如何实现可写流 [英] How to implement a writable stream

问题描述

我想将数据从亚马逊运动流传输到s3日志或Bunyan日志.

I want to pipe data from an amazon kinesis stream to a an s3 log or a bunyan log.

该示例适用于文件写入流或stdout.我将如何伪造自己的可写流?

The sample works with a file write stream or stdout. How would I implmeny my own writable stream?

//this works
var file = fs.createWriteStream('my.log')
kinesisSource.pipe(file)

这表示没有方法开"，这是行不通的

this doesn't work saying it has no method 'on'

var stream = {}; //process.stdout works however
stream.writable = true;
stream.write =function(data){
    console.log(data);
};
kinesisSource.pipe(stream);

我必须为自己的自定义可写流实现哪些方法，文档似乎表明我需要实现写"而不是上"

what methods do I have to implement for my own custom writable stream, the docs seem to indicate I need to implement 'write' and not 'on'

推荐答案

要创建自己的可写流，您有三种可能.

To create your own writable stream, you have three possibilities.

为此，您需要1)扩展Writable类2)在您自己的构造函数中调用Writable构造函数3)在流对象的原型中定义一个_write()方法.

For this you'll need 1) to extend the Writable class 2) to call the Writable constructor in your own constructor 3) define a _write() method in the prototype of your stream object.

这是一个例子:

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

function EchoStream () { // step 2
  stream.Writable.call(this);
};
util.inherits(EchoStream, stream.Writable); // step 1
EchoStream.prototype._write = function (chunk, encoding, done) { // step 3
  console.log(chunk.toString());
  done();
}

var myStream = new EchoStream(); // instanciate your brand new stream
process.stdin.pipe(myStream);

扩展空的可写对象

您可以实例化一个空的Writable对象并实现_write()方法，而不是定义新的对象类型:

Extend an empty Writable object

Instead of defining a new object type, you can instanciate an empty Writable object and implement the _write() method:

var stream = require('stream');
var echoStream = new stream.Writable();
echoStream._write = function (chunk, encoding, done) {
  console.log(chunk.toString());
  done();
};

process.stdin.pipe(echoStream);

使用简化的构造函数API

如果您使用的是io.js，则可以使用简化的构造函数API :

var writable = new stream.Writable({
  write: function(chunk, encoding, next) {
    console.log(chunk.toString());
    next();
  }
});

在节点4+中使用ES6类

class EchoStream extends stream.Writable {
  _write(chunk, enc, next) {
    console.log(chunk.toString());
    next();
  }
}

这篇关于如何实现可写流的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！