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How to Capture File Upload Errors with RadAsyncUpload Custom Handler

Problem

How to throw errors that will be recognized by the "OnClientFileUploadFailed" handler when using a custom handler.

Description

The server returns a status code of 500 and a message similar to "HTTP Error code is: 500" or something like [HttpWebRequest_WebException_RemoteServer] in args.get_message(). This happens because uncaught exceptions trigger the standard ASP.NET error page mechanism and bury any exception info (if passed) in an HTML page in a response that expects JSON.

Solution

You can work around this by following these steps. You can find attached a small example below the list.

  1. Create a custom upload result class that has a field for the exception.

    CustomErrorAsyncUploadResult.cs

    public class CustomErrorAsyncUploadResult : IAsyncUploadResult
    {
       public CustomErrorAsyncUploadResult()
       {
    
       }
    
       public string CustomError
       {
           get;
           set;
       }
    
       public long ContentLength
       {
           get;
           set;
       }
    
       public string ContentType
       {
           get;
           set;
       }
    
       public string FileName
       {
           get;
           set;
       }
    }
    
  2. Catch the exception in the handler and populate the custom field.

    myHandler.ashx.cs

    public class myHandler : AsyncUploadHandler
    {
       protected override IAsyncUploadResult Process(UploadedFile file, HttpContext context,  IAsyncUploadConfiguration configuration, string tempFileName)
       {
           CustomErrorAsyncUploadResult result =  CreateDefaultUploadResult<CustomErrorAsyncUploadResult>(file);
           try
           {
               throw new Exception("file did not validate/upload for <insert reason here>");
           }
           catch (Exception ex)
           {
               //for example, remove some information, make sure to add the custom field for  the error
               result.ContentLength = 0;
               result.ContentType = "";
               result.CustomError = ex.Message;
           }
           return result;
       }
    }
    
  3. Return an imitation of success to the client and handle the OnClientFileUploaded event.

    <telerik:RadAsyncUpload runat="server" ID="RadAsyncUpload1" HttpHandlerUrl="~/myHandler.ashx" OnClientFileUploaded="OnClientFileUploaded" OnClientFileUploadFailed="OnClientFileUploadFailed"></telerik:RadAsyncUpload>
    
  4. Check for the presence of an error and if so - invalidate the file row.

    function OnClientFileUploaded(sender, args) {
       var info = args.get_fileInfo();
       if (info.CustomError != null) {
           var row = args.get_row();
           sender._updateRowImage(row, 'fail');
           sender._updateCancelButton(row);
           $telerik.$(".ruFileProgressWrap", row).remove();
    
           alert(info.CustomError);
       }
    }
    
  5. Handle the OnClientFileUploadFailed event just in case to capture any errors.

    function OnClientFileUploadFailed(sender, args) {
       args.set_handled(true);
    }
    

    See Also

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