https://github.com/yvan-sraka/base64decode/

main.rs

fn main() {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).unwrap();
    println!("Input: {}", input);
    let result = input
        .trim()
        .chars()
        .filter(|&ch| ch != '=')
        .map(|ch| {
            let ascii = ch as i8;
            let convert = match ch {
                '0'..='9' => ascii + 4,
                'a'..='z' => ascii - 71,
                'A'..='Z' => ascii - 65,
                '+' => 62,
                '/' => 63,
                _ => panic!(),
            };
            format!("{:#08b}", convert)[2..].to_string()
        })
        .collect::<String>()
        .chars()
        .collect::<Vec<char>>()
        .chunks(8)
        .map(|chunk| {
            let num_str = chunk.iter().collect::<String>();
            usize::from_str_radix(&num_str, 2).unwrap() as u8
        })
        .collect::<Vec<_>>();
    let output = String::from(std::str::from_utf8(&result).unwrap());
    println!("Output: {}", output);
}

oneliner.rs

fn main(){let mut i=String::new();std::io::stdin().read_line(&mut i).unwrap();println!("Input: {}",i);let r=i.trim().chars().filter(|&c|c!='=').map(|c|{let a=c as i8;let t=match c{'0'..='9'=>a+4,'a'..='z'=>a-71,'A'..='Z'=>a-65,'+'=>62,'/'=>63,_=>panic!()};format!("{:#08b}",t)[2..].to_string()}).collect::<String>().chars().collect::<Vec<char>>().chunks(8).map(|h|{let n=h.iter().collect::<String>();usize::from_str_radix(&n,2).unwrap() as u8}).collect::<Vec<_>>();let o=String::from(std::str::from_utf8(&r).unwrap());println!("Output: {}",o);}