"""
Implementation of the Client FQDN option as specified in :rfc:`4704`.
"""
from struct import pack
from dhcpkit.ipv6.messages import AdvertiseMessage, RebindMessage, RenewMessage, ReplyMessage, RequestMessage, \
SolicitMessage
from dhcpkit.ipv6.options import Option
from dhcpkit.utils import encode_domain, parse_domain_bytes
from typing import Union
OPTION_CLIENT_FQDN = 39
[docs]class ClientFQDNOption(Option):
"""
To update the IPv6-address-to-FQDN mapping, a DHCPv6 server needs to
know the FQDN of the client for the addresses for the client's IA_NA
bindings. To allow the client to convey its FQDN to the server, this
document defines a new DHCPv6 option called "Client FQDN". The
Client FQDN option also contains Flags that DHCPv6 clients and
servers use to negotiate who does which updates.
The code for this option is 39. Its minimum length is 1 octet.
The format of the DHCPv6 Client FQDN option is shown below::
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_FQDN | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flags | |
+-+-+-+-+-+-+-+-+ |
. .
. domain-name .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code
OPTION_CLIENT_FQDN (39).
option-len
1 + length of domain name.
flags
flag bits used between client and server to negotiate who performs which updates.
domain-name
the partial or fully qualified domain name (with length option-len - 1).
The Client FQDN option MUST only appear in a message's options field
and applies to all addresses for all IA_NA bindings in the
transaction.
4.1. The Flags Field
The format of the Flags field is::
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |N|O|S|
+-+-+-+-+-+-+-+-+
The "S" bit indicates whether the server SHOULD or SHOULD NOT perform
the AAAA RR (FQDN-to-address) DNS updates. A client sets the bit to
0 to indicate that the server SHOULD NOT perform the updates and 1 to
indicate that the server SHOULD perform the updates. The state of
the bit in the reply from the server indicates the action to be taken
by the server; if it is 1, the server has taken responsibility for
AAAA RR updates for the FQDN.
The "O" bit indicates whether the server has overridden the client's
preference for the "S" bit. A client MUST set this bit to 0. A
server MUST set this bit to 1 if the "S" bit in its reply to the
client does not match the "S" bit received from the client.
The "N" bit indicates whether the server SHOULD NOT perform any DNS
updates. A client sets this bit to 0 to request that the server
SHOULD perform updates (the PTR RR and possibly the AAAA RR based on
the "S" bit) or to 1 to request that the server SHOULD NOT perform
any DNS updates. A server sets the "N" bit to indicate whether the
server SHALL (0) or SHALL NOT (1) perform DNS updates. If the "N"
bit is 1, the "S" bit MUST be 0.
The remaining bits in the Flags field are reserved for future
assignment. DHCPv6 clients and servers that send the Client FQDN
option MUST clear the MBZ bits, and they MUST ignore these bits.
4.2. The Domain Name Field
The Domain Name part of the option carries all or part of the FQDN of
a DHCPv6 client. The data in the Domain Name field MUST be encoded
as described in Section 8 of [5]. In order to determine whether the
FQDN has changed between message exchanges, the client and server
MUST NOT alter the Domain Name field contents unless the FQDN has
actually changed.
A client MAY be configured with a fully qualified domain name or with
a partial name that is not fully qualified. If a client knows only
part of its name, it MAY send a name that is not fully qualified,
indicating that it knows part of the name but does not necessarily
know the zone in which the name is to be embedded.
To send a fully qualified domain name, the Domain Name field is set
to the DNS-encoded domain name including the terminating zero-length
label. To send a partial name, the Domain Name field is set to the
DNS-encoded domain name without the terminating zero-length label.
A client MAY also leave the Domain Name field empty if it desires the
server to provide a name.
Servers SHOULD send the complete fully qualified domain name in
Client FQDN options.
"""
option_type = OPTION_CLIENT_FQDN
def __init__(self, flags: int = 0, domain_name: str = None):
self.flags = flags
self.domain_name = domain_name
@property
def server_aaaa_update(self):
"""
Extract the S flag
:return: Whether the S flag is set
"""
return bool(self.flags & 1)
@server_aaaa_update.setter
def server_aaaa_update(self, value: bool):
"""
Set/unset the S flag
:param value: The new value of the S flag
"""
if value:
self.flags |= 1
else:
self.flags &= ~1
@property
def server_aaaa_override(self):
"""
Extract the O flag
:return: Whether the O flag is set
"""
return bool(self.flags & 2)
@server_aaaa_override.setter
def server_aaaa_override(self, value: bool):
"""
Set/unset the O flag
:param value: The new value of the O flag
"""
if value:
self.flags |= 2
else:
self.flags &= ~2
@property
def no_server_dns_update(self):
"""
Extract the N flag
:return: Whether the N flag is set
"""
return bool(self.flags & 4)
@no_server_dns_update.setter
def no_server_dns_update(self, value: bool):
"""
Set/unset the N flag
:param value: The new value of the N flag
"""
if value:
self.flags |= 4
else:
self.flags &= ~4
[docs] def validate(self):
"""
Validate that the contents of this object conform to protocol specs.
"""
# Allow for empty domain name
if self.domain_name:
# Otherwise try to encode it
encode_domain(self.domain_name, allow_relative=True)
[docs] def load_from(self, buffer: bytes, offset: int = 0, length: int = None) -> int:
"""
Load the internal state of this object from the given buffer. The buffer may
contain more data after the structured element is parsed. This data is ignored.
:param buffer: The buffer to read data from
:param offset: The offset in the buffer where to start reading
:param length: The amount of data we are allowed to read from the buffer
:return: The number of bytes used from the buffer
"""
my_offset, option_len = self.parse_option_header(buffer, offset, length)
header_offset = my_offset
# Get the flags
self.flags = buffer[offset + my_offset]
my_offset += 1
# Parse the domain name
max_offset = option_len + header_offset # The option_len field counts bytes *after* the header fields
domain_name_len, self.domain_name = parse_domain_bytes(buffer, offset=offset + my_offset, length=option_len - 1,
allow_relative=True)
my_offset += domain_name_len
if my_offset != max_offset:
raise ValueError('Option length does not match the combined length of the included domain name')
return my_offset
[docs] def save(self) -> Union[bytes, bytearray]:
"""
Save the internal state of this object as a buffer.
:return: The buffer with the data from this element
"""
domain_buffer = encode_domain(self.domain_name)
buffer = bytearray()
buffer.extend(pack('!HHB', self.option_type, 1 + len(domain_buffer), self.flags))
buffer.extend(domain_buffer)
return buffer
SolicitMessage.add_may_contain(ClientFQDNOption, 0, 1)
AdvertiseMessage.add_may_contain(ClientFQDNOption, 0, 1)
RequestMessage.add_may_contain(ClientFQDNOption, 0, 1)
RenewMessage.add_may_contain(ClientFQDNOption, 0, 1)
RebindMessage.add_may_contain(ClientFQDNOption, 0, 1)
ReplyMessage.add_may_contain(ClientFQDNOption, 0, 1)