Added message cache import/export

src/Discord.Net/DiscordClient.Messages.cs

@@ -1,4 +1,5 @@
 using Discord.API;
+using Newtonsoft.Json;
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -27,8 +28,10 @@ namespace Discord
 				msg.Cache(); //Builds references
 				return msg;
             }
-        }
+		}
-	}
+		public void Import(Message[] messages)
+			=> Import(messages.ToDictionary(x => x.Id));
+    }
 
 	public class MessageEventArgs : EventArgs
 	{
@@ -214,7 +217,6 @@ namespace Discord
 			}
 		}
 
-
 		/// <summary> Downloads last count messages from the server, returning all messages before or after relativeMessageId, if it's provided. </summary>
 		public async Task<Message[]> DownloadMessages(Channel channel, int count, long? relativeMessageId = null, RelativeDirection relativeDir = RelativeDirection.Before, bool useCache = true)
 		{
@@ -255,6 +257,22 @@ namespace Discord
 			return new Message[0];
 		}
 		
+		/// <summary> Deserializes messages from JSON format and imports them into the message cache.</summary>
+		public void ImportMessages(string json)
+		{
+			if (json == null) throw new ArgumentNullException(nameof(json));
+
+			var msgs = JsonConvert.DeserializeObject<Message[]>(json);
+			_messages.Import(msgs);
+		}
+		/// <summary> Serializes the message cache for a given channel to JSON.</summary>
+		public string ExportMessages(Channel channel)
+		{
+			if (channel == null) throw new ArgumentNullException(nameof(channel));
+
+			return JsonConvert.SerializeObject(channel.Messages);
+		}
+
 		private Task MessageQueueLoop()
 		{
 			var cancelToken = _cancelToken;

src/Discord.Net/Helpers/AsyncCollection.cs

@@ -94,6 +94,15 @@ namespace Discord
 			}
 			return result;
 		}
+		protected void Import(IEnumerable<KeyValuePair<TKey, TValue>> items)
+		{
+			lock (_writerLock)
+			{
+				foreach (var pair in items)
+					_dictionary.TryAdd(pair.Key, pair.Value);
+			}
+		}
+
 		public TValue TryRemove(TKey key)
 		{
 			if (_dictionary.ContainsKey(key))
@@ -110,6 +119,15 @@ namespace Discord
 			}
 			return null;
 		}
+		public void Clear()
+		{
+			lock (_writerLock)
+			{
+				_dictionary.Clear();
+                RaiseCleared();
+			}
+        }
+
 		public TValue Remap(TKey oldKey, TKey newKey)
 		{
 			if (_dictionary.ContainsKey(oldKey))
@@ -124,14 +142,6 @@ namespace Discord
 			}
 			return null;
 		}
-		public void Clear()
-		{
-			lock (_writerLock)
-			{
-				_dictionary.Clear();
-                RaiseCleared();
-			}
-        }
 
 		public IEnumerator<TValue> GetEnumerator() => _dictionary.Select(x => x.Value).GetEnumerator();
 		IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();