从两个管道流创建Node.js流

Question

如果可能，我想通过管道将两个Node.js流合并为一个。我正在使用转换流。

换句话说，我希望我的图书馆归还myStream给人们使用。例如，他们可以写：

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

在内部，我使用的是第三方vendorStream，它可以完成一些工作，并插入包含在我自己的逻辑中myInternalStream。因此，以上内容将转换为：

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

我可以那样做吗？我已经尝试过了，var myStream = vendorStream.pipe(myInternalStream)但这显然行不通。

为了与进行类比bash，假设我想编写一个程序来检查h某个流（tail -n 1 | grep h）的最后一行中是否存在该字母，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。

这是我到目前为止的内容：

// 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"]

这是可能吗？让我知道我要做什么不清楚。

谢谢！

Answer 1

您可以查看要传送到流中的内容，然后将其传送到您unpipe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);