Read a single utf8 char using rust

read-utf8-char.rs

// See: https://en.wikipedia.org/wiki/UTF-8#Encoding

fn read_char<T: Read>(data: &mut T) -> char {
    let b = read_u8(data);
    let value;
    if (b & 0b1111_1000) == 0b1111_0000 {
        value = (((b & 0b0000_0111) as u32) << 18)
            + (((read_u8(data) & 0b0011_1111) as u32) << 12)
            + (((read_u8(data) & 0b0011_1111) as u32) << 6)
            + ((read_u8(data) & 0b0011_1111) as u32);
    } else if (b & 0b1111_0000) == 0b1110_0000 {
        value = (((b & 0b0000_1111) as u32) << 12)
            + (((read_u8(data) & 0b0011_1111) as u32) << 6)
            + ((read_u8(data) & 0b0011_1111) as u32);
    } else if (b & 0b1110_0000) == 0b1100_0000 {
        value = (((b & 0b0001_1111) as u32) << 6) + ((read_u8(data) & 0b0011_1111) as u32);
    } else {
        value = b as u32;
    }
    char::from_u32(value).unwrap()
}
    
fn read_u8<T: Read>(data: &mut T) -> u8 {
    let mut buf = [0; 1];
    data.read_exact(&mut buf).unwrap();
    buf[0]
}
    
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_char() {
        let data = vec![0xF0, 0x9F, 0x99, 0x82];
        assert_eq!(read_char(&mut &data[..]), '🙂');
    }
}