Rust cutting long utf strings

main.rs

// https://play.rust-lang.org/?version=beta&mode=debug&edition=2018&gist=d99b8ff32cda06ad450c2de61b2053bf
   fn main() {
             // Limit file name to 200 bytes or less if char is boundary
             let mut title_raw = "🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴🚴";
             // let mut title_raw = "🚴Billie Eilish - text=\"Everything I Wanted\" song_spot=\"M\" MediaBaseId=\"2548688\" itunesTrackId=\"0\" amgTrackId=\"-1\" amgArtistId=\"0\" TAID=\"31132274\" TPID=\"83782299\" cartcutId=\"0416383001\" amgArtworkURL=\"http://image.iheart.com/bell-ingestion-pipeline-production-umg/full/00602508508462_20191114020958327/19UM1IM00404_T1_cvrart.jpg\" length=\"00:04:02\" unsID=\"-1\" spotInstanceId=\"-1\"🚴";
             // let mut title_raw = "Billie Eilish - Everything I Wanted";
            
                let mut limit = 200;
                while (title_raw.len() > 200) && (!title_raw.is_char_boundary(limit)) {
                    limit -= 1;
                }
                
                title_raw = &title_raw[..limit.min(title_raw.len())];
                let title = title_raw.to_string();

    println!("{}", title_raw);
    println!("{}", title_raw.len());
    println!("{}", title);
}