(from awebb)

This patch adds an additional handler to the existing BaseHttpServer. 
It does not affect any of the existing behaviors except insofar as the 
new handler may be selected.

It is selected first because its Agent-oriented nature means that it 
should not be pre-empted.  The new handler type is defined by IHttpAgentHandler 
in Framework/Servers and has two interface methods: Match and Handle.

The Match function returns a boolean result based upon examination of 
information presented in the User-Agent header.

The Handle function expects to get the request and response instances 
associated with the flow. The handler is responsible for ALL activity 
associated with the request except in the event of an unhandled exception, 
in which case the HandleAgentRequest routine will generate a 500 status 
message and close the stream.

There are two immediateley apparent (and VERY easy to implement) 
improvements that could be made:

   1. The Match call could be allowed to operate over the entire 
      request context., rather than just agent identity.
   2. The Handler could return a boolean indication of whether or not 
      the request was actually handled, and if not, the remaining handler 
      mechanism could take a shot at it. This would eliminate issues 
      arising from pre-empted streams.

OpenSim/Framework/Servers/BaseHttpServer.cs

@@ -49,8 +49,9 @@ namespace OpenSim.Framework.Servers
         protected HttpListener m_httpListener;
         protected Dictionary<string, XmlRpcMethod> m_rpcHandlers = new Dictionary<string, XmlRpcMethod>();
         protected LLSDMethod m_llsdHandler = null;
-        protected Dictionary<string, IRequestHandler> m_streamHandlers = new Dictionary<string, IRequestHandler>();
+        protected Dictionary<string, IRequestHandler> m_streamHandlers  = new Dictionary<string, IRequestHandler>();
-        protected Dictionary<string, GenericHTTPMethod> m_HTTPHandlers = new Dictionary<string, GenericHTTPMethod>();
+        protected Dictionary<string, GenericHTTPMethod> m_HTTPHandlers  = new Dictionary<string, GenericHTTPMethod>();
+        protected Dictionary<string, IHttpAgentHandler> m_agentHandlers = new Dictionary<string, IHttpAgentHandler>();
 
         protected uint m_port;
         protected bool m_ssl = false;
@@ -119,6 +120,18 @@ namespace OpenSim.Framework.Servers
             return false;
         }
 
+        public bool AddAgentHandler(string agent, IHttpAgentHandler handler)
+        {
+            if (!m_agentHandlers.ContainsKey(agent))
+            {
+                m_agentHandlers.Add(agent, handler);
+                return true;
+            }
+
+            //must already have a handler for that path so return false
+            return false;
+        }
+
         public bool SetLLSDHandler(LLSDMethod handler)
         {
             m_llsdHandler = handler;
@@ -139,7 +152,21 @@ namespace OpenSim.Framework.Servers
                 OSHttpRequest request = new OSHttpRequest(context.Request);
                 OSHttpResponse response = new OSHttpResponse(context.Response);
 
-                response.KeepAlive = false;
+                if (request.UserAgent != null)
+                {
+
+                    IHttpAgentHandler agentHandler;
+
+                    if (TryGetAgentHandler(request.UserAgent, out agentHandler))
+                    {
+                        m_log.DebugFormat("[HTTP-AGENT] Handler located for {0}", request.UserAgent);
+                        HandleAgentRequest(agentHandler, request, response);
+                    }
+                    return;
+                }
+
+                IRequestHandler requestHandler;
+                response.KeepAlive   = false;
                 response.SendChunked = false;
 
                 string path = request.RawUrl;
@@ -147,10 +174,9 @@ namespace OpenSim.Framework.Servers
 
                 //m_log.DebugFormat("[BASE HTTP SERVER]: Handling {0} request for {1}", request.HttpMethod, path);
                 
-                IRequestHandler requestHandler;
-
                 if (TryGetStreamHandler(handlerKey, out requestHandler))
                 {
+                    
                     // Okay, so this is bad, but should be considered temporary until everything is IStreamHandler.
                     byte[] buffer;
                     if (requestHandler is IStreamedRequestHandler)
@@ -184,24 +210,25 @@ namespace OpenSim.Framework.Servers
                     {
                         m_log.WarnFormat("[BASE HTTP SERVER]: HTTP request abnormally terminated.");
                     }
+                    return;
                 }
-                else
+                
+                switch (request.ContentType)
                 {
-                    switch (request.ContentType)
+                case null:
-                    {
+                case "text/html":
-                        case null:
+                    HandleHTTPRequest(request, response);
-                        case "text/html":
+                    return;
-                            HandleHTTPRequest(request, response);
+
-                            break;
+                case "application/xml+llsd":
-                        case "application/xml+llsd":
+                    HandleLLSDRequests(request, response);
-                            HandleLLSDRequests(request, response);
+                    return;
-                            break;
+
-                        case "text/xml":
+                case "text/xml":
-                        case "application/xml":
+                case "application/xml":
-                        default:
+                default:
-                            HandleXmlRpcRequests(request, response);
+                    HandleXmlRpcRequests(request, response);
-                            break;
+                    return;
-                    }
                 }
             }
             catch (SocketException)
@@ -274,6 +301,26 @@ namespace OpenSim.Framework.Servers
             }
         }
 
+        private bool TryGetAgentHandler(string agent, out IHttpAgentHandler agentHandler)
+        {
+            agentHandler = null;
+            try
+            {
+                foreach(IHttpAgentHandler handler in m_agentHandlers.Values)
+                {
+                    if(handler.Match(agent))
+                    {
+                        agentHandler = handler;
+                        return true;
+                    }
+                }
+            }
+            catch(KeyNotFoundException) {}
+
+            return false;
+
+        }
+
         /// <summary>
         /// Try all the registered xmlrpc handlers when an xmlrpc request is received.
         /// Sends back an XMLRPC unknown request response if no handler is registered for the requested method.
@@ -416,6 +463,36 @@ namespace OpenSim.Framework.Servers
             }
         }
 
+        /// <summary>
+        /// A specific agent handler was provided. Such a handler is expecetd to have an
+        /// intimate, and highly specific relationship with the client. Consequently,
+        /// nothing is done here.
+        /// </summary>
+        /// <param name="handler"></param>
+        /// <param name="request"></param>
+        /// <param name="response"></param>
+
+        private void HandleAgentRequest(IHttpAgentHandler handler, OSHttpRequest request, OSHttpResponse response)
+        {
+
+            // In the case of REST, then handler is responsible for ALL aspects of 
+            // the request/response handling. Nothing is done here, not even encoding.
+
+            try
+            {
+                handler.Handle(request, response);
+            }
+            catch (Exception e)
+            {
+                m_log.Warn("[HTTP-AGENT]: Error - " + e.Message);
+                response.SendChunked   = false;
+                response.KeepAlive     = false;
+                response.StatusCode    = 500;
+                response.OutputStream.Close();
+            }
+
+        }
+
         public void HandleHTTPRequest(OSHttpRequest request, OSHttpResponse response)
         {
             switch (request.HttpMethod)

OpenSim/Framework/Servers/IHttpAgentHandler.cs

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) Contributors, http://opensimulator.org/
+ * See CONTRIBUTORS.TXT for a full list of copyright holders.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the OpenSim Project nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+using System.Collections;
+using System.IO;
+using System.Net;
+
+namespace OpenSim.Framework.Servers
+{
+    public interface IHttpAgentHandler
+    {
+        void Handle(OSHttpRequest req, OSHttpResponse resp);
+        bool Match(string agent);
+    }
+}