// // AsyncPop3Client.cs // // Author: Jeffrey Stedfast // // Copyright (c) 2013-2020 .NET Foundation and Contributors // // 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. // using System; using System.IO; using System.Net; using System.Text; using System.Threading; using System.Net.Sockets; using System.Threading.Tasks; using System.Collections.Generic; using MimeKit; using MailKit.Security; namespace MailKit.Net.Pop3 { public partial class Pop3Client { ///

/// Asynchronously authenticate using the specified SASL mechanism. ///

/// /// Authenticates using the specified SASL mechanism. /// For a list of available SASL authentication mechanisms supported by the server, /// check the property after the service has been /// connected. /// /// An asynchronous task context. /// The SASL mechanism. /// The cancellation token. /// /// is null. /// /// /// The has been disposed. /// /// /// The is not connected. /// /// /// The is already authenticated. /// /// /// The operation was canceled via the cancellation token. /// /// /// Authentication using the supplied credentials has failed. /// /// /// A SASL authentication error occurred. /// /// /// An I/O error occurred. /// /// /// A POP3 command failed. /// /// /// An POP3 protocol error occurred. /// public override Task AuthenticateAsync (SaslMechanism mechanism, CancellationToken cancellationToken = default (CancellationToken)) { return AuthenticateAsync (mechanism, true, cancellationToken); } ///

/// Asynchronously authenticates using the supplied credentials. ///

/// /// If the POP3 server supports the APOP authentication mechanism, /// then APOP is used. /// If the APOP authentication mechanism is not supported and the /// server supports one or more SASL authentication mechanisms, then /// the SASL mechanisms that both the client and server support are tried /// in order of greatest security to weakest security. Once a SASL /// authentication mechanism is found that both client and server support, /// the credentials are used to authenticate. /// If the server does not support SASL or if no common SASL mechanisms /// can be found, then the USER and PASS commands are used as a /// fallback. /// To prevent the usage of certain authentication mechanisms, /// simply remove them from the hash set /// before calling this method. /// In the case of the APOP authentication mechanism, remove it from the /// property instead. /// /// An asynchronous task context. /// The text encoding to use for the user's credentials. /// The user's credentials. /// The cancellation token. /// /// is null. /// -or- /// is null. /// /// /// The has been disposed. /// /// /// The is not connected. /// /// /// The is already authenticated. /// /// /// The operation was canceled via the cancellation token. /// /// /// Authentication using the supplied credentials has failed. /// /// /// A SASL authentication error occurred. /// /// /// An I/O error occurred. /// /// /// A POP3 command failed. /// /// /// An POP3 protocol error occurred. /// public override Task AuthenticateAsync (Encoding encoding, ICredentials credentials, CancellationToken cancellationToken = default (CancellationToken)) { return AuthenticateAsync (encoding, credentials, true, cancellationToken); } ///

/// Asynchronously establish a connection to the specified POP3 or POP3/S server. ///

/// /// Establishes a connection to the specified POP3 or POP3/S server. /// If the has a value of 0, then the /// parameter is used to determine the default port to /// connect to. The default port used with /// is 995. All other values will use a default port of 110. /// If the has a value of /// , then the is used /// to determine the default security options. If the has a value /// of 995, then the default options used will be /// . All other values will use /// . /// Once a connection is established, properties such as /// and will be /// populated. /// /// ///

///


		/// An asynchronous task context.
		/// The host name to connect to.
		/// The port to connect to. If the specified port is 0, then the default port will be used.
		/// The secure socket options to when connecting.
		/// The cancellation token.
		/// 
		///  is null.
		/// 
		/// 
		///  is not between 0 and 65535.
		/// 
		/// 
		/// The  is a zero-length string.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is already connected.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		///  was set to
		/// 
		/// and the POP3 server does not support the STLS extension.
		/// 
		/// 
		/// A socket error occurred trying to connect to the remote host.
		/// 
		/// 
		/// An error occurred during the SSL/TLS negotiations.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// A POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task ConnectAsync (string host, int port = 0, SecureSocketOptions options = SecureSocketOptions.Auto, CancellationToken cancellationToken = default (CancellationToken))
		{
			return ConnectAsync (host, port, options, true, cancellationToken);
		}

		/// 
		/// Asynchronously establish a connection to the specified POP3 or POP3/S server using the provided socket.
		/// 
		/// 
		/// Establishes a connection to the specified POP3 or POP3/S server using
		/// the provided socket.
		/// If the  has a value of
		/// , then the  is used
		/// to determine the default security options. If the  has a value
		/// of 995, then the default options used will be
		/// . All other values will use
		/// .
		/// Once a connection is established, properties such as
		///  and  will be
		/// populated.
		/// With the exception of using the  to determine the
		/// default  to use when the  value
		/// is , the  and
		///  parameters are only used for logging purposes.
		/// 
		/// An asynchronous task context.
		/// The socket to use for the connection.
		/// The host name to connect to.
		/// The port to connect to. If the specified port is 0, then the default port will be used.
		/// The secure socket options to when connecting.
		/// The cancellation token.
		/// 
		///  is null.
		/// -or-
		///  is null.
		/// 
		/// 
		///  is not between 0 and 65535.
		/// 
		/// 
		///  is not connected.
		/// -or-
		/// The  is a zero-length string.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is already connected.
		/// 
		/// 
		///  was set to
		/// 
		/// and the POP3 server does not support the STLS extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An error occurred during the SSL/TLS negotiations.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// A POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task ConnectAsync (Socket socket, string host, int port = 0, SecureSocketOptions options = SecureSocketOptions.Auto, CancellationToken cancellationToken = default (CancellationToken))
		{
			return ConnectAsync (socket, host, port, options, true, cancellationToken); 
		}

		/// 
		/// Asynchronously establish a connection to the specified POP3 or POP3/S server using the provided stream.
		/// 
		/// 
		/// Establishes a connection to the specified POP3 or POP3/S server using
		/// the provided stream.
		/// If the  has a value of
		/// , then the  is used
		/// to determine the default security options. If the  has a value
		/// of 995, then the default options used will be
		/// . All other values will use
		/// .
		/// Once a connection is established, properties such as
		///  and  will be
		/// populated.
		/// With the exception of using the  to determine the
		/// default  to use when the  value
		/// is , the  and
		///  parameters are only used for logging purposes.
		/// 
		/// An asynchronous task context.
		/// The socket to use for the connection.
		/// The host name to connect to.
		/// The port to connect to. If the specified port is 0, then the default port will be used.
		/// The secure socket options to when connecting.
		/// The cancellation token.
		/// 
		///  is null.
		/// -or-
		///  is null.
		/// 
		/// 
		///  is not between 0 and 65535.
		/// 
		/// 
		/// The  is a zero-length string.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is already connected.
		/// 
		/// 
		///  was set to
		/// 
		/// and the POP3 server does not support the STLS extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An error occurred during the SSL/TLS negotiations.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// A POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task ConnectAsync (Stream stream, string host, int port = 0, SecureSocketOptions options = SecureSocketOptions.Auto, CancellationToken cancellationToken = default (CancellationToken))
		{
			return ConnectAsync (stream, host, port, options, true, cancellationToken);
		}

		/// 
		/// Asynchronously disconnect the service.
		/// 
		/// 
		/// If  is true, a QUIT command will be issued in order to disconnect cleanly.
		/// 
		/// 
		/// 
		/// 
		/// An asynchronous task context.
		/// If set to true, a QUIT command will be issued in order to disconnect cleanly.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		public override Task DisconnectAsync (bool quit, CancellationToken cancellationToken = default (CancellationToken))
		{
			return DisconnectAsync (quit, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the message count.
		/// 
		/// 
		/// Asynchronously gets the message count.
		/// 
		/// The message count.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override async Task GetMessageCountAsync (CancellationToken cancellationToken = default (CancellationToken))
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			await UpdateMessageCountAsync (true, cancellationToken).ConfigureAwait (false);

			return Count;
		}

		/// 
		/// Ping the POP3 server to keep the connection alive.
		/// 
		/// Mail servers, if left idle for too long, will automatically drop the connection.
		/// An asynchronous task context.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task NoOpAsync (CancellationToken cancellationToken = default (CancellationToken))
		{
			return NoOpAsync (true, cancellationToken);
		}

		/// 
		/// Asynchronously enable UTF8 mode.
		/// 
		/// 
		/// The POP3 UTF8 extension allows the client to retrieve messages in the UTF-8 encoding and
		/// may also allow the user to authenticate using a UTF-8 encoded username or password.
		/// 
		/// An asynchronous task context.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  has already been authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// The POP3 server does not support the UTF8 extension.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public Task EnableUTF8Async (CancellationToken cancellationToken = default (CancellationToken))
		{
			return EnableUTF8Async (true, cancellationToken);
		}

		/// 
		/// Asynchronously get the list of languages supported by the POP3 server.
		/// 
		/// 
		/// If the POP3 server supports the LANG extension, it is possible to
		/// query the list of languages supported by the POP3 server that can
		/// be used for error messages.
		/// 
		/// The supported languages.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// The POP3 server does not support the LANG extension.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public Task> GetLanguagesAsync (CancellationToken cancellationToken = default (CancellationToken))
		{
			return GetLanguagesAsync (true, cancellationToken);
		}

		/// 
		/// Asynchronously set the language used by the POP3 server for error messages.
		/// 
		/// 
		/// If the POP3 server supports the LANG extension, it is possible to
		/// set the language used by the POP3 server for error messages.
		/// 
		/// An asynchronous task context.
		/// The language code.
		/// The cancellation token.
		/// 
		///  is null.
		/// 
		/// 
		///  is empty.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// The POP3 server does not support the LANG extension.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public Task SetLanguageAsync (string lang, CancellationToken cancellationToken = default (CancellationToken))
		{
			return SetLanguageAsync (lang, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the UID of the message at the specified index.
		/// 
		/// 
		/// Gets the UID of the message at the specified index.
		/// Not all servers support UIDs, so you should first check the
		///  property for the  flag or
		/// the  convenience property.
		/// 
		/// The message UID.
		/// The message index.
		/// The cancellation token.
		/// 
		///  is not a valid message index.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task GetMessageUidAsync (int index, CancellationToken cancellationToken = default (CancellationToken))
		{
			return GetMessageUidAsync (index, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the full list of available message UIDs.
		/// 
		/// 
		/// Gets the full list of available message UIDs.
		/// Not all servers support UIDs, so you should first check the
		///  property for the  flag or
		/// the  convenience property.
		/// 
		/// 
		/// 
		/// 
		/// The message uids.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetMessageUidsAsync (CancellationToken cancellationToken = default (CancellationToken))
		{
			return GetMessageUidsAsync (true, cancellationToken);
		}

		/// 
		/// Asynchronously get the size of the specified message, in bytes.
		/// 
		/// 
		/// Gets the size of the specified message, in bytes.
		/// 
		/// The message size, in bytes.
		/// The index of the message.
		/// The cancellation token.
		/// 
		///  is not a valid message index.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task GetMessageSizeAsync (int index, CancellationToken cancellationToken = default (CancellationToken))
		{
			return GetMessageSizeAsync (index, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the sizes for all available messages, in bytes.
		/// 
		/// 
		/// Gets the sizes for all available messages, in bytes.
		/// 
		/// The message sizes, in bytes.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetMessageSizesAsync (CancellationToken cancellationToken = default (CancellationToken))
		{
			return GetMessageSizesAsync (true, cancellationToken);
		}

		/// 
		/// Asynchronously get the headers for the message at the specified index.
		/// 
		/// 
		/// Gets the headers for the message at the specified index.
		/// 
		/// The message headers.
		/// The index of the message.
		/// The cancellation token.
		/// 
		///  is not a valid message index.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task GetMessageHeadersAsync (int index, CancellationToken cancellationToken = default (CancellationToken))
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (index < 0 || index >= total)
				throw new ArgumentOutOfRangeException (nameof (index));

			var ctx = new DownloadHeaderContext (this, parser);

			return ctx.DownloadAsync (index + 1, true, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the headers for the messages at the specified indexes.
		/// 
		/// 
		/// Gets the headers for the messages at the specified indexes.
		/// When the POP3 server supports the 
		/// extension, this method will likely be more efficient than using
		///  for each message because
		/// it will batch the commands to reduce latency.
		/// 
		/// The headers for the specified messages.
		/// The indexes of the messages.
		/// The cancellation token.
		/// 
		///  is null.
		/// 
		/// 
		/// One or more of the  are invalid.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetMessageHeadersAsync (IList indexes, CancellationToken cancellationToken = default (CancellationToken))
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (indexes == null)
				throw new ArgumentNullException (nameof (indexes));

			if (indexes.Count == 0)
				return Task.FromResult ((IList) new HeaderList[0]);

			var seqids = new int[indexes.Count];

			for (int i = 0; i < indexes.Count; i++) {
				if (indexes[i] < 0 || indexes[i] >= total)
					throw new ArgumentException ("One or more of the indexes are invalid.", nameof (indexes));

				seqids[i] = indexes[i] + 1;
			}

			var ctx = new DownloadHeaderContext (this, parser);

			return ctx.DownloadAsync (seqids, true, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the headers of the messages within the specified range.
		/// 
		/// 
		/// Gets the headers of the messages within the specified range.
		/// When the POP3 server supports the 
		/// extension, this method will likely be more efficient than using
		///  for each message because
		/// it will batch the commands to reduce latency.
		/// 
		/// The headers of the messages within the specified range.
		/// The index of the first message to get.
		/// The number of messages to get.
		/// The cancellation token.
		/// 
		///  and  do not specify
		/// a valid range of messages.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetMessageHeadersAsync (int startIndex, int count, CancellationToken cancellationToken = default (CancellationToken))
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (startIndex < 0 || startIndex >= total)
				throw new ArgumentOutOfRangeException (nameof (startIndex));

			if (count < 0 || count > (total - startIndex))
				throw new ArgumentOutOfRangeException (nameof (count));

			if (count == 0)
				return Task.FromResult ((IList) new HeaderList[0]);

			var seqids = new int[count];

			for (int i = 0; i < count; i++)
				seqids[i] = startIndex + i + 1;

			var ctx = new DownloadHeaderContext (this, parser);

			return ctx.DownloadAsync (seqids, true, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the message at the specified index.
		/// 
		/// 
		/// Gets the message at the specified index.
		/// 
		/// 
		/// 
		/// 
		/// The message.
		/// The index of the message.
		/// The cancellation token.
		/// The progress reporting mechanism.
		/// 
		///  is not a valid message index.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task GetMessageAsync (int index, CancellationToken cancellationToken = default (CancellationToken), ITransferProgress progress = null)
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (index < 0 || index >= total)
				throw new ArgumentOutOfRangeException (nameof (index));

			var ctx = new DownloadMessageContext (this, parser, progress);

			return ctx.DownloadAsync (index + 1, false, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the messages at the specified indexes.
		/// 
		/// 
		/// Gets the messages at the specified indexes.
		/// When the POP3 server supports the 
		/// extension, this method will likely be more efficient than using
		///  for each message
		/// because it will batch the commands to reduce latency.
		/// 
		/// The messages.
		/// The indexes of the messages.
		/// The cancellation token.
		/// The progress reporting mechanism.
		/// 
		///  is null.
		/// 
		/// 
		/// One or more of the  are invalid.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetMessagesAsync (IList indexes, CancellationToken cancellationToken = default (CancellationToken), ITransferProgress progress = null)
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (indexes == null)
				throw new ArgumentNullException (nameof (indexes));

			if (indexes.Count == 0)
				return Task.FromResult ((IList) new MimeMessage[0]);

			var seqids = new int[indexes.Count];

			for (int i = 0; i < indexes.Count; i++) {
				if (indexes[i] < 0 || indexes[i] >= total)
					throw new ArgumentException ("One or more of the indexes are invalid.", nameof (indexes));

				seqids[i] = indexes[i] + 1;
			}

			var ctx = new DownloadMessageContext (this, parser, progress);

			return ctx.DownloadAsync (seqids, false, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the messages within the specified range.
		/// 
		/// 
		/// Gets the messages within the specified range.
		/// When the POP3 server supports the 
		/// extension, this method will likely be more efficient than using
		///  for each message
		/// because it will batch the commands to reduce latency.
		/// 
		/// 
		/// 
		/// 
		/// The messages.
		/// The index of the first message to get.
		/// The number of messages to get.
		/// The cancellation token.
		/// The progress reporting mechanism.
		/// 
		///  and  do not specify
		/// a valid range of messages.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetMessagesAsync (int startIndex, int count, CancellationToken cancellationToken = default (CancellationToken), ITransferProgress progress = null)
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (startIndex < 0 || startIndex >= total)
				throw new ArgumentOutOfRangeException (nameof (startIndex));

			if (count < 0 || count > (total - startIndex))
				throw new ArgumentOutOfRangeException (nameof (count));

			if (count == 0)
				return Task.FromResult ((IList) new MimeMessage[0]);

			var seqids = new int[count];

			for (int i = 0; i < count; i++)
				seqids[i] = startIndex + i + 1;

			var ctx = new DownloadMessageContext (this, parser, progress);

			return ctx.DownloadAsync (seqids, false, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the message or header stream at the specified index.
		/// 
		/// 
		/// Gets the message or header stream at the specified index.
		/// 
		/// The message or header stream.
		/// The index of the message.
		/// true if only the headers should be retrieved; otherwise, false.
		/// The cancellation token.
		/// The progress reporting mechanism.
		/// 
		///  is not a valid message index.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task GetStreamAsync (int index, bool headersOnly = false, CancellationToken cancellationToken = default (CancellationToken), ITransferProgress progress = null)
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (index < 0 || index >= total)
				throw new ArgumentOutOfRangeException (nameof (index));

			var ctx = new DownloadStreamContext (this, progress);

			return ctx.DownloadAsync (index + 1, headersOnly, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the message or header streams at the specified indexes.
		/// 
		/// 
		/// Get the message or header streams at the specified indexes.
		/// If the POP3 server supports the 
		/// extension, this method will likely be more efficient than using
		///  for each message
		/// because it will batch the commands to reduce latency.
		/// 
		/// The message or header streams.
		/// The indexes of the messages.
		/// true if only the headers should be retrieved; otherwise, false.
		/// The cancellation token.
		/// The progress reporting mechanism.
		/// 
		///  is null.
		/// 
		/// 
		/// One or more of the  are invalid.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetStreamsAsync (IList indexes, bool headersOnly = false, CancellationToken cancellationToken = default (CancellationToken), ITransferProgress progress = null)
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (indexes == null)
				throw new ArgumentNullException (nameof (indexes));

			if (indexes.Count == 0)
				return Task.FromResult ((IList) new Stream[0]);

			var seqids = new int[indexes.Count];

			for (int i = 0; i < indexes.Count; i++) {
				if (indexes[i] < 0 || indexes[i] >= total)
					throw new ArgumentException ("One or more of the indexes are invalid.", nameof (indexes));

				seqids[i] = indexes[i] + 1;
			}

			var ctx = new DownloadStreamContext (this, progress);

			return ctx.DownloadAsync (seqids, headersOnly, true, cancellationToken);
		}

		/// 
		/// Asynchronously get the message or header streams within the specified range.
		/// 
		/// 
		/// Gets the message or header streams within the specified range.
		/// If the POP3 server supports the 
		/// extension, this method will likely be more efficient than using
		///  for each message
		/// because it will batch the commands to reduce latency.
		/// 
		/// The message or header streams.
		/// The index of the first stream to get.
		/// The number of streams to get.
		/// true if only the headers should be retrieved; otherwise, false.
		/// The cancellation token.
		/// The progress reporting mechanism.
		/// 
		///  and  do not specify
		/// a valid range of messages.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The POP3 server does not support the UIDL extension.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task> GetStreamsAsync (int startIndex, int count, bool headersOnly = false, CancellationToken cancellationToken = default (CancellationToken), ITransferProgress progress = null)
		{
			CheckDisposed ();
			CheckConnected ();
			CheckAuthenticated ();

			if (startIndex < 0 || startIndex >= total)
				throw new ArgumentOutOfRangeException (nameof (startIndex));

			if (count < 0 || count > (total - startIndex))
				throw new ArgumentOutOfRangeException (nameof (count));

			if (count == 0)
				return Task.FromResult ((IList) new Stream[0]);

			var seqids = new int[count];

			for (int i = 0; i < count; i++)
				seqids[i] = startIndex + i + 1;

			var ctx = new DownloadStreamContext (this, progress);

			return ctx.DownloadAsync (seqids, headersOnly, true, cancellationToken);
		}

		/// 
		/// Asynchronously mark the specified message for deletion.
		/// 
		/// 
		/// Messages marked for deletion are not actually deleted until the session
		/// is cleanly disconnected
		/// (see ).
		/// 
		/// 
		/// 
		/// 
		/// An asynchronous task context.
		/// The index of the message.
		/// The cancellation token.
		/// 
		///  is not a valid message index.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task DeleteMessageAsync (int index, CancellationToken cancellationToken = default (CancellationToken))
		{
			return DeleteMessageAsync (index, true, cancellationToken);
		}

		/// 
		/// Asynchronously mark the specified messages for deletion.
		/// 
		/// 
		/// Messages marked for deletion are not actually deleted until the session
		/// is cleanly disconnected
		/// (see ).
		/// 
		/// An asynchronous task context.
		/// The indexes of the messages.
		/// The cancellation token.
		/// 
		///  is null.
		/// 
		/// 
		/// One or more of the  are invalid.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task DeleteMessagesAsync (IList indexes, CancellationToken cancellationToken = default (CancellationToken))
		{
			return DeleteMessagesAsync (indexes, true, cancellationToken);
		}

		/// 
		/// Asynchronously mark the specified range of messages for deletion.
		/// 
		/// 
		/// Messages marked for deletion are not actually deleted until the session
		/// is cleanly disconnected
		/// (see ).
		/// 
		/// 
		/// 
		/// 
		/// An asynchronous task context.
		/// The index of the first message to mark for deletion.
		/// The number of messages to mark for deletion.
		/// The cancellation token.
		/// 
		///  and  do not specify
		/// a valid range of messages.
		/// 
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task DeleteMessagesAsync (int startIndex, int count, CancellationToken cancellationToken = default (CancellationToken))
		{
			return DeleteMessagesAsync (startIndex, count, true, cancellationToken);
		}

		/// 
		/// Asynchronously mark all messages for deletion.
		/// 
		/// 
		/// Messages marked for deletion are not actually deleted until the session
		/// is cleanly disconnected
		/// (see ).
		/// 
		/// An asynchronous task context.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override async Task DeleteAllMessagesAsync (CancellationToken cancellationToken = default (CancellationToken))
		{
			if (total > 0)
				await DeleteMessagesAsync (0, total, cancellationToken).ConfigureAwait (false);
		}

		/// 
		/// Asynchronously reset the state of all messages marked for deletion.
		/// 
		/// 
		/// Messages marked for deletion are not actually deleted until the session
		/// is cleanly disconnected
		/// (see ).
		/// 
		/// An awaitable task.
		/// The cancellation token.
		/// 
		/// The  has been disposed.
		/// 
		/// 
		/// The  is not connected.
		/// 
		/// 
		/// The  is not authenticated.
		/// 
		/// 
		/// The operation was canceled via the cancellation token.
		/// 
		/// 
		/// An I/O error occurred.
		/// 
		/// 
		/// The POP3 command failed.
		/// 
		/// 
		/// A POP3 protocol error occurred.
		/// 
		public override Task ResetAsync (CancellationToken cancellationToken = default (CancellationToken))
		{
			return ResetAsync (true, cancellationToken);
		}
	}
}