从JavaScript对象创建Node.js可读流 - 最简单的方法

Question

任何人都可以解释为什么我在使用节点v0.10.21运行以下代码后出现错误？

我知道我可以JSON.stringify()那个对象以获得或多或少相同的结果,这里的要点是理解stream.Readable当objectMode设置为true时.

错误:

net.js:612
    throw new TypeError('invalid data');
          ^
TypeError: invalid data
    at WriteStream.Socket.write (net.js:612:11)
    at write (_stream_readable.js:583:24)
    at flow (_stream_readable.js:592:7)
    at _stream_readable.js:560:7
    at process._tickCallback (node.js:415:13)
    at Function.Module.runMain (module.js:499:11)
    at startup (node.js:119:16)
    at node.js:901:3

代码:

var stream = require('stream');
var edad = require(__dirname + '/public/edad.json');

var rs = new stream.Readable({ objectMode: true });

rs.push(edad);
rs.push(null);
rs.pipe(process.stdout);

Answer 1

rs是一个objectMode流,但process.stdout不是,所以它期望将Buffer实例写入其中.由于它获取了错误的数据类型,因此会抛出错误.

如果您希望能够像这样管道对象,则需要一个支持写入对象和读取为缓冲区的中间流.

像这样的东西:

var stream = require('stream');
var util = require('util');

function StringifyStream(){
    stream.Transform.call(this);

    this._readableState.objectMode = false;
    this._writableState.objectMode = true;
}
util.inherits(StringifyStream, stream.Transform);

StringifyStream.prototype._transform = function(obj, encoding, cb){
    this.push(JSON.stringify(obj));
    cb();
};


var edad = require(__dirname + '/public/edad.json');

var rs = new stream.Readable({ objectMode: true });
rs.push(edad);
rs.push(null);

rs.pipe(new StringifyStream()).pipe(process.stdout);