/mcs/class/System/System.Net/WebClient.cs

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//
// System.Net.WebClient
//
// Authors:
// 	Lawrence Pit (loz@cable.a2000.nl)
//	Gonzalo Paniagua Javier (gonzalo@ximian.com)
//	Atsushi Enomoto (atsushi@ximian.com)
//	Miguel de Icaza (miguel@ximian.com)
//      Martin Baulig (martin.baulig@googlemail.com)
//	Marek Safar (marek.safar@gmail.com)
//
// Copyright 2003 Ximian, Inc. (http://www.ximian.com)
// Copyright 2006, 2010 Novell, Inc. (http://www.novell.com)
// Copyright 2012 Xamarin Inc. (http://www.xamarin.com)
//
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//
// Notes on CancelAsync and Async methods:
//
//    WebClient.CancelAsync is implemented by calling Thread.Interrupt
//    in our helper thread.   The various async methods have to cancel
//    any ongoing requests by calling request.Abort () at that point.
//    In a few places (UploadDataCore, UploadValuesCore,
//    UploadFileCore) we catch the ThreadInterruptedException and
//    abort the request there.
//
//    Higher level routines (the async callbacks) also need to catch
//    the exception and raise the OnXXXXCompleted events there with
//    the "canceled" flag set to true. 
//
//    In a few other places where these helper routines are not used
//    (OpenReadAsync for example) catching the ThreadAbortException
//    also must abort the request.
//
//    The Async methods currently differ in their implementation from
//    the .NET implementation in that we manually catch any other
//    exceptions and correctly raise the OnXXXXCompleted passing the
//    Exception that caused the problem.   The .NET implementation
//    does not seem to have a mechanism to flag errors that happen
//    during downloads though.    We do this because we still need to
//    catch the exception on these helper threads, or we would
//    otherwise kill the application (on the 2.x profile, uncaught
//    exceptions in threads terminate the application).
//
using System;
using System.Collections.Specialized;
using System.ComponentModel;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;
using System.Text;
using System.Threading;
using System.Net.Cache;
#if NET_4_5
using System.Threading.Tasks;
#endif

namespace System.Net 
{
	[ComVisible(true)]
	public class WebClient : Component
	{
		static readonly string urlEncodedCType = "application/x-www-form-urlencoded";
		static byte [] hexBytes;
		ICredentials credentials;
		WebHeaderCollection headers;
		WebHeaderCollection responseHeaders;
		Uri baseAddress;
		string baseString;
		NameValueCollection queryString;
		bool is_busy;
		bool async;
		bool proxySet = false;
		Thread async_thread;
		Encoding encoding = Encoding.Default;
		IWebProxy proxy;
//		RequestCachePolicy cache_policy;
#if NET_4_5
		CancellationTokenSource cts;
#endif

		// Constructors
		static WebClient ()
		{
			hexBytes = new byte [16];
			int index = 0;
			for (int i = '0'; i <= '9'; i++, index++)
				hexBytes [index] = (byte) i;

			for (int i = 'a'; i <= 'f'; i++, index++)
				hexBytes [index] = (byte) i;
		}
		
		public WebClient ()
		{
		}
		
		// Properties
		
		public string BaseAddress {
			get {
				if (baseString == null) {
					if (baseAddress == null)
						return string.Empty;
				}

				baseString = baseAddress.ToString ();
				return baseString;
			}
			
			set {
				if (value == null || value.Length == 0) {
					baseAddress = null;
				} else {
					baseAddress = new Uri (value);
				}
			}
		}

		static Exception GetMustImplement ()
		{
			return new NotImplementedException ();
		}
		
		[MonoTODO ("Value can be set but is currently ignored")]
		public RequestCachePolicy CachePolicy
		{
			get {
				throw GetMustImplement ();
			}
			set { /*cache_policy = value;*/ }
		}

		[MonoTODO ("Value can be set but is ignored")]
		public bool UseDefaultCredentials
		{
			get {
				throw GetMustImplement ();
			}
			set {
				// This makes no sense in mono
			}
		}
		
		public ICredentials Credentials {
			get { return credentials; }
			set { credentials = value; }
		}

		public WebHeaderCollection Headers {
			get {
				if (headers == null)
					headers = new WebHeaderCollection ();

				return headers;
			}
			set { headers = value; }
		}
		
		public NameValueCollection QueryString {
			get {
				if (queryString == null)
					queryString = new NameValueCollection ();

				return queryString;
			}
			set { queryString = value; }
		}
		
		public WebHeaderCollection ResponseHeaders {
			get { return responseHeaders; }
		}

		public Encoding Encoding {
			get { return encoding; }
			set {
				if (value == null)
					throw new ArgumentNullException ("Encoding");
				encoding = value;
			}
		}

		public IWebProxy Proxy {
			get {
				if (!proxySet)
					return WebRequest.DefaultWebProxy;

				return proxy;
			}
			set {
				proxy = value;
				proxySet = true;
			}
		}

		public bool IsBusy {
			get {
#if NET_4_5
				return is_busy || (cts != null);
#else
				return is_busy;
#endif
			}
		}
		// Methods

		void CheckBusy ()
		{
			if (IsBusy)
				throw new NotSupportedException ("WebClient does not support concurrent I/O operations.");
		}

		void SetBusy ()
		{
			lock (this) {
				CheckBusy ();
				is_busy = true;
			}
		}

		//   DownloadData

		public byte [] DownloadData (string address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return DownloadData (CreateUri (address));
		}

		public byte [] DownloadData (Uri address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			try {
				SetBusy ();
				async = false;
				return DownloadDataCore (address, null);
			} finally {
				is_busy = false;
			}
		}

		byte [] DownloadDataCore (Uri address, object userToken)
		{
			WebRequest request = null;
			
			try {
				request = SetupRequest (address);
				return ReadAll (request, userToken);
			} catch (ThreadInterruptedException){
				if (request != null)
					request.Abort ();
				throw new WebException ("User canceled the request", WebExceptionStatus.RequestCanceled);
			} catch (WebException) {
				throw;
			} catch (Exception ex) {
				throw new WebException ("An error occurred performing a WebClient request.", ex);
			}
		}

		//   DownloadFile

		public void DownloadFile (string address, string fileName)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			DownloadFile (CreateUri (address), fileName);
		}

		public void DownloadFile (Uri address, string fileName)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (fileName == null)
				throw new ArgumentNullException ("fileName");

			try {
				SetBusy ();
				async = false;
				DownloadFileCore (address, fileName, null);
			} catch (WebException) {
				throw;
			} catch (Exception ex) {
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			} finally {
				is_busy = false;
			}
		}

		void DownloadFileCore (Uri address, string fileName, object userToken)
		{
			WebRequest request = null;
			
			using (FileStream f = new FileStream (fileName, FileMode.Create)) {
				try {
					request = SetupRequest (address);
					WebResponse response = GetWebResponse (request);
					Stream st = response.GetResponseStream ();
					
					int cLength = (int) response.ContentLength;
					int length = (cLength <= -1 || cLength > 32*1024) ? 32*1024 : cLength;
					byte [] buffer = new byte [length];
					
					int nread = 0;
					long notify_total = 0;
					while ((nread = st.Read (buffer, 0, length)) != 0){
						if (async){
							notify_total += nread;
							OnDownloadProgressChanged (
								new DownloadProgressChangedEventArgs (notify_total, response.ContentLength, userToken));
												      
						}
						f.Write (buffer, 0, nread);
					}
				} catch (ThreadInterruptedException){
					if (request != null)
						request.Abort ();
					throw;
				}
			}
		}

		//   OpenRead

		public Stream OpenRead (string address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			return OpenRead (CreateUri (address));
		}

		public Stream OpenRead (Uri address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			WebRequest request = null;
			try {
				SetBusy ();
				async = false;
				request = SetupRequest (address);
				WebResponse response = GetWebResponse (request);
				return response.GetResponseStream ();
			} catch (WebException) {
				throw;
			} catch (Exception ex) {
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			} finally {
				is_busy = false;
			}
		}

		//   OpenWrite

		public Stream OpenWrite (string address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return OpenWrite (CreateUri (address));
		}
		
		public Stream OpenWrite (string address, string method)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return OpenWrite (CreateUri (address), method);
		}

		public Stream OpenWrite (Uri address)
		{
			return OpenWrite (address, (string) null);
		}

		public Stream OpenWrite (Uri address, string method)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			try {
				SetBusy ();
				async = false;
				WebRequest request = SetupRequest (address, method, true);
				return request.GetRequestStream ();
			} catch (WebException) {
				throw;
			} catch (Exception ex) {
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			} finally {
				is_busy = false;
			}
		}

		private string DetermineMethod (Uri address, string method, bool is_upload)
		{
			if (method != null)
				return method;

			if (address.Scheme == Uri.UriSchemeFtp)
				return (is_upload) ? "STOR" : "RETR";

			return (is_upload) ? "POST" : "GET";
		}

		//   UploadData

		public byte [] UploadData (string address, byte [] data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return UploadData (CreateUri (address), data);
		}
		
		public byte [] UploadData (string address, string method, byte [] data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return UploadData (CreateUri (address), method, data);
		}

		public byte [] UploadData (Uri address, byte [] data)
		{
			return UploadData (address, (string) null, data);
		}

		public byte [] UploadData (Uri address, string method, byte [] data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");

			try {
				SetBusy ();
				async = false;
				return UploadDataCore (address, method, data, null);
			} catch (WebException) {
				throw;
			} catch (Exception ex) {
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			} finally {
				is_busy = false;
			}
		}

		byte [] UploadDataCore (Uri address, string method, byte [] data, object userToken)
		{
			WebRequest request = SetupRequest (address, method, true);
			try {
				int contentLength = data.Length;
				request.ContentLength = contentLength;
				using (Stream stream = request.GetRequestStream ()) {
					stream.Write (data, 0, contentLength);
				}
				
				return ReadAll (request, userToken);
			} catch (ThreadInterruptedException){
				if (request != null)
					request.Abort ();
				throw;
			}
		}

		//   UploadFile

		public byte [] UploadFile (string address, string fileName)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return UploadFile (CreateUri (address), fileName);
		}

		public byte [] UploadFile (Uri address, string fileName)
		{
			return UploadFile (address, (string) null, fileName);
		}
		
		public byte [] UploadFile (string address, string method, string fileName)
		{
			return UploadFile (CreateUri (address), method, fileName);
		}

		public byte [] UploadFile (Uri address, string method, string fileName)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (fileName == null)
				throw new ArgumentNullException ("fileName");

			try {
				SetBusy ();
				async = false;
				return UploadFileCore (address, method, fileName, null);
			} catch (WebException) {
				throw;
			} catch (Exception ex) {
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			} finally {
				is_busy = false;
			}
		}

		byte [] UploadFileCore (Uri address, string method, string fileName, object userToken)
		{
			string fileCType = Headers ["Content-Type"];
			if (fileCType != null) {
				string lower = fileCType.ToLower ();
				if (lower.StartsWith ("multipart/"))
					throw new WebException ("Content-Type cannot be set to a multipart" +
								" type for this request.");
			} else {
				fileCType = "application/octet-stream";
			}

			bool needs_boundary = (method != "PUT"); // only verified case so far
			string boundary = null;
			if (needs_boundary) {
				boundary = "------------" + DateTime.Now.Ticks.ToString ("x");
				Headers ["Content-Type"] = String.Format ("multipart/form-data; boundary={0}", boundary);
			}
			Stream reqStream = null;
			Stream fStream = null;
			byte [] resultBytes = null;

			fileName = Path.GetFullPath (fileName);

			WebRequest request = null;
			try {
				fStream = File.OpenRead (fileName);
				request = SetupRequest (address, method, true);
				reqStream = request.GetRequestStream ();
				byte [] bytes_boundary = null;
				if (needs_boundary) {
					bytes_boundary = Encoding.ASCII.GetBytes (boundary);
					reqStream.WriteByte ((byte) '-');
					reqStream.WriteByte ((byte) '-');
					reqStream.Write (bytes_boundary, 0, bytes_boundary.Length);
					reqStream.WriteByte ((byte) '\r');
					reqStream.WriteByte ((byte) '\n');
					string partHeaders = String.Format ("Content-Disposition: form-data; " +
									    "name=\"file\"; filename=\"{0}\"\r\n" +
									    "Content-Type: {1}\r\n\r\n",
									    Path.GetFileName (fileName), fileCType);

					byte [] partHeadersBytes = Encoding.UTF8.GetBytes (partHeaders);
					reqStream.Write (partHeadersBytes, 0, partHeadersBytes.Length);
				}
				int nread;
				long bytes_sent = 0;
				long file_size = -1;
				long step = 16384; // every 16kB
				if (fStream.CanSeek) {
					file_size = fStream.Length;
					step = file_size / 100;
				}
				var upload_args = new UploadProgressChangedEventArgs (0, 0, bytes_sent, file_size, 0, userToken);
				OnUploadProgressChanged (upload_args);
				byte [] buffer = new byte [4096];
				long sum = 0;
				while ((nread = fStream.Read (buffer, 0, 4096)) > 0) {
					reqStream.Write (buffer, 0, nread);
					bytes_sent += nread;
					sum += nread;
					if (sum >= step || nread < 4096) {
						int percent = 0;
						if (file_size > 0)
							percent = (int) (bytes_sent * 100 / file_size);
						upload_args = new UploadProgressChangedEventArgs (0, 0, bytes_sent, file_size, percent, userToken);
						OnUploadProgressChanged (upload_args);
						sum = 0;
					}
				}

				if (needs_boundary) {
					reqStream.WriteByte ((byte) '\r');
					reqStream.WriteByte ((byte) '\n');
					reqStream.WriteByte ((byte) '-');
					reqStream.WriteByte ((byte) '-');
					reqStream.Write (bytes_boundary, 0, bytes_boundary.Length);
					reqStream.WriteByte ((byte) '-');
					reqStream.WriteByte ((byte) '-');
					reqStream.WriteByte ((byte) '\r');
					reqStream.WriteByte ((byte) '\n');
				}
				reqStream.Close ();
				reqStream = null;
				resultBytes = ReadAll (request, userToken);
			} catch (ThreadInterruptedException){
				if (request != null)
					request.Abort ();
				throw;
			} finally {
				if (fStream != null)
					fStream.Close ();

				if (reqStream != null)
					reqStream.Close ();
			}
			
			return resultBytes;
		}
		
		public byte[] UploadValues (string address, NameValueCollection data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return UploadValues (CreateUri (address), data);
		}
		
		public byte[] UploadValues (string address, string method, NameValueCollection data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			return UploadValues (CreateUri (address), method, data);
		}

		public byte[] UploadValues (Uri address, NameValueCollection data)
		{
			return UploadValues (address, (string) null, data);
		}

		public byte[] UploadValues (Uri address, string method, NameValueCollection data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");

			try {
				SetBusy ();
				async = false;
				return UploadValuesCore (address, method, data, null);
			} catch (WebException) {
				throw;
			} catch (Exception ex) {
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			} finally {
				is_busy = false;
			}
		}

		byte[] UploadValuesCore (Uri uri, string method, NameValueCollection data, object userToken)
		{
			string cType = Headers ["Content-Type"];
			if (cType != null && String.Compare (cType, urlEncodedCType, true) != 0)
				throw new WebException ("Content-Type header cannot be changed from its default " +
							"value for this request.");

			Headers ["Content-Type"] = urlEncodedCType;
			WebRequest request = SetupRequest (uri, method, true);
			try {
				MemoryStream tmpStream = new MemoryStream ();
				foreach (string key in data) {
					byte [] bytes = Encoding.UTF8.GetBytes (key);
					UrlEncodeAndWrite (tmpStream, bytes);
					tmpStream.WriteByte ((byte) '=');
					bytes = Encoding.UTF8.GetBytes (data [key]);
					UrlEncodeAndWrite (tmpStream, bytes);
					tmpStream.WriteByte ((byte) '&');
				}
				
				int length = (int) tmpStream.Length;
				if (length > 0)
					tmpStream.SetLength (--length); // remove trailing '&'
				
				byte [] buf = tmpStream.GetBuffer ();
				request.ContentLength = length;
				using (Stream rqStream = request.GetRequestStream ()) {
					rqStream.Write (buf, 0, length);
				}
				tmpStream.Close ();
				
				return ReadAll (request, userToken);
			} catch (ThreadInterruptedException) {
				request.Abort ();
				throw;
			}
		}

		public string DownloadString (string address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return encoding.GetString (DownloadData (CreateUri (address)));
		}

		public string DownloadString (Uri address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return encoding.GetString (DownloadData (CreateUri (address)));
		}

		public string UploadString (string address, string data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");

			byte [] resp = UploadData (address, encoding.GetBytes (data));
			return encoding.GetString (resp);
		}

		public string UploadString (string address, string method, string data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");

			byte [] resp = UploadData (address, method, encoding.GetBytes (data));
			return encoding.GetString (resp);
		}

		public string UploadString (Uri address, string data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");

			byte [] resp = UploadData (address, encoding.GetBytes (data));
			return encoding.GetString (resp);
		}

		public string UploadString (Uri address, string method, string data)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");

			byte [] resp = UploadData (address, method, encoding.GetBytes (data));
			return encoding.GetString (resp);
		}

		public event DownloadDataCompletedEventHandler DownloadDataCompleted;
		public event AsyncCompletedEventHandler DownloadFileCompleted;
		public event DownloadProgressChangedEventHandler DownloadProgressChanged;
		public event DownloadStringCompletedEventHandler DownloadStringCompleted;
		public event OpenReadCompletedEventHandler OpenReadCompleted;
		public event OpenWriteCompletedEventHandler OpenWriteCompleted;
		public event UploadDataCompletedEventHandler UploadDataCompleted;
		public event UploadFileCompletedEventHandler UploadFileCompleted;
		public event UploadProgressChangedEventHandler UploadProgressChanged;
		public event UploadStringCompletedEventHandler UploadStringCompleted;
		public event UploadValuesCompletedEventHandler UploadValuesCompleted;

		Uri CreateUri (string address)
		{
			Uri uri;
			try {
				if (baseAddress == null)
					uri = new Uri (address);
				else
					uri = new Uri (baseAddress, address);
				return CreateUri (uri);
			} catch {
			}
			return new Uri (Path.GetFullPath (address));
		}

		Uri CreateUri (Uri address)
		{
			Uri result = address;
			if (baseAddress != null && !result.IsAbsoluteUri) {
				try {
					result = new Uri (baseAddress, result.OriginalString);
				} catch {
					return result; // Not much we can do here.
				}
			}

			string query = result.Query;
			if (String.IsNullOrEmpty (query))
				query = GetQueryString (true);
			UriBuilder builder = new UriBuilder (address);
			if (!String.IsNullOrEmpty (query))
				builder.Query = query.Substring (1);
			return builder.Uri;
		}

		string GetQueryString (bool add_qmark)
		{
			if (queryString == null || queryString.Count == 0)
				return null;

			StringBuilder sb = new StringBuilder ();
			if (add_qmark)
				sb.Append ('?');

			foreach (string key in queryString)
				sb.AppendFormat ("{0}={1}&", key, UrlEncode (queryString [key]));

			if (sb.Length != 0)
				sb.Length--; // removes last '&' or the '?' if empty.

			if (sb.Length == 0)
				return null;

			return sb.ToString ();
		}

		WebRequest SetupRequest (Uri uri)
		{
			WebRequest request = GetWebRequest (uri);
			if (proxySet)
				request.Proxy = Proxy;
			if (credentials != null)
				request.Credentials = credentials;
			else if (!String.IsNullOrEmpty (uri.UserInfo)) {
				// Perhaps this should be done by the underlying URI handler?
				ICredentials creds = GetCredentials (uri.UserInfo);
				if (creds != null)
					request.Credentials = creds;
			}

			// Special headers. These are properties of HttpWebRequest.
			// What do we do with other requests differnt from HttpWebRequest?
			if (headers != null && headers.Count != 0 && (request is HttpWebRequest)) {
				HttpWebRequest req = (HttpWebRequest) request;
				string expect = headers ["Expect"];
				string contentType = headers ["Content-Type"];
				string accept = headers ["Accept"];
				string connection = headers ["Connection"];
				string userAgent = headers ["User-Agent"];
				string referer = headers ["Referer"];
				headers.RemoveInternal ("Expect");
				headers.RemoveInternal ("Content-Type");
				headers.RemoveInternal ("Accept");
				headers.RemoveInternal ("Connection");
				headers.RemoveInternal ("Referer");
				headers.RemoveInternal ("User-Agent");
				request.Headers = headers;

				if (expect != null && expect.Length > 0)
					req.Expect = expect;

				if (accept != null && accept.Length > 0)
					req.Accept = accept;

				if (contentType != null && contentType.Length > 0)
					req.ContentType = contentType;

				if (connection != null && connection.Length > 0)
					req.Connection = connection;

				if (userAgent != null && userAgent.Length > 0)
					req.UserAgent = userAgent;

				if (referer != null && referer.Length > 0)
					req.Referer = referer;
			}

			responseHeaders = null;
			return request;
		}

		WebRequest SetupRequest (Uri uri, string method, bool is_upload)
		{
			WebRequest request = SetupRequest (uri);
			request.Method = DetermineMethod (uri, method, is_upload);
			return request;
		}

		static NetworkCredential GetCredentials (string user_info)
		{
			string [] creds = user_info.Split (':');
			if (creds.Length != 2)
				return null;

			if (creds [0].IndexOf ('\\') != -1) {
				string [] user = creds [0].Split ('\\');
				if (user.Length != 2)
					return null;
				return new NetworkCredential (user [1], creds [1], user [0]);
			}
			return new NetworkCredential (creds [0], creds [1]);
		}

		byte [] ReadAll (WebRequest request, object userToken)
		{
			WebResponse response = GetWebResponse (request);
			Stream stream = response.GetResponseStream ();
			int length = (int) response.ContentLength;
			HttpWebRequest wreq = request as HttpWebRequest;

			if (length > -1 && wreq != null && (int) wreq.AutomaticDecompression != 0) {
				string content_encoding = ((HttpWebResponse) response).ContentEncoding;
				if (((content_encoding == "gzip" && (wreq.AutomaticDecompression & DecompressionMethods.GZip) != 0)) ||
					((content_encoding == "deflate" && (wreq.AutomaticDecompression & DecompressionMethods.Deflate) != 0)))
					length = -1;
			}

			MemoryStream ms = null;
			bool nolength = (length == -1);
			int size = ((nolength) ? 8192 : length);
			if (nolength)
				ms = new MemoryStream ();

			long total = 0;
			int nread = 0;
			int offset = 0;
			byte [] buffer = new byte [size];
			while ((nread = stream.Read (buffer, offset, size)) != 0) {
				if (nolength) {
					ms.Write (buffer, 0, nread);
				} else {
					offset += nread;
					size -= nread;
				}
				if (async){
					total += nread;
					OnDownloadProgressChanged (new DownloadProgressChangedEventArgs (total, length, userToken));
				}
			}

			if (nolength)
				return ms.ToArray ();

			return buffer;
		}

		string UrlEncode (string str)
		{
			StringBuilder result = new StringBuilder ();

			int len = str.Length;
			for (int i = 0; i < len; i++) {
				char c = str [i];
				if (c == ' ')
					result.Append ('+');
				else if ((c < '0' && c != '-' && c != '.') ||
					 (c < 'A' && c > '9') ||
					 (c > 'Z' && c < 'a' && c != '_') ||
					 (c > 'z')) {
					result.Append ('%');
					int idx = ((int) c) >> 4;
					result.Append ((char) hexBytes [idx]);
					idx = ((int) c) & 0x0F;
					result.Append ((char) hexBytes [idx]);
				} else {
					result.Append (c);
				}
			}

			return result.ToString ();
		}

		static void UrlEncodeAndWrite (Stream stream, byte [] bytes)
		{
			if (bytes == null)
				return;

			int len = bytes.Length;
			if (len == 0)
				return;

			for (int i = 0; i < len; i++) {
				char c = (char) bytes [i];
				if (c == ' ')
					stream.WriteByte ((byte) '+');
				else if ((c < '0' && c != '-' && c != '.') ||
					 (c < 'A' && c > '9') ||
					 (c > 'Z' && c < 'a' && c != '_') ||
					 (c > 'z')) {
					stream.WriteByte ((byte) '%');
					int idx = ((int) c) >> 4;
					stream.WriteByte (hexBytes [idx]);
					idx = ((int) c) & 0x0F;
					stream.WriteByte (hexBytes [idx]);
				} else {
					stream.WriteByte ((byte) c);
				}
			}
		}

		public void CancelAsync ()
		{
			lock (this){
#if NET_4_5
				if (cts != null) {
					cts.Cancel ();
					return;
				}
#endif

				if (async_thread == null)
					return;

				//
				// We first flag things as done, in case the Interrupt hangs
				// or the thread decides to hang in some other way inside the
				// event handlers, or if we are stuck somewhere else.  This
				// ensures that the WebClient object is reusable immediately
				//
				Thread t = async_thread;
				CompleteAsync ();
				t.Interrupt ();
			}
		}

		void CompleteAsync ()
		{
			lock (this) {
				is_busy = false;
				async_thread = null;
#if NET_4_5
				if (cts != null)
					cts.Dispose ();
				cts = null;
#endif
			}
		}

		//    DownloadDataAsync

		public void DownloadDataAsync (Uri address)
		{
			DownloadDataAsync (address, null);
		}

		public void DownloadDataAsync (Uri address, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			
			lock (this) {
				SetBusy ();
				async = true;
				
				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					try {
						byte [] data = DownloadDataCore ((Uri) args [0], args [1]);
						OnDownloadDataCompleted (
							new DownloadDataCompletedEventArgs (data, null, false, args [1]));
					} catch (Exception e){
						bool canceled = false;
						WebException we = e as WebException;
						if (we != null)
							canceled = we.Status == WebExceptionStatus.RequestCanceled;
						OnDownloadDataCompleted (
							new DownloadDataCompletedEventArgs (null, e, canceled, args [1]));
					}
				});
				object [] cb_args = new object [] { CreateUri (address), userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    DownloadFileAsync

		public void DownloadFileAsync (Uri address, string fileName)
		{
			DownloadFileAsync (address, fileName, null);
		}

		public void DownloadFileAsync (Uri address, string fileName, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (fileName == null)
				throw new ArgumentNullException ("fileName");
			
			lock (this) {
				SetBusy ();
				async = true;

				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					try {
						DownloadFileCore ((Uri) args [0], (string) args [1], args [2]);
						OnDownloadFileCompleted (
							new AsyncCompletedEventArgs (null, false, args [2]));
					} catch (ThreadInterruptedException){
						OnDownloadFileCompleted (
							new AsyncCompletedEventArgs (null, true, args [2]));
					} catch (Exception e){
						OnDownloadFileCompleted (
							new AsyncCompletedEventArgs (e, false, args [2]));
					}});
				object [] cb_args = new object [] { CreateUri (address), fileName, userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    DownloadStringAsync

		public void DownloadStringAsync (Uri address)
		{
			DownloadStringAsync (address, null);
		}

		public void DownloadStringAsync (Uri address, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			
			lock (this) {
				SetBusy ();
				async = true;

				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					try {
						string data = encoding.GetString (DownloadDataCore ((Uri) args [0], args [1]));
						OnDownloadStringCompleted (
							new DownloadStringCompletedEventArgs (data, null, false, args [1]));
					} catch (Exception e){
						bool canceled = false;
						WebException we = e as WebException;
						if (we != null)
							canceled = we.Status == WebExceptionStatus.RequestCanceled;
						OnDownloadStringCompleted (
							new DownloadStringCompletedEventArgs (null, e, canceled, args [1]));
					}});
				object [] cb_args = new object [] { CreateUri (address), userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    OpenReadAsync

		public void OpenReadAsync (Uri address)
		{
			OpenReadAsync (address, null);
		}

		public void OpenReadAsync (Uri address, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			
			lock (this) {
				SetBusy ();
				async = true;

				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					WebRequest request = null;
					try {
						request = SetupRequest ((Uri) args [0]);
						WebResponse response = GetWebResponse (request);
						Stream stream = response.GetResponseStream ();
						OnOpenReadCompleted (
							new OpenReadCompletedEventArgs (stream, null, false, args [1]));
					} catch (ThreadInterruptedException){
						if (request != null)
							request.Abort ();
						
						OnOpenReadCompleted (new OpenReadCompletedEventArgs (null, null, true, args [1]));
					} catch (Exception e){
						OnOpenReadCompleted (new OpenReadCompletedEventArgs (null, e, false, args [1]));
					} });
				object [] cb_args = new object [] { CreateUri (address), userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    OpenWriteAsync

		public void OpenWriteAsync (Uri address)
		{
			OpenWriteAsync (address, null);
		}

		public void OpenWriteAsync (Uri address, string method)
		{
			OpenWriteAsync (address, method, null);
		}

		public void OpenWriteAsync (Uri address, string method, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			lock (this) {
				SetBusy ();
				async = true;

				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					WebRequest request = null;
					try {
						request = SetupRequest ((Uri) args [0], (string) args [1], true);
						Stream stream = request.GetRequestStream ();
						OnOpenWriteCompleted (
							new OpenWriteCompletedEventArgs (stream, null, false, args [2]));
					} catch (ThreadInterruptedException){
						if (request != null)
							request.Abort ();
						OnOpenWriteCompleted (
							new OpenWriteCompletedEventArgs (null, null, true, args [2]));
					} catch (Exception e){
						OnOpenWriteCompleted (
							new OpenWriteCompletedEventArgs (null, e, false, args [2]));
					}});
				object [] cb_args = new object [] { CreateUri (address), method, userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    UploadDataAsync

		public void UploadDataAsync (Uri address, byte [] data)
		{
			UploadDataAsync (address, null, data);
		}

		public void UploadDataAsync (Uri address, string method, byte [] data)
		{
			UploadDataAsync (address, method, data, null);
		}

		public void UploadDataAsync (Uri address, string method, byte [] data, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");
			
			lock (this) {
				SetBusy ();
				async = true;

				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					byte [] data2;

					try {
						data2 = UploadDataCore ((Uri) args [0], (string) args [1], (byte []) args [2], args [3]);
					
						OnUploadDataCompleted (
							new UploadDataCompletedEventArgs (data2, null, false, args [3]));
					} catch (ThreadInterruptedException){
						OnUploadDataCompleted (
							new UploadDataCompletedEventArgs (null, null, true, args [3]));
					} catch (Exception e){
						OnUploadDataCompleted (
							new UploadDataCompletedEventArgs (null, e, false, args [3]));
					}});
				object [] cb_args = new object [] { CreateUri (address), method, data,  userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    UploadFileAsync

		public void UploadFileAsync (Uri address, string fileName)
		{
			UploadFileAsync (address, null, fileName);
		}

		public void UploadFileAsync (Uri address, string method, string fileName)
		{
			UploadFileAsync (address, method, fileName, null);
		}

		public void UploadFileAsync (Uri address, string method, string fileName, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (fileName == null)
				throw new ArgumentNullException ("fileName");

			lock (this) {
				SetBusy ();
				async = true;

				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					byte [] data;

					try {
						data = UploadFileCore ((Uri) args [0], (string) args [1], (string) args [2], args [3]);
						OnUploadFileCompleted (
							new UploadFileCompletedEventArgs (data, null, false, args [3]));
					} catch (ThreadInterruptedException){
						OnUploadFileCompleted (
							new UploadFileCompletedEventArgs (null, null, true, args [3]));
					} catch (Exception e){
						OnUploadFileCompleted (
							new UploadFileCompletedEventArgs (null, e, false, args [3]));
					}});
				object [] cb_args = new object [] { CreateUri (address), method, fileName,  userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    UploadStringAsync

		public void UploadStringAsync (Uri address, string data)
		{
			UploadStringAsync (address, null, data);
		}

		public void UploadStringAsync (Uri address, string method, string data)
		{
			UploadStringAsync (address, method, data, null);
		}

		public void UploadStringAsync (Uri address, string method, string data, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");
			
			lock (this) {
				CheckBusy ();
				async = true;
				
				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;

					try {
						string data2 = UploadString ((Uri) args [0], (string) args [1], (string) args [2]);
						OnUploadStringCompleted (
							new UploadStringCompletedEventArgs (data2, null, false, args [3]));
					} catch (ThreadInterruptedException){
						OnUploadStringCompleted (
							new UploadStringCompletedEventArgs (null, null, true, args [3]));
					} catch (Exception e){
						OnUploadStringCompleted (
							new UploadStringCompletedEventArgs (null, e, false, args [3]));
					}});
				object [] cb_args = new object [] { CreateUri (address), method, data, userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		//    UploadValuesAsync

		public void UploadValuesAsync (Uri address, NameValueCollection data)
		{
			UploadValuesAsync (address, null, data);
		}

		public void UploadValuesAsync (Uri address, string method, NameValueCollection data)
		{
			UploadValuesAsync (address, method, data, null);
		}

		public void UploadValuesAsync (Uri address, string method, NameValueCollection data, object userToken)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (data == null)
				throw new ArgumentNullException ("data");

			lock (this) {
				CheckBusy ();
				async = true;

				async_thread = new Thread (delegate (object state) {
					object [] args = (object []) state;
					try {
						byte [] values = UploadValuesCore ((Uri) args [0], (string) args [1], (NameValueCollection) args [2], args [3]);
						OnUploadValuesCompleted (
							new UploadValuesCompletedEventArgs (values, null, false, args [3]));
					} catch (ThreadInterruptedException){
						OnUploadValuesCompleted (
							new UploadValuesCompletedEventArgs (null, null, true, args [3]));
					} catch (Exception e){
						OnUploadValuesCompleted (
							new UploadValuesCompletedEventArgs (null, e, false, args [3]));
					}});
				object [] cb_args = new object [] { CreateUri (address), method, data,  userToken };
				async_thread.IsBackground = true;
				async_thread.Start (cb_args);
			}
		}

		protected virtual void OnDownloadDataCompleted (DownloadDataCompletedEventArgs e)
		{
			CompleteAsync ();
			if (DownloadDataCompleted != null)
				DownloadDataCompleted (this, e);
		}

		protected virtual void OnDownloadFileCompleted (AsyncCompletedEventArgs e)
		{
			CompleteAsync ();
			if (DownloadFileCompleted != null)
				DownloadFileCompleted (this, e);
		}

		protected virtual void OnDownloadProgressChanged (DownloadProgressChangedEventArgs e)
		{
			if (DownloadProgressChanged != null)
				DownloadProgressChanged (this, e);
		}

		protected virtual void OnDownloadStringCompleted (DownloadStringCompletedEventArgs e)
		{
			CompleteAsync ();
			if (DownloadStringCompleted != null)
				DownloadStringCompleted (this, e);
		}

		protected virtual void OnOpenReadCompleted (OpenReadCompletedEventArgs e)
		{
			CompleteAsync ();
			if (OpenReadCompleted != null)
				OpenReadCompleted (this, e);
		}

		protected virtual void OnOpenWriteCompleted (OpenWriteCompletedEventArgs e)
		{
			CompleteAsync ();
			if (OpenWriteCompleted != null)
				OpenWriteCompleted (this, e);
		}

		protected virtual void OnUploadDataCompleted (UploadDataCompletedEventArgs e)
		{
			CompleteAsync ();
			if (UploadDataCompleted != null)
				UploadDataCompleted (this, e);
		}

		protected virtual void OnUploadFileCompleted (UploadFileCompletedEventArgs e)
		{
			CompleteAsync ();
			if (UploadFileCompleted != null)
				UploadFileCompleted (this, e);
		}

		protected virtual void OnUploadProgressChanged (UploadProgressChangedEventArgs e)
		{
			if (UploadProgressChanged != null)
				UploadProgressChanged (this, e);
		}

		protected virtual void OnUploadStringCompleted (UploadStringCompletedEventArgs e)
		{
			CompleteAsync ();
			if (UploadStringCompleted != null)
				UploadStringCompleted (this, e);
		}

		protected virtual void OnUploadValuesCompleted (UploadValuesCompletedEventArgs e)
		{
			CompleteAsync ();
			if (UploadValuesCompleted != null)
				UploadValuesCompleted (this, e);
		}

		protected virtual WebResponse GetWebResponse (WebRequest request, IAsyncResult result)
		{
			WebResponse response = request.EndGetResponse (result);
			responseHeaders = response.Headers;
			return response;
		}

		protected virtual WebRequest GetWebRequest (Uri address)
		{
			return WebRequest.Create (address);
		}

		protected virtual WebResponse GetWebResponse (WebRequest request)
		{
			WebResponse response = request.GetResponse ();
			responseHeaders = response.Headers;
			return response;
		}
		
#if NET_4_5

		// DownloadDataTaskAsync
		
		public Task<byte[]> DownloadDataTaskAsync (string address)
		{
			return DownloadDataTaskAsync (CreateUri (address));
		}

		public async Task<byte[]> DownloadDataTaskAsync (Uri address)
		{
			WebRequest request = null;
			WebResponse response = null;
			try {
				SetBusy ();
				cts = new CancellationTokenSource ();
				request = await SetupRequestAsync (address);
				response = await GetWebResponseTaskAsync (request, cts.Token);
				var result = await ReadAllTaskAsync (request, response, cts.Token);

				// Has to run on original context
				OnDownloadDataCompleted (new DownloadDataCompletedEventArgs (result, null, false, null));
				return result;
			} catch (WebException ex) {
				OnDownloadDataCompleted (new DownloadDataCompletedEventArgs (null, ex, false, null));
				throw;
			} catch (OperationCanceledException) {
				if (request != null)
					request.Abort ();
				OnDownloadDataCompleted (new DownloadDataCompletedEventArgs (null, null, true, null));
				throw;
			} catch (Exception ex) {
				OnDownloadDataCompleted (new DownloadDataCompletedEventArgs (null, ex, true, null));
				throw new WebException ("An error occurred performing a WebClient request.", ex);
			} finally {
				if (response != null)
					response.Close ();
			}
		}

		Task<WebRequest> SetupRequestAsync (Uri address)
		{
			return Task.Factory.StartNew (() => SetupRequest (address));
		}

		async Task<WebRequest> SetupRequestAsync (Uri address, string method, bool is_upload)
		{
			WebRequest request = await SetupRequestAsync (address).ConfigureAwait (false);
			request.Method = DetermineMethod (address, method, is_upload);
			return request;
		}
		
		async Task<WebResponse> GetWebResponseTaskAsync (WebRequest request, CancellationToken token)
		{
			token.ThrowIfCancellationRequested ();
			WebResponse response = await request.GetResponseAsync ().ConfigureAwait (false);
			token.ThrowIfCancellationRequested ();
			responseHeaders = response.Headers;
			return response;
		}
		
		async Task<byte[]> ReadAllTaskAsync (WebRequest request, WebResponse response, CancellationToken token)
		{
			Stream stream = response.GetResponseStream ();
			int length = (int)response.ContentLength;
			HttpWebRequest wreq = request as HttpWebRequest;

			if (length > -1 && wreq != null && (int)wreq.AutomaticDecompression != 0) {
				string content_encoding = ((HttpWebResponse)response).ContentEncoding;
				if (((content_encoding == "gzip" && (wreq.AutomaticDecompression & DecompressionMethods.GZip) != 0)) ||
					((content_encoding == "deflate" && (wreq.AutomaticDecompression & DecompressionMethods.Deflate) != 0)))
					length = -1;
			}

			MemoryStream ms = null;
			bool nolength = (length == -1);
			int size = ((nolength) ? 8192 : length);
			if (nolength)
				ms = new MemoryStream ();

			long total = 0;
			int nread = 0;
			int offset = 0;
			byte [] buffer = new byte [size];
			token.ThrowIfCancellationRequested ();
			while ((nread = await stream.ReadAsync (buffer, offset, size, token)) != 0) {
				if (nolength) {
					ms.Write (buffer, 0, nread);
				} else {
					offset += nread;
					size -= nread;
				}
				total += nread;
				OnDownloadProgressChanged (new DownloadProgressChangedEventArgs (total, length, null));
				token.ThrowIfCancellationRequested ();
			}
			
			return nolength ? ms.ToArray () : buffer;
		}
		
		// DownloadFileTaskAsync
		
		public Task DownloadFileTaskAsync (string address, string fileName)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return DownloadFileTaskAsync (CreateUri (address), fileName);
		}

		public async Task DownloadFileTaskAsync (Uri address, string fileName)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			if (fileName == null)
				throw new ArgumentNullException ("fileName");
			
			WebRequest request = null;
			WebResponse response = null;

			try {
				SetBusy ();
				cts = new CancellationTokenSource ();
				request = await SetupRequestAsync (address);
				response = await GetWebResponseTaskAsync (request, cts.Token);
				await DownloadFileTaskAsyncCore (request, response, fileName, cts.Token);
				OnDownloadFileCompleted (new AsyncCompletedEventArgs (null, false, null));
			} catch (WebException ex) {
				OnDownloadFileCompleted (new AsyncCompletedEventArgs (ex, false, null));
				throw;
			} catch (OperationCanceledException) {
				if (request != null)
					request.Abort ();
				OnDownloadFileCompleted (new AsyncCompletedEventArgs (null, true, null));
				throw;
			} catch (Exception ex) {
				OnDownloadFileCompleted (new AsyncCompletedEventArgs (ex, false, null));
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			} finally {
				if (response != null)
					response.Close ();
			}
		}

		async Task DownloadFileTaskAsyncCore (WebRequest request, WebResponse response,
		                                      string fileName, CancellationToken token)
		{
			using (FileStream f = new FileStream (fileName, FileMode.Create)) {
				Stream st = response.GetResponseStream ();
					
				int cLength = (int)response.ContentLength;
				int length = (cLength <= -1 || cLength > 32 * 1024) ? 32 * 1024 : cLength;
				byte [] buffer = new byte [length];
					
				int nread = 0;
				long notify_total = 0;
				token.ThrowIfCancellationRequested ();
				while ((nread = await st.ReadAsync (buffer, 0, length, token)) != 0) {
					notify_total += nread;
					OnDownloadProgressChanged (
						new DownloadProgressChangedEventArgs (notify_total, response.ContentLength, null));
					token.ThrowIfCancellationRequested ();
					await f.WriteAsync (buffer, 0, nread, token);
					token.ThrowIfCancellationRequested ();
				}
			}
		}
		
		// OpenReadTaskAsync
		
		public Task<Stream> OpenReadTaskAsync (string address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");
			return OpenReadTaskAsync (CreateUri (address));
		}

		public async Task<Stream> OpenReadTaskAsync (Uri address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			WebRequest request = null;
			try {
				SetBusy ();
				cts = new CancellationTokenSource ();
				request = await SetupRequestAsync (address);
				WebResponse response = await GetWebResponseTaskAsync (request, cts.Token);
				var result = response.GetResponseStream ();
				cts.Token.ThrowIfCancellationRequested ();
				OnOpenReadCompleted (new OpenReadCompletedEventArgs (result, null, false, null));
				return result;
			} catch (WebException ex) {
				OnOpenReadCompleted (new OpenReadCompletedEventArgs (null, ex, false, null));
				throw;
			} catch (OperationCanceledException) {
				if (request != null)
					request.Abort ();
				OnOpenReadCompleted (new OpenReadCompletedEventArgs (null, null, true, null));
				throw;
			} catch (Exception ex) {
				OnOpenReadCompleted (new OpenReadCompletedEventArgs (null, ex, false, null));
				throw new WebException ("An error occurred " +
					"performing a WebClient request.", ex);
			}
		}
		
		// DownloadStringTaskAsync
		
		public Task<string> DownloadStringTaskAsync (string address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			return DownloadStringTaskAsync (CreateUri (address));
		}

		public async Task<string> DownloadStringTaskAsync (Uri address)
		{
			if (address == null)
				throw new ArgumentNullException ("address");

			WebRequest request = null;
			WebResponse response = null;

			try {
				SetBusy ();
				cts = new CancellationTokenSource ();
				request = await SetupRequestAsync (address);
				response = await GetWebResponseTaskAsync (request…