如何在 rxjs 中使用节点的转换流？

Question

我已经使用rxjs一段时间了，我喜欢如何使用它的运算符进行逻辑编程，而不是命令式编程。然而，我也喜欢node的流，它们也是高度可组合的，所以我的明显反应是同时使用它们，但除了在rxjs的书中为其绑定之外，我还没有看到它被提及很多（实际上，我根本没有）。

所以，我的问题是，我如何利用RxJS上npm中的所有转换流？或者，这可能吗
示例：-

var fs = require('fs');
var csv = require('csv-parse')({delimiter:';'});
var src = fs.createReadStream('./myFile.csv');
src.pipe(csv).pipe(process.stdout);

本质上，我想这样做：-

var fs = require('fs');
var csv = require('csv-parse')({delimiter:';'});
var rx= require('rx-node');
var src = fs.createReadStream('./myFile.csv');
var obj = rx.fromReadableStream(src);
obj.pipe(csb).map(x=>console.log(x));

过去我被告知要使用highland，但我在这里严格寻找rxjs解决方案。

Answer 1

您不必使用rx-node，但您可以！记住：All streams are event emitters!。

准备：input.txt

Hello World!
Hello World!
Hello World!
Hello World!
Hello World!

运行：

npm install through2 split2 rx rx-node

并且在index.js:中

var Rx = require('rx');
Rx.Node = require('rx-node');
var fs = require('fs');
var th2 = require('through2');
var split2 = require('split2');
var file = fs.createReadStream('./input.txt').on('error', console.log.bind(console, 'fs err'));
var transform = th2(function(ch, en, cb) {
  cb(null, ch.toString());
}).on('error', function(err) {
  console.log(err, err.toString());
});
// All streams are event emitters ! (one way without using rx-node)
// var subs = Rx.Observable.fromEvent(transform, 'data').share();
// subs
//   .map(value => 'Begin line: ' + value)
//   .subscribe(value => console.log(value));
// rx-node has convenience functions (another way)
var subs = Rx.Node.fromTransformStream(transform).share()
  .map(value => 'Begin line: ' + value)
  .subscribe(value => console.log(value));
file.pipe(split2()).pipe(transform);

输出：

Begin line: Hello World!
Begin line: Hello World!
Begin line: Hello World!
Begin line: Hello World!
Begin line: Hello World!

Answer 2

EdinM给出了一个在节点转换流中使用RxJS的好的一般示例，但您最初的问题仍未得到解答。由于几天前我遇到了几乎相同的问题，我想努力为那些不熟悉在Node中使用RxJS的人回答这个问题。我将使用csv-streamify，而不是使用csv-parse模块。让我们设置基本结构：

test_data.csv：

thing,name,owner,loc
chair,sitty,billy,san fran
table,setty,bryan,new oak

运行：

$ npm install rx rx-node csv-streamify

index.js:

"use strict";
const Rx = require('rx');
Rx.Node = require('rx-node');
const fs = require('fs');
const csv = require('csv-streamify');

//Setting up the transform-stream CSV parser
let config = {
  delimiter: ',',       // comma, semicolon, whatever
  newline: 'n',        // newline character (use rn for CRLF files)
  quote: '"',           // what's considered a quote
  empty: '',            // empty fields are replaced by this
  //objectMode: true,   //parses csv table into an array of objects
  //columns: true       //uses column headers for the object fields
};
let parseCsv = csv(config);
//Setting up the RxJS Observer
function onNext (x) {
    //do your side-effects here, after the data has 
    //gone through the observables operator chain
    console.log('Next: ' + x); 
};
function onError (err) {
    console.log('Error: ' + err);
};
function onComplete () {
    console.log('Completed');
};
let readStream = fs.createReadStream('test_files/test_data.csv');
readStream.pipe(parseCsv);
let subscription = Rx.Node.fromTransformStream(parseCsv)
    //do something with the data with an operator such as:
    //.map()
    .subscribe(onNext, onError, onComplete);

现在让我们运行代码：

$ node index.js

我们将得到这个输出：

Next: ["thing","name","owner","locr"]
Next: ["chair","sitty","billy","san franr"]
Next: ["table","setty","bryan","new oak"]
Completed

结语

如果您在csv配置对象中将objectMode和columns设置为true，然后使用映射运算符来投影此sideEffect函数，如下所示：

function sideEffect (v){ 
  console.log(v) 
  return v;
};
let subscription = Rx.Node.fromTransformStream(parseCsv)
  .map(sideEffect)
  .subscribe(onNext, onError, onComplete);

您将得到以下输出：

{ thing: 'chair',
  name: 'sitty',
  owner: 'billy',
  'locr': 'san franr' }
Next: [object Object]
{ thing: 'table',
  name: 'setty',
  owner: 'bryan',
  'locr': 'new oak' }
Next: [object Object]
Completed