bug in dhcp pack method

[giovanni-bellini-argo]

when building a dhcp packet

from dpkt.dhcp import (
    DHCP,
    DHCP_OPT_MSGTYPE,
    DHCPDISCOVER
)

packet = DHCP(chaddr=b'ffffffffffff').pack()

the pack method fails with:
struct.error: argument for 's' must be a bytes object.

the opts values are expected to be stored as bytes but the default values are strings.

the fix is really easy, either modify the default value to byte objects

opts = (
        (DHCP_OPT_MSGTYPE, chr(DHCPDISCOVER).encode()),
        (DHCP_OPT_PARAM_REQ, ''.join(map(chr, (DHCP_OPT_REQ_IP,
                                               DHCP_OPT_ROUTER,
                                               DHCP_OPT_NETMASK,
                                               DHCP_OPT_DNS_SVRS))).encode())
    )  # list of (type, data) tuples

or add a check in the pack_opts func and transform data there

def pack_opts(self):
        """Return packed options string."""
        if not self.opts:
            return b''
        l_ = []
        for t, data in self.opts:
            if isinstance(data, str): data = data.encode()
            l_.append(struct.pack("BB%is" % len(data), t, len(data), data))
        l_.append(b'\xff')
        return b''.join(l_)

---

Details:

• Python 3.10.12