过滤node.js中的Stream对象 [英] Filtering Stream object in node.js

问题描述

在我看来，在Node.js中处理某些类型数据的优雅方法是链接处理对象，如UNIX管道。

It seems to me that an elegant way to process certain kinds of data in Node.js would be to chain processing objects, like UNIX pipes.

例如， grep：

function Grep(pattern) {
    ...
}
util.inherits(Grep, stream.Stream);

Grep.prototype.???? = ???????  // What goes here?

grep = new Grep(/foo/);

process.stdin.pipe(grep);
myStream.pipe(process.stdout);

然而，我并不清楚如何为了这个需要覆盖各种Stream方法工作。

However it's not at all clear to me how the various Stream methods need to be overridden in order for this to work.

如何创建一个简单地从输入复制到输出的Stream对象？据推测，更复杂的过滤流变得微不足道。

How can I create a Stream object that simply copies from its input to its output? Presumably with that answered, more sophisticated filtering streams become trivial.

更新：感觉好像以下应该有效（用CoffeeScript表示，所以我没有用JS语法填充此框！）：

Update: it feels as if the following should work (expressed in CoffeeScript, so I don't fill this box with JS syntax!):

class Forwarder extends stream.Stream
    write: (chunk, encoding) ->
        @emit 'data', chunk
    end: (chunk, encoding) =>
        if chunk?
            @emit 'data', chunk
        @emit 'end'

fwd = new Forwarder()
fwd.pipe(process.stdout);
process.stdin.pipe(fwd);
process.stdin.resume();

然而，在此脚本中捕获内容不会输出任何内容。在脚本中显式调用'fwd.write（）'会导致stdout输出。

However catting something to this script doesn't output anything. Calling 'fwd.write()' explicitly in the script does cause output on stdout.

推荐答案

你非常接近。

因为您使用的是非常低级的流类，所以需要设置流可写属性以使其成为可写流。如果您正在从流中读取，则需要设置可读属性。此结束事件也没有任何参数。

Because you are using the very low-level stream class, you need to set the stream writable property to make it a writable stream. If you were reading from the stream, you'd need to set the readable property. Also the end event doesn't have any arguments.

class Forwarder extends stream.Stream
  constructor: ->
    @writable = true
  write: (chunk, encoding) ->
    @emit 'data', chunk
  end: ->
    @emit 'end'

fwd = new Forwarder()
fwd.pipe(process.stdout);
process.stdin.pipe(fwd);
process.stdin.resume();

更新

以上答案适用于节点中的V1流<= 0.8。如果你使用> 0.8，Node已经添加了更多旨在扩展的特定类，所以你会使用更像这样的东西：

Update

The answer above applied to V1 streams in Node <= 0.8. If you are using > 0.8, Node has added more specific classes that are designed to be extended, so you would use something more like this:

class Forwarder extends stream.Transform
    _transform: (chunk, encoding, callback) ->
      this.push(chunk);
      callback();

处理 chunk 并实际推送你的碎片想要。

Processing chunk and pushing the pieces you actually want.

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