Serving files in Kayak, contributed by RichB at https://groups.google.com/forum/#!msg/kayak-http/ivzlD8HoF9w/7reCjodx2-AJ%5B1-25%5D

FileProducer.cs

    // from RichB, https://groups.google.com/forum/#!msg/kayak-http/ivzlD8HoF9w/7reCjodx2-AJ%5B1-25%5D

    
    class FileProducer : IDataProducer
    {

        // Members
        private string m_fileName;
        private FileStream m_fileStream;
        private IDataConsumer m_consumer;
        
        // Constructor
        public FileProducer(string fileName)
        {

            // The stream that we'll serve up
            m_fileStream = null;

            // Check that the file that we are going to serve actually exists
            if (File.Exists(fileName) == false)
            {
                throw new Exception("File does not exist");
            }
            else
            {
                m_fileName = fileName;
            }

        }


        // Returns either a continuation or NULL if no continuation
        public IDisposable Connect(IDataConsumer channel)
        {

            // Store a handle to the data consumer
            m_consumer = channel;

            // Open the file that we want to send
            m_fileStream = File.OpenRead(m_fileName);

            // Send data
            Send();

            // Return a handle to a disconnector
            return new FileDisconnector(m_fileStream);

        }


        private void Send()
        {

            // Buffer to hold bytes read from file

            byte[] buffer = new byte[1024];

            // If the file is closed
            if (m_fileStream.CanRead == false)
            {
                return;
            }

            // Set up an async callback to write data to the consumer
            m_fileStream.BeginRead(buffer, 0, buffer.Length, new AsyncCallback(x =>
                {

                    // Wait for a read on the file to complete
                    int bytesRead = m_fileStream.EndRead(x);

                    // Will the consumer invoke continuation?
                    bool waitOnClient = m_consumer.OnData(new ArraySegment<byte>(buffer, 0, bytesRead), Send);

                    // If we've hit the end of the stream
                    if (m_fileStream.Position >= m_fileStream.Length)
                    {
                        m_fileStream.Close();
                        m_consumer.OnEnd();
                        return;
                    }

                    // If we aren't waiting on the client to request more data
                    else if (waitOnClient == false)
                    {
                        Send();
                    }

                }), null);

        }

    }


    class FileDisconnector : IDisposable
    {

        // Members
        private FileStream m_fileStream;

        // Constructor
        public FileDisconnector(FileStream fileStream)
        {
            m_fileStream = fileStream;
        }

        public void Dispose()
        {
            m_fileStream.Close();
        }

    }

One way this could be improved is if the buffer was only allocated one, in the constructor say. Also, it could catch the exceptions thrown by BeginRead or EndRead and yield them via OnError.