Question

I’m trying to call a simple web service like this, on the client side:

$.ajax({
    type: "POST",
    url: "/service/local/newsservice.asmx/DoPost", // "/news/post/do",
    data: {
        title: _title,
        markdown: _markdown,
        categoryId: 1
    },
    success: function (data) {
        alert("success!");
    }
});

The actual service is:

[WebService(Namespace = "http://service.site.com/service/news")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[ToolboxItem(false)]
[ScriptService]
public class NewsService : System.Web.Services.WebService
{
    [WebMethod]
    [ScriptMethod]
    public static void DoPost(string title, string markdown, int categoryId)
    {
        if (!(Roles.IsUserInRole("Owner") || Roles.IsUserInRole("Administrator")))
            return;

        CommunityNews.Post(title, markdown, categoryId);
    }
}

When using the rewritten URL, which points to "/service/local/newsservice.asmx/DoPost", I get the following error:

The HTTP verb POST used to access path
‘/service/local/newsservice.asmx/DoPost’ is not allowed.

When I use the plain URL, I get this instead (via Firebug, the application silently fails):

DoPost Web Service method name is not valid.

What could be going on?

Answer 1

The built-in way of calling a web service in ASP.NET is to use a service reference, which creates JavaScript objects for you to call your web service methods.

ServiceReference Class

To call Web service methods from ECMAScript (JavaScript), you must
include a service reference in the ASP.NET page and apply the
ScriptServiceAttribute attribute to the Web service class definition.
If you include a service reference to a Web service in the
ScriptManager or ScriptManagerProxy control inside the ASP.NET page,
JavaScript objects will be instantiated in the browser.

The proxy objects will be used to do the following:

• Make asynchronous requests in JavaScript to Web service methods,

• Initialize instances of proxies of server data types, in
  particular for use as input parameters for invoking Web methods.

Since you’re using jQuery instead of the proxy objects created for ASP.NET AJAX, you might have to check a couple things are configured properly:

Exposing Web Services to Client Script

To enable Web service calls from [ASP.NET AJAX] script, you must register the
ScriptHandlerFactory HTTP handler in the application’s Web.config
file. The handler processes calls made from script to .asmx Web
services. The following example shows the Web.config element for
adding the handler.

These configuration settings are already part of the Web.config file
template for any new AJAX-enabled Web sites that you create in
Microsoft Visual Studio 2005.

<system.web>   
  <httpHandlers>
    <remove verb="*" path="*.asmx"/> 
    <add verb="*" path="*.asmx" 
      type="System.Web.Script.Services.ScriptHandlerFactory"
      validate="false"/>   
  </httpHandlers> 
<system.web>

For Web service calls that are not issued from ASP.NET AJAX script,
the ScriptHandlerFactory handler delegates the call to the default
handler, which uses SOAP instead of JSON format. The delegation is
performed automatically and you do not have to take any action unless
you want to disable the use of the SOAP protocol for the Web services.
In that case, you must enter the following configuration setting in
the Web.config file.

<system.web>   
  <webServices>
    <protocols>
      <clear/>
    </protocols>   
  </webServices> 
</system.web>