SubscriptionClient carried over.

code/MessengerApi.SubscriptionClient/Model/Subscription.cs

@@ -0,0 +1,52 @@
+using MessengerApi.Model.Messages;
+
+namespace MessengerApi.Model
+{
+    /// <summary>
+    /// See <see cref="SubscriptionClient"/> if you need to subscribe. It will give you one of these upon subscribing. 
+    /// Also see <see cref="OnMessage"/> for what happens where you actually receive message for this sub.
+    /// </summary>
+    public class Subscription : IDisposable
+    {
+        public string MessageTypeMask { get; private set; }
+
+        public event EventHandler<InboxMessage> OnMessage;
+
+        internal SubscriptionClient client;
+
+        private bool isDisposed;
+
+        internal Subscription(string messageTypeMask, SubscriptionClient client)
+        {
+            MessageTypeMask = messageTypeMask;
+            this.client = client;
+        }
+
+        internal void Message(InboxMessage message)
+        {
+            OnMessage?.Invoke(this, message);
+        }
+
+        public void Dispose()
+        {
+            if (isDisposed)
+            {
+                return;
+            }
+
+            AssertNotDisposedOrThrow();
+            client.Unsubscribe(this);
+            Dispose();
+
+            isDisposed = true;
+        }
+
+        private void AssertNotDisposedOrThrow()
+        {
+            if (isDisposed)
+            {
+                throw new ObjectDisposedException(MessageTypeMask);
+            }
+        }
+    }
+}