restrict identity name

see discussion https://forum.duniter.org/t/format-du-userid/10147

primitives/duniter/src/lib.rs

@@ -16,15 +16,20 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
-/// Bound length; forbid trailing or double spaces; accept only ascii alphanumeric or punctuation or space
+/// Rules for valid identity names are defined below
+/// - Bound length to 64
+/// - forbid trailing or double spaces
+/// - accept only ascii alphanumeric or punctuation or space
 pub fn validate_idty_name(idty_name: &[u8]) -> bool {
     idty_name.len() >= 3
-        && idty_name.len() <= 64
-        && idty_name[0] != 32
-        && idty_name[idty_name.len() - 1] != 32
+        && idty_name.len() <= 64 // length smaller than 64
+        && idty_name[0] != 32 // does not start with space
+        && idty_name[idty_name.len() - 1] != 32 // does not end with space
+        // all characters are alphanumeric or punctuation or space
         && idty_name
             .iter()
             .all(|c| c.is_ascii_alphanumeric() || c.is_ascii_punctuation() || *c == 32)
+        // disallow two consecutive spaces
         && idty_name
             .iter()
             .zip(idty_name.iter().skip(1))