Web Page update without polling

Question

I'm developing a web app where a user can request a service and a provider will be available to respond to him. So, When a user requests for some sort of service, our application will send a notification to the provider (asking him to respond to the user). What I'm trying to do is: when a user requests a service, the provider gets the notification instantly (something like facebook does).

One way to get this is using AJAX to send requests to the server every 5-10 secs; what we call is polling (so far i know). But, this method has some defects, i see:-

• Since, the request will be sent every 5-10 secs, it will be a load to the server to manipulate requests and return empty data(very frequently).
• Also its useless to send requests to the server even when there are not any updates.
• Imagine someone request a service just after the server has responded to a request. So, providers must have to wait another 5-10 secs to get a notification that someone has requested something.

So, I wanted to know if there is some technique where we can update our web page instantly when a change occurs in our system without polling requests using AJAX.

Answer 1

here is a simple Server Sent Event Script using php.

support

https://developer.mozilla.org/en-US/docs/Web/API/EventSource

js

var sse=new EventSource("sse.php");
sse.onmessage=function(e){
 document.body.innerHTML=e.data;
};

sse.php

header('Content-Type: text/event-stream'); // specific sse mimetype
header('Cache-Control: no-cache'); // no cache
while(true) {
 if(/*something changes*/){
  echo "id: ".time().PHP_EOL;
  echo "data: ".$data.PHP_EOL;
  echo PHP_EOL;
 }
  ob_flush(); // clear memory
  flush(); // clear memory
  sleep(10);// seconds 
}

this keeps the connection open with the client,

then it checks if something is changed ... db/file whatever

outputs the data if changed

and then clears the php cache

waits 10 seconds and does it again.

---

As you can see the client recieves the data only if something changes on the server

but i totally don't know how the server could handle 1000's of people.

---

node.js would be a better way. but it depends what languages you are using and/or if you can actually use node.js.

websockets is both ways.

server sent event is oneway.(you need this)

EDIT

more data inside the sse response:

js

var sse=new EventSource("sse.php");
sse.onmessage=function(e){
 console.log(JSON.parse(e.data))
};

sse.php

header('Content-Type: text/event-stream'); // specific sse mimetype
header('Cache-Control: no-cache'); // no cache
while(true) {
 if(/*something changes*/){
  echo "id: ".time().PHP_EOL;

  $dataArray=array('id'=>$id,'name'=>$name,'more'=>$more);
  echo "data: ".json_encode($dataArray).PHP_EOL;

  echo PHP_EOL;

 }
  ob_flush(); // clear memory
  flush(); // clear memory
  sleep(10);// seconds 
}

if you need some more info just ask