fn split_der_key()

in cert-storage-inspector/src/main.rs [115:156]

• 42 lines of code
• 13 McCabe index (conditional complexity)

fn split_der_key(key: &[u8]) -> Result<(&[u8], &[u8]), SimpleError> {
    if key.len() < 2 {
        return Err(SimpleError::from("key too short to be DER"));
    }
    let first_len_byte = key[1] as usize;
    if first_len_byte < 0x80 {
        if key.len() < first_len_byte + 2 {
            return Err(SimpleError::from("key too short"));
        }
        return Ok(key.split_at(first_len_byte + 2 as usize));
    }
    if first_len_byte == 0x80 {
        return Err(SimpleError::from("unsupported ASN.1"));
    }
    if first_len_byte == 0x81 {
        if key.len() < 3 {
            return Err(SimpleError::from("key too short to be DER"));
        }
        let len = key[2] as usize;
        if len < 0x80 {
            return Err(SimpleError::from("bad DER"));
        }
        if key.len() < len + 3 {
            return Err(SimpleError::from("key too short"));
        }
        return Ok(key.split_at(len + 3));
    }
    if first_len_byte == 0x82 {
        if key.len() < 4 {
            return Err(SimpleError::from("key too short to be DER"));
        }
        let len = (key[2] as usize) << 8 | key[3] as usize;
        if len < 256 {
            return Err(SimpleError::from("bad DER"));
        }
        if key.len() < len + 4 {
            return Err(SimpleError::from("key too short"));
        }
        return Ok(key.split_at(len + 4));
    }
    Err(SimpleError::from("key too long"))
}