1 files changed, 107 insertions, 0 deletions
diff --git a/src/DotNetOpenAuth.Messaging/Messaging/Bindings/StandardExpirationBindingElement.cs b/src/DotNetOpenAuth.Messaging/Messaging/Bindings/StandardExpirationBindingElement.cs
new file mode 100644
index 0000000..4396c16
--- /dev/null
+++ b/src/DotNetOpenAuth.Messaging/Messaging/Bindings/StandardExpirationBindingElement.cs
@@ -0,0 +1,107 @@
+//-----------------------------------------------------------------------
+// <copyright file="StandardExpirationBindingElement.cs" company="Andrew Arnott">
+//     Copyright (c) Andrew Arnott. All rights reserved.
+// </copyright>
+//-----------------------------------------------------------------------
+
+namespace DotNetOpenAuth.Messaging.Bindings {
+	using System;
+	using DotNetOpenAuth.Configuration;
+
+	/// <summary>
+	/// A message expiration enforcing binding element that supports messages
+	/// implementing the <see cref="IExpiringProtocolMessage"/> interface.
+	/// </summary>
+	internal class StandardExpirationBindingElement : IChannelBindingElement {
+		/// <summary>
+		/// Initializes a new instance of the <see cref="StandardExpirationBindingElement"/> class.
+		/// </summary>
+		internal StandardExpirationBindingElement() {
+		}
+
+		#region IChannelBindingElement Properties
+
+		/// <summary>
+		/// Gets the protection offered by this binding element.
+		/// </summary>
+		/// <value><see cref="MessageProtections.Expiration"/></value>
+		MessageProtections IChannelBindingElement.Protection {
+			get { return MessageProtections.Expiration; }
+		}
+
+		/// <summary>
+		/// Gets or sets the channel that this binding element belongs to.
+		/// </summary>
+		public Channel Channel { get; set; }
+
+		#endregion
+
+		/// <summary>
+		/// Gets the maximum age a message implementing the 
+		/// <see cref="IExpiringProtocolMessage"/> interface can be before
+		/// being discarded as too old.
+		/// </summary>
+		protected internal static TimeSpan MaximumMessageAge {
+			get { return Configuration.DotNetOpenAuthSection.Configuration.Messaging.MaximumMessageLifetime; }
+		}
+
+		#region IChannelBindingElement Methods
+
+		/// <summary>
+		/// Sets the timestamp on an outgoing message.
+		/// </summary>
+		/// <param name="message">The outgoing message.</param>
+		/// <returns>
+		/// The protections (if any) that this binding element applied to the message.
+		/// Null if this binding element did not even apply to this binding element.
+		/// </returns>
+		public MessageProtections? ProcessOutgoingMessage(IProtocolMessage message) {
+			IExpiringProtocolMessage expiringMessage = message as IExpiringProtocolMessage;
+			if (expiringMessage != null) {
+				expiringMessage.UtcCreationDate = DateTime.UtcNow;
+				return MessageProtections.Expiration;
+			}
+
+			return null;
+		}
+
+		/// <summary>
+		/// Reads the timestamp on a message and throws an exception if the message is too old.
+		/// </summary>
+		/// <param name="message">The incoming message.</param>
+		/// <returns>
+		/// The protections (if any) that this binding element applied to the message.
+		/// Null if this binding element did not even apply to this binding element.
+		/// </returns>
+		/// <exception cref="ExpiredMessageException">Thrown if the given message has already expired.</exception>
+		/// <exception cref="ProtocolException">
+		/// Thrown when the binding element rules indicate that this message is invalid and should
+		/// NOT be processed.
+		/// </exception>
+		public MessageProtections? ProcessIncomingMessage(IProtocolMessage message) {
+			IExpiringProtocolMessage expiringMessage = message as IExpiringProtocolMessage;
+			if (expiringMessage != null) {
+				// Yes the UtcCreationDate is supposed to always be in UTC already,
+				// but just in case a given message failed to guarantee that, we do it here.
+				DateTime creationDate = expiringMessage.UtcCreationDate.ToUniversalTimeSafe();
+				DateTime expirationDate = creationDate + MaximumMessageAge;
+				if (expirationDate < DateTime.UtcNow) {
+					throw new ExpiredMessageException(expirationDate, expiringMessage);
+				}
+
+				// Mitigate HMAC attacks (just guessing the signature until they get it) by 
+				// disallowing post-dated messages.
+				ErrorUtilities.VerifyProtocol(
+					creationDate <= DateTime.UtcNow + DotNetOpenAuthSection.Configuration.Messaging.MaximumClockSkew,
+					MessagingStrings.MessageTimestampInFuture,
+					creationDate);
+
+				return MessageProtections.Expiration;
+			}
+
+			return null;
+		}
+
+		#endregion
+	}
+}