/*
 * Copyright (c) Citrix Systems, Inc.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 *   1) Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 * 
 *   2) 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.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "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
 * COPYRIGHT HOLDER OR 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.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Net.Security;
using System.Security.Authentication;
using System.Security.Cryptography.X509Certificates;
using System.Runtime.Serialization;
using XenAdmin.Core;

namespace XenAPI
{
    public partial class HTTP
    {
        [Serializable]
        public class TooManyRedirectsException : Exception
        {
            private readonly int redirect;
            private readonly Uri uri;

            public TooManyRedirectsException(int redirect, Uri uri)
            {
                this.redirect = redirect;
                this.uri = uri;
            }
            
            public TooManyRedirectsException() : base() { }

            public TooManyRedirectsException(string message) : base(message) { }

            public TooManyRedirectsException(string message, Exception exception) : base(message, exception) { }

            protected TooManyRedirectsException(SerializationInfo info, StreamingContext context)
                : base(info, context)
            {
                redirect = info.GetInt32("redirect");
                uri = (Uri)info.GetValue("uri", typeof(Uri));
            }

            public override void GetObjectData(SerializationInfo info, StreamingContext context)
            {
                if (info == null)
                {
                    throw new ArgumentNullException("info");
                }

                info.AddValue("redirect", redirect);
                info.AddValue("uri", uri, typeof(Uri));

                base.GetObjectData(info, context);
            }
        }

        [Serializable]
        public class BadServerResponseException : Exception
        {
            public BadServerResponseException() : base() { }

            public BadServerResponseException(string message) : base(message) { }

            public BadServerResponseException(string message, Exception exception) : base(message, exception) { }

            protected BadServerResponseException(SerializationInfo info, StreamingContext context) : base(info, context) { }
        }

        [Serializable]
        public class CancelledException : Exception
        {
            public CancelledException() : base() { }

            public CancelledException(string message) : base(message) { }

            public CancelledException(string message, Exception exception) : base(message, exception) { }

            protected CancelledException(SerializationInfo info, StreamingContext context) : base(info, context) { }
        }

        [Serializable]
        public class ProxyServerAuthenticationException : Exception
        {
            public ProxyServerAuthenticationException() : base() { }

            public ProxyServerAuthenticationException(string message) : base(message) { }

            public ProxyServerAuthenticationException(string message, Exception exception) : base(message, exception) { }

            protected ProxyServerAuthenticationException(SerializationInfo info, StreamingContext context) : base(info, context) { }
        }

        public delegate bool FuncBool();
        public delegate void UpdateProgressDelegate(int percent);
        public delegate void DataCopiedDelegate(long bytes);

        // Size of byte buffer used for GETs and PUTs
        // (not the socket rx buffer)
        public const int BUFFER_SIZE = 32 * 1024;
        public const int MAX_REDIRECTS = 10;

        public const int DEFAULT_HTTPS_PORT = 443;

        #region Helper functions

        private static void WriteLine(String txt, Stream stream)
        {
            byte[] bytes = System.Text.Encoding.ASCII.GetBytes(String.Format("{0}\r\n", txt));
            stream.Write(bytes, 0, bytes.Length);
        }

        private static void WriteLine(Stream stream)
        {
            WriteLine("", stream);
        }

        private static string ReadLine(Stream stream)
        {
            System.Text.StringBuilder result = new StringBuilder();
            while (true)
            {
                int b = stream.ReadByte();
                if (b == -1)
                    throw new EndOfStreamException();
                char c = Convert.ToChar(b);
                result.Append(c);
                if (c == '\n')
                    return result.ToString();
            }
        }

        /// <summary>
        /// Read HTTP headers, doing any redirects as necessary
        /// </summary>
        /// <param name="stream"></param>
        /// <returns>True if a redirect has occurred - headers will need to be resent.</returns>
        private static bool ReadHttpHeaders(ref Stream stream, IWebProxy proxy, bool nodelay, int timeout_ms, List<string> headers = null)
        {
            // read headers/fields
            string line = ReadLine(stream), initialLine = line, transferEncodingField = null;
            if (string.IsNullOrEmpty(initialLine)) // sanity check
                return false;
            while (!string.IsNullOrEmpty(line) && !string.IsNullOrWhiteSpace(line))
            {
                if (headers != null)
                {
                    RemoveNewLineEnding(ref line);
                    headers.Add(line);
                    if (line == "Transfer-Encoding: Chunked")
                        transferEncodingField = line;
                }
                line = ReadLine(stream);
            }

            // read chunks
            string entityBody = "";
            if (!string.IsNullOrEmpty(transferEncodingField))
            {
                int lastChunkSize = -1;
                do
                {
                    string chunkSizeStr = ReadLine(stream);
                    RemoveNewLineEnding(ref chunkSizeStr);
                    int chunkSize = int.Parse(chunkSizeStr, System.Globalization.NumberStyles.HexNumber);

                    byte[] bytes = new byte[chunkSize];
                    stream.Read(bytes, 0, chunkSize);

                    if (headers != null)
                    {
                        string str = System.Text.Encoding.ASCII.GetString(bytes);
                        string[] split = str.Split(new string[] { "\r\n" }, StringSplitOptions.RemoveEmptyEntries);
                        headers.AddRange(split);
                        
                        entityBody += str;
                    }

                    line = ReadLine(stream); // empty line in the end of chunk

                    lastChunkSize = chunkSize;
                }
                while (lastChunkSize != 0);

                if (headers != null)
                {
                    RemoveNewLineEnding(ref entityBody);
                    headers.Add(entityBody); // keep entityBody if it's needed for Digest authentication (when qop="auth-int")
                }
            }
            else
            {
                // todo: handle other transfer types, in case "Transfer-Encoding: Chunked" isn't used
            }

            // handle server response
            int code = getResultCode(initialLine);
            switch (code)
            {
                case 407: // authentication error; caller must handle this case
                case 200:
                    break;

                case 302:
                    string url = "";
                    foreach (string header in headers)
                    {
                        if (header.StartsWith("Location: "))
                        {
                            url = header.Substring(10);
                            break;
                        }
                    }
                    Uri redirect = new Uri(url.Trim());
                    stream.Close();
                    stream = ConnectStream(redirect, proxy, nodelay, timeout_ms);
                    return true; // headers need to be sent again

                default:
                    stream.Close();
                    throw new BadServerResponseException(string.Format("Received error code {0} from the server", initialLine));
            }

            return false;
        }

        public static int getResultCode(string line)
        {
            string[] bits = line.Split(new char[] { ' ' });
            return (bits.Length < 2 ? 0 : Int32.Parse(bits[1]));
        }

        public static bool UseSSL(Uri uri)
        {
            return uri.Scheme == "https" || uri.Port == DEFAULT_HTTPS_PORT;
        }

        private static bool ValidateServerCertificate(
              object sender,
              X509Certificate certificate,
              X509Chain chain,
              SslPolicyErrors sslPolicyErrors)
        {
            return true;
        }

        public static long CopyStream(Stream inStream, Stream outStream,
            DataCopiedDelegate progressDelegate, FuncBool cancellingDelegate)
        {
            long bytesWritten = 0;
            byte[] buffer = new byte[BUFFER_SIZE];
            DateTime lastUpdate = DateTime.Now;

            while (cancellingDelegate == null || !cancellingDelegate())
            {
                int bytesRead = inStream.Read(buffer, 0, buffer.Length);
                if (bytesRead == 0)
                    break;
                outStream.Write(buffer, 0, bytesRead);
                bytesWritten += bytesRead;

                if (progressDelegate != null &&
                    DateTime.Now - lastUpdate > TimeSpan.FromMilliseconds(500))
                {
                    progressDelegate(bytesWritten);
                    lastUpdate = DateTime.Now;
                }
            }

            if (cancellingDelegate != null && cancellingDelegate())
                throw new CancelledException();

            if (progressDelegate != null)
                progressDelegate(bytesWritten);

            return bytesWritten;
        }

        /// <summary>
        /// Build a URI from a hostname, a path, and some query arguments
        /// </summary>
        /// <param name="args">An even-length array, alternating argument names and values</param>
        /// <returns></returns>
        public static Uri BuildUri(string hostname, string path, params object[] args)
        {
            // The last argument may be an object[] in its own right, in which case we need
            // to flatten the array.
            List<object> flatargs = new List<object>();
            foreach (object arg in args)
            {
                if (arg is IEnumerable<object>)
                    flatargs.AddRange((IEnumerable<object>)arg);
                else
                    flatargs.Add(arg);
            }

            UriBuilder uri = new UriBuilder();
            uri.Scheme = "https";
            uri.Port = DEFAULT_HTTPS_PORT;
            uri.Host = hostname;
            uri.Path = path;

            StringBuilder query = new StringBuilder();
            for (int i = 0; i < flatargs.Count - 1; i += 2)
            {
                string kv;

                // If the argument is null, don't include it in the URL
                if (flatargs[i + 1] == null)
                    continue;

                // bools are special because some xapi calls use presence/absence and some
                // use "b=true" (not "True") and "b=false". But all accept "b=true" or absent.
                if (flatargs[i + 1] is bool)
                {
                    if (!((bool)flatargs[i + 1]))
                        continue;
                    kv = flatargs[i] + "=true";
                }
                else
                    kv = flatargs[i] + "=" + Uri.EscapeDataString(flatargs[i + 1].ToString());

                if (query.Length != 0)
                    query.Append('&');
                query.Append(kv);
            }
            uri.Query = query.ToString();

            return uri.Uri;
        }

        private static List<string> GetFields(List<string> lines, string field)
        {
            List<string> fields = new List<string>();
            foreach (string line in lines)
                if (line.StartsWith(field))
                    fields.Add(line);
            return fields;
        }

        private static string GetField(List<string> lines, string field)
        {
            foreach (string line in lines)
                if (line.StartsWith(field))
                    return line;
            return null;
        }

        private static string GetPartOrNull(string str, int partIndex)
        {
            string[] parts = str.Split(new char[] { ' ' }, partIndex + 2, StringSplitOptions.RemoveEmptyEntries);
            return partIndex < parts.Length - 1 ? parts[partIndex] : null;
        }

        private static void RemoveNewLineEnding(ref string str)
        {
            if (string.IsNullOrEmpty(str))
                return;
            if (str.EndsWith("\r\n"))
                str = str.Substring(0, str.Length - 2);
            else if (str.EndsWith("\n"))
                str = str.Substring(0, str.Length - 1);
        }

        #endregion

        private static NetworkStream ConnectSocket(Uri uri, bool nodelay, int timeout_ms)
        {
            AddressFamily addressFamily = uri.HostNameType == UriHostNameType.IPv6
                                              ? AddressFamily.InterNetworkV6
                                              : AddressFamily.InterNetwork;
            Socket socket =
                new Socket(addressFamily, SocketType.Stream, ProtocolType.Tcp);
            socket.NoDelay = nodelay;
            //socket.ReceiveBufferSize = 64 * 1024;
            socket.ReceiveTimeout = timeout_ms;
            socket.SendTimeout = timeout_ms;
            socket.Connect(uri.Host, uri.Port);

            return new NetworkStream(socket, true);
        }

        /// <summary>
        /// This function will connect a stream to a uri (host and port), 
        /// negotiating proxies and SSL
        /// </summary>
        /// <param name="uri"></param>
        /// <param name="timeout_ms">Timeout, in ms. 0 for no timeout.</param>
        /// <returns></returns>
        public static Stream ConnectStream(Uri uri, IWebProxy proxy, bool nodelay, int timeout_ms)
        {
            IMockWebProxy mockProxy = proxy != null ? proxy as IMockWebProxy : null;
            if (mockProxy != null)
                return mockProxy.GetStream(uri);

            Stream stream;
            bool useProxy = proxy != null && !proxy.IsBypassed(uri);

            if (useProxy)
            {
                Uri proxyURI = proxy.GetProxy(uri);
                stream = ConnectSocket(proxyURI, nodelay, timeout_ms);
            }
            else
            {
                stream = ConnectSocket(uri, nodelay, timeout_ms);
            }

            try
            {
                if (useProxy)
                {
                    string line = String.Format("CONNECT {0}:{1} HTTP/1.0", uri.Host, uri.Port);
                    WriteLine(line, stream);
                    WriteLine(stream);

                    List<string> initialResponse = new List<string>();
                    ReadHttpHeaders(ref stream, proxy, nodelay, timeout_ms, initialResponse);

                    AuthenticateProxy(ref stream, uri, proxy, nodelay, timeout_ms, initialResponse, line);
                }

                if (UseSSL(uri))
                {
                    SslStream sslStream = new SslStream(stream, false,
                        new RemoteCertificateValidationCallback(ValidateServerCertificate), null);
                    sslStream.AuthenticateAsClient("", null, SslProtocols.Tls | SslProtocols.Tls11 | SslProtocols.Tls12, true);

                    stream = sslStream;
                }

                return stream;
            }
            catch
            {
                stream.Close();
                throw;
            }
        }

        private static void AuthenticateProxy(ref Stream stream, Uri uri, IWebProxy proxy, bool nodelay, int timeout_ms, List<string> initialResponse, string header)
        {
            // perform authentication only if proxy requires it
            List<string> fields = GetFields(initialResponse, "Proxy-Authenticate:");
            if (fields.Count > 0)
            {
                // clean up (if initial server response specifies "Proxy-Connection: Close" then stream cannot be re-used)
                string field = GetField(initialResponse, "Proxy-Connection: Close");
                if (!string.IsNullOrEmpty(field))
                {
                    stream.Close();
                    Uri proxyURI = proxy.GetProxy(uri);
                    stream = ConnectSocket(proxyURI, nodelay, timeout_ms);
                }
            
                if (proxy.Credentials == null)
                    throw new BadServerResponseException(string.Format("Received error code {0} from the server", initialResponse[0]));
                NetworkCredential credentials = proxy.Credentials.GetCredential(uri, null);

                string basicField = GetField(fields, "Proxy-Authenticate: Basic");
                string digestField = GetField(fields, "Proxy-Authenticate: Digest");
                if (!string.IsNullOrEmpty(basicField))
                {
                    string authenticationFieldReply = String.Format("Proxy-Authorization: Basic {0}",
                        Convert.ToBase64String(Encoding.UTF8.GetBytes(credentials.UserName + ":" + credentials.Password)));
                    WriteLine(header, stream);
                    WriteLine(authenticationFieldReply, stream);
                    WriteLine(stream);
                }
                else if (!string.IsNullOrEmpty(digestField))
                {
                    string authenticationFieldReply = string.Format(
                        "Proxy-Authorization: Digest username=\"{0}\", uri=\"{1}:{2}\"",
                        credentials.UserName, uri.Host, uri.Port);

                    string directiveString = digestField.Substring(27, digestField.Length - 27);
                    string[] directives = directiveString.Split(new string[] { ", ", "\"" }, StringSplitOptions.RemoveEmptyEntries);

                    string algorithm = null;    // optional
                    string opaque = null;       // optional
                    string qop = null;          // optional
                    string realm = null;
                    string nonce = null;

                    for (int i = 0; i < directives.Length; ++i)
                    {
                        switch (directives[i])
                        {
                            case "stale=":
                                if (directives[++i].ToLower() == "true")
                                    throw new ProxyServerAuthenticationException("Stale nonce in Digest authentication attempt.");
                                break;
                            case "realm=":
                                authenticationFieldReply += string.Format(", {0}\"{1}\"", directives[i], directives[++i]);
                                realm = directives[i];
                                break;
                            case "nonce=":
                                authenticationFieldReply += string.Format(", {0}\"{1}\"", directives[i], directives[++i]);
                                nonce = directives[i];
                                break;
                            case "opaque=":
                                authenticationFieldReply += string.Format(", {0}\"{1}\"", directives[i], directives[++i]);
                                opaque = directives[i];
                                break;
                            case "algorithm=":
                                authenticationFieldReply += string.Format(", {0}\"{1}\"", directives[i], directives[++i]);
                                algorithm = directives[i];
                                break;
                            case "qop=":
                                List<string> qops = new List<string>(directives[++i].Split(new char[] { ',' }));
                                if (qops.Count > 0)
                                {
                                    if (qops.Contains("auth"))
                                        qop = "auth";
                                    else if (qops.Contains("auth-int"))
                                        qop = "auth-int";
                                    else
                                        throw new ProxyServerAuthenticationException(
                                            "Digest authentication's quality-of-protection directive of is not supported.");
                                    authenticationFieldReply += string.Format(", qop=\"{0}\"", qop);
                                }
                                break;
                            default:
                                break;
                        }
                    }

                    string clientNonce = "X3nC3nt3r"; // todo: generate random string
                    if (qop != null)
                        authenticationFieldReply += string.Format(", cnonce=\"{0}\"", clientNonce);

                    string nonceCount = "00000001"; // todo: track nonces and their corresponding nonce counts
                    if (qop != null)
                        authenticationFieldReply += string.Format(", nc={0}", nonceCount);

                    string HA1 = "";
                    string scratch = string.Format("{0}:{1}:{2}", credentials.UserName, realm, credentials.Password);
                    if (algorithm == null || algorithm == "MD5")
                        HA1 = EncryptionUtils.MD5Hash(scratch);
                    else
                        HA1 = EncryptionUtils.MD5Hash(string.Format("{0}:{1}:{2}", EncryptionUtils.MD5Hash(scratch), nonce, clientNonce));

                    string HA2 = "";
                    scratch = GetPartOrNull(header, 0);
                    scratch = string.Format("{0}:{1}:{2}", scratch ?? "CONNECT", uri.Host, uri.Port);
                    if (qop == null || qop == "auth")
                        HA2 = EncryptionUtils.MD5Hash(scratch);
                    else
                    {
                        string entityBody = initialResponse[initialResponse.Count - 1]; // entity body should have been stored as last element of initialResponse
                        string str = string.Format("{0}:{1}", scratch, EncryptionUtils.MD5Hash(entityBody));
                        HA2 = EncryptionUtils.MD5Hash(str);
                    }

                    string response = "";
                    if (qop == null)
                        response = EncryptionUtils.MD5Hash(string.Format("{0}:{1}:{2}", HA1, nonce, HA2));
                    else
                        response = EncryptionUtils.MD5Hash(string.Format("{0}:{1}:{2}:{3}:{4}:{5}", HA1, nonce, nonceCount, clientNonce, qop, HA2));

                    authenticationFieldReply += string.Format(", response=\"{0}\"", response);

                    WriteLine(header, stream);
                    WriteLine(authenticationFieldReply, stream);
                    WriteLine(stream);
                }
                else
                {
                    string authType = GetPartOrNull(fields[0], 1);
                    throw new ProxyServerAuthenticationException(
                        string.Format("Proxy server's {0} authentication method is not supported.", authType ?? "chosen"));
                }

                // handle authentication attempt response
                List<string> authenticatedResponse = new List<string>();
                ReadHttpHeaders(ref stream, proxy, nodelay, timeout_ms, authenticatedResponse);
                if (authenticatedResponse.Count == 0)
                    throw new BadServerResponseException("No response from the proxy server after authentication attempt.");
                switch (getResultCode(authenticatedResponse[0]))
                {
                    case 200:
                        break;
                    case 407:
                        throw new ProxyServerAuthenticationException("Proxy server denied access due to wrong credentials.");
                    default:
                        throw new BadServerResponseException(string.Format(
                            "Received error code {0} from the server", authenticatedResponse[0]));
                }
            }
        }

        private static Stream DO_HTTP(Uri uri, IWebProxy proxy, bool nodelay, int timeout_ms, params string[] headers)
        {
            Stream stream = ConnectStream(uri, proxy, nodelay, timeout_ms);

            int redirects = 0;

            do
            {
                if (redirects > MAX_REDIRECTS)
                    throw new TooManyRedirectsException(redirects, uri);

                redirects++;

                foreach (string header in headers)
                    WriteLine(header, stream);
                WriteLine(stream);

                stream.Flush();
            }
            while (ReadHttpHeaders(ref stream, proxy, nodelay, timeout_ms));

            return stream;
        }

        //
        // The following functions do all the HTTP headers related stuff
        // returning the stream ready for use
        //

        public static Stream CONNECT(Uri uri, IWebProxy proxy, String session, int timeout_ms)
        {
            return DO_HTTP(uri, proxy, true, timeout_ms,
                string.Format("CONNECT {0} HTTP/1.0", uri.PathAndQuery),
                string.Format("Host: {0}", uri.Host),
                string.Format("Cookie: session_id={0}", session));
        }

        public static Stream PUT(Uri uri, IWebProxy proxy, long ContentLength, int timeout_ms)
        {
            return DO_HTTP(uri, proxy, false, timeout_ms,
                string.Format("PUT {0} HTTP/1.0", uri.PathAndQuery),
                string.Format("Host: {0}", uri.Host),
                string.Format("Content-Length: {0}", ContentLength));
        }

        public static Stream GET(Uri uri, IWebProxy proxy, int timeout_ms)
        {
            return DO_HTTP(uri, proxy, false, timeout_ms,
                string.Format("GET {0} HTTP/1.0", uri.PathAndQuery),
                string.Format("Host: {0}", uri.Host));
        }

        /// <summary>
        /// A general HTTP PUT method, with delegates for progress and cancelling. May throw various exceptions.
        /// </summary>
        /// <param name="progressDelegate">Delegate called periodically (500ms) with percent complete</param>
        /// <param name="cancellingDelegate">Delegate called periodically to see if need to cancel</param>
        /// <param name="uri">URI to PUT to</param>
        /// <param name="proxy">A proxy to handle the HTTP connection</param>
        /// <param name="path">Path to file to put</param>
        /// <param name="timeout_ms">Timeout for the connection in ms. 0 for no timeout.</param>
        public static void Put(UpdateProgressDelegate progressDelegate, FuncBool cancellingDelegate,
            Uri uri, IWebProxy proxy, string path, int timeout_ms)
        {
            using (Stream fileStream = new FileStream(path, FileMode.Open, FileAccess.Read),
                requestStream = PUT(uri, proxy, fileStream.Length, timeout_ms))
            {
                long len = fileStream.Length;
                DataCopiedDelegate dataCopiedDelegate = delegate(long bytes)
                    {
                        if (progressDelegate != null && len > 0)
                            progressDelegate((int)((bytes * 100) / len));
                    };

                CopyStream(fileStream, requestStream, dataCopiedDelegate, cancellingDelegate);
            }
        }

        /// <summary>
        /// A general HTTP GET method, with delegates for progress and cancelling. May throw various exceptions.
        /// </summary>
        /// <param name="dataRxDelegate">Delegate called periodically (500 ms) with the number of bytes transferred</param>
        /// <param name="cancellingDelegate">Delegate called periodically to see if need to cancel</param>
        /// <param name="uri">URI to GET from</param>
        /// <param name="proxy">A proxy to handle the HTTP connection</param>
        /// <param name="path">Path to file to receive the data</param>
        /// <param name="timeout_ms">Timeout for the connection in ms. 0 for no timeout.</param>
        public static void Get(DataCopiedDelegate dataCopiedDelegate, FuncBool cancellingDelegate,
            Uri uri, IWebProxy proxy, string path, int timeout_ms)
        {
            string tmpFile = Path.GetTempFileName();
            try
            {
                using (Stream fileStream = new FileStream(tmpFile, FileMode.Create, FileAccess.Write, FileShare.None),
                    downloadStream = GET(uri, proxy, timeout_ms))
                {
                    CopyStream(downloadStream, fileStream, dataCopiedDelegate, cancellingDelegate);
                    fileStream.Flush();
                }

                File.Delete(path);
                File.Move(tmpFile, path);
            }
            finally
            {
                File.Delete(tmpFile);
            }
        }
    }
}