HttpRequest.Form collection gets cleared after Managed HttpModule - asp.net

Question

I’m suffering this issue I can’t find an explanation for.
Have a website that handles ASP and ASPX requests.
All requests run through a custom managed module, named MyModule, let’s say for “logging purposes”.
This is the WebConfig:
<configuration>
<system.web>
<compilation debug="true" targetFramework="4.5" />
<httpRuntime targetFramework="4.5" />
</system.web>
<system.webServer>
<modules runAllManagedModulesForAllRequests="true">
<add name="MyModule" type="MySample.MyModule" preCondition="managedHandler" />
</modules>
</system.webServer>
</configuration>
So, if a form is posted to /action.asp via AJAX, an html form, or whatever, on /action.asp I can see and print the data on the Request.Form collection.
This is /action.asp
<%#LANGUAGE="VBSCRIPT" CODEPAGE="65001"%>
<%
dim count
count = Request.Form.Count
Response.write("Result: " & count)
Response.End()
%>
But, if in my custom managed module I just “PEEK” at the form collection before it’s handled by the ASP page, the collection disappears, it’s no longer available to /action.asp
This is the MyModule:
namespace MySample
{
public class MyModule : IHttpModule
{
public MyModule()
{
}
public void Init(HttpApplication context)
{
context.BeginRequest += context_BeginRequest;
}
void context_BeginRequest(object sender, EventArgs e)
{
/*
* ALL REQUESTS PASS THROUGH THIS POINT BEFORE CONTINUING.
* COUNTING THE ITEMS ON THE FORM WILL CAUSE THE FORM-COLLECTION
* TO BE CLEARED WHEN IT'S HANDLED BY ASP.
*/
int count = HttpContext.Current.Request.Form.Count;
}
public void Dispose()
{
}
}
}
It’s extremely odd. If I “comment” the count line, the form collection is handled unmodified to the ASP page. I just have to peek at it to run it.
I want to find an explanation for this backed up with some documentation, not just a hunch.
I can’t set to false the runAllManagedModulesForAllRequests, this is not an option.
I debugged the request through different .NET method calls, and many things happen when you query the Form object on .NET HttpRequest object,
// Form collection
/// Gets a collection of Form variables.
public NameValueCollection Form {
get {
EnsureForm();
if (_flags[needToValidateForm]) {
_flags.Clear(needToValidateForm);
ValidateHttpValueCollection(_form, RequestValidationSource.Form);
}
return _form;
}
}
// Populates the Form property but does not hook up validation.
internal HttpValueCollection EnsureForm() {
if (_form == null) {
_form = new HttpValueCollection();
/// THE FOLLWING METHOD AS A LOT OF SUB-CALLS AS WELL
if (_wr != null)
FillInFormCollection();
_form.MakeReadOnly();
}
return _form;
}
Is what I am experiencing an expected behavior ? What’s the documentation or the reasoning to back up this behavior ?