Catching “Maximum request length exceeded”

Question

I'm writing an upload function, and have problems catching "System.Web.HttpException: Maximum request length exceeded" with files larger than the specified max size in httpRuntimein web.config (max size set to 5120). I'm using a simple <input> for the file.

The problem is that the exception is thrown before the upload button's click-event, and the exception happens before my code is run. So how do I catch and handle the exception?

EDIT: The exception is thrown instantly, so I'm pretty sure it's not a timeout issue due to slow connections.

Answer 1

As you probably know, the maximum request length is configured in TWO places.

1. maxRequestLength - controlled at the ASP.NET app level
2. maxAllowedContentLength - under <system.webServer>, controlled at the IIS level

The first case is covered by other answers to this question.

To catch THE SECOND ONE you need to do this in global.asax:

protected void Application_EndRequest(object sender, EventArgs e)
{
    //check for the "file is too big" exception if thrown at the IIS level
    if (Response.StatusCode == 404 && Response.SubStatusCode == 13)
    {
        Response.Write("Too big a file"); //just an example
        Response.End();
    }
}

Answer 2

There is no easy way to catch such exception unfortunately. What I do is either override the OnError method at the page level or the Application_Error in global.asax, then check if it was a Max Request failure and, if so, transfer to an error page.

protected override void OnError(EventArgs e) .....


private void Application_Error(object sender, EventArgs e)
{
    if (GlobalHelper.IsMaxRequestExceededException(this.Server.GetLastError()))
    {
        this.Server.ClearError();
        this.Server.Transfer("~/error/UploadTooLarge.aspx");
    }
}

It's a hack but the code below works for me

const int TimedOutExceptionCode = -2147467259;
public static bool IsMaxRequestExceededException(Exception e)
{
    // unhandled errors = caught at global.ascx level
    // http exception = caught at page level

    Exception main;
    var unhandled = e as HttpUnhandledException;

    if (unhandled != null && unhandled.ErrorCode == TimedOutExceptionCode)
    {
        main = unhandled.InnerException;
    }
    else
    {
        main = e;
    }


    var http = main as HttpException;

    if (http != null && http.ErrorCode == TimedOutExceptionCode)
    {
        // hack: no real method of identifying if the error is max request exceeded as 
        // it is treated as a timeout exception
        if (http.StackTrace.Contains("GetEntireRawContent"))
        {
            // MAX REQUEST HAS BEEN EXCEEDED
            return true;
        }
    }

    return false;
}

Answer 3

A solution that works with IIS7 and upwards: Display custom error page when file upload exceeds allowed size in ASP.NET MVC

Answer 4

One way to do this is to set the maximum size in web.config as has already been stated above e.g.

<system.web>         
    <httpRuntime maxRequestLength="102400" />     
</system.web>

then when you handle the upload event, check the size and if its over a specific amount, you can trap it e.g.

protected void btnUploadImage_OnClick(object sender, EventArgs e)
{
    if (fil.FileBytes.Length > 51200)
    {
         TextBoxMsg.Text = "file size must be less than 50KB";
    }
}

Answer 5

In IIS 7 and beyond:

web.config file:

<system.webServer>
  <security >
    <requestFiltering>
      <requestLimits maxAllowedContentLength="[Size In Bytes]" />
    </requestFiltering>
  </security>
</system.webServer>

You can then check in code behind, like so:

If FileUpload1.PostedFile.ContentLength > 2097152 Then ' (2097152 = 2 Mb)
  ' Exceeded the 2 Mb limit
  ' Do something
End If

Just make sure the [Size In Bytes] in the web.config is greater than the size of the file you wish to upload then you won't get the 404 error. You can then check the file size in code behind using the ContentLength which would be much better

Answer 6

After tag

<security>
     <requestFiltering>
         <requestLimits maxAllowedContentLength="4500000" />
     </requestFiltering>
</security>

add the following tag

 <httpErrors errorMode="Custom" existingResponse="Replace">
  <remove statusCode="404" subStatusCode="13" />
  <error statusCode="404" subStatusCode="13" prefixLanguageFilePath="" path="http://localhost/ErrorPage.aspx" responseMode="Redirect" />
</httpErrors>

you can add the Url to the error page...