No transport error while consuming WCF service in a REST way

Question

Hi,

Here is a small article on when we usually face No Transport error and how to get rid of it.

I recently worked on a sample application using “app for Office” (New in Visual Studio 11.0)

What is “app for Office”?

An app for Office is basically a webpage that is hosted inside an Office client application. You can use apps to extend the functionality of a document, email message, meeting request, or appointment. Apps can run in multiple environments and clients, including rich Office desktop clients, Office Web Apps, mobile browsers, and also on-premises and in the cloud.

What can an app for Office do?

An app for Office can do pretty much anything a webpage can do inside the browser, such as the following:

• Provide an interactive UI and custom logic through      JavaScript. (Develop UI using HTML and JavaScript)
• Use JavaScript frameworks such as jQuery.
• Connect to REST endpoints and web services via      HTTP and AJAX.
• Run server-side code or logic, if the page is      implemented using a server-side scripting language such as ASP or PHP.

As “app for Office” doesn’t have an option to write server side scripting (unlike code behind or in-line coding feature in ASP.NET/MVC) we will have to go for web service or WCF service and consume the service using any JavaScript framework like Jquery.

I wrote a simple WCF service to hook up with server side code and consumed the service using Jquery as follows

$(document).ready(function () {
$.ajax({
type: "GET",
url: "http://localhost/MyService.svc/rh/data?id=" + $('#sampleType').val(),
processData: false,
contentType: "application/json; charset=utf-8",
dataType: "json",
crossDomain: true,
success: function (data) {

alert(data)
}
},
error: function (xhr, status, error) {
alert(error);

}
});
});

I encountered an error saying “No Transport” when I executed the client application.  I did some investigation on this and found out the root cause that cross-domain request was disabled. But I was really not sure whether it was at my WCF service end or “app for Office” client end. I added Client Access policy and Cross-domain-policy xml files to WCF service in order to enable cross-domain request  so that service will accept any type requests sent form different domains.

Client Access policy

<?xml version="1.0" encoding="utf-8" ?>

<access-policy>

  <cross-domain-access>

    <policy>

      <allow-from http-request-headers="*">

        <domain uri="*"/>

      </allow-from>

      <grant-to>

        <resource include-subpaths="true" path="/"/>

      </grant-to>

    </policy>

  </cross-domain-access>

</access-policy>

Cross-domain-policy

<?xml version="1.0"?>

<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">

<cross-domain-policy>

            <allow-http-request-headers-from domain="*" headers="*"/>

</cross-domain-policy>

Both the policies should be in different XML files

But this didn’t solve my problem. After a little bit more investigation I found exactly where and how to enable-cross domain requests.

Solution

We need to enable cross-domain requests in environments that do not support cross-domain requests.

“Cors is equal to true if a browser can create an XMLHttpRequest object and if thatXMLHttpRequest object has a withCredentials property. To enable cross-domain requests in environments that do not support cors yet but do allow cross-domain XHRrequests (windows gadget, etc), set $.support.cors = true;”

You just have to add jQuery.support.cors = true; in your client scripting and it works perfectly fine.

[Cors- Cross-Origin Resource Sharing]

A simple example:

$.support.cors = true;
$(document).ready(function () {
$.ajax({
type: "GET",
url: "http://localhost/MyService.svc/rh/data?id=" + $('#sampleType').val(),
processData: false,
contentType: "application/json; charset=utf-8",
dataType: "json",
crossDomain: true,
success: function (data) {

alert(data)
}
},
error: function (xhr, status, error) {
alert(error);

}
});
});

Hope this will be helpful.

Thanks

Answer 1

This is fantastic, u resolved!!!

---

Software Developer

Answer 2

good one to save hell lot of time for any developer.....

Please keep posting such issue to the world.