add onLinkTap to MessageWidget

lib/src/message_text.dart

@@ -11,10 +11,12 @@ class MessageText extends StatelessWidget {
     @required this.message,
     @required this.messageTheme,
     this.onMentionTap,
+    this.onLinkTap,
   }) : super(key: key);
 
   final Message message;
   final void Function(User) onMentionTap;
+  final void Function(String) onLinkTap;
   final MessageTheme messageTheme;
 
   @override
@@ -35,7 +37,11 @@ class MessageText extends StatelessWidget {
             print('tap on ${mentionedUser.name}');
           }
         } else {
-          launchURL(context, link);
+          if (onLinkTap != null) {
+            onLinkTap(link);
+          } else {
+            launchURL(context, link);
+          }
         }
       },
       styleSheet: MarkdownStyleSheet.fromTheme(

lib/src/message_widget.dart

@@ -97,6 +97,9 @@ class MessageWidget extends StatefulWidget {
   /// The function called when tapping on UserAvatar
   final void Function(User) onUserAvatarTap;
 
+  /// The function called when tapping on a link
+  final void Function(String) onLinkTap;
+
   final List<Read> readList;
 
   /// If true show the users username next to the timestamp of the message
@@ -128,6 +131,7 @@ class MessageWidget extends StatefulWidget {
     this.showDeleteMessage = true,
     this.showEditMessage = true,
     this.onUserAvatarTap,
+    this.onLinkTap,
     this.onMessageActions,
     this.editMessageInputBuilder,
     this.textBuilder,
@@ -764,6 +768,7 @@ class _MessageWidgetState extends State<MessageWidget> {
     return widget.textBuilder != null
         ? widget.textBuilder(context, widget.message)
         : MessageText(
+            onLinkTap: widget.onLinkTap,
             message: widget.message,
             onMentionTap: widget.onMentionTap,
             messageTheme: widget.messageTheme,