Nodejs，expressjs - 如何提供延迟响应

Question

I am building a webservice, for which i am using nodejs, phantomjs and expressjs. I am learning all the three.

I want to serve a delayed response to the clients after processing their query. Like for example,

I am processing certain inputs from my client, then, i want to process the data at the backend which will take approx 10 sec on an avg. Then i wanted to serve this page to the client.

Is it possible in node to send multiple responses to the same request or delayed responses so that the template will automatically update the contents.

Or , should i use the same method , like store the json in a file in the server , then serve the page with ajax which will query the page.

please help me. here is the code which i wrote ,

app-server.js(the main file):

// import express module
var express = require('express');
var bodyParser = require('body-parser');
var app = express();

// define all required template files to be served and also define the template engine
app.engine('.html', require('ejs').__express);
app.set('views', __dirname + '/views');
app.set('view engine', 'html');

// Useful modules
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}));

// import the routes
require('./router')(app);
app.listen(8080);

router.js:

var crypto = require('crypto');
var express = require('express');

module.exports = function (app) {

    // define the static routes.
    app.use('/static', express.static('./static'));
    app.use('/media', express.static('./media'));

    //defining the controller.
    var parserlib = require('./controller.js')

    // Define the home root path
    app.get('/', function (req, res) {
        // shows the home search page.
        res.render('index', {content:'template success'});
    });

    app.get('/search', function(req, res){
        res.redirect('/');
    });

    app.post('/search', parserlib.parserlib);
}

controller.js:

var crypto = require('crypto');
var path = require('path')
var childProcess = require('child_process')

exports.parserlib= function(req, res){

    var output = '';
    var url = req.body.search_url;

    var childArgs = [
     path.join(__dirname, 'external-script.js'),
     url,
    ]

    // execute the script in a separate thread.
    childProcess.execFile(binPath, childArgs, function(err, stdout, stderr) {
        // handle results
        console.log(stdout);
        output = stdout;
        //console.log(err);
        //res.send(output);
    });
    //res.send(output);
};

so , what i want to see is, first send a response to client stating that its loading, then i want to update the with processed data. In other languages its not possible to send multiple responses. Not sure about nodejs.

Also, do i have to store the json output from the processed lib to a file and then use ajax to query ? or is it possible to directly update the json object to the client ?

Thanks

Answer 1

This is just not how HTTP works. The clients won't expect it. This has nothing to do with Node or any other framework. The way to do what you're attempting is to actually send a response that the thing is loading, and then have some other mechanism for reporting state.

As an example, you might design a RESTful API. In that RESTful API you might define a endpoint for creating new things:

POST /api/things

The client would post data to that to create a new thing. The response should be something that provides a location of the newly created resource, for example an HTTP 301 to /api/things/1 .

If the user goes to /api/things/1 and the thing isn't done getting made yet, then you can either do a temporary redirect (303) to /api/things/1/status which provides some helpful status information, or just issue a 404.

If you actually want to send back server-side pushes of status information, then you should be looking at WebSockets or a pure Socket API of some kind, neither of which is provided by Express, but both of which are available in Node (checkout the socket.io library and the net core library)