Display Exception Message from Custom HTTP Handler

[Gary]

I have made my own custom HTTP handler to run some server side validation on files before the upload completes. I have 2 questions:

1. If the file does not pass validation, I would like to display an error on the upload page under the uploaded file. How can I do that?
2. If the file does not pass validation, I would like to delete it (or not have it save to the disk at all in the first place). Is there a way to do that?

Thanks.

[Hristo Valyavicharski]

Hi Gary,

You may create result, which will be return on the client after the file is send to handler then check this custom result on the client and remove the row:

CustomResult.cs

public class CustomResult : AsyncUploadResult
{
    public int StatusCode { get; set; }
    public string Message { get; set; }
}

Handler.ashx

public class Handler : AsyncUploadHandler, System.Web.SessionState.IRequiresSessionState
{

    protected override IAsyncUploadResult Process(UploadedFile file, HttpContext context, IAsyncUploadConfiguration configuration, string tempFileName)
    {
        CustomResult result = CreateDefaultUploadResult<CustomResult>(file);


        string targetFolder = context.Server.MapPath("~/Uploads/");
        string fileName = file.GetName();

        if (file.GetExtension() == ".jpg")
        {
            file.SaveAs(targetFolder + fileName);
            result.StatusCode = 201;
            result.Message = "File was uploaded successfully.";
        }
        else
        {
            result.StatusCode = 415;
            result.Message = "Error! File extension is not allowed";
        }

        return result;
    }
}

ASPX:

function OnClientFileUploaded(sender, args) {
    //check what is the result returned by the handler
    if (args.get_fileInfo().StatusCode == 415) {
        //remove the selected file
        args.get_row().remove();
        //display a notification
        alert(args.get_fileInfo().Message);
    }
}

Sample is attached.

Regards,
Hristo Valyavicharski
Telerik

[Gary]

Thank you Hristo. That seems to work well.

But in my case, I am only allowing 1 file upload and when I remove the row with "args.get_row().remove()", the uploaded file listing gets removed, but the select box does not reappear so the user can't select another file. If I comment out the line that removes the file, then the file is there with a little green circle next to it that seems to show that the file was uploaded successfully - even though an error message shows up..

What I would really like, is if the file would remain listed, but with a little red circle next to it - the same thing that happens when someone selects a file with an extension that is not in the allowed list. How can I do that?

[Gary]

I also see that even if the file fails validation in the HTTP handler, it still gets saved to the "~/AppData/RadUploadTemp" folder. When it fails, I don't want it to hit my hard drive at all. How can I stop this from happening?

[Hristo Valyavicharski]

Hi Gary,

If you need to make validation of the file type or size better use AllowedFileExtensions and MaxFileSize properties of the AsyncUpload instead validate them into the handler.

<telerik:RadAsyncUpload
    ID="RadAsyncUpload1"
    OnClientFileUploaded="OnClientFileUploaded"
    HttpHandlerUrl="~/Handler.ashx"
    AllowedFileExtensions="jpg"
    MaxFileInputsCount="1"
    MaxFileSize="99999"
    TargetFolder="~/Uploads"
    runat="server">
</telerik:RadAsyncUpload>

After you return the result from the handler you will have to set the red circle manually: 

function OnClientFileUploaded(sender, args) {
    if (args.get_fileInfo().StatusCode == 415) {
        setTimeout(function () {
            $(args.get_row()).find('span .ruUploadProgress').removeClass('ruUploadFailure');
            $(args.get_row()).find('span .ruUploadProgress').addClass('ruUploadFailure');
        }, 100);
    }
}

Regarding your other question. All files are stored first into the temporary folder. Some of them will be uploaded successfully and may be moved automatically to the Target folder or after you call File.SaveAs() method. However all files that remains into the temporary folder will be cleared automatically by the RadAsyncUpload on every 4 hours. This can be changed as you set the TemporaryFileExpiration property.

Regards,
Hristo Valyavicharski
Telerik

[Gary]

I added that JS code and it works perfectly.

I am using the allowed extensions option. But I also check server side with other checks that ignore the extension in case a malicious user has spoofed the file extension. 

Thanks for your help!