How can I tell when HTTP Headers have been sent in an ASP.NET application?

Question

Long story short, I have an ASP.NET application I\'m trying to debug and at some point, in very particular circumstances, the application will throw exceptions at a Respon

Answer 1

Samuel's reply just solved this problem for me (+1). I can't paste a code sample in a comment, but in the interest of helping others, here's how I used the event he suggested to add a HeadersWritten property to my IHTTPHandler:

protected bool HeadersWritten { get; private set; }

void ApplicationInstance_BeginRequest(object sender, EventArgs e)
{
    HeadersWritten = false;
}

void ApplicationInstance_PreSendRequestHeaders(object sender, EventArgs e)
{
    HeadersWritten = true;
}

public void ProcessRequest(HttpContextBase context)
{
    context.ApplicationInstance.PreSendRequestHeaders += new EventHandler(ApplicationInstance_PreSendRequestHeaders);
    do_some_stuff();
}

In my code that would break if I mess with headers too late, I simply check the HeadersWritten property first:

if (!HeadersWritten)
{
    Context.Response.StatusDescription = get_custom_description(Context.Response.StatusCode);
}