Verify username for special characters on signup

src/routes/user.rs

@@ -309,7 +309,8 @@ fn delete(name: String, conn: DbConn, user: User, mut cookies: Cookies) -> Optio
     )
 )]
 struct NewUserForm {
-    #[validate(length(min = "1", message = "Username can't be empty"))]
+    #[validate(length(min = "1", message = "Username can't be empty"),
+        custom( function = "validate_username", message = "User name is not allowed to contain any of < > & @ ' or \""))]
     username: String,
     #[validate(email(message = "Invalid email"))]
     email: String,
@@ -337,6 +338,14 @@ fn passwords_match(form: &NewUserForm) -> Result<(), ValidationError> {
     }
 }
 
+fn validate_username(username: &str) -> Result<(), ValidationError> {
+    if username.contains(&['<', '>', '&', '@', '\'', '"'][..]) {
+        Err(ValidationError::new("username_illegal_char"))
+    } else {
+        Ok(())
+    }
+}
+
 #[post("/users/new", data = "<data>")]
 fn create(conn: DbConn, data: LenientForm<NewUserForm>) -> Result<Redirect, Template> {
     if !Instance::get_local(&*conn)