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Ajax and PHP

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A three hour tutorial I gave at PHP Quebec on the challenges, theory, and concepts behind making asynchronous JavaScript calls for Web 2.0 Applications using PHP

A three hour tutorial I gave at PHP Quebec on the challenges, theory, and concepts behind making asynchronous JavaScript calls for Web 2.0 Applications using PHP

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    Ajax and PHP Ajax and PHP Presentation Transcript

    • Ajax and PHP John Coggeshall
    • Welcome!
      • Who am I: John Coggeshall
        • Sr. Technical Consultant, Zend Technologies
        • Author PHP 5 Unleashed
        • Zend Educational Advisory Board
        • Speaker on PHP-related topics worldwide
        • Geek
    • Why are we here?
      • We’re here to discuss AJAX
        • … and PHP
        • … and XML
        • … and Javascript
        • … and Networks
      • In this three hour tutorial, I’ll be explaining a number of AJAX-related concepts
    • Fair Warning
      • I’ll warn you right now – I work for Zend, not Netscape
        • I am not a client-side developer
        • I do not know which browsers support which constructs of Javascript under which conditions using which technologies on which operating system
        • I am a PHP developer responsible for scaling numerous mission-critical PHP sites and technologies
        • I do understand Internet architectures and how to scale them in practical environments
        • I do understand enough about AJAX as a technology to speak intelligently
        • Don’t expect a lot of flashy AJAX demos here
    • The basics
      • So, what does AJAX stand for anyway?
        • A synchronous J avascript a nd X ML
      • The basic idea:
        • Javascript is the reigning champion of the client side
          • Image roll-overs
          • DHTML
          • Client-side form processing
        • Not all information and processes can be given to the client
          • Insecure / Untrusted
          • Simple processing ability restrictions
    • Asynchronous Javascript
      • AJAX allows us to take advantage of the server for information, while leaving the GUI-related items to the client
      • It’s not a new technology
        • Just has a neat acronym now
      • How’s it work?
        • Javascript applications perform requests to the server using an agreed protocol
        • The server responds in kind with the requested information
        • All of this takes place without reloading the page
          • Asynchronous of the client
        • Javascript then processes the result and manipulates the page
    • Don’t confuse technologies
      • Is AJAX Gmail / Google Maps?
        • No
      • Is AJAX Prototype or Script.aculo.us?
        • No
      • Is AJAX Ruby-on-Rails?
        • No
      • AJAX is simply the idea of enabling your browser to communicate asynchronously with the server to provide a more rich user “Web 2.0” experience.
    • Implementing AJAX
      • Step 1: Open a asynchronous connection from the client to the server
      • Step 2: Perform a request against the server using an agreed upon protocol
      • Step 3: Process the results via Javascript and manipulate the client without causing a full refresh of the page
      <SCRIPT language=&quot;JavaScript&quot;> <!-- pic1= new Image(100,25); pic1.src=&quot;http://example.com/getRandomImage.php&quot;; //--> </SCRIPT>
    • “ Traditional” AJAX
      • Despite the misconceptions on what exactly AJAX is, it does have a traditional approach
        • XMLHttpRequest object
          • Available in most modern browsers
          • Identical in concept to the Image object
        • Allows you to retrieve data from the server without performing an entirely new request
      • Requests are generally made in conjunction with a particular Javascript event
        • i.e. onBlur of a zip-code field which automatically finds out the city / state
    • “ Traditional” AJAX
      • Okay, so here we go:
        • <input type=“text” size=“5” onBlur=“updateCityState()”>
      • Now all we need to do is implement a javascript updateCityState() function that creates an XMLHttpRequest object
      • Then we take that object and request a PHP page http://www.example.com/getCityState.php?zip=14214
      • … parse the result
      • … update the city and state input fields to reflect the new information!
    • Browser Wars Revisited
      • Ah, if only it were that simple
        • Unfortunately, XMLHttpRequest is implemented in different ways on each browser
        • Requires lots of Javascript black-magic that I don’t know to ensure you’re creating the proper object the proper way
      • My solution: Google
        • This problem has been solved a million times over so I won’t re-explain the wheel here
    • Establishing a Protocol
      • Now that you’ve made a request back to the web server (in this case, using PHP and HTTP GET) time to deal with the response
        • This is where things really go amuck
      • There is no standard AJAX protocol, the data can be anything
        • Comma separated fields
        • Serialized Javascript
        • Custom XML
        • SOAP
        • URLEncoded fields
        • 20 bytes of data, each byte representing a command
    • Establishing a Protocol
      • While there are no standards per-se, there are common techniques
        • Future versions of PHP will support JSON encoding by default
        • Allows you to pass complex data types back and forth between PHP and Javascript fairly easily
        • You can download JSON encoding support from PECL
          • http://pecl.php.net/package/json
          • $json_enc = json_encode(array(1,2,3));
          • $json_dec_var = json_decode(‘{ “abc”:12 }’);
          • javascript:eval(‘{ “abc”:12}’); // return foo.abc in JS
    • AJAX without XmlHttpRequest
      • Now that you have the basic jist, the cleaver among you must realize that XmlHttpRequest isn’t necessary
      • With some crafty HTML you can do your AJAX request using “standard” browser facilities
        • Step 1: Use Javascript to create a new <SCRIPT> tag in the document
        • Set the source of this script tag dynamically to our PHP backend URL and provide the “output element” ID we are interested in manipulating
        • Have our backend written in PHP process the request and return Javascript manipulating that ID as we saw fit.
      • http://www.phpit.net/article/ajax-php-without-xmlhttprequest/2/
    • I said it was a synchronous
      • Regardless of the approach you use to generate an AJAX request, always remember that it is an ASYNCHRNONOUS request.
        • Performing a behind the scenes synchronous request stands a very good chance of locking up IE
        • Every second the server takes the respond to the client in a synchronous request is a second the browser is not responding to input
        • Bad.. Bad… BAD
    • HTTP GET vs. POST
      • This one personally really urkes me about web developers
        • GET is for GETTING data
        • POST is for POSTING data
      • Sending a GET request should never cause an update on the server
        • Reason 1: GET requests should be bookmark-able
        • Reason 2: GET requests should be cache-able
      • If you use AJAX for anything other then retrieving data then use HTTP POST for those actions
    • Why I am scared of AJAX
    • One of the biggest problems with AJAX
      • Let’s imagine that each request sent over the wire is like a car driving from point A (the client) to point B (the server)
      • Roads are Networks
    • One of the biggest problems with AJAX
    • One of the biggest problems with AJAX
      • Simple requests seem to work just fine…
    • One of the biggest problems with AJAX
    • One of the biggest problems with AJAX
    • One of the biggest problems with AJAX
    • One of the biggest problems with AJAX
      • The problem with AJAX has to do with multiple dependent asynchronous requests
        • You can’t rely on any order of operations in classical AJAX models
    • One of the biggest problems with AJAX
    • One of the biggest problems with AJAX
    • One of the biggest problems with AJAX
    • One of the biggest problems with AJAX
    • Some requests will happen faster
      • When working with AJAX, always know you cannot rely on one request finishing before the next is triggered
      • Requests can take different lengths of time based on a huge array of factors
        • Server load and Network load come to mind
      • Can really mess up your application
      • Bad news: None of the current AJAX toolkits account for this latency
    • Developing with Latency in mind
      • A number of tools exist for developing AJAX applications with latency in mind
        • AJAX Proxy is a good example
          • http://ajaxblog.com/archives/2005/08/08/ajax-proxy-02
          • Allows you to simulate latency in your requests
        • You can use it in conjunction with “SwitchProxy” to point your browser at a different proxy server to use it
          • http://www.roundtwo.com/product/switchproxy
      • Not a true solution, but at least let’s you test for the problem.
    • AJAX: Redefining the notion of state?
      • Now that we are talking about AJAX intelligently, let’s talk about a very important aspect to the modern web application: sessions
        • Sessions allow current web applications to maintain state across stateless HTTP requests
    • Throw cookies away?
      • In AJAX models, these session cookies are no longer necessary
        • In-memory data received from the server during an AJAX request is state
        • Lends itself much more to the classical MVC / Messaging model of client-side applications
        • As long as the user doesn’t “close” the application….
          • Clicking reload
          • Closing the window
        • …. Then they’re state is being tracked
    • Requests per second (Traditional)
      • Other then actually working, scaling a web application is the most important architectural consideration
        • (accurate) Requests per second is key metric
      • Consider what happens during a single server/single client exchange
    • Requests per second (Traditional)
      • Servers are limited to a maximum requests per second by numerous factors
      • To scale:
        • Make the maximum sustainable RPS number as high as possible
          • Faster script execution times
          • Faster database access
        • Make the most of every request
          • Avoid costly unnecessary handshakes
          • Intelligently segment content
    • Requests per second (Traditional)
      • Common scaling trick: static content farms
        • Off-load non-logic-based content serving to lightweight and fast HTTP servers
    • Requests per second (AJAX)
      • Looking at the AJAX philosophy it’s clear a different request pattern exists
        • Relatively heavy and common load spikes
        • Very frequent and relatively quick follow-up requests
      • While some tricks can be borrowed from the old models, clearly a new pattern of scaling must be introduced
    • Optimizing AJAX pages
      • Single-serve client libraries
        • Use tools to combine multiple JavaScript/CSS files into a single giant file to reduce the load on the server to a single request to load the application logic
          • Can be cached on the client
      • Avoid first-execution spikes
        • Design your applications upon initial execution to perform a single AJAX request to effectively populate the entire page
          • Reduces strain on both the pipeline and on your backend database servers
    • A thought
    • The Future of AJAX?
    • Thank you! Questions?