Added IAttachment and several missing properties.

src/Discord.Net/API/Common/EmbedThumbnail.cs

@@ -9,8 +9,8 @@ namespace Discord.API
         [JsonProperty("proxy_url")]
         public string ProxyUrl { get; set; }
         [JsonProperty("height")]
-        public int Height { get; set; }
+        public Optional<int> Height { get; set; }
         [JsonProperty("width")]
-        public int Width { get; set; }
+        public Optional<int> Width { get; set; }
     }
 }

src/Discord.Net/Entities/Messages/Attachment.cs

@@ -2,17 +2,25 @@
 
 namespace Discord
 {
-    public struct Attachment
+    internal class Attachment : IAttachment
     {
         public ulong Id { get; }
-        public int Size { get; }
         public string Filename { get; }
+        public string Url { get; }
+        public string ProxyUrl { get; }
+        public int Size { get; }
+        public int? Height { get; }
+        public int? Width { get; }
 
         public Attachment(Model model)
         {
             Id = model.Id;
-            Size = model.Size;
             Filename = model.Filename;
+            Size = model.Size;
+            Url = model.Url;
+            ProxyUrl = model.ProxyUrl;
+            Height = model.Height.IsSpecified ? model.Height.Value : (int?)null;
+            Width = model.Width.IsSpecified ? model.Width.Value : (int?)null;
         }
     }
 }

src/Discord.Net/Entities/Messages/EmbedThumbnail.cs

@@ -18,6 +18,12 @@ namespace Discord
         }
 
         internal EmbedThumbnail(Model model)
-            : this(model.Url, model.ProxyUrl, model.Height, model.Width) { }
+            : this(
+                  model.Url, 
+                  model.ProxyUrl,
+                  model.Height.IsSpecified ? model.Height.Value : (int?)null,
+                  model.Width.IsSpecified ? model.Width.Value : (int?)null)
+        {
+        }
     }
 }

src/Discord.Net/Entities/Messages/IAttachment.cs

@@ -0,0 +1,14 @@
+namespace Discord
+{
+    public interface IAttachment
+    {
+        ulong Id { get; }
+
+        string Filename { get; }
+        string Url { get; }
+        string ProxyUrl { get; }
+        int Size { get; }
+        int? Height { get; }
+        int? Width { get; }
+    }
+}

src/Discord.Net/Entities/Messages/IMessage.cs

@@ -25,7 +25,7 @@ namespace Discord
         /// <summary> Gets the author of this message. </summary>
         IUser Author { get; }
         /// <summary> Returns a collection of all attachments included in this message. </summary>
-        IReadOnlyCollection<Attachment> Attachments { get; }
+        IReadOnlyCollection<IAttachment> Attachments { get; }
         /// <summary> Returns a collection of all embeds included in this message. </summary>
         IReadOnlyCollection<IEmbed> Embeds { get; }
         /// <summary> Returns a collection of channel ids mentioned in this message. </summary>

src/Discord.Net/Entities/Messages/Message.cs

@@ -23,7 +23,7 @@ namespace Discord
         public IMessageChannel Channel { get; }
         public IUser Author { get; }
         
-        public IReadOnlyCollection<Attachment> Attachments { get; private set; }
+        public IReadOnlyCollection<IAttachment> Attachments { get; private set; }
         public IReadOnlyCollection<IEmbed> Embeds { get; private set; }
         public IReadOnlyCollection<ulong> MentionedChannelIds { get; private set; }
         public IReadOnlyCollection<IRole> MentionedRoles { get; private set; }