从两个管道流创建 Node.js 流

Question

如果可能的话，我想通过管道将两个 Node.js 流合并为一个。我正在使用Transform 流。

换句话说，我希望我的库返回myStream 供人们使用。例如，他们可以写：

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

在内部，我正在使用第三方vendorStream，它可以做一些工作，插入到myInternalStream 中包含的我自己的逻辑中。所以上面的内容将转化为：

process.stdin.pipe(vendorStream).pipe(myInternalStream).pipe(process.stdout);

我可以这样做吗？我试过var myStream = vendorStream.pipe(myInternalStream)，但这显然不起作用。

为了与bash 进行类比，假设我想编写一个程序来检查字母h 是否出现在某个流的最后一行（tail -n 1 | grep h）中，我可以创建一个shell 脚本：

# myscript.sh
tail -n 1 | grep h

然后如果人们这样做：

$ printf "abc\ndef\nghi" | . myscript.sh

它只是工作。

这是我目前所拥有的：

// Combine a pipe of two streams into one stream

var util = require('util')
  , Transform = require('stream').Transform;

var chunks1 = [];
var stream1 = new Transform();
var soFar = '';
stream1._transform = function(chunk, encoding, done) {
  chunks1.push(chunk.toString());
  var pieces = (soFar + chunk).split('\n');
  soFar = pieces.pop();
  for (var i = 0; i < pieces.length; i++) {
    var piece = pieces[i];
    this.push(piece);
  }
  return done();
};

var chunks2 = [];
var count = 0;
var stream2 = new Transform();
stream2._transform = function(chunk, encoding, done) {
  chunks2.push(chunk.toString());
  count = count + 1;
  this.push(count + ' ' + chunk.toString() + '\n');
  done();
};

var stdin = process.stdin;
var stdout = process.stdout;

process.on('exit', function () {
    console.error('chunks1: ' + JSON.stringify(chunks1));
    console.error('chunks2: ' + JSON.stringify(chunks2));
});
process.stdout.on('error', process.exit);


// stdin.pipe(stream1).pipe(stream2).pipe(stdout);

// $ (printf "abc\nd"; sleep 1; printf "ef\nghi\n") | node streams-combine.js
// Outputs:
// 1 abc
// 2 def
// 3 ghi
// chunks1: ["abc\nd","ef\nghi\n"]
// chunks2: ["abc","def","ghi"]

// Best working solution I could find
var stream3 = function(src) {
  return src.pipe(stream1).pipe(stream2);
};
stream3(stdin).pipe(stdout);

// $ (printf "abc\nd"; sleep 1; printf "ef\nghi\n") | node streams-combine.js
// Outputs:
// 1 abc
// 2 def
// 3 ghi
// chunks1: ["abc\nd","ef\nghi\n"]
// chunks2: ["abc","def","ghi"]

这有可能吗？如果不清楚我想要做什么，请告诉我。

谢谢！

Answer 1

您可以观察要传送到您的流的内容，然后unpipe 并将其传送到您感兴趣的流中：

var PassThrough = require('stream').PassThrough;

var stream3 = new PassThrough();

// When a source stream is piped to us, undo that pipe, and save
// off the source stream piped into our internally managed streams.
stream3.on('pipe', function(source) {
  source.unpipe(this);
  this.transformStream = source.pipe(stream1).pipe(stream2);
});

// When we're piped to another stream, instead pipe our internal
// transform stream to that destination.
stream3.pipe = function(destination, options) {
  return this.transformStream.pipe(destination, options);
};

stdin.pipe(stream3).pipe(stdout);

您可以将此功能提取到您自己的可构造流类中：

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

var StreamCombiner = function() {
  this.streams = Array.prototype.slice.apply(arguments);

  this.on('pipe', function(source) {
    source.unpipe(this);
    for(i in this.streams) {
      source = source.pipe(this.streams[i]);
    }
    this.transformStream = source;
  });
};

util.inherits(StreamCombiner, PassThrough);

StreamCombiner.prototype.pipe = function(dest, options) {
  return this.transformStream.pipe(dest, options);
};

var stream3 = new StreamCombiner(stream1, stream2);
stdin.pipe(stream3).pipe(stdout);

Answer 2

一种选择可能是使用multipipe，它允许您将多个转换链接在一起，包装为单个转换流：

// my-stream.js
var multipipe = require('multipipe');

module.exports = function createMyStream() {
  return multipipe(vendorStream, myInternalStream);
};

那么你可以这样做：

var createMyStream = require('./my-stream');

var myStream = createMyStream();

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

澄清：这使得标准输入通过vendorStream，然后是myInternalStream，最后是stdout。