Improved validation of display names (Fixes #3436) (#3437)

* Fixed validation of display names

Fixed validation of display names: reject names beginning with invisible unicode characters.

* Formatting

Formatting fix.

* Expanded list of forbidden Unicode characters. Validation now checks for disallowed characters anywhere in the name.

* Formatting

* Added a comment detailing source of the list of invisible chars.

crates/utils/src/utils/validation.rs

@@ -24,6 +24,62 @@ const BIO_MAX_LENGTH: usize = 300;
 const SITE_NAME_MAX_LENGTH: usize = 20;
 const SITE_NAME_MIN_LENGTH: usize = 1;
 const SITE_DESCRIPTION_MAX_LENGTH: usize = 150;
+//Invisible unicode characters, taken from https://invisible-characters.com/
+const FORBIDDEN_DISPLAY_CHARS: [char; 53] = [
+  '\u{0009}',
+  '\u{00a0}',
+  '\u{00ad}',
+  '\u{034f}',
+  '\u{061c}',
+  '\u{115f}',
+  '\u{1160}',
+  '\u{17b4}',
+  '\u{17b5}',
+  '\u{180e}',
+  '\u{2000}',
+  '\u{2001}',
+  '\u{2002}',
+  '\u{2003}',
+  '\u{2004}',
+  '\u{2005}',
+  '\u{2006}',
+  '\u{2007}',
+  '\u{2008}',
+  '\u{2009}',
+  '\u{200a}',
+  '\u{200b}',
+  '\u{200c}',
+  '\u{200d}',
+  '\u{200e}',
+  '\u{200f}',
+  '\u{202f}',
+  '\u{205f}',
+  '\u{2060}',
+  '\u{2061}',
+  '\u{2062}',
+  '\u{2063}',
+  '\u{2064}',
+  '\u{206a}',
+  '\u{206b}',
+  '\u{206c}',
+  '\u{206d}',
+  '\u{206e}',
+  '\u{206f}',
+  '\u{3000}',
+  '\u{2800}',
+  '\u{3164}',
+  '\u{feff}',
+  '\u{ffa0}',
+  '\u{1d159}',
+  '\u{1d173}',
+  '\u{1d174}',
+  '\u{1d175}',
+  '\u{1d176}',
+  '\u{1d177}',
+  '\u{1d178}',
+  '\u{1d179}',
+  '\u{1d17a}',
+];
 
 fn has_newline(name: &str) -> bool {
   name.contains('\n')
@@ -42,8 +98,8 @@ pub fn is_valid_actor_name(name: &str, actor_name_max_length: usize) -> LemmyRes
 
 // Can't do a regex here, reverse lookarounds not supported
 pub fn is_valid_display_name(name: &str, actor_name_max_length: usize) -> LemmyResult<()> {
-  let check = !name.starts_with('@')
-    && !name.starts_with('\u{200b}')
+  let check = !name.contains(FORBIDDEN_DISPLAY_CHARS)
+    && !name.starts_with('@')
     && name.chars().count() >= 3
     && name.chars().count() <= actor_name_max_length
     && !has_newline(name);