Ajax and PHP
John Coggeshall
Copyright © 2006, Zend Technologies Inc.
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
Oct. 18, 2005
#2
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
Oct. 18, 2005
#3
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
Oct. 18, 2005
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The basics
• So, what does AJAX stand for anyway?
Asynchronous Javascript and XML
• 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
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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
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Don‟t confuse technologies
• Is AJAX Gmail / Google Maps? • Is AJAX Prototype or Script.aculo.us? • Is AJAX Ruby-on-Rails?
No No 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.
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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
Oct. 18, 2005
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“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
• Requests are generally made in conjunction with
a particular Javascript event
out the city / state
performing an entirely new request
i.e. onBlur of a zip-code field which automatically finds
Oct. 18, 2005
#9
“Traditional” AJAX
• Okay, so here we go:
• • • •
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!
Oct. 18, 2005
# 10
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
Oct. 18, 2005
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Establishing a Protocol
• Now that you’ve made a request back to the
This is where things really go amuck
web server (in this case, using PHP and HTTP GET) time to deal with the response
can be anything
• There is no standard AJAX protocol, the data
Comma separated fields Serialized Javascript Custom XML SOAP URLEncoded fields 20 bytes of data, each byte representing a command
Oct. 18, 2005
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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
Oct. 18, 2005
# 13
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 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-withoutxmlhttprequest/2/
Oct. 18, 2005
# 14
I said it was asynchronous
• 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
Oct. 18, 2005
# 15
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
Oct. 18, 2005
# 16
Why I am scared of AJAX
Copyright © 2006, Zend Technologies Inc.
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
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One of the biggest problems with AJAX
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One of the biggest problems with AJAX
• Simple requests seem to work just fine…
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One of the biggest problems with AJAX
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One of the biggest problems with AJAX
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One of the biggest problems with AJAX
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One of the biggest problems with AJAX
• The problem with AJAX has to do with multiple
dependent asynchronous requests
AJAX models
You can‟t rely on any order of operations in classical
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One of the biggest problems with AJAX
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One of the biggest problems with AJAX
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One of the biggest problems with AJAX
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One of the biggest problems with AJAX
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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
Oct. 18, 2005
# 29
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
• http://www.roundtwo.com/product/switchproxy
point your browser at a different proxy server to use it
• Not a true solution, but at least let’s you test for
the problem.
Oct. 18, 2005
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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
Oct. 18, 2005
# 31
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
Oct. 18, 2005
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Requests per second (Traditional)
• Other then actually working, scaling a web
(accurate) Requests per second is key metric
application is the most important architectural consideration
• Consider what happens during a single
server/single client exchange
Oct. 18, 2005
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Requests per second (Traditional)
• Servers are limited to a maximum requests per •
second by numerous factors To scale:
possible
• Faster script execution times • Faster database access
Make the maximum sustainable RPS number as high as
Make the most of every request
• Avoid costly unnecessary handshakes • Intelligently segment content
Oct. 18, 2005
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Requests per second (Traditional)
• Common scaling trick: static content farms
Off-load non-logic-based content serving to
lightweight and fast HTTP servers
Oct. 18, 2005
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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
Oct. 18, 2005
# 36
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
Oct. 18, 2005
# 37
A thought
Oct. 18, 2005
# 38
The Future of AJAX?
Copyright © 2006, Zend Technologies Inc.
Thank you!
Questions?
Copyright © 2006, Zend Technologies Inc.