Tag Archives: cross domain

Test Cross Domain Ajax In Chrome

01 Jun 2012

If you are like myself and leave the server-side stuff to those who like doing that type thing (well, I dabble here and there) then you love to find ways to avoid asking them to do stuff for. In the world of HTML 5 mobile application development you are always integrating with some service and often its cross-domain. If for some reason your cross-domain calls are not using JSONP but perhaps regular JSON or SOAP/XML you will immediately run into problems testing your mobile application within Chrome.

Chrome is really where you want to do your development as it takes too much time to compile an app and load onto a device just so you can test though yes, you do ultimately want to test on-device. WEINRE takes some of the pain out but it still has a mild sting to it. Anyway you can still use Chrome for your cross-domain non JSONP requests. Just start it up with a switch to disable web security – the switch is:

–disable-web-security

What I do is have two shortcuts on my desktop – a normal one for Chrome in all of its default glory, and another one specifically for development that will launch Chrome with its web security feature disabled.

So how does one go about using this handy switch/feature? First, create a shortcut on your desktop to Chrome. Don’t know how to do that? Well my friend, thats what Google is for. Next, make a copy of the shortcut – rename it to something obvious, for example “Chrome Security Disabled” or similar.

Next right-click and choose properties. You should see something like this:

Next, note the field that is hilited – the one labeled “Target”. That’s the path to the Chrome executable. type a space after the exe and paste in the switch as seen below:

Hit “Apply”, then “OK”. Thats it!

There are many more switches that you can use, they are documented at the Google Chrome Repository.

Don’t forget that you have to make sure you kill all chrome instances first, or the command line switches won’t have any effect. In VISTA if you have an instance of Chrome open and try to edit the target of a shortcut the edit won’t take. Again, close all Chrome instances first.

Also don’t’ forget that you have security disabled! Its easy to think everything works fine in Chrome when it won’t in the real world and can be a source of frustration when you wonder why your app works on your computer but not when deployed to a server. Another impact of forgetting that you have lowered your security is browsing the Internet in general – you will need to completely shutdown Chrome and then start a “normal” Chrome instance to regain previously disabled security features.

Cross-Domain Ajax and XML with jQuery

07 May 2012

Did a fun little thing today – built a jQuery/PHP-based Cost of Living (COL) calculator for a city’s website (sorry, have to be vague on the client’s name) utilizing the data from www.coli.org.

Coli.org provides a service that allows interested parties to compare the cost of living across a range of criteria between two different locations within the Untied States.

Typically as in this case the destination location is the city that is providing the calculator. The intent is to allow potential new residents to compare their current cost of living to the destination city.

To start with you will need to query two of the services on page load – one to get the list of origin locations and another to get the list of destination locations (typically one or two locations – and if you want only one destination you could easily hard code the value of the city via a hidden form field or similar). Once you receive this data you will need to populate two select lists to allow the user to make their selections. With that data you will then query another web service to get the results. Further manipulation of the returned data on the client side with some math will get you percentages and adjusted income.

Approach

There are a couple of ways to approach this – server-side or client-side. As I’m a front-end guy my approach then was to do Ajax knowing that jQuery makes it trivial to do AJAX and parse XML. However, since this was going to be a cross-domain call a 100% client-side solution wouldn’t be possible. Instead, I would have to use something that wouldn’t be subject to a browser’s cross-domain policy – a proxy to act as the go-between for client and the web service. The server the site is hosted on supports PHP and so that dictated the tech to use. A little research revealed PHP’s cURL and a few lines of code later I had myself the proxy that I needed to accomplish the cross-domain service calls.

Proxy

One thing I noticed in the live examples that Coli.org provided is that the GUID was exposed which seemed unnecessary to me. So, instead of following their implementation examples verbatim I placed the GUID into the PHP proxy thereby keeping it secure. Of course, Coli.org might be mitigating GUID abuse by restricting calls to registered domains – I’ve no idea, but in any event, it seemed to be a better approach to not expose it if possible.

If you’re looking into using the Coli.org data by mirroring my approach you’ll be interested in the proxy, which I’ve provided below:

...

define ('HOSTNAME', 'http://www.coli.org/_clicktocomparews/service.asmx/');
$path = $_GET['ws_path'];
$url = HOSTNAME.$path;
$session = curl_init($url);
if ($_GET['ws_path']) {
     $getvars = '';
     while ($element = current($_GET)) {
          $getvars .= key($_GET).'='.$element.'&';
          next($_GET);
     }
     $getvars .= '&licenseeGUID={_YOUR_GUID_GOES_HERE_}';
     curl_setopt ($session, CURLOPT_POST, true);
     curl_setopt ($session, CURLOPT_POSTFIELDS, $getvars);
}

curl_setopt($session, CURLOPT_HEADER, false);
curl_setopt($session, CURLOPT_RETURNTRANSFER, true);
$xml = curl_exec($session);
header("Content-Type: text/xml");
echo $xml;
curl_close($session)

...

All you need to do is to replace the string “_YOUR_GUID_GOES_HERE_” with the GUID that Coli.org gives you and as long as your server supports cURL your proxy is ready to be used. Note that the curly braces surrounding the numeric GUID is necessary.

AJAX & jQuery

Next is the AJAX. jQuery really makes it easy to do AJAX, here’s a stripped down version of my AJAX call to the Proxy:

...
function doAjax(wsPath,args){
   var dataStr = args ? 'ws_path=' + wsPath + '&' + args : 'ws_path=' + wsPath;
   $.ajax({
      url:      '/col_proxy.php',
      data:      dataStr + '&action=compute',
      dataType: 'xml',
      error:     function(xhr,status,err){
         //console.log(status + '\n' + err);
      },
      success:function(responseData,status,xhr){
         // console.log('success')
      });
}
...

So lets break this down, doAjax() expects two arguments to be passed to it. “wsPath” is the web service path, “args” are the arguments to be sent to the webservice. You would use the success callback to process the returned XML.

The web service paths for Coli.org’s web services are the following (as can be publicly seen here):

  • GetComparisonDetail
  • GetComparisonSummary
  • GetFromCommonPlaceTotal
  • GetFromLocations
  • GetPeriodInfo
  • GetSampleLocations
  • GetToCommonPlaceTotal
  • GetToLocations

Since I need the list of origin and destination locations first before any other web service can be used I call doAjax() via $(document).ready with the following placed at the end of my script:

...
$(document).ready(function(){
... 
... 
  // bottom of script
  (function init(){
    doAjax('GetFromLocations',null);
    doAjax('GetToLocations',null);
  })();
}); 

The “init” function is self-invoking and as you might have guessed, “GetFromLocations” is the web service for getting the list of origin locations, and “GetToLocations” provides the list of possible destination locations. These two services don’t require any extra attributes so the second argument to doAjax() is simply passed null.

The next task would be to call another webservice once the origin and destination cities have been selected by passing the data that repesents the city selections and the desired web service path. I didn’t use all of the webservices that Coli.org has availiable as they weren’t needed for my application. For my needs only two more calls were needed: “GetComparisonDetail” and “GetComparisonSummary”. In both of these cases the required name-value pairs to send along are:

  • fromCity
  • toCity

So then, knowing this and we would would pass the web service name as the first argument for doAjax() and construct the name/value pair string to be the value of the second argument. Something that in your own application may look similar to this:

...
// put together the "from" and to" name value pairs
// where "fromVal" is the origin city code and
// "toVal" is the destination city code
var args = 'fromCity=' + fromVal + '&toCity=' + toVal;

// specify the web service to use
var wServiceName = 'GetComparisonSummary';

// query the webservice
doAjax(wServiceName,args);
...

Processing XML

The result from a successful web service call will be XML. Coli.org unfortunately doesn’t provide XML samples so you’ll have to discover this on your own. What I did was to construct the entire web service call **sans proxy** directly in my browser’s address bar. The entire call, from www.colie.org… all the way to the GUID and any other necessary arguments – and then hit enter on my keyboard. If succesfull the XML response will appear in-browser.

Here’s an example of discovering the XML structure via a direct link in a browser:

http://www.coli.org/_clicktocomparews/service.asmx/GetFromLocations?licenseeGUID={_YOUR_GUID_HERE}

Here is a portion of the returned XML:

...

  
  T-Bone SteakFairbanksAK110.439.2655586592178789Q12011
T-Bone SteakWarsawIN19.79.2655586592178789Q12011
Ground BeefFairbanksAK13.83.0240502793296091Q12011
...

Once you know the XML structure the next few steps couldn’t be easier – in this case, each location is described as an XML node/tag called “Table”. Within this node are other nodes that themselves contain the specific values that you are looking for, such as:

  • Category_Name
  • Place_Name
  • State
  • Cost

In jQuery to find any node/tag within an XML doc simply use the “find()” method and you will get an array of all matching nodes. looking back at the doAjax() sample code we can see that the success callback assigns the returned XML to “responseData”. So then we have all the piecess to this rather small puzzle. To find all of the “Table” nodes within “responseData” our jQuery code would be:

...
var tableArray = $(responseData).find('Table');
...

This gives us all the “Table” nodes – but… we of course have to loop through each one looking for the specific values that we need and while a for loop would work here to iterate through each “Table” we should instead utilize chaining and jQuery’s built-in iterator, the “each()” method, and its callback:

...
$(responseData).find('Table').each(function(){
  // additional processing instructions here;
});
...

Pretty cool how chaining allows us to do multiple things simultaneously, right? This is a rather small chaining example too, but anyway, the next step is to find the desired values within each individual “Table” node. This is quite simple as well, see the next example:

...
$(responseData).find('Table').each(function(){
  var cname = $(this).find('Category_Name').text();
  var pname = $(this).find('Place_Name').text();
});
...

The $(this) statement in this context simply means “the current Table node” – then we look for the specific child node inside the current Table by again using the find() method. And on the end, we use the “text()” method to pull the text that is within the desired nodes. Here we are pulling the text for the “Category_Name” and “Place_Name” nodes which again are child nodes of “Table”.

THis is great, but this code doesn’t do us much good at this point as all we end up with are the Category and Place values of the very last Table in two variables. Instead we would actualy use this to populate the page with HTML for each individual Table. We can quickly print out the results to the page by appending html to a pre-existing div. As seen in the following example our existing div is called “tableResults”:

...
$(responseData).find('Table').each(function(){
  var currentRow =  '

Category: ' + $(this).find('Category_Name').text(); currentRow += ', Location: ' +$(this).find('Place_Name').text() + '

'; $('#tableResults').append(currentRow) }); ...

This will print out the Category and Location of each Table node within the mentioned pre-existing div called “tableResults”. Note that I’ve wrapped each set of Table data in a P tag. This gives us some automatic padding between lines which makes things a little more visually appealing. This sample is pretty basic, you’ll of course want to do more in your own application.

And… (drum roll)… thats about it. This was just a brief overview of the technical aspects of integrating into Coli.org’s web services via client-side technologies, not a complete functional example though with the code samples above – and complete working PHP-based proxy – you should be able to integrate with their web services quite easily or at the very least get a jump start on a similar project of your own.

XHR Post in Sencha Touch 1 & PhoneGap

13 Feb 2012

Sencha Touch has built in support for JSONP via “GET”, but if you have a lot of data to send you may quickly run into the GET character limit which varies across browsers. For a lot of data, “POST” is the preferred method and may be even preferred over GET for security reasons. The rub is that form POSTs will reload a page meaning that your app will reload and you’ll lose whatever state you had. That means we’ll have to do the POST via AJAX.

The astute among you might first ask about the cross domain policy and how it would prevent such a thing from happening (which JSONP by definition allows but is not useful here because its essentially a GET). As PhoneGap loads your Sencha Touch project via the file:// protocol cross domain XHR (XMLHttpRequest) is thus possible. Files loaded in this manner a free of the same domain policy.

With that aside it appears that Sencha Touch 1 just doesn’t have AJAX form posts as part of its framework but we can use Ext.Ajax.request() which allows us to set the desired form method and gives us success and error callbacks and even a timeout – which Ext.util.JSONP.request() lacks (bonus!).

The only additional setup is to add android.permission.INTERNET to the android manifest and to add the domain that you’re posting to to the whitelist in iOS. There has been some discussion about whitelisting in PhoneGap, it might be worthwhile to see how its evolved.

Here is a code snippet showing how the Ext.Ajax.request() method can be utilized within Sencha Touch:

...
Ext.Ajax.request({
	url: 'http://www.somewhere.com',
	method:'POST',
	params: 'configuration object goes here',
	scope:this,
	timeout:15000,
	disableCaching:true,
	failure: function(responseObj, opts){
		// handle your error response object here
	},
	success: function(responseObj, opts){
		// handle your success response object here
	}
});
...

The configuration object is simply something along these lines: {name:value,name:value,name:value,……}