public void TestBase64Encode ()
		{
			using (var original = new MemoryStream ()) {
				using (var file = File.OpenRead ("../../TestData/encoders/photo.b64"))
					file.CopyTo (original, 4096);

				using (var encoded = new MemoryStream ()) {
					using (var filtered = new FilteredStream (encoded)) {
						filtered.Add (EncoderFilter.Create (ContentEncoding.Base64));

						using (var file = File.OpenRead ("../../TestData/encoders/photo.jpg"))
							file.CopyTo (filtered, 4096);

						filtered.Flush ();
					}

					var buf0 = original.GetBuffer ();
					var buf1 = encoded.GetBuffer ();
					int n = (int) original.Length;

					Assert.AreEqual (original.Length, encoded.Length, "Encoded length is incorrect.");

					for (int i = 0; i < n; i++)
						Assert.AreEqual (buf0[i], buf1[i], "The byte at offset {0} does not match.", i);
				}
			}
		}

		public ImapReplayCommand (string command, string resource)
		{
			Command = command;

			using (var stream = GetType ().Assembly.GetManifestResourceStream ("UnitTests.Net.Imap.Resources." + resource)) {
				var memory = new MemoryBlockStream ();

				using (var filtered = new FilteredStream (memory)) {
					filtered.Add (new Unix2DosFilter ());
					stream.CopyTo (filtered, 4096);
				}

				Response = memory.ToArray ();
			}
		}

		public void TestDecodeSimpleYEncMessage ()
		{
			using (var file = File.OpenRead ("../../TestData/yenc/simple.msg")) {
				var message = MimeMessage.Load (file);

				using (var decoded = new MemoryStream ()) {
					var ydec = new YDecoder ();

					using (var filtered = new FilteredStream (decoded)) {
						filtered.Add (new DecoderFilter (ydec));

						((MimePart) message.Body).ContentObject.WriteTo (filtered);
					}

					Assert.AreEqual (584, decoded.Length, "The decoded size does not match.");
					Assert.AreEqual (0xded29f4f, ydec.Checksum ^ 0xffffffff, "The checksum does not match.");
				}
			}
		}

		public void TestBase64Decode ()
		{
			using (var original = new MemoryStream ()) {
				using (var file = File.OpenRead ("../../TestData/encoders/photo.jpg"))
					file.CopyTo (original, 4096);

				using (var decoded = new MemoryStream ()) {
					using (var file = File.OpenRead ("../../TestData/encoders/photo.b64")) {
						using (var filtered = new FilteredStream (file)) {
							filtered.Add (DecoderFilter.Create (ContentEncoding.Base64));
							filtered.CopyTo (decoded, 4096);
						}
					}

					var buf0 = original.GetBuffer ();
					var buf1 = decoded.GetBuffer ();
					int n = (int) original.Length;

					Assert.AreEqual (original.Length, decoded.Length, "Decoded length is incorrect.");

					for (int i = 0; i < n; i++)
						Assert.AreEqual (buf0[i], buf1[i], "The byte at offset {0} does not match.", i);
				}
			}

			var decoder = new Base64Decoder ();
			var output = new byte[4096];

			Assert.AreEqual (ContentEncoding.Base64, decoder.Encoding);

			for (int i = 0; i < base64EncodedPatterns.Length; i++) {
				decoder.Reset ();
				var buf = Encoding.ASCII.GetBytes (base64EncodedPatterns[i]);
				int n = decoder.Decode (buf, 0, buf.Length, output);
				var actual = Encoding.ASCII.GetString (output, 0, n);
				Assert.AreEqual (base64DecodedPatterns[i], actual, "Failed to decode base64EncodedPatterns[{0}]", i);
			}

			for (int i = 0; i < base64EncodedLongPatterns.Length; i++) {
				decoder.Reset ();
				var buf = Encoding.ASCII.GetBytes (base64EncodedLongPatterns[i]);
				int n = decoder.Decode (buf, 0, buf.Length, output);

				for (int j = 0; j < n; j++)
					Assert.AreEqual (output[j], (byte) (j + i), "Failed to decode base64EncodedLongPatterns[{0}]", i);
			}
		}

        void Data(MimeMessage message, CancellationToken cancellationToken)
        {
            var response = SendCommand ("DATA", cancellationToken);

            if (response.StatusCode != SmtpStatusCode.StartMailInput)
                throw new SmtpCommandException (SmtpErrorCode.UnexpectedStatusCode, response.StatusCode, response.Response);

            var options = FormatOptions.Default.Clone ();
            options.NewLineFormat = NewLineFormat.Dos;

            options.HiddenHeaders.Add (HeaderId.ContentLength);
            options.HiddenHeaders.Add (HeaderId.ResentBcc);
            options.HiddenHeaders.Add (HeaderId.Bcc);

            using (var filtered = new FilteredStream (stream)) {
                filtered.Add (new SmtpDataFilter ());
                message.WriteTo (options, filtered, cancellationToken);
                filtered.Flush ();
            }

            stream.Write (EndData, 0, EndData.Length);

            response = ReadResponse (cancellationToken);

            switch (response.StatusCode) {
            default:
                throw new SmtpCommandException (SmtpErrorCode.MessageNotAccepted, response.StatusCode, response.Response);
            case SmtpStatusCode.AuthenticationRequired:
                throw new UnauthorizedAccessException (response.Response);
            case SmtpStatusCode.Ok:
                break;
            }
        }

		/// <summary>
		/// Verify the specified DKIM-Signature header.
		/// </summary>
		/// <remarks>
		/// Verifies the specified DKIM-Signature header.
		/// </remarks>
		/// <param name="options">The formatting options.</param>
		/// <param name="dkimSignature">The DKIM-Signature header.</param>
		/// <param name="publicKeyLocator">The public key locator service.</param>
		/// <param name="cancellationToken">The cancellation token.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <para><paramref name="options"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="dkimSignature"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="publicKeyLocator"/> is <c>null</c>.</para>
		/// </exception>
		/// <exception cref="System.ArgumentException">
		/// <paramref name="dkimSignature"/> is not a DKIM-Signature header.
		/// </exception>
		/// <exception cref="System.FormatException">
		/// The DKIM-Signature header value is malformed.
		/// </exception>
		/// <exception cref="System.OperationCanceledException">
		/// The operation was canceled via the cancellation token.
		/// </exception>
		bool Verify (FormatOptions options, Header dkimSignature, IDkimPublicKeyLocator publicKeyLocator, CancellationToken cancellationToken = default (CancellationToken))
		{
			if (options == null)
				throw new ArgumentNullException ("options");

			if (dkimSignature == null)
				throw new ArgumentNullException ("dkimSignature");

			if (dkimSignature.Id != HeaderId.DkimSignature)
				throw new ArgumentException ("The dkimSignature parameter MUST be a DKIM-Signature header.", "dkimSignature");

			if (publicKeyLocator == null)
				throw new ArgumentNullException ("publicKeyLocator");

			var parameters = ParseDkimSignature (dkimSignature.Value);
			DkimCanonicalizationAlgorithm headerAlgorithm, bodyAlgorithm;
			DkimSignatureAlgorithm signatureAlgorithm;
			AsymmetricKeyParameter key;
			string d, s, q, h, bh, b;
			int maxLength;

			ValidateDkimSignatureParameters (parameters, out signatureAlgorithm, out headerAlgorithm, out bodyAlgorithm,
				out d, out s, out q, out h, out bh, out b, out maxLength);

			key = publicKeyLocator.LocatePublicKey (q, d, s, cancellationToken);

			options = options.Clone ();
			options.NewLineFormat = NewLineFormat.Dos;

			// first check the body hash (if that's invalid, then the entire signature is invalid)
			var hash = Convert.ToBase64String (DkimHashBody (options, signatureAlgorithm, bodyAlgorithm, maxLength));

			if (hash != bh)
				return false;

			using (var stream = new DkimSignatureStream (DkimGetDigestSigner (signatureAlgorithm, key))) {
				using (var filtered = new FilteredStream (stream)) {
					filtered.Add (options.CreateNewLineFilter ());

					DkimWriteHeaders (options, h.Split (':'), headerAlgorithm, filtered);

					// now include the DKIM-Signature header that we are verifying,
					// but only after removing the "b=" signature value.
					var header = GetSignedDkimSignatureHeader (dkimSignature);

					switch (headerAlgorithm) {
					case DkimCanonicalizationAlgorithm.Relaxed:
						DkimWriteHeaderRelaxed (options, filtered, header);
						break;
					default:
						DkimWriteHeaderSimple (options, filtered, header);
						break;
					}

					filtered.Flush ();
				}

				return stream.VerifySignature (b);
			}
		}

		byte[] DkimHashBody (FormatOptions options, DkimSignatureAlgorithm signatureAlgorithm, DkimCanonicalizationAlgorithm bodyCanonicalizationAlgorithm, int maxLength)
		{
			using (var stream = new DkimHashStream (signatureAlgorithm, maxLength)) {
				using (var filtered = new FilteredStream (stream)) {
					filtered.Add (options.CreateNewLineFilter ());

					if (bodyCanonicalizationAlgorithm == DkimCanonicalizationAlgorithm.Relaxed)
						filtered.Add (new DkimRelaxedBodyFilter ());
					else
						filtered.Add (new DkimSimpleBodyFilter ());

					if (Body != null) {
						try {
							Body.Headers.Suppress = true;
							Body.WriteTo (options, stream, CancellationToken.None);
						} finally {
							Body.Headers.Suppress = false;
						}
					}

					filtered.Flush ();
				}

				return stream.GenerateHash ();
			}
		}

		/// <summary>
		/// Creates a new <see cref="MultipartSigned"/>.
		/// </summary>
		/// <remarks>
		/// Cryptographically signs the entity using the supplied signer in order
		/// to generate a detached signature and then adds the entity along with
		/// the detached signature data to a new multipart/signed part.
		/// </remarks>
		/// <returns>A new <see cref="MultipartSigned"/> instance.</returns>
		/// <param name="ctx">The S/MIME context to use for signing.</param>
		/// <param name="signer">The signer.</param>
		/// <param name="entity">The entity to sign.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <para><paramref name="ctx"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="signer"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="entity"/> is <c>null</c>.</para>
		/// </exception>
		/// <exception cref="Org.BouncyCastle.Cms.CmsException">
		/// An error occurred in the cryptographic message syntax subsystem.
		/// </exception>
		public static MultipartSigned Create (SecureMimeContext ctx, CmsSigner signer, MimeEntity entity)
		{
			if (ctx == null)
				throw new ArgumentNullException ("ctx");

			if (signer == null)
				throw new ArgumentNullException ("signer");

			if (entity == null)
				throw new ArgumentNullException ("entity");

			PrepareEntityForSigning (entity);

			using (var memory = new MemoryBlockStream ()) {
				using (var filtered = new FilteredStream (memory)) {
					// Note: see rfc3156, section 3 - second note
					filtered.Add (new ArmoredFromFilter ());

					// Note: see rfc3156, section 5.4 (this is the main difference between rfc2015 and rfc3156)
					filtered.Add (new TrailingWhitespaceFilter ());

					// Note: see rfc2015 or rfc3156, section 5.1
					filtered.Add (new Unix2DosFilter ());

					entity.WriteTo (filtered);
					filtered.Flush ();
				}

				memory.Position = 0;

				// Note: we need to parse the modified entity structure to preserve any modifications
				var parser = new MimeParser (memory, MimeFormat.Entity);
				var parsed = parser.ParseEntity ();
				memory.Position = 0;

				// sign the cleartext content
				var micalg = ctx.GetDigestAlgorithmName (signer.DigestAlgorithm);
				var signature = ctx.Sign (signer, memory);
				var signed = new MultipartSigned ();

				// set the protocol and micalg Content-Type parameters
				signed.ContentType.Parameters["protocol"] = ctx.SignatureProtocol;
				signed.ContentType.Parameters["micalg"] = micalg;

				// add the modified/parsed entity as our first part
				signed.Add (parsed);

				// add the detached signature as the second part
				signed.Add (signature);

				return signed;
			}
		}

		/// <summary>
		/// Writes the <see cref="MimeKit.MimePart"/> to the specified output stream.
		/// </summary>
		/// <remarks>
		/// Writes the MIME part to the output stream.
		/// </remarks>
		/// <param name="options">The formatting options.</param>
		/// <param name="stream">The output stream.</param>
		/// <param name="cancellationToken">A cancellation token.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <para><paramref name="options"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="stream"/> is <c>null</c>.</para>
		/// </exception>
		/// <exception cref="System.OperationCanceledException">
		/// The operation was canceled via the cancellation token.
		/// </exception>
		/// <exception cref="System.IO.IOException">
		/// An I/O error occurred.
		/// </exception>
		public override void WriteTo (FormatOptions options, Stream stream, CancellationToken cancellationToken = default (CancellationToken))
		{
			base.WriteTo (options, stream, cancellationToken);

			if (ContentObject == null)
				return;

			var cancellable = stream as ICancellableStream;

			if (ContentObject.Encoding != encoding) {
				if (encoding == ContentEncoding.UUEncode) {
					var begin = string.Format ("begin 0644 {0}", FileName ?? "unknown");
					var buffer = Encoding.UTF8.GetBytes (begin);

					if (cancellable != null) {
						cancellable.Write (buffer, 0, buffer.Length, cancellationToken);
						cancellable.Write (options.NewLineBytes, 0, options.NewLineBytes.Length, cancellationToken);
					} else {
						cancellationToken.ThrowIfCancellationRequested ();
						stream.Write (buffer, 0, buffer.Length);
						stream.Write (options.NewLineBytes, 0, options.NewLineBytes.Length);
					}
				}

				// transcode the content into the desired Content-Transfer-Encoding
				using (var filtered = new FilteredStream (stream)) {
					filtered.Add (EncoderFilter.Create (encoding));

					if (encoding != ContentEncoding.Binary)
						filtered.Add (options.CreateNewLineFilter (true));

					ContentObject.DecodeTo (filtered, cancellationToken);
					filtered.Flush (cancellationToken);
				}

				if (encoding == ContentEncoding.UUEncode) {
					var buffer = Encoding.ASCII.GetBytes ("end");

					if (cancellable != null) {
						cancellable.Write (buffer, 0, buffer.Length, cancellationToken);
						cancellable.Write (options.NewLineBytes, 0, options.NewLineBytes.Length, cancellationToken);
					} else {
						cancellationToken.ThrowIfCancellationRequested ();
						stream.Write (buffer, 0, buffer.Length);
						stream.Write (options.NewLineBytes, 0, options.NewLineBytes.Length);
					}
				}
			} else if (encoding != ContentEncoding.Binary) {
				using (var filtered = new FilteredStream (stream)) {
					// Note: if we are writing the top-level MimePart, make sure it ends with a new-line so that
					// MimeMessage.WriteTo() *always* ends with a new-line.
					filtered.Add (options.CreateNewLineFilter (Headers.Suppress));
					ContentObject.WriteTo (filtered, cancellationToken);
					filtered.Flush (cancellationToken);
				}
			} else {
				ContentObject.WriteTo (stream, cancellationToken);
			}
		}

		/// <summary>
		/// Gets the decoded text content using the provided charset to override
		/// the charset specified in the Content-Type parameters.
		/// </summary>
		/// <remarks>
		/// Uses the provided charset encoding to convert the raw text content
		/// into a unicode string, overriding any charset specified in the
		/// Content-Type header.
		/// </remarks>
		/// <returns>The decoded text.</returns>
		/// <param name="charset">The charset encoding to use.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <paramref name="charset"/> is <c>null</c>.
		/// </exception>
		public string GetText (Encoding charset)
		{
			if (charset == null)
				throw new ArgumentNullException ("charset");

			using (var memory = new MemoryStream ()) {
				using (var filtered = new FilteredStream (memory)) {
					filtered.Add (new CharsetFilter (charset, Encoding.UTF8));

					ContentObject.DecodeTo (filtered);
					filtered.Flush ();

#if PORTABLE
					var buffer = memory.ToArray ();
					int length = buffer.Length;
#else
					var buffer = memory.GetBuffer ();
					int length = (int) memory.Length;
#endif

					return Encoding.UTF8.GetString (buffer, 0, length);
				}
			}
		}

		Stream GetResponseStream (ImapReplayCommand command)
		{
			MemoryStream memory;

			if (testUnixFormat) {
				memory = new MemoryStream ();

				using (var filtered = new FilteredStream (memory)) {
					filtered.Add (new Dos2UnixFilter ());
					filtered.Write (command.Response, 0, command.Response.Length);
					filtered.Flush ();
				}

				memory.Position = 0;
			} else {
				memory = new MemoryStream (command.Response, false);
			}

			return memory;
		}

		/// <summary>
		/// Create a multipart/encrypted MIME part by encrypting the specified entity.
		/// </summary>
		/// <remarks>
		/// Encrypts the entity to the specified recipients, encapsulating the result in a
		/// new multipart/encrypted part.
		/// </remarks>
		/// <returns>A new <see cref="MultipartEncrypted"/> instance containing
		/// the encrypted version of the specified entity.</returns>
		/// <param name="ctx">The OpenPGP cryptography context to use for encrypting.</param>
		/// <param name="algorithm">The encryption algorithm.</param>
		/// <param name="recipients">The recipients for the encrypted entity.</param>
		/// <param name="entity">The entity to sign and encrypt.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <para><paramref name="ctx"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="recipients"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="entity"/> is <c>null</c>.</para>
		/// </exception>
		/// <exception cref="System.ArgumentException">
		/// One or more of the recipient keys cannot be used for encrypting.
		/// </exception>
		/// <exception cref="System.NotSupportedException">
		/// THe specified encryption algorithm is not supported.
		/// </exception>
		public static MultipartEncrypted Encrypt (OpenPgpContext ctx, EncryptionAlgorithm algorithm, IEnumerable<MailboxAddress> recipients, MimeEntity entity)
		{
			if (ctx == null)
				throw new ArgumentNullException (nameof (ctx));

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

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

			using (var memory = new MemoryBlockStream ()) {
				using (var filtered = new FilteredStream (memory)) {
					filtered.Add (new Unix2DosFilter ());

					entity.WriteTo (filtered);
					filtered.Flush ();
				}

				memory.Position = 0;

				var encrypted = new MultipartEncrypted ();
				encrypted.ContentType.Parameters["protocol"] = ctx.EncryptionProtocol;

				// add the protocol version part
				encrypted.Add (new ApplicationPgpEncrypted ());

				// add the encrypted entity as the second part
				encrypted.Add (ctx.Encrypt (algorithm, recipients, memory));

				return encrypted;
			}
		}

        /// <summary>
        /// Gets the decoded text content using the provided charset to override
        /// the charset specified in the Content-Type parameters.
        /// </summary>
        /// <returns>The decoded text.</returns>
        /// <param name="charset">The charset encoding to use.</param>
        /// <exception cref="System.ArgumentNullException">
        /// <paramref name="charset"/> is <c>null</c>.
        /// </exception>
        public string GetText(Encoding charset)
        {
            if (charset == null)
                throw new ArgumentNullException ("charset");

            using (var memory = new MemoryStream ()) {
                using (var filtered = new FilteredStream (memory)) {
                    filtered.Add (new CharsetFilter (charset, Encoding.UTF8));

                    ContentObject.DecodeTo (filtered);
                    filtered.Flush ();

                    return Encoding.UTF8.GetString (memory.GetBuffer (), 0, (int) memory.Length);
                }
            }
        }

		/// <summary>
		/// Writes the message to the specified output stream.
		/// </summary>
		/// <remarks>
		/// Writes the message to the output stream using the provided formatting options.
		/// </remarks>
		/// <param name="options">The formatting options.</param>
		/// <param name="stream">The output stream.</param>
		/// <param name="cancellationToken">A cancellation token.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <para><paramref name="options"/> is <c>null</c>.</para>
		/// <para>-or-</para>
		/// <para><paramref name="stream"/> is <c>null</c>.</para>
		/// </exception>
		/// <exception cref="System.OperationCanceledException">
		/// The operation was canceled via the cancellation token.
		/// </exception>
		/// <exception cref="System.IO.IOException">
		/// An I/O error occurred.
		/// </exception>
		public void WriteTo (FormatOptions options, Stream stream, CancellationToken cancellationToken = default (CancellationToken))
		{
			if (options == null)
				throw new ArgumentNullException ("options");

			if (stream == null)
				throw new ArgumentNullException ("stream");

			if (version == null && Body != null && Body.Headers.Count > 0)
				MimeVersion = new Version (1, 0);

			if (Body == null) {
				Headers.WriteTo (options, stream, cancellationToken);

				cancellationToken.ThrowIfCancellationRequested ();
				stream.Write (options.NewLineBytes, 0, options.NewLineBytes.Length);
			} else {
				cancellationToken.ThrowIfCancellationRequested ();

				using (var filtered = new FilteredStream (stream)) {
					filtered.Add (options.CreateNewLineFilter ());

					foreach (var header in MergeHeaders ()) {
						if (options.HiddenHeaders.Contains (header.Id))
							continue;

						cancellationToken.ThrowIfCancellationRequested ();

						var name = Encoding.ASCII.GetBytes (header.Field);

						filtered.Write (name, 0, name.Length);
						filtered.WriteByte ((byte) ':');
						filtered.Write (header.RawValue, 0, header.RawValue.Length);
					}

					filtered.Flush ();
				}

				options.WriteHeaders = false;
				Body.WriteTo (options, stream, cancellationToken);
			}
		}

		static void ExtractAttachments (TnefReader reader, BodyBuilder builder)
		{
			var attachMethod = TnefAttachMethod.ByValue;
			var filter = new BestEncodingFilter ();
			var prop = reader.TnefPropertyReader;
			MimePart attachment = null;
			int outIndex, outLength;
			TnefAttachFlags flags;
			string[] mimeType;
			byte[] attachData;
			string text;

			do {
				if (reader.AttributeLevel != TnefAttributeLevel.Attachment)
					break;

				switch (reader.AttributeTag) {
				case TnefAttributeTag.AttachRenderData:
					attachMethod = TnefAttachMethod.ByValue;
					attachment = new MimePart ();
					break;
				case TnefAttributeTag.Attachment:
					if (attachment == null)
						break;

					while (prop.ReadNextProperty ()) {
						switch (prop.PropertyTag.Id) {
						case TnefPropertyId.AttachLongFilename:
							attachment.FileName = prop.ReadValueAsString ();
							break;
						case TnefPropertyId.AttachFilename:
							if (attachment.FileName == null)
								attachment.FileName = prop.ReadValueAsString ();
							break;
						case TnefPropertyId.AttachContentLocation:
							text = prop.ReadValueAsString ();
							if (Uri.IsWellFormedUriString (text, UriKind.Absolute))
								attachment.ContentLocation = new Uri (text, UriKind.Absolute);
							else if (Uri.IsWellFormedUriString (text, UriKind.Relative))
								attachment.ContentLocation = new Uri (text, UriKind.Relative);
							break;
						case TnefPropertyId.AttachContentBase:
							text = prop.ReadValueAsString ();
							attachment.ContentBase = new Uri (text, UriKind.Absolute);
							break;
						case TnefPropertyId.AttachContentId:
							attachment.ContentId = prop.ReadValueAsString ();
							break;
						case TnefPropertyId.AttachDisposition:
							text = prop.ReadValueAsString ();
							if (attachment.ContentDisposition == null)
								attachment.ContentDisposition = new ContentDisposition (text);
							else
								attachment.ContentDisposition.Disposition = text;
							break;
						case TnefPropertyId.AttachData:
							var stream = prop.GetRawValueReadStream ();
							var content = new MemoryStream ();
							var guid = new byte[16];

							if (attachMethod == TnefAttachMethod.EmbeddedMessage) {
								var tnef = new TnefPart ();

								foreach (var param in attachment.ContentType.Parameters)
									tnef.ContentType.Parameters[param.Name] = param.Value;

								if (attachment.ContentDisposition != null)
									tnef.ContentDisposition = attachment.ContentDisposition;

								attachment = tnef;
							}

							// read the GUID
							stream.Read (guid, 0, 16);

							// the rest is content
							using (var filtered = new FilteredStream (content)) {
								filtered.Add (filter);
								stream.CopyTo (filtered, 4096);
								filtered.Flush ();
							}

							content.Position = 0;

							attachment.ContentTransferEncoding = filter.GetBestEncoding (EncodingConstraint.SevenBit);
							attachment.ContentObject = new ContentObject (content);
							filter.Reset ();

							builder.Attachments.Add (attachment);
							break;
						case TnefPropertyId.AttachMethod:
							attachMethod = (TnefAttachMethod) prop.ReadValueAsInt32 ();
							break;
						case TnefPropertyId.AttachMimeTag:
							mimeType = prop.ReadValueAsString ().Split ('/');
							if (mimeType.Length == 2) {
								attachment.ContentType.MediaType = mimeType[0].Trim ();
								attachment.ContentType.MediaSubtype = mimeType[1].Trim ();
							}
							break;
//.........这里部分代码省略.........

		/// <summary>
		/// Calculates the most efficient content encoding given the specified constraint.
		/// </summary>
		/// <remarks>
		/// If no <see cref="ContentObject"/> is set, <see cref="ContentEncoding.SevenBit"/> will be returned.
		/// </remarks>
		/// <returns>The most efficient content encoding.</returns>
		/// <param name="constraint">The encoding constraint.</param>
		/// <param name="maxLineLength">The maximum allowable length for a line (not counting the CRLF). Must be between <c>72</c> and <c>998</c> (inclusive).</param>
		/// <param name="cancellationToken">A cancellation token.</param>
		/// <exception cref="System.ArgumentOutOfRangeException">
		/// <para><paramref name="maxLineLength"/> is not between <c>72</c> and <c>998</c> (inclusive).</para>
		/// <para>-or-</para>
		/// <para><paramref name="constraint"/> is not a valid value.</para>
		/// </exception>
		/// <exception cref="System.OperationCanceledException">
		/// The operation was canceled via the cancellation token.
		/// </exception>
		/// <exception cref="System.IO.IOException">
		/// An I/O error occurred.
		/// </exception>
		public ContentEncoding GetBestEncoding (EncodingConstraint constraint, int maxLineLength, CancellationToken cancellationToken = default (CancellationToken))
		{
			if (ContentObject == null)
				return ContentEncoding.SevenBit;

			using (var measure = new MeasuringStream ()) {
				using (var filtered = new FilteredStream (measure)) {
					var filter = new BestEncodingFilter ();

					filtered.Add (filter);
					ContentObject.DecodeTo (filtered, cancellationToken);
					filtered.Flush ();

					return filter.GetBestEncoding (constraint, maxLineLength);
				}
			}
		}

		/// <summary>
		/// Computes the MD5 checksum of the content.
		/// </summary>
		/// <remarks>
		/// Computes the MD5 checksum of the MIME content in its canonical
		/// format and then base64-encodes the result.
		/// </remarks>
		/// <returns>The md5sum of the content.</returns>
		/// <exception cref="System.InvalidOperationException">
		/// The <see cref="ContentObject"/> is <c>null</c>.
		/// </exception>
		public string ComputeContentMd5 ()
		{
			if (ContentObject == null)
				throw new InvalidOperationException ("Cannot compute Md5 checksum without a ContentObject.");

			using (var stream = ContentObject.Open ()) {
				byte[] checksum;

				using (var filtered = new FilteredStream (stream)) {
					if (ContentType.Matches ("text", "*"))
						filtered.Add (new Unix2DosFilter ());

					using (var md5 = MD5.Create ())
						checksum = md5.ComputeHash (filtered);
				}

				var base64 = new Base64Encoder (true);
				var digest = new byte[base64.EstimateOutputLength (checksum.Length)];
				int n = base64.Flush (checksum, 0, checksum.Length, digest);

				return Encoding.ASCII.GetString (digest, 0, n);
			}
		}

		/// <summary>
		/// Opens the decoded content stream.
		/// </summary>
		/// <remarks>
		/// Provides a means of reading the decoded content without having to first write it to another
		/// stream using <see cref="DecodeTo(System.IO.Stream,System.Threading.CancellationToken)"/>.
		/// </remarks>
		/// <returns>The decoded content stream.</returns>
		public Stream Open ()
		{
			content.Seek (0, SeekOrigin.Begin);

			var filtered = new FilteredStream (content);
			filtered.Add (DecoderFilter.Create (Encoding));

			return filtered;
		}

        /// <summary>
        /// Decodes the content stream into another stream.
        /// </summary>
        /// <remarks>
        /// Uses the <see cref="Encoding"/> to decode the content stream to the output stream.
        /// </remarks>
        /// <param name="stream">The output stream.</param>
        /// <param name="cancellationToken">A cancellation token.</param>
        /// <exception cref="System.ArgumentNullException">
        /// <paramref name="stream"/> is <c>null</c>.
        /// </exception>
        /// <exception cref="System.OperationCanceledException">
        /// The operation was canceled via the cancellation token.
        /// </exception>
        /// <exception cref="System.IO.IOException">
        /// An I/O error occurred.
        /// </exception>
        public void DecodeTo(Stream stream, CancellationToken cancellationToken)
        {
            if (stream == null)
                throw new ArgumentNullException ("stream");

            using (var filtered = new FilteredStream (stream)) {
                filtered.Add (DecoderFilter.Create (Encoding));
                WriteTo (filtered, cancellationToken);
                filtered.Flush ();
            }
        }

        static void ExtractMapiProperties(TnefReader reader, MimeMessage message, BodyBuilder builder)
        {
            var prop = reader.TnefPropertyReader;

            while (prop.ReadNextProperty ()) {
                switch (prop.PropertyTag.Id) {
                case TnefPropertyId.InternetMessageId:
                    if (prop.PropertyTag.ValueTnefType == TnefPropertyType.String8 ||
                        prop.PropertyTag.ValueTnefType == TnefPropertyType.Unicode) {
                        message.MessageId = prop.ReadValueAsString ();
                        Console.WriteLine ("Message Property: {0} = {1}", prop.PropertyTag.Id, message.MessageId);
                    } else {
                        Assert.Fail ("Unknown property type for Message-Id: {0}", prop.PropertyTag.ValueTnefType);
                    }
                    break;
                case TnefPropertyId.Subject:
                    if (prop.PropertyTag.ValueTnefType == TnefPropertyType.String8 ||
                        prop.PropertyTag.ValueTnefType == TnefPropertyType.Unicode) {
                        message.Subject = prop.ReadValueAsString ();
                        Console.WriteLine ("Message Property: {0} = {1}", prop.PropertyTag.Id, message.Subject);
                    } else {
                        Assert.Fail ("Unknown property type for Subject: {0}", prop.PropertyTag.ValueTnefType);
                    }
                    break;
                case TnefPropertyId.RtfCompressed:
                    if (prop.PropertyTag.ValueTnefType == TnefPropertyType.String8 ||
                        prop.PropertyTag.ValueTnefType == TnefPropertyType.Unicode ||
                        prop.PropertyTag.ValueTnefType == TnefPropertyType.Binary) {
                        var rtf = new TextPart ("rtf");
                        rtf.ContentType.Name = "body.rtf";

                        var converter = new RtfCompressedToRtf ();
                        var content = new MemoryStream ();

                        using (var filtered = new FilteredStream (content)) {
                            filtered.Add (converter);

                            using (var compressed = prop.GetRawValueReadStream ()) {
                                compressed.CopyTo (filtered, 4096);
                                filtered.Flush ();
                            }
                        }

                        rtf.ContentObject = new ContentObject (content);
                        content.Position = 0;

                        builder.Attachments.Add (rtf);

                        Console.WriteLine ("Message Property: {0} = <compressed rtf data>", prop.PropertyTag.Id);
                    } else {
                        Assert.Fail ("Unknown property type for {0}: {1}", prop.PropertyTag.Id, prop.PropertyTag.ValueTnefType);
                    }
                    break;
                case TnefPropertyId.BodyHtml:
                    if (prop.PropertyTag.ValueTnefType == TnefPropertyType.String8 ||
                        prop.PropertyTag.ValueTnefType == TnefPropertyType.Unicode ||
                        prop.PropertyTag.ValueTnefType == TnefPropertyType.Binary) {
                        var html = new TextPart ("html");
                        html.ContentType.Name = "body.html";
                        html.Text = prop.ReadValueAsString ();

                        builder.Attachments.Add (html);

                        Console.WriteLine ("Message Property: {0} = {1}", prop.PropertyTag.Id, html.Text);
                    } else {
                        Asse