How To Detect Browsers and Mobile Devices With PHP

Browsing the Internet with your favorite “client” is based on strict rules (communications protocols) , they are handled automatically  , so you don’t have to worry about them . Probably the most used protocol is the Transmission Control Protocol (TCP) which  is connection-oriented .
Connection-oriented means that , before any data can be transmitted , a reliable connection must be obtained (instantiated) and acknowledged . The instatiation of this connection ( accomplished in 3 steps ) is done  with  “header” messages  which are send between the two nodes (client–server)  . While browser’s headers  notify the server what resources he would like to receive , server’s headers notify the acception of the connection and some other directives  (content-type , caching , redirecting ) . TCP’s three way handshaking technique is referred to as the 3-way handshake or as “SYN-SYN-ACK” and is the method used to establish TCP socket connections and tear down TCP socket connections over the network .

One of client’s (browsers) instantiation  header ,   is the Accept header ,  which takes a list of options ,  tells the server what file formats , or more correctly MIME-types , the browser is looking for . The result of a “ echo $_SERVER[‘HTTP_ACCEPT’] ; ” will return a string with the following signature  :
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 

To minimize the Back-and-forth communication (during instantiation ) the content negotiation happens in a single  list of options which are indicated by the “relative quality parameter”  (q) and its value (qvalue) — application/xml;q=0.9,*/*;q=0.8 —- . 

Another header worth to mention is the “$_SERVER[‘HTTP_USER_AGENT’]” , it’s signature is similar to  the following string :
Mozilla/5.0 (Windows NT 5.1) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.75 Safari/535.7
A quick Browser-type detection could be made as :
“echo  strpos($_SERVER[‘HTTP_USER_AGENT’],’Chrome’) ? “Yes” : “No” ; ”

The hottest device out there right now seems to be the iPad , it’s HTTP_USER_AGENT – signature is : Mozilla/5.0 (iPad; U; CPU OS 3_2 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Version/4.0.4 Mobile/7B334b Safari/531.21.10
Detecting IPad’s could be done as :
echo (Bool) stripos($_SERVER[‘HTTP_USER_AGENT’] ,’iPad’) ? “Yes” : “No” ;
Detecting Android could be done as :
echo (Bool) stripos($_SERVER[‘HTTP_USER_AGENT’] ,’android’) ? “Yes” : “No” ; 
Using some logic from Drew Douglass’ excellent mobile redirection post , we can redirect users to a mobile version of a website if we desire to do so  .

I have over-simplified the theory as my intention was to give the basic concepts of Browser detection . We don’t really have to know more about it , as there are excellent open-source PHP Classes developed under the GPL licence . Two of these Classes   are :

• browser.php : It has a long list of features ,  a basic example how to use this Class is :

  < ?php
  
  require_once('Browser.php');
  $browser = new Browser();
  if( ! ( $browser->getBrowser() == Browser::BROWSER_FIREFOX && $browser->getVersion() >= 2 ) ) {
  echo ‘You have FireFox version 2 or greater’;
  }
  
  ?>
  

• Mobile_Detect.php : As its name notifies , it detect mobile devices . A basic example how to use this Class is :

  include("Mobile_Detect.php");
  $detect = new Mobile_Detect();
  if ($detect->isAndroid()) {
   // code to run for the Google Android platform
  	}
  
  

Examine HTML headers in Firefox and Google Chrome :

In Firefox just install the firebug plugin , open the page for which you would like to examine HTTP headers and enable  Firebug (Press F12) -> Click on Page Speed , then click on Resources and then on the left, click on the + sign of every HTTP request you would like to examine . You can view the header code without expanding the request .
In Google Chrome , open the page for which you would like to examine the HTTP headers . Press Ctrl + Shift + i, shortcut key for Developers Tool . Click on “Network” tab , from the left-column select on  every HTTP request you would like to examine (header tab) .

Links worth to visit :

• Header Field Definitions
• Chrome extension that lets you quickly view HTTP Response Headers of a URL