Base64 Encode

to_base64.rs

const S_BASE_64: [char; 64] = [
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
    'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
    'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
    '5', '6', '7', '8', '9', '+', '/',
];
fn to_base64(bytes: &[u8]) -> String {
    let mut dst = String::new();
    let mut padding = 0;

    for chunk in bytes.chunks(3) {
        let (a, b, c) = match chunk {
            [a, b, c] => (*a, *b, *c),
            [a, b] => {
                padding = 1;
                (*a, *b, 0)
            }
            [a] => {
                padding = 2;
                (*a, 0, 0)
            }
            _ => unreachable!(),
        };
        let n = ((a as u32) << 16) | ((b as u32) << 8) | c as u32;
        dst.push(S_BASE_64[((n >> 18) & 0x3F) as usize]);
        dst.push(S_BASE_64[((n >> 12) & 0x3F) as usize]);
        if padding < 2 {
            dst.push(S_BASE_64[((n >> 6) & 0x3F) as usize]);
        }
        if padding < 1 {
            dst.push(S_BASE_64[(n & 0x3F) as usize]);
        }
    }
    for _ in 0..padding {
        dst.push('=');
    }
    dst
}