In-depth understanding of stream and pipe in nodejs

This article mainly introduces the principles and implementation of understanding the stream and pipe mechanism of nodejs. It has certain reference value. Interested friends can refer to it

Preface

Someone asked me about pipe a few days ago. I found that although I have used nodejs for a long time, I often avoid using stream because I don’t use it much each time. As a result, I have never been familiar with it. Now I am re-learning and sorting it out. related information.

Learn stream through nodeschool

nodeschool has a stream-adventure tutorial to teach the use of stream, it is very simple

Simple stream for pipe

First of all, we can locate the input to the output through the pipeline. The input and output can be the console or file stream or http request, such as

##

process.stdin.pipe(process.stdout)
process.stdin.pipe(fs.createWriteStream(path))
fs.createReadStream(path).pipe(process.stdin)

Processing in the middle of the pipe

var through2 = require('through2');
var stream = through2(write,end)
process.stdin
  .pipe(stream)
  .pipe(process.stdout);

function write(line,_,next){
  this.push(line.toString().toUpperCase())
  next();
})
function end(done){
  done();
})

stream is converted into a normal callback

var concat = require('concat-stream');

var reverseStream=concat(function(text){
  console.log(text.toString().split("").reverse().join(""));
})

process.stdin.pipe(reverseStream)

Stream in http server

var http = require('http');
var server = http.createServer(function(req,res){
  req.pipe(res);
})

serves as both input and output Stream

var request = require('request');
var r = request.post('http://localhost:8099');
process.stdin.pipe(r).pipe(process.stdout)

Branch pipeline

var trumpet = require('trumpet');
var through2 = require('through2');
var fs = require('fs');
var tr = trumpet();
var stream = tr.select('.loud').createStream();
var upper = through2(function(buf,_,next){
  this.push(buf.toString().toUpperCase());
  next();
})
stream.pipe(upper).pipe(stream);
process.stdin.pipe(tr).pipe(process.stdout);

Combined input and output stream example

var spawn = require('child_process').spawn;
var duplexer2 = require('duplexer2');

module.exports = function(cmd, args){
  var c = spawn(cmd,args)
  return duplexer2(c.stdin,c.stdout)
}

Summary

• Stream is divided into readable and writeble

##Stream controls the flow direction through the pipe method
httpServer and httpClient and file system and process.stdin\out\err can usually be used as stream
Stream can be converted into ordinary variables by on(event), ordinary variables Can be converted into stream by write
Stream itself can be split, merged, and filtered

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