Function find_last_utf8_boundary

crates/vm/src/stdlib/_io.rs:6115–6138

Find the last valid UTF-8 boundary in a byte slice.

(buf: &[u8], len: usize)

    /// Find the last valid UTF-8 boundary in a byte slice.
    fn find_last_utf8_boundary(buf: &[u8], len: usize) -> usize {
        let len = len.min(buf.len());
        for count in 1..=4.min(len) {
            let c = buf[len - count];
            if c < 0x80 {
                return len;
            }
            if c >= 0xc0 {
                let expected = if c < 0xe0 {
                    2
                } else if c < 0xf0 {
                    3
                } else {
                    4
                };
                if count < expected {
                    // Incomplete multibyte sequence
                    return len - count;
                }
                return len;
            }
        }
        len
    }

    #[pyattr]
    #[pyclass(module = "_io", name = "_WindowsConsoleIO", base = _RawIOBase)]