How do I implement basic Long Polling

Question

I can find lots of information on how Long Polling works  For example  this  and this   but no simple examples of how to implement this in code   All I can find is cometd  which relies on the Dojo JS framework  and a fairly complex server system    Basically  how would I use Apache to serve the requests  and how would I write a simple script  say  in PHP  which would  long-poll  the server for new messages   The example doesn t have to be scaleable  secure or complete  it just needs to work

User · Answer

Below is a long polling solution I have developed for Inform8 Web. Basically you override the class and implement the loadData method. When the loadData returns a value or the operation times out it will print the result and return.

If the processing of your script may take longer than 30 seconds you may need to alter the set_time_limit() call to something longer.

Apache 2.0 license. Latest version on github https://github.com/ryanhend/Inform8/blob/master/Inform8-web/src/config/lib/Inform8/longpoll/LongPoller.php

Ryan

abstract class LongPoller {

  protected $sleepTime = 5;
  protected $timeoutTime = 30;

  function __construct() {
  }


  function setTimeout($timeout) {
    $this->timeoutTime = $timeout;
  }

  function setSleep($sleep) {
    $this->sleepTime = $sleepTime;
  }


  public function run() {
    $data = NULL;
    $timeout = 0;

    set_time_limit($this->timeoutTime + $this->sleepTime + 15);

    //Query database for data
    while($data == NULL && $timeout < $this->timeoutTime) {
      $data = $this->loadData();
      if($data == NULL){

        //No new orders, flush to notify php still alive
        flush();

        //Wait for new Messages
        sleep($this->sleepTime);
        $timeout += $this->sleepTime;
      }else{
        echo $data;
        flush();
      }
    }

  }


  protected abstract function loadData();

}

User · Answer

Here is a simple long-polling example in PHP by Erik Dubbelboer using the Content-type  multipart x-mixed-replace header    lt    header  Content-type  multipart x-mixed-replace  boundary endofsection        Keep in mind that the empty line is important to separate the headers    from the content  echo  Content-type  text plain  After 5 seconds this will go away and a cat will appear    --endofsection    flush       Don t forget to flush the content to the browser    sleep 5     echo  Content-type  image jpg       stream   fopen  cat jpg    rb    fpassthru  stream   fclose  stream    echo   --endofsection      And here is a demo   http   dubbelboer com multipart php

User · Answer

It s simpler than I initially thought   Basically you have a page that does nothing  until the data you want to send is available  say  a new message arrives    Here is a really basic example  which sends a simple string after 2-10 seconds  1 in 3 chance of returning an error 404  to show error handling in the coming Javascript example   msgsrv php   lt  php if rand 1 3     1          Fake an error        header  HTTP 1 0 404 Not Found        die          Send a string after a random number of seconds  2-10     sleep rand 2 10    echo  Hi  Have a random number      rand 1 10      gt    Note  With a real site  running this on a regular web-server like Apache will quickly tie up all the  worker threads  and leave it unable to respond to other requests   There are ways around this  but it is recommended to write a  long-poll server  in something like Python s twisted  which does not rely on one thread per request  cometD is an popular one  which is available in several languages   and Tornado is a new framework made specifically for such tasks  it was built for FriendFeed s long-polling code     but as a simple example  Apache is more than adequate  This script could easily be written in any language  I chose Apache PHP as they are very common  and I happened to be running them locally   Then  in Javascript  you request the above file  msg srv php   and wait for a response   When you get one  you act upon the data  Then you request the file and wait again  act upon the data  and repeat   What follows is an example of such a page   When the page is loaded  it sends the initial request for the msgsrv php file   If it succeeds  we append the message to the  messages div  then after 1 second we call the waitForMsg function again  which triggers the wait   The 1 second setTimeout   is a really basic rate-limiter  it works fine without this  but if msgsrv php always returns instantly  with a syntax error  for example  - you flood the browser and it can quickly freeze up  This would better be done checking if the file contains a valid JSON response  and or keeping a running total of requests-per-minute second  and pausing appropriately   If the page errors  it appends the error to the  messages div  waits 15 seconds and then tries again  identical to how we wait 1 second after each message   The nice thing about this approach is it is very resilient  If the clients internet connection dies  it will timeout  then try and reconnect - this is inherent in how long polling works  no complicated error-handling is required  Anyway  the long poller htm code  using the jQuery framework    lt html gt   lt head gt       lt title gt BargePoller lt  title gt       lt script src  http   ajax googleapis com ajax libs jquery 1 2 6 jquery min js  type  text javascript  charset  utf-8  gt  lt  script gt        lt style type  text css  media  screen  gt        body  background  000 color  fff font-size  9em           msg  background  aaa padding  2em  border-bottom 1px  000 solid         old  background-color  246499          new  background-color  3B9957        error  background-color  992E36        lt  style gt        lt script type  text javascript  charset  utf-8  gt      function addmsg type  msg              Simple helper to add a div          type is the name of a CSS class  old new error           msg is the contents of the div                messages   append                lt div class  msg    type     gt    msg    lt  div gt                         function waitForMsg               This requests the url  msgsrv php          When it complete  or errors              ajax               type   GET               url   msgsrv php                async  true     If set to non-async  browser shows page as  Loading                  cache  false              timeout 50000     Timeout in ms                 success  function data      called when request to barge php completes                    addmsg  new   data      Add response to a  msg div  with the  new  class                    setTimeout                      waitForMsg     Request next message                        1000      after 1 seconds                                                  error  function XMLHttpRequest  textStatus  errorThrown                   addmsg  error   textStatus          errorThrown                         setTimeout                      waitForMsg     Try again after                          15000      milliseconds  15seconds                                             document  ready function            waitForMsg       Start the inital request                 lt  script gt   lt  head gt   lt body gt       lt div id  messages  gt           lt div class  msg old  gt              BargePoll message requester           lt  div gt       lt  div gt   lt  body gt   lt  html gt

User · Answer

Here is a simple long-polling example in PHP by Erik Dubbelboer using the Content-type  multipart x-mixed-replace header    lt    header  Content-type  multipart x-mixed-replace  boundary endofsection        Keep in mind that the empty line is important to separate the headers    from the content  echo  Content-type  text plain  After 5 seconds this will go away and a cat will appear    --endofsection    flush       Don t forget to flush the content to the browser    sleep 5     echo  Content-type  image jpg       stream   fopen  cat jpg    rb    fpassthru  stream   fclose  stream    echo   --endofsection      And here is a demo   http   dubbelboer com multipart php

User · Answer

I used this to get to grips with Comet  I have also set up Comet using the Java Glassfish server and found lots of other examples by subscribing to cometdaily com

User · Answer

I ve got a really simple chat example as part of slosh   Edit   since everyone s pasting their code in here   This is the complete JSON-based multi-user chat using long-polling and slosh   This is a demo of how to do the calls  so please ignore the XSS problems   Nobody should deploy this without sanitizing it first   Notice that the client always has a connection to the server  and as soon as anyone sends a message  everyone should see it roughly instantly    lt  xml version  1 0  encoding  UTF-8   gt   lt  DOCTYPE html PUBLIC  -  W3C  DTD XHTML 1 0 Strict  EN     http   www w3 org TR xhtml1 DTD xhtml1-strict dtd  gt   lt  -- Copyright  c  2008 Dustin Sallings  lt dustin html spy net gt  -- gt   lt html lang  en  gt     lt head gt       lt title gt slosh chat lt  title gt       lt script type  text javascript        src  http   code jquery com jquery-latest js  gt  lt  script gt       lt link title  Default  rel  stylesheet  media  screen  href  style css    gt     lt  head gt      lt body gt       lt h1 gt Welcome to Slosh Chat lt  h1 gt        lt div id  messages  gt         lt div gt           lt span class  from  gt First   lt  span gt           lt span class  msg  gt Welcome to chat  Please don t hurt each other  lt  span gt         lt  div gt       lt  div gt        lt form method  post  action     gt         lt div gt Nick   lt input id  from  type  text  name  from   gt  lt  div gt         lt div gt Message  lt  div gt         lt div gt  lt textarea id  msg  name  msg  gt  lt  textarea gt  lt  div gt         lt div gt  lt input type  submit  value  Say it  id  submit   gt  lt  div gt       lt  form gt        lt script type  text javascript  gt        function gotData json  st            var msgs     messages              each json res  function idx  p              var from   p from 0            var msg   p msg 0            msgs append   lt div gt  lt span class  from  gt     from      lt  span gt                    lt span class  msg  gt     msg     lt  span gt  lt  div gt                            The jQuery wrapped msgs above does not work here          var msgs document getElementById  messages            msgs scrollTop   msgs scrollHeight                 function getNewComments               getJSON   topics chat json   gotData                    document  ready function               document  ajaxStop getNewComments              form   submit function                 post   topics chat      form   serialize               return false                      getNewComments                   lt  script gt     lt  body gt   lt  html gt

User · Answer

Why not consider the web sockets instead of long polling  They are much efficient and easy to setup  However they are supported only in modern browsers  Here is a quick reference

User · Answer

Here are some classes I use for long-polling in C   There are basically 6 classes  see below     Controller  Processes actions required to create a valid response  db operations etc   Processor  Manages asynch communication with the web page  itself  IAsynchProcessor  The service processes instances that implement this interface Sevice  Processes request objects that implement IAsynchProcessor Request  The IAsynchProcessor wrapper containing your response  object  Response  Contains custom objects or fields

User · Answer

I used this to get to grips with Comet  I have also set up Comet using the Java Glassfish server and found lots of other examples by subscribing to cometdaily com

User · Answer

You can try icomet https   github com ideawu icomet   a C1000K C   comet server built with libevent  icomet also provides a JavaScript library  it is easy to use as simple as  var comet   new iComet       sign url   http       app host     sign obj     obj      sub url   http       icomet host     sub       callback  function msg              on server push         alert msg content               icomet supports a wide range of Browsers and OSes  including Safari iOS  Mac   IEs Windows   Firefox  Chrome  etc

User · Answer

Simplest NodeJS  const http   require  http     const server   http createServer  req  res    gt      SomeVeryLongAction res        server on  clientError    err  socket    gt      socket end  HTTP 1 1 400 Bad Request r n r n         server listen 8000       the long running task - simplified to setTimeout here    but can be async  wait from websocket service - whatever really function SomeVeryLongAction response      setTimeout response end  10000       Production wise scenario in Express for exmaple you would get response in the middleware  Do you what you need to do  can scope out all of the long polled methods to Map or something  that is visible to other flows   and invoke  lt Response gt  response end   whenever you are ready  There is nothing special about long polled connections  Rest is just how you normally structure your application   If you dont know what i mean by scoping out  this should give you idea  const http   require  http    var responsesArray        const server   http createServer  req  res    gt         not dealing with connection      put it on stack  array in this case    responsesArray push res        end this is where normal api flow ends      server on  clientError    err  socket    gt      socket end  HTTP 1 1 400 Bad Request r n r n            and eventually when we are ready to resolve    that if is there just to ensure you actually     called endpoint before the timeout kicks in function SomeVeryLongAction       if   responsesArray length         let localResponse   responsesArray shift        localResponse end              simulate some action out of endpoint flow setTimeout SomeVeryLongAction  10000   server listen 8000     As you see  you could really respond to all connections  one  do whatever you want  There is id for every request so you should be able to use map and access specific out of api call

User · Answer

Thanks for the code  dbr  Just a small typo in long poller htm around the line  1000      after 1 seconds      I think it should be   1000         after 1 seconds      for it to work   For those interested  I tried a Django equivalent  Start a new Django project  say lp for long polling   django-admin py startproject lp   Call the app msgsrv for message server   python manage py startapp msgsrv   Add the following lines to settings py to have a templates directory   import os path PROJECT DIR   os path dirname   file    TEMPLATE DIRS         os path join PROJECT DIR   templates        Define your URL patterns in urls py as such   from django views generic simple import direct to template from lp msgsrv views import retmsg  urlpatterns   patterns          r  msgsrv  php    retmsg        r  long poller  htm    direct to template    template    long poller htm         And msgsrv views py should look like   from random import randint from time import sleep from django http import HttpResponse  HttpResponseNotFound  def retmsg request       if randint 1 3     1          return HttpResponseNotFound   lt h1 gt Page not found lt  h1 gt        else          sleep randint 2 10           return HttpResponse  Hi  Have a random number   s    str randint 1 10      Lastly  templates long poller htm should be the same as above with typo corrected  Hope this helps

User · Answer

I ve got a really simple chat example as part of slosh   Edit   since everyone s pasting their code in here   This is the complete JSON-based multi-user chat using long-polling and slosh   This is a demo of how to do the calls  so please ignore the XSS problems   Nobody should deploy this without sanitizing it first   Notice that the client always has a connection to the server  and as soon as anyone sends a message  everyone should see it roughly instantly    lt  xml version  1 0  encoding  UTF-8   gt   lt  DOCTYPE html PUBLIC  -  W3C  DTD XHTML 1 0 Strict  EN     http   www w3 org TR xhtml1 DTD xhtml1-strict dtd  gt   lt  -- Copyright  c  2008 Dustin Sallings  lt dustin html spy net gt  -- gt   lt html lang  en  gt     lt head gt       lt title gt slosh chat lt  title gt       lt script type  text javascript        src  http   code jquery com jquery-latest js  gt  lt  script gt       lt link title  Default  rel  stylesheet  media  screen  href  style css    gt     lt  head gt      lt body gt       lt h1 gt Welcome to Slosh Chat lt  h1 gt        lt div id  messages  gt         lt div gt           lt span class  from  gt First   lt  span gt           lt span class  msg  gt Welcome to chat  Please don t hurt each other  lt  span gt         lt  div gt       lt  div gt        lt form method  post  action     gt         lt div gt Nick   lt input id  from  type  text  name  from   gt  lt  div gt         lt div gt Message  lt  div gt         lt div gt  lt textarea id  msg  name  msg  gt  lt  textarea gt  lt  div gt         lt div gt  lt input type  submit  value  Say it  id  submit   gt  lt  div gt       lt  form gt        lt script type  text javascript  gt        function gotData json  st            var msgs     messages              each json res  function idx  p              var from   p from 0            var msg   p msg 0            msgs append   lt div gt  lt span class  from  gt     from      lt  span gt                    lt span class  msg  gt     msg     lt  span gt  lt  div gt                            The jQuery wrapped msgs above does not work here          var msgs document getElementById  messages            msgs scrollTop   msgs scrollHeight                 function getNewComments               getJSON   topics chat json   gotData                    document  ready function               document  ajaxStop getNewComments              form   submit function                 post   topics chat      form   serialize               return false                      getNewComments                   lt  script gt     lt  body gt   lt  html gt

User · Answer

Thanks for the code  dbr  Just a small typo in long poller htm around the line  1000      after 1 seconds      I think it should be   1000         after 1 seconds      for it to work   For those interested  I tried a Django equivalent  Start a new Django project  say lp for long polling   django-admin py startproject lp   Call the app msgsrv for message server   python manage py startapp msgsrv   Add the following lines to settings py to have a templates directory   import os path PROJECT DIR   os path dirname   file    TEMPLATE DIRS         os path join PROJECT DIR   templates        Define your URL patterns in urls py as such   from django views generic simple import direct to template from lp msgsrv views import retmsg  urlpatterns   patterns          r  msgsrv  php    retmsg        r  long poller  htm    direct to template    template    long poller htm         And msgsrv views py should look like   from random import randint from time import sleep from django http import HttpResponse  HttpResponseNotFound  def retmsg request       if randint 1 3     1          return HttpResponseNotFound   lt h1 gt Page not found lt  h1 gt        else          sleep randint 2 10           return HttpResponse  Hi  Have a random number   s    str randint 1 10      Lastly  templates long poller htm should be the same as above with typo corrected  Hope this helps

User · Answer

Simplest NodeJS  const http   require  http     const server   http createServer  req  res    gt      SomeVeryLongAction res        server on  clientError    err  socket    gt      socket end  HTTP 1 1 400 Bad Request r n r n         server listen 8000       the long running task - simplified to setTimeout here    but can be async  wait from websocket service - whatever really function SomeVeryLongAction response      setTimeout response end  10000       Production wise scenario in Express for exmaple you would get response in the middleware  Do you what you need to do  can scope out all of the long polled methods to Map or something  that is visible to other flows   and invoke  lt Response gt  response end   whenever you are ready  There is nothing special about long polled connections  Rest is just how you normally structure your application   If you dont know what i mean by scoping out  this should give you idea  const http   require  http    var responsesArray        const server   http createServer  req  res    gt         not dealing with connection      put it on stack  array in this case    responsesArray push res        end this is where normal api flow ends      server on  clientError    err  socket    gt      socket end  HTTP 1 1 400 Bad Request r n r n            and eventually when we are ready to resolve    that if is there just to ensure you actually     called endpoint before the timeout kicks in function SomeVeryLongAction       if   responsesArray length         let localResponse   responsesArray shift        localResponse end              simulate some action out of endpoint flow setTimeout SomeVeryLongAction  10000   server listen 8000     As you see  you could really respond to all connections  one  do whatever you want  There is id for every request so you should be able to use map and access specific out of api call

User · Answer

I think the client looks like a normal asynchronous AJAX request  but you expect it to take a  long time  to come back   The server then looks like this   while   hasNewData        usleep 50    outputNewData      So  the AJAX request goes to the server  probably including a timestamp of when it was last update so that your hasNewData   knows what data you have already got  The server then sits in a loop sleeping until new data is available   All the while  your AJAX request is still connected  just hanging there waiting for data  Finally  when new data is available  the server gives it to your AJAX request and closes the connection

User · Answer

For a ASP NET MVC implementation  look at SignalR which is available on NuGet   note that the NuGet is often out of date from the Git source which gets very frequent commits   Read more about SignalR on a blog on by Scott Hanselman

User · Answer

It s simpler than I initially thought   Basically you have a page that does nothing  until the data you want to send is available  say  a new message arrives    Here is a really basic example  which sends a simple string after 2-10 seconds  1 in 3 chance of returning an error 404  to show error handling in the coming Javascript example   msgsrv php   lt  php if rand 1 3     1          Fake an error        header  HTTP 1 0 404 Not Found        die          Send a string after a random number of seconds  2-10     sleep rand 2 10    echo  Hi  Have a random number      rand 1 10      gt    Note  With a real site  running this on a regular web-server like Apache will quickly tie up all the  worker threads  and leave it unable to respond to other requests   There are ways around this  but it is recommended to write a  long-poll server  in something like Python s twisted  which does not rely on one thread per request  cometD is an popular one  which is available in several languages   and Tornado is a new framework made specifically for such tasks  it was built for FriendFeed s long-polling code     but as a simple example  Apache is more than adequate  This script could easily be written in any language  I chose Apache PHP as they are very common  and I happened to be running them locally   Then  in Javascript  you request the above file  msg srv php   and wait for a response   When you get one  you act upon the data  Then you request the file and wait again  act upon the data  and repeat   What follows is an example of such a page   When the page is loaded  it sends the initial request for the msgsrv php file   If it succeeds  we append the message to the  messages div  then after 1 second we call the waitForMsg function again  which triggers the wait   The 1 second setTimeout   is a really basic rate-limiter  it works fine without this  but if msgsrv php always returns instantly  with a syntax error  for example  - you flood the browser and it can quickly freeze up  This would better be done checking if the file contains a valid JSON response  and or keeping a running total of requests-per-minute second  and pausing appropriately   If the page errors  it appends the error to the  messages div  waits 15 seconds and then tries again  identical to how we wait 1 second after each message   The nice thing about this approach is it is very resilient  If the clients internet connection dies  it will timeout  then try and reconnect - this is inherent in how long polling works  no complicated error-handling is required  Anyway  the long poller htm code  using the jQuery framework    lt html gt   lt head gt       lt title gt BargePoller lt  title gt       lt script src  http   ajax googleapis com ajax libs jquery 1 2 6 jquery min js  type  text javascript  charset  utf-8  gt  lt  script gt        lt style type  text css  media  screen  gt        body  background  000 color  fff font-size  9em           msg  background  aaa padding  2em  border-bottom 1px  000 solid         old  background-color  246499          new  background-color  3B9957        error  background-color  992E36        lt  style gt        lt script type  text javascript  charset  utf-8  gt      function addmsg type  msg              Simple helper to add a div          type is the name of a CSS class  old new error           msg is the contents of the div                messages   append                lt div class  msg    type     gt    msg    lt  div gt                         function waitForMsg               This requests the url  msgsrv php          When it complete  or errors              ajax               type   GET               url   msgsrv php                async  true     If set to non-async  browser shows page as  Loading                  cache  false              timeout 50000     Timeout in ms                 success  function data      called when request to barge php completes                    addmsg  new   data      Add response to a  msg div  with the  new  class                    setTimeout                      waitForMsg     Request next message                        1000      after 1 seconds                                                  error  function XMLHttpRequest  textStatus  errorThrown                   addmsg  error   textStatus          errorThrown                         setTimeout                      waitForMsg     Try again after                          15000      milliseconds  15seconds                                             document  ready function            waitForMsg       Start the inital request                 lt  script gt   lt  head gt   lt body gt       lt div id  messages  gt           lt div class  msg old  gt              BargePoll message requester           lt  div gt       lt  div gt   lt  body gt   lt  html gt

User · Answer

It s simpler than I initially thought   Basically you have a page that does nothing  until the data you want to send is available  say  a new message arrives    Here is a really basic example  which sends a simple string after 2-10 seconds  1 in 3 chance of returning an error 404  to show error handling in the coming Javascript example   msgsrv php   lt  php if rand 1 3     1          Fake an error        header  HTTP 1 0 404 Not Found        die          Send a string after a random number of seconds  2-10     sleep rand 2 10    echo  Hi  Have a random number      rand 1 10      gt    Note  With a real site  running this on a regular web-server like Apache will quickly tie up all the  worker threads  and leave it unable to respond to other requests   There are ways around this  but it is recommended to write a  long-poll server  in something like Python s twisted  which does not rely on one thread per request  cometD is an popular one  which is available in several languages   and Tornado is a new framework made specifically for such tasks  it was built for FriendFeed s long-polling code     but as a simple example  Apache is more than adequate  This script could easily be written in any language  I chose Apache PHP as they are very common  and I happened to be running them locally   Then  in Javascript  you request the above file  msg srv php   and wait for a response   When you get one  you act upon the data  Then you request the file and wait again  act upon the data  and repeat   What follows is an example of such a page   When the page is loaded  it sends the initial request for the msgsrv php file   If it succeeds  we append the message to the  messages div  then after 1 second we call the waitForMsg function again  which triggers the wait   The 1 second setTimeout   is a really basic rate-limiter  it works fine without this  but if msgsrv php always returns instantly  with a syntax error  for example  - you flood the browser and it can quickly freeze up  This would better be done checking if the file contains a valid JSON response  and or keeping a running total of requests-per-minute second  and pausing appropriately   If the page errors  it appends the error to the  messages div  waits 15 seconds and then tries again  identical to how we wait 1 second after each message   The nice thing about this approach is it is very resilient  If the clients internet connection dies  it will timeout  then try and reconnect - this is inherent in how long polling works  no complicated error-handling is required  Anyway  the long poller htm code  using the jQuery framework    lt html gt   lt head gt       lt title gt BargePoller lt  title gt       lt script src  http   ajax googleapis com ajax libs jquery 1 2 6 jquery min js  type  text javascript  charset  utf-8  gt  lt  script gt        lt style type  text css  media  screen  gt        body  background  000 color  fff font-size  9em           msg  background  aaa padding  2em  border-bottom 1px  000 solid         old  background-color  246499          new  background-color  3B9957        error  background-color  992E36        lt  style gt        lt script type  text javascript  charset  utf-8  gt      function addmsg type  msg              Simple helper to add a div          type is the name of a CSS class  old new error           msg is the contents of the div                messages   append                lt div class  msg    type     gt    msg    lt  div gt                         function waitForMsg               This requests the url  msgsrv php          When it complete  or errors              ajax               type   GET               url   msgsrv php                async  true     If set to non-async  browser shows page as  Loading                  cache  false              timeout 50000     Timeout in ms                 success  function data      called when request to barge php completes                    addmsg  new   data      Add response to a  msg div  with the  new  class                    setTimeout                      waitForMsg     Request next message                        1000      after 1 seconds                                                  error  function XMLHttpRequest  textStatus  errorThrown                   addmsg  error   textStatus          errorThrown                         setTimeout                      waitForMsg     Try again after                          15000      milliseconds  15seconds                                             document  ready function            waitForMsg       Start the inital request                 lt  script gt   lt  head gt   lt body gt       lt div id  messages  gt           lt div class  msg old  gt              BargePoll message requester           lt  div gt       lt  div gt   lt  body gt   lt  html gt

User · Answer

I ve got a really simple chat example as part of slosh   Edit   since everyone s pasting their code in here   This is the complete JSON-based multi-user chat using long-polling and slosh   This is a demo of how to do the calls  so please ignore the XSS problems   Nobody should deploy this without sanitizing it first   Notice that the client always has a connection to the server  and as soon as anyone sends a message  everyone should see it roughly instantly    lt  xml version  1 0  encoding  UTF-8   gt   lt  DOCTYPE html PUBLIC  -  W3C  DTD XHTML 1 0 Strict  EN     http   www w3 org TR xhtml1 DTD xhtml1-strict dtd  gt   lt  -- Copyright  c  2008 Dustin Sallings  lt dustin html spy net gt  -- gt   lt html lang  en  gt     lt head gt       lt title gt slosh chat lt  title gt       lt script type  text javascript        src  http   code jquery com jquery-latest js  gt  lt  script gt       lt link title  Default  rel  stylesheet  media  screen  href  style css    gt     lt  head gt      lt body gt       lt h1 gt Welcome to Slosh Chat lt  h1 gt        lt div id  messages  gt         lt div gt           lt span class  from  gt First   lt  span gt           lt span class  msg  gt Welcome to chat  Please don t hurt each other  lt  span gt         lt  div gt       lt  div gt        lt form method  post  action     gt         lt div gt Nick   lt input id  from  type  text  name  from   gt  lt  div gt         lt div gt Message  lt  div gt         lt div gt  lt textarea id  msg  name  msg  gt  lt  textarea gt  lt  div gt         lt div gt  lt input type  submit  value  Say it  id  submit   gt  lt  div gt       lt  form gt        lt script type  text javascript  gt        function gotData json  st            var msgs     messages              each json res  function idx  p              var from   p from 0            var msg   p msg 0            msgs append   lt div gt  lt span class  from  gt     from      lt  span gt                    lt span class  msg  gt     msg     lt  span gt  lt  div gt                            The jQuery wrapped msgs above does not work here          var msgs document getElementById  messages            msgs scrollTop   msgs scrollHeight                 function getNewComments               getJSON   topics chat json   gotData                    document  ready function               document  ajaxStop getNewComments              form   submit function                 post   topics chat      form   serialize               return false                      getNewComments                   lt  script gt     lt  body gt   lt  html gt

User · Answer

This is a nice 5-minute screencast on how to do long polling using PHP  amp  jQuery  http   screenr com SNH  Code is quite similar to dbr s example above

User · Answer

Take a look at this blog post which has code for a simple chat app in Python Django gevent

User · Answer

It s simpler than I initially thought   Basically you have a page that does nothing  until the data you want to send is available  say  a new message arrives    Here is a really basic example  which sends a simple string after 2-10 seconds  1 in 3 chance of returning an error 404  to show error handling in the coming Javascript example   msgsrv php   lt  php if rand 1 3     1          Fake an error        header  HTTP 1 0 404 Not Found        die          Send a string after a random number of seconds  2-10     sleep rand 2 10    echo  Hi  Have a random number      rand 1 10      gt    Note  With a real site  running this on a regular web-server like Apache will quickly tie up all the  worker threads  and leave it unable to respond to other requests   There are ways around this  but it is recommended to write a  long-poll server  in something like Python s twisted  which does not rely on one thread per request  cometD is an popular one  which is available in several languages   and Tornado is a new framework made specifically for such tasks  it was built for FriendFeed s long-polling code     but as a simple example  Apache is more than adequate  This script could easily be written in any language  I chose Apache PHP as they are very common  and I happened to be running them locally   Then  in Javascript  you request the above file  msg srv php   and wait for a response   When you get one  you act upon the data  Then you request the file and wait again  act upon the data  and repeat   What follows is an example of such a page   When the page is loaded  it sends the initial request for the msgsrv php file   If it succeeds  we append the message to the  messages div  then after 1 second we call the waitForMsg function again  which triggers the wait   The 1 second setTimeout   is a really basic rate-limiter  it works fine without this  but if msgsrv php always returns instantly  with a syntax error  for example  - you flood the browser and it can quickly freeze up  This would better be done checking if the file contains a valid JSON response  and or keeping a running total of requests-per-minute second  and pausing appropriately   If the page errors  it appends the error to the  messages div  waits 15 seconds and then tries again  identical to how we wait 1 second after each message   The nice thing about this approach is it is very resilient  If the clients internet connection dies  it will timeout  then try and reconnect - this is inherent in how long polling works  no complicated error-handling is required  Anyway  the long poller htm code  using the jQuery framework    lt html gt   lt head gt       lt title gt BargePoller lt  title gt       lt script src  http   ajax googleapis com ajax libs jquery 1 2 6 jquery min js  type  text javascript  charset  utf-8  gt  lt  script gt        lt style type  text css  media  screen  gt        body  background  000 color  fff font-size  9em           msg  background  aaa padding  2em  border-bottom 1px  000 solid         old  background-color  246499          new  background-color  3B9957        error  background-color  992E36        lt  style gt        lt script type  text javascript  charset  utf-8  gt      function addmsg type  msg              Simple helper to add a div          type is the name of a CSS class  old new error           msg is the contents of the div                messages   append                lt div class  msg    type     gt    msg    lt  div gt                         function waitForMsg               This requests the url  msgsrv php          When it complete  or errors              ajax               type   GET               url   msgsrv php                async  true     If set to non-async  browser shows page as  Loading                  cache  false              timeout 50000     Timeout in ms                 success  function data      called when request to barge php completes                    addmsg  new   data      Add response to a  msg div  with the  new  class                    setTimeout                      waitForMsg     Request next message                        1000      after 1 seconds                                                  error  function XMLHttpRequest  textStatus  errorThrown                   addmsg  error   textStatus          errorThrown                         setTimeout                      waitForMsg     Try again after                          15000      milliseconds  15seconds                                             document  ready function            waitForMsg       Start the inital request                 lt  script gt   lt  head gt   lt body gt       lt div id  messages  gt           lt div class  msg old  gt              BargePoll message requester           lt  div gt       lt  div gt   lt  body gt   lt  html gt

User · Answer

You can try icomet https   github com ideawu icomet   a C1000K C   comet server built with libevent  icomet also provides a JavaScript library  it is easy to use as simple as  var comet   new iComet       sign url   http       app host     sign obj     obj      sub url   http       icomet host     sub       callback  function msg              on server push         alert msg content               icomet supports a wide range of Browsers and OSes  including Safari iOS  Mac   IEs Windows   Firefox  Chrome  etc

User · Answer

I used this to get to grips with Comet  I have also set up Comet using the Java Glassfish server and found lots of other examples by subscribing to cometdaily com

User · Answer

For a ASP NET MVC implementation  look at SignalR which is available on NuGet   note that the NuGet is often out of date from the Git source which gets very frequent commits   Read more about SignalR on a blog on by Scott Hanselman

User · Answer

I ve got a really simple chat example as part of slosh   Edit   since everyone s pasting their code in here   This is the complete JSON-based multi-user chat using long-polling and slosh   This is a demo of how to do the calls  so please ignore the XSS problems   Nobody should deploy this without sanitizing it first   Notice that the client always has a connection to the server  and as soon as anyone sends a message  everyone should see it roughly instantly    lt  xml version  1 0  encoding  UTF-8   gt   lt  DOCTYPE html PUBLIC  -  W3C  DTD XHTML 1 0 Strict  EN     http   www w3 org TR xhtml1 DTD xhtml1-strict dtd  gt   lt  -- Copyright  c  2008 Dustin Sallings  lt dustin html spy net gt  -- gt   lt html lang  en  gt     lt head gt       lt title gt slosh chat lt  title gt       lt script type  text javascript        src  http   code jquery com jquery-latest js  gt  lt  script gt       lt link title  Default  rel  stylesheet  media  screen  href  style css    gt     lt  head gt      lt body gt       lt h1 gt Welcome to Slosh Chat lt  h1 gt        lt div id  messages  gt         lt div gt           lt span class  from  gt First   lt  span gt           lt span class  msg  gt Welcome to chat  Please don t hurt each other  lt  span gt         lt  div gt       lt  div gt        lt form method  post  action     gt         lt div gt Nick   lt input id  from  type  text  name  from   gt  lt  div gt         lt div gt Message  lt  div gt         lt div gt  lt textarea id  msg  name  msg  gt  lt  textarea gt  lt  div gt         lt div gt  lt input type  submit  value  Say it  id  submit   gt  lt  div gt       lt  form gt        lt script type  text javascript  gt        function gotData json  st            var msgs     messages              each json res  function idx  p              var from   p from 0            var msg   p msg 0            msgs append   lt div gt  lt span class  from  gt     from      lt  span gt                    lt span class  msg  gt     msg     lt  span gt  lt  div gt                            The jQuery wrapped msgs above does not work here          var msgs document getElementById  messages            msgs scrollTop   msgs scrollHeight                 function getNewComments               getJSON   topics chat json   gotData                    document  ready function               document  ajaxStop getNewComments              form   submit function                 post   topics chat      form   serialize               return false                      getNewComments                   lt  script gt     lt  body gt   lt  html gt

User · Answer

I think the client looks like a normal asynchronous AJAX request  but you expect it to take a  long time  to come back   The server then looks like this   while   hasNewData        usleep 50    outputNewData      So  the AJAX request goes to the server  probably including a timestamp of when it was last update so that your hasNewData   knows what data you have already got  The server then sits in a loop sleeping until new data is available   All the while  your AJAX request is still connected  just hanging there waiting for data  Finally  when new data is available  the server gives it to your AJAX request and closes the connection

User · Answer

Tornado is designed for long-polling  and includes a very minimal  few hundred lines of Python  chat app in  examples chatdemo   including server code and JS client code  It works like this    Clients use JS to ask for an updates since  number of last message   server URLHandler receives these and adds a callback to respond to the client to a queue   When the server gets a new message  the onmessage event fires  loops through the callbacks  and sends the messages  The client-side JS receives the message  adds it to the page  then asks for updates since this new message ID

User · Answer

This is one of the scenarios that PHP is a very bad choice for  As previously mentioned  you can tie up all of your Apache workers very quickly doing something like this  PHP is built for start  execute  stop  It s not built for start  wait   execute  stop  You ll bog down your server very quickly and find that you have incredible scaling problems   That said  you can still do this with PHP and have it not kill your server using the nginx HttpPushStreamModule  http   wiki nginx org HttpPushStreamModule  You setup nginx in front of Apache  or whatever else  and it will take care of holding open the concurrent connections  You just respond with payload by sending data to an internal address which you could do with a background job or just have the messages fired off to people that were waiting whenever the new requests come in  This keeps PHP processes from sitting open during long polling   This is not exclusive to PHP and can be done using nginx with any backend language  The concurrent open connections load is equal to Node js so the biggest perk is that it gets you out of NEEDING Node for something like this    You see a lot of other people mentioning other language libraries for accomplishing long polling and that s with good reason  PHP is just not well built for this type of behavior naturally

User · Answer

Tornado is designed for long-polling  and includes a very minimal  few hundred lines of Python  chat app in  examples chatdemo   including server code and JS client code  It works like this    Clients use JS to ask for an updates since  number of last message   server URLHandler receives these and adds a callback to respond to the client to a queue   When the server gets a new message  the onmessage event fires  loops through the callbacks  and sends the messages  The client-side JS receives the message  adds it to the page  then asks for updates since this new message ID

User · Answer

The WS-I group published something called  Reliable Secure Profile  that has a Glass Fish and  NET implementation that apparently inter-operate well   With any luck there is a Javascript implementation out there as well   There is also a Silverlight implementation that uses HTTP Duplex   You can connect javascript to the Silverlight object to get callbacks when a push occurs   There are also commercial paid versions as well

User · Answer

This is a nice 5-minute screencast on how to do long polling using PHP  amp  jQuery  http   screenr com SNH  Code is quite similar to dbr s example above

User · Answer

Take a look at this blog post which has code for a simple chat app in Python Django gevent

User · Answer

I think the client looks like a normal asynchronous AJAX request  but you expect it to take a  long time  to come back   The server then looks like this   while   hasNewData        usleep 50    outputNewData      So  the AJAX request goes to the server  probably including a timestamp of when it was last update so that your hasNewData   knows what data you have already got  The server then sits in a loop sleeping until new data is available   All the while  your AJAX request is still connected  just hanging there waiting for data  Finally  when new data is available  the server gives it to your AJAX request and closes the connection

User · Answer

Why not consider the web sockets instead of long polling  They are much efficient and easy to setup  However they are supported only in modern browsers  Here is a quick reference

User · Answer

Below is a long polling solution I have developed for Inform8 Web. Basically you override the class and implement the loadData method. When the loadData returns a value or the operation times out it will print the result and return.

If the processing of your script may take longer than 30 seconds you may need to alter the set_time_limit() call to something longer.

Apache 2.0 license. Latest version on github https://github.com/ryanhend/Inform8/blob/master/Inform8-web/src/config/lib/Inform8/longpoll/LongPoller.php

Ryan

abstract class LongPoller {

  protected $sleepTime = 5;
  protected $timeoutTime = 30;

  function __construct() {
  }


  function setTimeout($timeout) {
    $this->timeoutTime = $timeout;
  }

  function setSleep($sleep) {
    $this->sleepTime = $sleepTime;
  }


  public function run() {
    $data = NULL;
    $timeout = 0;

    set_time_limit($this->timeoutTime + $this->sleepTime + 15);

    //Query database for data
    while($data == NULL && $timeout < $this->timeoutTime) {
      $data = $this->loadData();
      if($data == NULL){

        //No new orders, flush to notify php still alive
        flush();

        //Wait for new Messages
        sleep($this->sleepTime);
        $timeout += $this->sleepTime;
      }else{
        echo $data;
        flush();
      }
    }

  }


  protected abstract function loadData();

}

User · Answer

This is one of the scenarios that PHP is a very bad choice for  As previously mentioned  you can tie up all of your Apache workers very quickly doing something like this  PHP is built for start  execute  stop  It s not built for start  wait   execute  stop  You ll bog down your server very quickly and find that you have incredible scaling problems   That said  you can still do this with PHP and have it not kill your server using the nginx HttpPushStreamModule  http   wiki nginx org HttpPushStreamModule  You setup nginx in front of Apache  or whatever else  and it will take care of holding open the concurrent connections  You just respond with payload by sending data to an internal address which you could do with a background job or just have the messages fired off to people that were waiting whenever the new requests come in  This keeps PHP processes from sitting open during long polling   This is not exclusive to PHP and can be done using nginx with any backend language  The concurrent open connections load is equal to Node js so the biggest perk is that it gets you out of NEEDING Node for something like this    You see a lot of other people mentioning other language libraries for accomplishing long polling and that s with good reason  PHP is just not well built for this type of behavior naturally

User · Answer

Here are some classes I use for long-polling in C   There are basically 6 classes  see below     Controller  Processes actions required to create a valid response  db operations etc   Processor  Manages asynch communication with the web page  itself  IAsynchProcessor  The service processes instances that implement this interface Sevice  Processes request objects that implement IAsynchProcessor Request  The IAsynchProcessor wrapper containing your response  object  Response  Contains custom objects or fields

User · Answer

I used this to get to grips with Comet  I have also set up Comet using the Java Glassfish server and found lots of other examples by subscribing to cometdaily com

User · Answer

I think the client looks like a normal asynchronous AJAX request  but you expect it to take a  long time  to come back   The server then looks like this   while   hasNewData        usleep 50    outputNewData      So  the AJAX request goes to the server  probably including a timestamp of when it was last update so that your hasNewData   knows what data you have already got  The server then sits in a loop sleeping until new data is available   All the while  your AJAX request is still connected  just hanging there waiting for data  Finally  when new data is available  the server gives it to your AJAX request and closes the connection

User · Answer

The WS-I group published something called  Reliable Secure Profile  that has a Glass Fish and  NET implementation that apparently inter-operate well   With any luck there is a Javascript implementation out there as well   There is also a Silverlight implementation that uses HTTP Duplex   You can connect javascript to the Silverlight object to get callbacks when a push occurs   There are also commercial paid versions as well

[php] How do I implement basic "Long Polling"?

Examples related to php

Examples related to http

Examples related to comet