的WebSocket，因为Dart客户端命令应用程序中的websocket.listen流处理程序将传递类型为Uint8List的数据.

I’ve implemented my own binary message protocol for simple request/response objects from a Dart client to a Java server. These are encoded in Dart as an Uint8List and on the remote server in Java as a ByteBuffer. The round trip works for the WebSocket in [dart:io] because the websocket.listen stream handler in the Dart client command app is passed data typed as Uint8List.

在[dart:html]中，从websocket.onMessage流接收到的MessageEvent.data中的响应数据被键入为Blob.我找不到将Blob转换为Uint8List的方法.因为响应通常是一个大型的二进制数字数组(双精度)，它将为虚拟滚动上下文提供数据，所以我想尽量减少复制.有人可以指出我正确的方向.

In [dart:html] the response data in MessageEvent.data received from the websocket.onMessage stream is typed as Blob. I’m not finding a way to convert the Blob to Uint8List. Because the response will often be a large binary array of numbers (double) that will be supplying data to a virtual scrolling context, I want to minimize copying. Could someone please point me in the right direction.

推荐答案

根据此

According to this article, you need to use a FileReader to do this.

此示例似乎有效，当我在Chrome中测试该结果时，结果类型为Uint8List.

This example seems to work, the result type is a Uint8List when I tested this in Chrome.

  var blob = new Blob(['abc']);  
  var r = new FileReader();
  r.readAsArrayBuffer(blob);
  r.onLoadEnd.listen((e) {
    var data = r.result;
    print(data.runtimeType);
  });

另一种选择是将 WebSocket.binaryType 设置为"arraybuffer".然后，MessageEvent.data将返回一个ByteBuffer，可以将其转换为Uint8List.请参见下面的示例.

Another option is to set WebSocket.binaryType to "arraybuffer". Then MessageEvent.data will return a ByteBuffer which can be turned into a Uint8List. See the example below.

import 'dart:html';
import 'dart:typed_data';

void main() {      

  var ws = new WebSocket('...')..binaryType = 'arraybuffer';

  ws.onMessage.listen((MessageEvent e) {
    ByteBuffer buf = e.data;
    var data = buf.asUint8List();
    // ...
  });
}

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