IIS DelegatingHandler gets overriden

I created a DelegatingHandler for my IIS hosted WebAPI that creates a custom response if the response code is 405.

This code gets executed and there are no other handlers registered. I verified this through debug and through logging.

However, the response I get in the end is the generic html code. It is as if my response is overwritten by IIS somehow.

Can somebody point me as to what handler produces this response:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<title>IIS 10.0 Detailed Error - 405.0 - Method Not Allowed</title> 
<style type="text/css"> 
.config_source code{font-size:.8em;color:#000000;} 
ul,ol{margin:10px 0 10px 5px;} 
fieldset{padding:0 15px 10px 15px;word-break:break-all;} 
.summary-container fieldset{padding-bottom:5px;margin-top:4px;} 
legend.no-expand-all{padding:2px 15px 4px 10px;margin:0 0 0 -12px;} 
legend{color:#333333;;margin:4px 0 8px -12px;_margin-top:0px; 
h3{font-size:1.4em;margin:10px 0 0 0;color:#CC0000;} 
h4{font-size:1.2em;margin:10px 0 5px 0; 
}#header{width:96%;margin:0 0 0 0;padding:6px 2% 6px 2%;font-family:"trebuchet MS",Verdana,sans-serif; 
}#content{margin:0 0 0 2%;position:relative;} 
.content-container p{margin:0 0 10px 0; 
}#server_version{width:96%;_height:1px;min-height:1px;margin:0 0 5px 0;padding:11px 2% 8px 2%;color:#FFFFFF; 
 background-color:#5A7FA5;border-bottom:1px solid #C1CFDD;border-top:1px solid #4A6C8E;font-weight:normal; 
}#server_version p{margin:5px 0;} 
table{margin:4px 0 4px 0;width:100%;border:none;} 
td,th{vertical-align:top;padding:3px 0;text-align:left;font-weight:normal;border:none;} 
thead th{background-color:#ebebeb;width:25%; 
}#details-right th{width:20%;} 
table tr.alt td,table tr.alt th{} 
.preferred{padding:0 5px 2px 5px;font-weight:normal;background:#006633;color:#FFF;font-size:.8em;} 
<div id="content"> 
<div class="content-container"> 
  <h3>HTTP Error 405.0 - Method Not Allowed</h3> 
  <h4>The page you are looking for cannot be displayed because an invalid method (HTTP verb) is being used.</h4> 
<div class="content-container"> 
 <fieldset><h4>Most likely causes:</h4> 
  <ul>  <li>The request sent to the Web server used an HTTP verb that is not allowed by the module configured to handle the request.</li>   <li>A request was sent to the server that contained an invalid HTTP verb.</li>  <li>The request is for static content and contains an HTTP verb other than GET or HEAD.</li>    <li>A request was sent to a virtual directory using the HTTP verb POST and the default document is a static file that does not support HTTP verbs other than GET or HEAD.</li> </ul> 
<div class="content-container"> 
 <fieldset><h4>Things you can try:</h4> 
  <ul>  <li>Verify the list of verbs enabled for the module handler this request was sent to, and ensure that this verb should be allowed for the Web site.</li>    <li>Check the IIS log file to see which verb is not allowed for the request.</li>   <li>Create a tracing rule to track failed requests for this HTTP status code. For more information about creating a tracing rule for failed requests, click <a href="http://go.microsoft.com/fwlink/?LinkID=66439">here</a>. </li> </ul> 
<div class="content-container"> 
 <fieldset><h4>Detailed Error Information:</h4> 
  <div id="details-left"> 
   <table border="0" cellpadding="0" cellspacing="0"> 
    <tr class="alt"><th>Module</th><td>&nbsp;&nbsp;&nbsp;ManagedPipelineHandler</td></tr> 
    <tr class="alt"><th>Handler</th><td>&nbsp;&nbsp;&nbsp;System.Web.Http.WebHost.HttpControllerHandler</td></tr> 
    <tr><th>Error Code</th><td>&nbsp;&nbsp;&nbsp;0x00000000</td></tr> 
  <div id="details-right"> 
   <table border="0" cellpadding="0" cellspacing="0"> 
    <tr class="alt"><th>Requested URL</th><td>&nbsp;&nbsp;&nbsp;</td></tr> 
    <tr><th>Physical Path</th><td>&nbsp;&nbsp;&nbsp;c:\inetpub\VHOST\TDMSWebIEEE20305Site\DerAdapter\tm</td></tr> 
    <tr class="alt"><th>Logon Method</th><td>&nbsp;&nbsp;&nbsp;Anonymous</td></tr> 
    <tr><th>Logon User</th><td>&nbsp;&nbsp;&nbsp;Anonymous</td></tr> 
   <div class="clear"></div> 
<div class="content-container"> 
 <fieldset><h4>More Information:</h4> 
  This error means that the request sent to the Web server contained an HTTP verb that is not allowed by the configured module handler for the request. 
  <p><a href="https://go.microsoft.com/fwlink/?LinkID=62293&amp;IIS70Error=405,0,0x00000000,17763">View more information &raquo;</a></p> 

The code of the handler is very simple:

protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
            var result = await base.SendAsync(request, cancellationToken);

            if (result.StatusCode != HttpStatusCode.MethodNotAllowed)
                return result;

            result.Content = GetResultContent(); //This is the method that simply creates a customized message
            result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/sep+xml");
            return result;

The handler is registered like this:

config.MessageHandlers.Add(new MethodNotAllowedHandler());

There are no other handlers.

1 answer

  • answered 2022-01-25 07:24 Vladimir Stokic

    What solved my problem is adding this to the web.config:

    <httpErrors existingResponse="Passthrough" />

    I found this on this link.

    I got there by pulling on a thread I got from the comment of Richard Deeming, so thanks for that.

    Basically, I needed IIS to not handle the errors received from my WebAPI, and this configuration setting tells it just that.

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