Logging raw HTTP request/response in ASP.NET MVC & IIS7

Question

I'm writing a web service (using ASP.NET MVC) and for support purposes we'd like to be able to log the requests and response in as close as possible to the raw, on-the-wire format (i.e including HTTP method, path, all headers, and the body) into a database.

What I'm not sure of is how to get hold of this data in the least 'mangled' way. I can re-constitute what I believe the request looks like by inspecting all the properties of the HttpRequest object and building a string from them (and similarly for the response) but I'd really like to get hold of the actual request/response data that's sent on the wire.

I'm happy to use any interception mechanism such as filters, modules, etc. and the solution can be specific to IIS7. However, I'd prefer to keep it in managed code only.

Any recommendations?

Edit: I note that HttpRequest has a SaveAs method which can save the request to disk but this reconstructs the request from the internal state using a load of internal helper methods that cannot be accessed publicly (quite why this doesn't allow saving to a user-provided stream I don't know). So it's starting to look like I'll have to do my best to reconstruct the request/response text from the objects... groan.

Edit 2: Please note that I said the whole request including method, path, headers etc. The current responses only look at the body streams which does not include this information.

Edit 3: Does nobody read questions around here? Five answers so far and yet not one even hints at a way to get the whole raw on-the-wire request. Yes, I know I can capture the output streams and the headers and the URL and all that stuff from the request object. I already said that in the question, see:

I can re-constitute what I believe the request looks like by inspecting all the properties of the HttpRequest object and building a string from them (and similarly for the response) but I'd really like to get hold of the actual request/response data that's sent on the wire.

If you know the complete raw data (including headers, url, http method, etc.) simply cannot be retrieved then that would be useful to know. Similarly if you know how to get it all in the raw format (yes, I still mean including headers, url, http method, etc.) without having to reconstruct it, which is what I asked, then that would be very useful. But telling me that I can reconstruct it from the HttpRequest/HttpResponse objects is not useful. I know that. I already said it.

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Please note: Before anybody starts saying this is a bad idea, or will limit scalability, etc., we'll also be implementing throttling, sequential delivery, and anti-replay mechanisms in a distributed environment, so database logging is required anyway. I'm not looking for a discussion of whether this is a good idea, I'm looking for how it can be done.

Answer 1

Definitely use an IHttpModule and implement the BeginRequest and EndRequest events.

All of the "raw" data is present between HttpRequest and HttpResponse, it just isn't in a single raw format. Here are the parts needed to build Fiddler-style dumps (about as close to raw HTTP as it gets):

request.HttpMethod + " " + request.RawUrl + " " + request.ServerVariables["SERVER_PROTOCOL"]
request.Headers // loop through these "key: value"
request.InputStream // make sure to reset the Position after reading or later reads may fail

For the response:

"HTTP/1.1 " + response.Status
response.Headers // loop through these "key: value"

Note that you cannot read the response stream so you have to add a filter to the Output stream and capture a copy.

In your BeginRequest, you will need to add a response filter:

HttpResponse response = HttpContext.Current.Response;
OutputFilterStream filter = new OutputFilterStream(response.Filter);
response.Filter = filter;

Store filter where you can get to it in the EndRequest handler. I suggest in HttpContext.Items. There can then get the full response data in filter.ReadStream().

Then implement OutputFilterStream using the Decorator pattern as a wrapper around a stream:

/// <summary>
/// A stream which keeps an in-memory copy as it passes the bytes through
/// </summary>
public class OutputFilterStream : Stream
{
    private readonly Stream InnerStream;
    private readonly MemoryStream CopyStream;

    public OutputFilterStream(Stream inner)
    {
        this.InnerStream = inner;
        this.CopyStream = new MemoryStream();
    }

    public string ReadStream()
    {
        lock (this.InnerStream)
        {
            if (this.CopyStream.Length <= 0L ||
                !this.CopyStream.CanRead ||
                !this.CopyStream.CanSeek)
            {
                return String.Empty;
            }

            long pos = this.CopyStream.Position;
            this.CopyStream.Position = 0L;
            try
            {
                return new StreamReader(this.CopyStream).ReadToEnd();
            }
            finally
            {
                try
                {
                    this.CopyStream.Position = pos;
                }
                catch { }
            }
        }
    }


    public override bool CanRead
    {
        get { return this.InnerStream.CanRead; }
    }

    public override bool CanSeek
    {
        get { return this.InnerStream.CanSeek; }
    }

    public override bool CanWrite
    {
        get { return this.InnerStream.CanWrite; }
    }

    public override void Flush()
    {
        this.InnerStream.Flush();
    }

    public override long Length
    {
        get { return this.InnerStream.Length; }
    }

    public override long Position
    {
        get { return this.InnerStream.Position; }
        set { this.CopyStream.Position = this.InnerStream.Position = value; }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        return this.InnerStream.Read(buffer, offset, count);
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        this.CopyStream.Seek(offset, origin);
        return this.InnerStream.Seek(offset, origin);
    }

    public override void SetLength(long value)
    {
        this.CopyStream.SetLength(value);
        this.InnerStream.SetLength(value);
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        this.CopyStream.Write(buffer, offset, count);
        this.InnerStream.Write(buffer, offset, count);
    }
}