TF-3267 Implement HTML attachment preview

core/lib/presentation/extensions/media_type_extension.dart

@@ -47,4 +47,9 @@ extension MediaTypeExtension on MediaType {
           fileName?.endsWith(Constant.pdfExtension) == true);
 
   bool get isEMLFile => mimeType == Constant.emlMimeType;
+
+  bool isHTMLFile({required String? fileName}) =>
+      mimeType == Constant.textHtmlMimeType ||
+      (mimeType == Constant.octetStreamMimeType &&
+          fileName?.endsWith(Constant.htmlExtension) == true);
 }

core/lib/presentation/utils/html_transformer/text/standardize_html_sanitizing_transformers.dart

@@ -20,6 +20,9 @@ class StandardizeHtmlSanitizingTransformers extends TextTransformer {
     'style',
     'body',
     'section',
+    'nav',
+    'main',
+    'footer',
   ];
 
   const StandardizeHtmlSanitizingTransformers();

core/lib/presentation/views/html_viewer/html_content_viewer_on_web_widget.dart

@@ -12,6 +12,7 @@ import 'package:flutter/cupertino.dart';
 import 'package:universal_html/html.dart' as html;
 
 typedef OnClickHyperLinkAction = Function(Uri?);
+typedef OnMailtoClicked = void Function(Uri? uri);
 
 class HtmlContentViewerOnWeb extends StatefulWidget {
 
@@ -21,13 +22,15 @@ class HtmlContentViewerOnWeb extends StatefulWidget {
   final TextDirection? direction;
 
   /// Handler for mailto: links
-  final Function(Uri?)? mailtoDelegate;
+  final OnMailtoClicked? mailtoDelegate;
 
   final OnClickHyperLinkAction? onClickHyperLinkAction;
 
-  // if widthContent is bigger than width of htmlContent, set this to true let widget able to resize to width of htmlContent 
+  // if widthContent is bigger than width of htmlContent, set this to true let widget able to resize to width of htmlContent
   final bool allowResizeToDocumentSize;
-  
+
+  final bool keepWidthWhileLoading;
+
   const HtmlContentViewerOnWeb({
     Key? key,
     required this.contentHtml,
@@ -37,6 +40,7 @@ class HtmlContentViewerOnWeb extends StatefulWidget {
     this.mailtoDelegate,
     this.direction,
     this.onClickHyperLinkAction,
+    this.keepWidthWhileLoading = false,
   }) : super(key: key);
 
   @override
@@ -99,7 +103,7 @@ class _HtmlContentViewerOnWebState extends State<HtmlContentViewerOnWeb> {
         }
       }
 
-      if (data['type'] != null && data['type'].contains('toDart: htmlWidth')) {
+      if (data['type'] != null && data['type'].contains('toDart: htmlWidth') && !widget.keepWidthWhileLoading) {
         final docWidth = data['width'] ?? _actualWidth;
         if (docWidth != null && mounted) {
           if (docWidth > _minWidth && widget.allowResizeToDocumentSize) {