Inject full Emoji to Reaction if we have it.

Reaction objects with custom Emoji are partial. If we know of this Emoji
(can find it on this client) then inject it. Otherwise, leave it as a
hollow Emoji. We can still react with a hollow Emoji, but can't get other
metadata about it.

discord/state.py

@@ -219,7 +219,7 @@ class ConnectionState:
 
     def parse_message_create(self, data):
         channel = self.get_channel(data.get('channel_id'))
-        message = Message(channel=channel, **data)
+        message = self._create_message(channel=channel, **data)
         self.dispatch('message', message)
         self.messages.append(message)
 
@@ -255,17 +255,14 @@ class ConnectionState:
     def parse_message_reaction_add(self, data):
         message = self._get_message(data['message_id'])
         if message is not None:
-            if data['emoji']['id']:
-                reaction_emoji = Emoji(server=None, **data['emoji'])
-            else:
-                reaction_emoji = data['emoji']['name']
-            reaction = utils.get(
-                message.reactions, emoji=reaction_emoji)
+            emoji = self._get_reaction_emoji(**data.pop('emoji'))
+            reaction = utils.get(message.reactions, emoji=emoji)
 
             is_me = data['user_id'] == self.user.id
 
             if not reaction:
-                reaction = Reaction(message=message, me=is_me, **data)
+                reaction = Reaction(
+                    message=message, emoji=emoji, me=is_me, **data)
                 message.reactions.append(reaction)
             else:
                 reaction.count += 1
@@ -280,12 +277,8 @@ class ConnectionState:
     def parse_message_reaction_remove(self, data):
         message = self._get_message(data['message_id'])
         if message is not None:
-            if data['emoji']['id']:
-                reaction_emoji = Emoji(server=None, **data['emoji'])
-            else:
-                reaction_emoji = data['emoji']['name']
-            reaction = utils.get(
-                message.reactions, emoji=reaction_emoji)
+            emoji = self._get_reaction_emoji(**data['emoji'])
+            reaction = utils.get(message.reactions, emoji=emoji)
 
             # if reaction isn't in the list, we crash. This means discord
             # sent bad data, or we stored improperly
@@ -680,6 +673,30 @@ class ConnectionState:
         else:
             return channel.server.get_member(id)
 
+    def _create_message(self, **message):
+        """Helper mostly for injecting reactions."""
+        reactions = [
+            self._create_reaction(**r) for r in message.pop('reactions', [])
+        ]
+        return Message(channel=message.pop('channel'),
+                       reactions=reactions, **message)
+
+    def _create_reaction(self, **reaction):
+        emoji = self._get_reaction_emoji(**reaction.pop('emoji'))
+        return Reaction(emoji=emoji, **reaction)
+
+    def _get_reaction_emoji(self, **data):
+        id = data['id']
+
+        if id is None:
+            return data['name']
+
+        for server in self.servers:
+            for emoji in server.emojis:
+                if emoji.id == id:
+                    return emoji
+        return Emoji(server=None, **data)
+
     def get_channel(self, id):
         if id is None:
             return None