add group parser

SignalServiceKit/src/Loki/Messaging/GroupParser.swift

@@ -0,0 +1,34 @@
+
+@objc public final class GroupParser : NSObject {
+    private let data: Data
+    
+    @objc public init(data: Data) {
+        self.data = data
+    }
+    
+    @objc public func parseGroupModels() -> [TSGroupModel] {
+        var index = 0
+        var result: [TSGroupModel] = []
+        while index < data.endIndex {
+            var uncheckedSize: UInt32? = try? data[index..<(index+4)].withUnsafeBytes { $0.pointee }
+            if let size = uncheckedSize, size >= data.count, let intermediate = try? data[index..<(index+4)].reversed() {
+                uncheckedSize = Data(intermediate).withUnsafeBytes { $0.pointee }
+            }
+            guard let size = uncheckedSize, size < data.count else { break }
+            let sizeAsInt = Int(size)
+            index += 4
+            guard index + sizeAsInt < data.count else { break }
+            let protoAsData = data[index..<(index+sizeAsInt)]
+            guard let proto = try? SSKProtoGroupDetails.parseData(protoAsData) else { break }
+            index += sizeAsInt
+            var groupModel = TSGroupModel.init(title: proto.name,
+                                               memberIds: proto.members,
+                                               image: nil,
+                                               groupId: proto.id,
+                                               groupType: GroupType.closedGroup,
+                                               adminIds: proto.admins)
+            result.append(groupModel)
+        }
+        return result
+    }
+}

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -1107,6 +1107,7 @@ NS_ASSUME_NONNULL_BEGIN
             OWSLogInfo(@"[Loki] Received group sync message.");
             NSData *data = syncMessage.groups.data;
             //  TODO: decode the data and handle the group info
+            GroupParser *parser = [[GroupParser alloc] initWithData:data];
         }
     } else {
         OWSLogWarn(@"Ignoring unsupported sync message.");