从可读流中读取对象会导致TypeError异常 [英] Reading objects from readable stream causes TypeError exception

问题描述

我正在努力使以下代码有效：

I'm trying to make the following code work:

var stream = require('stream');

class MyReadable extends stream.Readable {
  constructor(options) {
    super(options);
  }
  _read(size) {
    this.push({a: 1});
  }
}

var x = new MyReadable({objectMode: true});
x.pipe(process.stdout);

根据 Streams 文档node.js应该没有问题从这样的流中读取非字符串/非缓冲区对象，这要归功于 objectMode 选项被设置为真。然而我最终得到的是以下错误：

According to Streams documentation of node.js there should be no problem reading non-string/non-Buffer objects from such stream thanks to objectMode option being set to true. And yet what I end up with is the following error:

TypeError [ERR_INVALID_ARG_TYPE]: The "chunk" argument must be one of type string or Buffer
    at validChunk (_stream_writable.js:253:10)
    at WriteStream.Writable.write (_stream_writable.js:288:21)
    at MyReadable.ondata (_stream_readable.js:646:20)
    at MyReadable.emit (events.js:160:13)
    at MyReadable.Readable.read (_stream_readable.js:482:10)
    at flow (_stream_readable.js:853:34)
    at resume_ (_stream_readable.js:835:3)
    at process._tickCallback (internal/process/next_tick.js:152:19)
    at Function.Module.runMain (module.js:703:11)
    at startup (bootstrap_node.js:193:16)

如果将 this.push（{a：1}）更改为，让我们说 this.push（'abc'）那么一切都像魅力一样并且我的控制台窗口充斥着'abc'。

If this.push({a: 1}) was changed to, let's say this.push('abc') then everything works like a charm and my console window gets flooded with 'abc'.

另一方面，如果我设置 objectMode 到 false 并仍尝试推送 {a：1} 等对象，然后错误消息更改为：

On the other hand, if I set objectMode to false and still try to push objects like {a: 1} then the error message changes to:

TypeError [ERR_INVALID_ARG_TYPE]: The "chunk" argument must be one of type string, Buffer, or Uint8Array

所以 objectMode 确实改变了一些事情，但并不完全符合我的预期。

So objectMode does change some things but not exactly as I would expect it to.

我正在使用9.4.0版本的node.js。

I'm using 9.4.0 version of node.js.

推荐答案

stacktrace表明问题不在可读流，但在可写流中，您将它汇总到（ process.stdout ）。

The stacktrace indicates that the problem is not in the Readable stream, but in the Writable stream that you're piping it to (process.stdout).

将其替换为可写流 objectMode 设置为 true ，您的错误将消失。

Replace it with a Writable stream that has objectMode set to true, and your error will go away.

var stream = require('stream');

class MyReadable extends stream.Readable {
  constructor(options) {
    super(options);
  }
  _read(size) {
    this.push({a: 1});
  }
}

class MyWritable extends stream.Writable {
  constructor(options) {
    super(options);
  }
  _write(chunk) {
    console.log(chunk);
  }
}

var x = new MyReadable({objectMode: true});
x.pipe(new MyWritable({objectMode: true}));

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