HttpModule Multithreading and instances

[Shapiro]

I have a scenario where I log a resquest to a database table and update the
request with a corresponding response including the response time. I am using
an HttpModule to do this.

My challenge is how to corelate the response to a corresponding request. I
am looking for a sure proof threadsafe way to corelate a response to a
coresponding request message.


Two things that concerns me:-

1. I am using the onBeginRequest event to capture the request and persist it
in the database and a filter class inheriting from the stream class to
capture the response and update a request row in the database with the
correspond response using an Id I generate to correct the messages.

2. My question is that if I create a guid in the onBeginRequest method and
pass it as a parameter to the filter class will this work from correlation
and multithreading standpoint since the messgae Id is a private memebr
variable in the filter class and is accessed by the overriden write method?

sample code

private void OnBeginRequest( object sender, EventArgs args )
{
string requestContent = string.Empty;

// HttpApplication httpApp = sender as HttpApplication;

// current request context
HttpContext context = HttpContext.Current;

// long position = httpApp.Context.Request.InputStream.Position;
long position = context.Request.InputStream.Position;

// Stream requestStream = httpApp.Context.Request.InputStream;

Stream requestStream = context.Request.InputStream;

byte[] buffer = new byte[ requestStream.Length ];

int read = requestStream.Read( buffer, 0, (int)requestStream.Length
);

//reset the stream to the original position
// httpApp.Request.InputStream.Position = position;

context.Request.InputStream.Position = position;

requestContent = System.Web.HttpUtility.HtmlDecode(
System.Web.HttpUtility.UrlDecode(System.Text.Encoding.Default.GetString(
buffer ) ));

if( requestContent.Length == 0 ) return;

//generate message Id to corelate the request and resoponse
string messageId = System.Guid.NewGuid().ToString();

// For Get and Http posts remove the name from the name/value pair
requestContent = requestContent.Substring( requestContent.IndexOf( "=<" ) +
1 );

// append the messageId to the message
requestContent = requestContent.Insert( requestContent.LastIndexOf("/") - 1,
"<messageId>" + messageId + "</messageId>" );

LogRequestInfo( requestContent );

// apply the filter to access the response stream
// _responseStream = new ResponseStream( _httpApp.Response.Filter );

// httpApp.Context.Response.Filter = new ResponseStream(
HttpContext.Current.Response.Filter, messageId );
_responseStream = new ResponseStream( context.Response.Filter, messageId );
context.Response.Filter = _responseStream;

}


The critical question here is that there is very little documentation from
Microsoft on threading issues regarding use of httpmodules and how the
httpmodule instances are created and used.

sample filter class code

public sealed class ResponseStream : Stream
{
private Stream _responseStream;
private string _messageId;

public ResponseStream( Stream sink )
{
_responseStream = sink;
}

public ResponseStream( Stream sink, string messageId )
{
_responseStream = sink;
_messageId = messageId;
}

public override void Write( byte[] buffer, int offset, int count )
{
_responseStream.Write( buffer, offset, count );

// get the response string from the byte stream
string responseString = System.Web.HttpUtility.HtmlDecode(
System.Web.HttpUtility.UrlDecode(Encoding.Default.GetString( buffer ).Trim()
) );

//append the message Id to the response message
responseString = responseString.Insert( responseString.LastIndexOf("/") - 1,
"<messageId>" + _messageId + "</messageId>" );

// log the response
LogResponseInfo( responseString );
}


Thanks for your help in advance.
SOA Freak