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

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);
    }
}