Use properly encoded message bodys for patch views

If it doesn't say utf8 / contains invalid characters, force it to utf8.

Author: dutow

app/models/attachment.rb

@@ -10,6 +10,17 @@ def patch?
   def decoded_body
     Base64.decode64(body) if body.present?
   end
+
+  def decoded_body_utf8
+    raw = decoded_body
+    return unless raw
+
+    utf8 = raw.dup
+    utf8.force_encoding("UTF-8")
+    return utf8 if utf8.valid_encoding?
+
+    raw.encode("UTF-8", invalid: :replace, undef: :replace, replace: "\uFFFD")
+  end
 
   private
 

app/views/topics/_message.html.slim

@@ -60,7 +60,7 @@
                   = link_to "Download", attachment_path(attachment), class: "attachment-download", download: attachment.file_name, data: { turbo: false }
               pre.attachment-content
                 code.language-diff
-                  = attachment.decoded_body
+                  = attachment.decoded_body_utf8
           - else
             .attachment
               .attachment-info