/*
 * 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;
using System.IO;
using System.Reflection;
using System.Text;
using System.Security.Cryptography;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Collections.Specialized;
using OpenSim.Framework;
using OpenSim.Framework.Servers;
using libsecondlife;
using System.Xml;

namespace OpenSim.ApplicationPlugins.Rest.Inventory
{

    /// <summary>
    /// This class represents the current REST request. It
    /// encapsulates the request/response state and takes care 
    /// of response generation without exposing the REST handler
    /// to the actual mechanisms involved.
    ///
    /// This structure is created on entry to the Handler
    /// method and is disposed of upon return. It is part of
    /// the plug-in infrastructure, rather than the functionally
    /// specific REST handler, and fundamental changes to 
    /// this should be reflected in the Rest HandlerVersion. The
    /// object is instantiated, and may be extended by, any
    /// given handler. See the inventory handler for an example
    /// of this.
    ///
    /// If possible, the underlying request/response state is not
    /// changed until the handler explicitly issues a Respond call.
    /// This ensures that the request/response pair can be safely
    /// processed by subsequent, unrelated, handlers even id the
    /// agent handler had completed much of its processing. Think
    /// of it as a transactional req/resp capability.
    /// </summary>

    internal class RequestData
    {

        // HTTP Server interface data

        internal OSHttpRequest        request = null;
        internal OSHttpResponse       response = null;
        internal string               qprefix = null;

        // Request lifetime values

        internal byte[]               buffer = null;
        internal string               body = null;
        internal string               html = null;
        internal string               entity = null;
        internal string               path = null;
        internal string               method = null;
        internal string               statusDescription = null;
        internal string               redirectLocation = null;
        internal string[]             pathNodes = null;
        internal string[]             parameters = null;
        internal int                  statusCode = 0;
        internal bool                 handled = false;
        internal LLUUID               uuid = LLUUID.Zero;
        internal Encoding             encoding = Rest.Encoding;
        internal Uri                  uri = null;
        internal string               query = null;
        internal bool                 fail = false;
        internal string               hostname = "localhost";
        internal int                  port = 80;
        internal string               prefix = Rest.UrlPathSeparator;
        internal bool                 keepAlive = false;
        internal bool                 chunked = false;

        // Authentication related state
 
        internal bool                 authenticated = false;
        // internal string               scheme = Rest.AS_DIGEST;
        // internal string               scheme = Rest.AS_BASIC;
        internal string               scheme = null;
        internal string               realm = Rest.Realm;
        internal string               domain = null;
        internal string               nonce = null;
        internal string               cnonce = null;
        internal string               qop = Rest.Qop_Auth;
        internal string               opaque = null;
        internal string               stale = null;
        internal string               algorithm = Rest.Digest_MD5;
        internal string               authParms  = null;
        internal string               authPrefix = null;
        internal string               userName  = String.Empty;
        internal string               userPass  = String.Empty;
        internal LLUUID               client = LLUUID.Zero;

        // XML related state

        internal XmlWriter            writer = null;
        internal XmlReader            reader = null;

        // Internal working state

        private StringBuilder         sbuilder = new StringBuilder(1024);
        private MemoryStream          xmldata = null;

        private static readonly string[] EmptyPath = { String.Empty };

        // Session related tables. These are only needed if QOP is set to "auth-sess"
        // and for now at least, it is not. Session related authentication is of 
        // questionable merit in the context of REST anyway, but it is, arguably, more
        // secure.

        private static Dictionary<string,string>  cntable   = new Dictionary<string,string>();
        private static Dictionary<string,string>  sktable   = new Dictionary<string,string>();

        // This dictionary is used to keep track fo all of the parameters discovered
        // when the authorisation header is anaylsed.

        private        Dictionary<string,string>  authparms = new Dictionary<string,string>();

        // These regular expressions are used to decipher the various header entries.

        private static Regex schema      = new Regex("^\\s*(?<scheme>\\w+)\\s*.*",
                                                     RegexOptions.Compiled | RegexOptions.IgnoreCase);
        
        private static Regex basicParms  = new Regex("^\\s*(?:\\w+)\\s+(?<pval>\\S+)\\s*",
                                                     RegexOptions.Compiled | RegexOptions.IgnoreCase);
        
        private static Regex digestParm1 = new Regex("\\s*(?<parm>\\w+)\\s*=\\s*\"(?<pval>[^\"]+)\"",
                                                     RegexOptions.Compiled | RegexOptions.IgnoreCase);
        
        private static Regex digestParm2 = new Regex("\\s*(?<parm>\\w+)\\s*=\\s*(?<pval>[^\\p{P}\\s]+)",
                                                     RegexOptions.Compiled | RegexOptions.IgnoreCase);
        
        private static Regex reuserPass  = new Regex("\\s*(?<user>[^:]+)\\s*:\\s*(?<pass>\\S*)",
                                                     RegexOptions.Compiled | RegexOptions.IgnoreCase);
        
        // For efficiency, we create static instances of these objects

        private static MD5   md5hash     = MD5.Create();
        
        private static StringComparer sc = StringComparer.OrdinalIgnoreCase;

        // Constructor
        
        internal RequestData(OSHttpRequest p_request, OSHttpResponse p_response, string p_qprefix)
        {

            request  = p_request;
            response = p_response;
            qprefix = p_qprefix;

            sbuilder.Length = 0;

            encoding = request.ContentEncoding;
            if (encoding == null)
            {
                encoding = Rest.Encoding;
            }

            method = request.HttpMethod.ToLower();
            initUrl();

            initParameters(p_qprefix.Length);

        }

        // Just for convenience...

        internal string MsgId
        {
            get { return Rest.MsgId; }
        }

        // Defer authentication check until requested

        internal bool IsAuthenticated
        {
            get
            { 
                if (Rest.Authenticate)
                {
                    if (!authenticated)
                    {
                        authenticate();
                    }

                    return authenticated;
                }
                else return true;
            }
        }

        /// <summary>
        /// The REST handler has requested authentication. Authentication
        /// is considered to be with respect to the current values for
        /// Realm, domain, etc.
        ///
        /// This method checks to see if the current request is already
        /// authenticated for this domain. If it is, then it returns 
        /// true. If it is not, then it issues a challenge to the client
        /// and responds negatively to the request.
        /// </summary>

        private void authenticate()
        {

            string authdata  = request.Headers.Get("Authorization");
            string reqscheme = String.Empty;

            // If we don't have an authorization header, then this
            // user is certainly not authorized. This is the typical
            // pivot for the 1st request by a client.

            if (authdata == null)
            {
                Rest.Log.DebugFormat("{0} Challenge reason: No authorization data", MsgId);
                DoChallenge();
            }
            
            // So, we have authentication data, now we have to check to
            // see what we got and whether or not it is valid for the
            // current domain. To do this we need to interpret the data
            // provided in the Authorization header. First we need to
            // identify the scheme being used and route accordingly.

            MatchCollection matches = schema.Matches(authdata);

            foreach (Match m in matches)
            {
                Rest.Log.DebugFormat("{0} Scheme matched : {1}", MsgId, m.Groups["scheme"].Value);
                reqscheme = m.Groups["scheme"].Value.ToLower();
            }

            // If we want a specific authentication mechanism, make sure
            // we get it. null indicates we don't care. non-null indicates
            // a specific scheme requirement.

            if (scheme != null && scheme.ToLower() != reqscheme)
            {
                Rest.Log.DebugFormat("{0} Challenge reason: Requested scheme not acceptable", MsgId);
                DoChallenge();
            }

            // In the future, these could be made into plug-ins...
            // But for now at least we have no reason to use anything other
            // then MD5. TLS/SSL are taken care of elsewhere.

            switch (reqscheme)
            {
                case "digest" :
                    Rest.Log.DebugFormat("{0} Digest authentication offered", MsgId);
                    DoDigest(authdata);
                    break;

                case "basic" :
                    Rest.Log.DebugFormat("{0} Basic authentication offered", MsgId);
                    DoBasic(authdata);
                    break;
            }

            // If the current header is invalid, then a challenge is still needed.

            if (!authenticated)
            {
                Rest.Log.DebugFormat("{0} Challenge reason: Authentication failed", MsgId);
                DoChallenge();
            }

        }

        /// <summary>
        /// Construct the necessary WWW-Authenticate headers and fail the request
        /// with a NOT AUTHORIZED response. The parameters are the union of values
        /// required by the supported schemes.
        /// </summary>

        private void DoChallenge()
        {
            Flush();
            nonce = Rest.NonceGenerator(); // should be unique per 401 (and it is)
            Challenge(scheme, realm, domain, nonce, opaque, stale, algorithm, qop, authParms);
            Fail(Rest.HttpStatusCodeNotAuthorized, Rest.HttpStatusDescNotAuthorized);
        }

        /// <summary>
        /// Interpret a BASIC authorization claim
        /// This is here for completeness, it is not used.
        /// </summary>

        private void DoBasic(string authdata)
        {

            string response = null;

            MatchCollection matches = basicParms.Matches(authdata);

            // In the case of basic authentication there is
            // only expected to be a single argument.

            foreach (Match m in matches)
            {
                authparms.Add("response",m.Groups["pval"].Value);
                Rest.Log.DebugFormat("{0} Parameter matched : {1} = {2}", 
                                     MsgId, "response", m.Groups["pval"].Value);
            }

            // Did we get a valid response?

            if (authparms.TryGetValue("response", out response))
            {
                // Decode
                response = Rest.Base64ToString(response);
                Rest.Log.DebugFormat("{0} Auth response is: <{1}>", MsgId, response);

                // Extract user & password
                Match m = reuserPass.Match(response);
                userName = m.Groups["user"].Value;
                userPass = m.Groups["pass"].Value;

                // Validate against user database
                authenticated = Validate(userName,userPass);
            }

        }

        /// <summary>
        /// This is an RFC2617 compliant HTTP MD5 Digest authentication
        /// implementation. It has been tested with Firefox, Java HTTP client,
        /// and Miscrosoft's Internet Explorer V7.
        /// </summary>

        private void DoDigest(string authdata)
        {

            string response = null;

            MatchCollection matches = digestParm1.Matches(authdata);

            // Collect all of the supplied parameters and store them
            // in a dictionary (for ease of access)

            foreach (Match m in matches)
            {
                authparms.Add(m.Groups["parm"].Value,m.Groups["pval"].Value);
                Rest.Log.DebugFormat("{0} String Parameter matched : {1} = {2}", 
                                     MsgId, m.Groups["parm"].Value,m.Groups["pval"].Value);
            }

            // And pick up any tokens too

            matches = digestParm2.Matches(authdata);

            foreach (Match m in matches)
            {
                authparms.Add(m.Groups["parm"].Value,m.Groups["pval"].Value);
                Rest.Log.DebugFormat("{0} Tokenized Parameter matched : {1} = {2}", 
                                     MsgId, m.Groups["parm"].Value,m.Groups["pval"].Value);
            }

            // A response string MUST be returned, otherwise we are
            // NOT authenticated.

            Rest.Log.DebugFormat("{0} Validating authorization parameters", MsgId);

            if (authparms.TryGetValue("response", out response))
            {

                string temp   = null;

                do
                {

                    string nck = null;
                    string ncl = null;

                    // The userid is sent in clear text. Needed for the
                    // verification.

                    authparms.TryGetValue("username", out userName);

                    // All URI's of which this is a prefix are
                    // optimistically considered to be authenticated by the
                    // client. This is also needed to verify the response.

                    authparms.TryGetValue("uri", out authPrefix);

                    // There MUST be a nonce string present. We're not preserving any server
                    // side state and we can't validate the MD5 unless the client returns it
                    // to us, as it should.

                    if (!authparms.TryGetValue("nonce", out nonce) || nonce == null)
                    {
                        Rest.Log.WarnFormat("{0} Authentication failed: nonce missing", MsgId); 
                        break;
                    }

                    // If there is an opaque string present, it had better
                    // match what we sent.

                    if (authparms.TryGetValue("opaque", out temp))
                    {
                        if (temp != opaque)
                        {
                            Rest.Log.WarnFormat("{0} Authentication failed: bad opaque value", MsgId); 
                            break;
                        }
                    }

                    // If an algorithm string is present, it had better
                    // match what we sent.

                    if (authparms.TryGetValue("algorithm", out temp))
                    {
                        if (temp != algorithm)
                        {
                            Rest.Log.WarnFormat("{0} Authentication failed: bad algorithm value", MsgId); 
                            break;
                        }
                    }

                    // Quality of protection considerations...

                    if (authparms.TryGetValue("qop", out temp))
                    {

                        qop = temp.ToLower(); // replace with actual value used

                        // if QOP was specified then
                        // these MUST be present.

                        if (!authparms.ContainsKey("cnonce"))
                        {
                            Rest.Log.WarnFormat("{0} Authentication failed: cnonce missing", MsgId); 
                            break;
                        }

                        cnonce = authparms["cnonce"];

                        if (!authparms.TryGetValue("nc", out nck) || nck == null)
                        {
                            Rest.Log.WarnFormat("{0} Authentication failed: cnonce counter missing", MsgId); 
                            break;
                        }

                        Rest.Log.DebugFormat("{0} Comparing nonce indices", MsgId);

                        if (cntable.TryGetValue(nonce, out ncl))
                        {
                            Rest.Log.DebugFormat("{0} nonce values: Verify that request({1}) > Reference({2})", MsgId, nck, ncl);

                            if (Rest.Hex2Int(ncl) >= Rest.Hex2Int(nck))
                            {
                                Rest.Log.WarnFormat("{0} Authentication failed: bad cnonce counter", MsgId); 
                                break;
                            }
                            cntable[nonce] = nck;
                        }
                        else
                        {
                            lock (cntable) cntable.Add(nonce, nck);
                        }

                    }
                    else
                    {

                        qop = String.Empty;

                        // if QOP was not specified then
                        // these MUST NOT be present.
                        if (authparms.ContainsKey("cnonce"))
                        {
                            Rest.Log.WarnFormat("{0} Authentication failed: invalid cnonce", MsgId); 
                            break;
                        }
                        if (authparms.ContainsKey("nc"))
                        {
                            Rest.Log.WarnFormat("{0} Authentication failed: invalid cnonce counter[2]", MsgId); 
                            break;
                        }
                    }

                    // Validate the supplied userid/password info

                    authenticated = ValidateDigest(userName, nonce, cnonce, nck, authPrefix, response);

                } 
                while (false);

            }

        }

        // Indicate that authentication is required

        internal void Challenge(string scheme, string realm, string domain, string nonce,
                                string opaque, string stale, string alg,
                                string qop, string auth)
        {

            sbuilder.Length = 0;

            if (scheme == null || scheme == Rest.AS_BASIC)
            {

                sbuilder.Append(Rest.AS_BASIC);

                if (realm != null)
                {
                    sbuilder.Append(" realm=\"");
                    sbuilder.Append(realm);
                    sbuilder.Append("\"");
                }
                AddHeader(Rest.HttpHeaderWWWAuthenticate,sbuilder.ToString());
            }

            sbuilder.Length = 0;

            if (scheme == null || scheme == Rest.AS_DIGEST)
            {

                sbuilder.Append(Rest.AS_DIGEST);
                sbuilder.Append(" ");

                if (realm != null)
                {
                    sbuilder.Append("realm=");
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(realm);
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(Rest.CS_COMMA);
                }

                if (nonce != null)
                {
                    sbuilder.Append("nonce=");
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(nonce);
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(Rest.CS_COMMA);
                }

                if (opaque != null)
                {
                    sbuilder.Append("opaque=");
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(opaque);
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(Rest.CS_COMMA);
                }

                if (stale != null)
                {
                    sbuilder.Append("stale=");
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(stale);
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(Rest.CS_COMMA);
                }

                if (alg != null)
                {
                    sbuilder.Append("algorithm=");
                    sbuilder.Append(alg);
                    sbuilder.Append(Rest.CS_COMMA);
                }

                if (qop != String.Empty)
                {
                    sbuilder.Append("qop=");
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(qop);
                    sbuilder.Append(Rest.CS_DQUOTE);
                    sbuilder.Append(Rest.CS_COMMA);
                }

                if (auth != null)
                {
                    sbuilder.Append(auth);
                    sbuilder.Append(Rest.CS_COMMA);
                }

                // We don;t know the userid that will be used
                // so we cannot make any authentication domain 
                // assumptions. So the prefix will determine
                // this.

                sbuilder.Append("domain=");
                sbuilder.Append(Rest.CS_DQUOTE);
                sbuilder.Append(qprefix);
                sbuilder.Append(Rest.CS_DQUOTE);

                AddHeader(Rest.HttpHeaderWWWAuthenticate,sbuilder.ToString());

            }

        }

        /// <summary>
        /// This method provides validation in support of the BASIC 
        /// authentication method. This is not normaly expected to be
        /// used, but is included for completeness (and because I tried
        /// it first).
        /// </summary>

        private bool Validate(string user, string pass)
        {

            Rest.Log.DebugFormat("{0} Simple User Validation", MsgId);

            // Both values are required

            if (user == null || pass == null)
                return false;

            // Eliminate any leading or trailing spaces
            user = user.Trim();

            return vetPassword(user, pass);

        }

        /// <summary>
        /// This mechanism is used by the digest authetnication mechanism
        /// to return the user's password. In fact, because the OpenSim
        /// user's passwords are already hashed, and the HTTP mechanism 
        /// does not supply an open password, the hashed passwords cannot 
        /// be used unless the cliemt has used the same salting mechanism
        /// to has the password before using it in the authentication 
        /// algorithn. This is not inconceivable...
        /// </summary>

        private string getPassword(string user)
        {

            int x;
            string first;
            string last;

            // Distinguish the parts, if necessary
 
            if ((x=user.IndexOf(Rest.C_SPACE)) != -1)
            {
                first = user.Substring(0,x);
                last  = user.Substring(x+1);
            } 
            else
            {
                first = user;
                last  = String.Empty;
            }

            UserProfileData udata = Rest.UserServices.GetUserProfile(first, last);

            // If we don;t recognize the user id, perhaps it is god?

            if (udata == null)
            {
                Rest.Log.DebugFormat("{0} Administrator", MsgId);
                return Rest.GodKey;
            }
            else
            {
                Rest.Log.DebugFormat("{0} Normal User {1}", MsgId, user);
                return udata.PasswordHash;
            }

        }

        /// <summary>
        /// This is used by the BASIC authentication scheme to calculate
        /// the double hash used by OpenSim to encode user's passwords.
        /// It returns true, if the supplied password is actually correct.
        /// If the specified user-id is not recognized, but the password
        /// matches the God password, then this is accepted as an admin
        /// session.
        /// </summary>

        private bool vetPassword(string user, string pass)
        {

            int x;
            string HA1;
            string first;
            string last;

            // Distinguish the parts, if necessary
 
            if ((x=user.IndexOf(Rest.C_SPACE)) != -1)
            {
                first = user.Substring(0,x);
                last  = user.Substring(x+1);
            } 
            else
            {
                first = user;
                last  = String.Empty;
            }

            UserProfileData udata = Rest.UserServices.GetUserProfile(first, last);

            // If we don;t recognize the user id, perhaps it is god?

            if (udata == null)
                return pass == Rest.GodKey;

            HA1 = HashToString(pass);
            HA1 = HashToString(String.Format("{0}:{1}",HA1,udata.PasswordSalt));
            
            return (0 == sc.Compare(HA1, udata.PasswordHash));
            
        }

        // Validate the request-digest
        private bool ValidateDigest(string user, string nonce, string cnonce, string nck, string uri, string response)
        {

            string patt = null;
            string payl = String.Empty;
            string KDS  = null;
            string HA1  = null;
            string HA2  = null;
            string pass = getPassword(user);

            // Generate H(A1)

            if (algorithm == Rest.Digest_MD5Sess)
            {
                if (!sktable.ContainsKey(cnonce))
                {
                    patt = String.Format("{0}:{1}:{2}:{3}:{4}", user, realm, pass, nonce, cnonce);
                    HA1  = HashToString(patt);
                    sktable.Add(cnonce, HA1);
                }
                else
                {
                    HA1  = sktable[cnonce];
                }
            }
            else
            {
                patt = String.Format("{0}:{1}:{2}", user, realm, pass);
                HA1  = HashToString(patt);
            }

            // Generate H(A2)

            if (qop == "auth-int")
            {
                patt = String.Format("{0}:{1}:{2}", request.HttpMethod, uri, HashToString(payl));
            }
            else
            {
                patt = String.Format("{0}:{1}", request.HttpMethod, uri);
            }

            HA2  = HashToString(patt);

            // Generate Digest
              
            if (qop != String.Empty)
            {
                patt = String.Format("{0}:{1}:{2}:{3}:{4}:{5}", HA1, nonce, nck, cnonce, qop, HA2);
            }
            else
            {
                patt = String.Format("{0}:{1}:{2}", HA1, nonce, HA2);
            }

            KDS = HashToString(patt);

            // Compare the generated sequence with the original

            return (0 == sc.Compare(KDS, response));

        }

        private string HashToString(string pattern)
        {

            Rest.Log.DebugFormat("{0} Generate <{1}>", MsgId, pattern);

            byte[] hash = md5hash.ComputeHash(encoding.GetBytes(pattern));

            sbuilder.Length = 0;

            for (int i = 0; i < hash.Length; i++)
            {
                sbuilder.Append(hash[i].ToString("x2"));
            }

            Rest.Log.DebugFormat("{0} Hash = <{1}>", MsgId, sbuilder.ToString());

            return sbuilder.ToString();

        }

        internal void Complete()
        {
            statusCode = Rest.HttpStatusCodeOK;
            statusDescription = Rest.HttpStatusDescOK;
        }

        internal void Redirect(string Url, bool temp)
        {

            redirectLocation = Url;

            if (temp)
            {
                statusCode = Rest.HttpStatusCodeTemporaryRedirect;
                statusDescription = Rest.HttpStatusDescTemporaryRedirect;
            }
            else
            {
                statusCode = Rest.HttpStatusCodePermanentRedirect;
                statusDescription = Rest.HttpStatusDescPermanentRedirect;
            }

            Fail(statusCode, statusDescription, true);

        }

        // Fail for an arbitrary reason. Just a failure with
        // headers.

        internal void Fail(int code, string message)
        {
            Fail(code, message, true);
        }

        // More adventurous. This failure also includes a 
        // specified entity.

        internal void Fail(int code, string message, string data)
        {
            buffer = null;
            body   = data;
            Fail(code, message, false);
        }

        internal void Fail(int code, string message, bool reset)
        {

            statusCode        = code;
            statusDescription = message;

            if (reset)
            {
                buffer            = null;
                SendHtml(message);
                body              = html;
            }

            if (Rest.DEBUG)
            {
                Rest.Log.DebugFormat("{0} Request Failure State Dump", MsgId);
                Rest.Log.DebugFormat("{0}     Scheme = {1}", MsgId, scheme);
                Rest.Log.DebugFormat("{0}      Realm = {1}", MsgId, realm);
                Rest.Log.DebugFormat("{0}     Domain = {1}", MsgId, domain);
                Rest.Log.DebugFormat("{0}      Nonce = {1}", MsgId, nonce);
                Rest.Log.DebugFormat("{0}     CNonce = {1}", MsgId, cnonce);
                Rest.Log.DebugFormat("{0}     Opaque = {1}", MsgId, opaque);
                Rest.Log.DebugFormat("{0}      Stale = {1}", MsgId, stale);
                Rest.Log.DebugFormat("{0}  Algorithm = {1}", MsgId, algorithm);
                Rest.Log.DebugFormat("{0}        QOP = {1}", MsgId, qop);
                Rest.Log.DebugFormat("{0} AuthPrefix = {1}", MsgId, authPrefix);
                Rest.Log.DebugFormat("{0}   UserName = {1}", MsgId, userName);
                Rest.Log.DebugFormat("{0}   UserPass = {1}", MsgId, userPass);
            }

            fail = true;

            Respond("Failure response");
           
            RestException re = new RestException(message+" <"+code+">");

            re.statusCode = code;
            re.statusDesc = message;
            re.httpmethod = method;
            re.httppath   = path;

            throw re;

        }

        // Reject this request

        internal void Reject()
        {
            Fail(Rest.HttpStatusCodeNotImplemented, Rest.HttpStatusDescNotImplemented);
        }

        // This MUST be called by an agent handler before it returns 
        // control to Handle, otherwise the request will be ignored.
        // This is called implciitly for the REST stream handlers and
        // is harmless if it is called twice.

        internal virtual bool Respond(string reason)
        {

            Rest.Log.DebugFormat("{0} Respond ENTRY, handled = {1}, reason = {2}", MsgId, handled, reason);

            if (!handled)
            {

                Rest.Log.DebugFormat("{0} Generating Response", MsgId);
                Rest.Log.DebugFormat("{0} Method is {1}", MsgId, method);

                // A Head request can NOT have a body!
                if (method != Rest.HEAD)
                {

                    Rest.Log.DebugFormat("{0} Response is not abbreviated", MsgId);

                    // If the writer is non-null then we know that an XML
                    // data component exists. Flush and close the writer and
                    // then convert the result to the expected buffer format
                    // unless the request has already been failed for some
                    // reason.

                    if (writer != null)
                    {
                        Rest.Log.DebugFormat("{0} XML Response handler extension ENTRY", MsgId);
                        Rest.Log.DebugFormat("{0} XML Response exists", MsgId);
                        writer.Flush();
                        writer.Close();
                        if (!fail)
                        {
                            buffer = xmldata.ToArray();
                            AddHeader("Content-Type","application/xml");
                        }
                        xmldata.Close();
                        Rest.Log.DebugFormat("{0} XML Response encoded", MsgId);
                        Rest.Log.DebugFormat("{0} XML Response handler extension EXIT", MsgId);
                    }

                    // If buffer != null, then we assume that 
                    // this has already been done some other
                    // way. For example, transfer encoding might
                    // have been done.

                    if (buffer == null)
                    {
                        if (body != null && body.Length > 0)
                        {
                            Rest.Log.DebugFormat("{0} String-based entity", MsgId);
                            buffer = encoding.GetBytes(body);
                        }
                    }

                    // OK, if the buffer contains something, regardless of how
                    // it got there, set various response headers accordingly.

                    if (buffer != null)
                    {
                        Rest.Log.DebugFormat("{0} Buffer-based entity", MsgId);
                        response.ContentLength64 = buffer.Length;
                    }
                    else
                    {
                        response.ContentLength64 = 0;
                    }

                    if (response.Headers.Get("Content-Encoding") == null)
                        response.ContentEncoding = encoding;

                    response.SendChunked     = chunked;
                    response.KeepAlive       = keepAlive;

                }

                // Set the status code & description. If nothing has been stored, 
                // we consider that a success.

                if (statusCode == 0)
                {
                    Complete();
                }

                // Set the response code in the actual carrier

                response.StatusCode = statusCode;

                // For a redirect we need to set the relocation header accordingly

                if (response.StatusCode == (int) Rest.HttpStatusCodeTemporaryRedirect || 
                    response.StatusCode == (int) Rest.HttpStatusCodePermanentRedirect)
                {
                    Rest.Log.DebugFormat("{0} Re-direct location is {1}", MsgId, redirectLocation);
                    response.RedirectLocation = redirectLocation;
                }

                // And include the status description if provided.

                if (statusDescription != null)
                {
                    Rest.Log.DebugFormat("{0} Status description is {1}", MsgId, statusDescription);
                    response.StatusDescription = statusDescription;
                }

                // Finally we send back our response.

                // We've left the setting of handled' until the
                // last minute because the header settings included
                // above are pretty harmless. But everything from
                // here on down probably leaves the response 
                // element unusable by anyone else.

                handled = true;

                DumpHeaders();

                // if (request.InputStream != null)
                // {
                //     Rest.Log.DebugFormat("{0} Closing input stream", MsgId);
                //     request.InputStream.Close();
                // }

                if (buffer != null && buffer.Length != 0)
                {
                    Rest.Log.DebugFormat("{0} Entity buffer, length = {1} : <{2}>", 
                                         MsgId, buffer.Length, encoding.GetString(buffer));
                    response.OutputStream.Write(buffer, 0, buffer.Length);
                }

                // Closing the outputstream should complete the transmission process

                Rest.Log.DebugFormat("{0} Closing output stream", MsgId);
                response.OutputStream.Close();

            }

            Rest.Log.DebugFormat("{0} Respond EXIT, handled = {1}, reason = {2}", MsgId, handled, reason);

            return handled;

        }

        // Add a header to the table. We need to allow
        // multiple instances of many of the headers.
        // If the 

        internal void AddHeader(string hdr, string data)
        {
            if (Rest.DEBUG)
            {
                Rest.Log.DebugFormat("{0}   Adding header: <{1}: {2}>", 
                         MsgId, hdr, data);
                if (response.Headers.Get(hdr) != null)
                {
                    Rest.Log.DebugFormat("{0} Multipe {1} headers will be generated>", 
                             MsgId, hdr);
                }
            }
            response.Headers.Add(hdr, data);
        }

        // Keep explicit track of any headers which
        // are to be removed.

        internal void RemoveHeader(string hdr)
        {
            if (Rest.DEBUG)
            {
                Rest.Log.DebugFormat("{0} Removing header: <{1}>", MsgId, hdr);
                if (response.Headers.Get(hdr) == null)
                {
                    Rest.Log.DebugFormat("{0} No such header existed", 
                             MsgId, hdr);
                }
            }
            response.Headers.Remove(hdr);
        }

        /// <summary>
        /// Dump headers that will be generated in the response
        /// </summary>

        internal void DumpHeaders()
        {
            if (Rest.DEBUG)
            {
                for (int i=0;i<response.Headers.Count;i++)
                {
                    Rest.Log.DebugFormat("{0} Header[{1}] : {2}", MsgId, i, 
                             response.Headers.Get(i));
                }
            }
        }

        /// <summary>
        /// Helper methods for deconstructing and reconstructing
        /// URI path data.
        /// </summary>

        private void initUrl()
        {

            uri = request.Url;

            if (query == null)
            {
                query = uri.Query;
            }

            // If the path has not been previously initialized,
            // do so now.

            if (path == null)
            {
                path = uri.AbsolutePath;
                if (path.EndsWith(Rest.UrlPathSeparator))
                    path = path.Substring(0,path.Length-1);
            }

            // If we succeeded in getting a path, perform any
            // additional pre-processing required.

            if (path != null) 
            {
                if (Rest.ExtendedEscape)
                {
                    // Handle "+". Not a standard substitution, but
                    // common enough...
                    path      = path.Replace(Rest.C_PLUS,Rest.C_SPACE);
                }
                pathNodes = path.Split(Rest.CA_PATHSEP);
            }
            else
            {
                pathNodes = EmptyPath;
            }

            // Elimiate any %-escaped values. This is left until here
            // so that escaped "+' are not mistakenly replaced.

            path = Uri.UnescapeDataString(path);

            // Request server context info

            hostname = uri.Host;
            port     = uri.Port;

        }

        internal int initParameters(int prfxlen)
        {

            if (prfxlen < path.Length-1)
            {
                parameters = path.Substring(prfxlen+1).Split(Rest.CA_PATHSEP);
            }
            else
            {
                parameters = new string[0];
            }
 
            // Generate a debug list of the decoded parameters

            if (Rest.DEBUG && prfxlen < path.Length-1)
            {
                Rest.Log.DebugFormat("{0} URI: Parameters: {1}", MsgId, path.Substring(prfxlen));
                for (int i = 0; i < parameters.Length; i++)
                { 
                    Rest.Log.DebugFormat("{0} Parameter[{1}]: {2}", MsgId, i, parameters[i]);
                }
            }

            return parameters.Length;

        }
                
        internal string[] PathNodes
        {
            get
            { 
                if (pathNodes == null)
                {
                    initUrl();
                }
                return pathNodes;
            }
        }
        
        internal string BuildUrl(int first, int last)
        {
           
            if (pathNodes == null)
            {
                initUrl();
            }

            if (first < 0)
            {
                first = first + pathNodes.Length;
            }

            if (last < 0)
            {
                last = last + pathNodes.Length;
                if (last < 0)
                {
                    return Rest.UrlPathSeparator;
                }
            }

            sbuilder.Length = 0;
            sbuilder.Append(Rest.UrlPathSeparator);

            if (first <= last)
            {
                for (int i = first; i <= last; i++)
                {
                    sbuilder.Append(pathNodes[i]);
                    sbuilder.Append(Rest.UrlPathSeparator);
                }
            }
            else
            {
                for (int i = last; i >= first; i--)
                {
                    sbuilder.Append(pathNodes[i]);
                    sbuilder.Append(Rest.UrlPathSeparator);
                }
            }

            return sbuilder.ToString();

        }

        // Setup the XML writer for output

        internal void initXmlWriter()
        {
            XmlWriterSettings settings = new XmlWriterSettings();
            xmldata = new MemoryStream();
            settings.Indent = true;
            settings.IndentChars = "    ";
            settings.Encoding = encoding;
            settings.CloseOutput = false;
            settings.OmitXmlDeclaration = true;
            settings.ConformanceLevel = ConformanceLevel.Fragment;
            writer = XmlWriter.Create(xmldata, settings);
        }

        internal void initXmlReader()
        {

            XmlReaderSettings        settings = new XmlReaderSettings();

            settings.ConformanceLevel             = ConformanceLevel.Fragment;
            settings.IgnoreComments               = true;
            settings.IgnoreWhitespace             = true;
            settings.IgnoreProcessingInstructions = true;
            settings.ValidationType               = ValidationType.None;

            reader = XmlReader.Create(request.InputStream,settings);

        }

        private void Flush()
        {
            byte[] dbuffer = new byte[8192];
            while (request.InputStream.Read(dbuffer,0,dbuffer.Length) != 0);
            return;
        }

        // This allows us to make errors a bit more apparent in REST

        internal void SendHtml(string text)
        {
            SendHtml("OpenSim REST Interface 1.0", text);
        }

        internal void SendHtml(string title, string text)
        {

            AddHeader(Rest.HttpHeaderContentType, "text/html");
            sbuilder.Length = 0;

            sbuilder.Append("<html>");
            sbuilder.Append("<head>");
            sbuilder.Append("<title>");
            sbuilder.Append(title);
            sbuilder.Append("</title>");
            sbuilder.Append("</head>");

            sbuilder.Append("<body>");
            sbuilder.Append("<br />");
            sbuilder.Append("<p>");
            sbuilder.Append(text);
            sbuilder.Append("</p>");
            sbuilder.Append("</body>");
            sbuilder.Append("</html>");

            html = sbuilder.ToString();

        }
    }
}