Room preview of room link: Try to get more information to display from the hs

Vector/AppDelegate.m

@@ -843,16 +843,17 @@
                 if (queryParams)
                 {
                     roomPreviewData = [[RoomPreviewData alloc] initWithRoomId:roomIdOrAlias emailInvitationParams:queryParams andSession:account.mxSession];
+                    [self showRoomPreview:roomPreviewData];
                 }
                 else
                 {
                     roomPreviewData = [[RoomPreviewData alloc] initWithRoomId:roomIdOrAlias andSession:account.mxSession];
 
-                    // TODO: Try to get more information about the room
+                    // Try to get more information about the room before opening its preview
-                    // We could attempt to do a room initialSync on it
+                    [roomPreviewData fetchPreviewData:^(BOOL successed) {
+                        [self showRoomPreview:roomPreviewData];
+                    }];
                 }
-
-                [self showRoomPreview:roomPreviewData];
             }
         }
         else

Vector/Model/Room/RoomPreviewData.h

@@ -44,7 +44,8 @@
 @property (nonatomic) MXSession *mxSession;
 
 /**
- TODO
+ Preview information.
+ They come from the `emailInvitationParams` or [self fetchPreviewData].
  */
 @property (nonatomic, readonly) NSString *roomName;
 @property (nonatomic, readonly) NSString *roomAvatarUrl;
@@ -60,4 +61,15 @@
 - (instancetype)initWithRoomId:(NSString*)roomId andSession:(MXSession*)mxSession;
 - (instancetype)initWithRoomId:(NSString*)roomId emailInvitationParams:(NSDictionary*)emailInvitationParams andSession:(MXSession*)mxSession;
 
+/**
+ Attempt to get more information from the homeserver about the room.
+
+ NOTE: This method is temporary while we do not support the full room preview
+       with preview of messages.
+ 
+ @param completion the block called when the request is complete. `successed` means
+        the homeserver provided some information.
+ */
+- (void)fetchPreviewData:(void (^)(BOOL successed))completion;
+
 @end

Vector/Model/Room/RoomPreviewData.m

@@ -43,4 +43,33 @@
     return self;
 }
 
+- (void)fetchPreviewData:(void (^)(BOOL))completion
+{
+    // Make an /initialSync request to get preview data
+    [_mxSession.matrixRestClient initialSyncOfRoom:_roomId withLimit:0 success:^(MXRoomInitialSync *roomInitialSync) {
+
+        MXRoomState *roomState = [[MXRoomState alloc] initWithRoomId:_roomId andMatrixSession:_mxSession andDirection:YES];
+
+        // Make roomState digest state events of the room
+        for (MXEvent *stateEvent in roomInitialSync.state)
+        {
+            // Skip members events as they are not not interesting here and can be numerous
+            if (stateEvent.eventType != MXEventTypeRoomMember)
+            {
+                [roomState handleStateEvent:stateEvent];
+            }
+        }
+
+        // Report retrieved data
+        _roomName = roomState.displayname;
+        _roomAvatarUrl = roomState.avatar;
+        _roomTopic = roomState.topic;
+
+        completion(YES);
+
+    } failure:^(NSError *error) {
+        completion(NO);
+    }];
+}
+
 @end