Class _ExtensionsField

scapy/layers/tls/extensions.py:796–860

class _ExtensionsField(StrLenField):
    islist = 1
    holds_packets = 1

    def i2len(self, pkt, i):
        if i is None:
            return 0
        return len(self.i2m(pkt, i))

    def getfield(self, pkt, s):
        tmp_len = self.length_from(pkt) or 0
        if tmp_len <= 0:
            return s, []
        return s[tmp_len:], self.m2i(pkt, s[:tmp_len])

    def i2m(self, pkt, i):
        if i is None:
            return b""
        if isinstance(pkt, _GenericTLSSessionInheritance):
            if not pkt.tls_session.frozen:
                s = b""
                for ext in i:
                    if isinstance(ext, _GenericTLSSessionInheritance):
                        ext.tls_session = pkt.tls_session
                        s += ext.raw_stateful()
                    else:
                        s += raw(ext)
                return s
        return b"".join(map(raw, i))

    def m2i(self, pkt, m):
        res = []
        while len(m) >= 4:
            t = struct.unpack("!H", m[:2])[0]
            tmp_len = struct.unpack("!H", m[2:4])[0]
            cls = _tls_ext_cls.get(t, TLS_Ext_Unknown)
            if cls is TLS_Ext_KeyShare:
                # TLS_Ext_KeyShare can be :
                #  - TLS_Ext_KeyShare_CH if the message is a ClientHello
                #  - TLS_Ext_KeyShare_SH if the message is a ServerHello
                #    and all parameters are accepted by the serveur
                #  - TLS_Ext_KeyShare_HRR if message is a ServerHello and
                #    the client has not provided a sufficient "key_share"
                #    extension
                from scapy.layers.tls.keyexchange_tls13 import (
                    _tls_ext_keyshare_cls, _tls_ext_keyshare_hrr_cls)
                # If SHA-256("HelloRetryRequest") == server_random,
                # this message is a HelloRetryRequest
                if pkt.random_bytes and \
                        pkt.random_bytes == _tls_hello_retry_magic:
                    cls = _tls_ext_keyshare_hrr_cls.get(pkt.msgtype, TLS_Ext_Unknown)  # noqa: E501
                else:
                    cls = _tls_ext_keyshare_cls.get(pkt.msgtype, TLS_Ext_Unknown)  # noqa: E501
            elif cls is TLS_Ext_PreSharedKey:
                from scapy.layers.tls.keyexchange_tls13 import _tls_ext_presharedkey_cls  # noqa: E501
                cls = _tls_ext_presharedkey_cls.get(pkt.msgtype, TLS_Ext_Unknown)  # noqa: E501
            elif cls is TLS_Ext_SupportedVersions:
                cls = _tls_ext_supported_version_cls.get(pkt.msgtype, TLS_Ext_Unknown)  # noqa: E501