fix(internet)!: keep MH option 6 prefixes with host bits and option 27 times past 9999 (#2702)

- The Mobile Network Prefix option fused its prefix and length into an
  IPv6Network, so a prefix with bits set past its length, or a length past
  128, raised a bare ValueError. RFC 3963 section 6.2 reads both fields as
  given and answers a prefix it cannot use with a status, not a discard, so
  the data model keeps them apart, as Home Network Prefix does: prefix_length
  is a new required field and prefix is the IPv6Address captured, the breaking
  change. The maker checks the length against its 8-bit field alone, takes a
  prefix_length keyword, and writes the bits past it.
- The Timestamp option turned a 48-bit second count past 9999 into a datetime,
  which raised a bare ValueError. RFC 5213 section 5.5 has the LMA answer such
  a time with a status rather than discard it, so timestamp is None there and
  pmip_timestamp keeps it. The seconds and fraction are no longer summed as one
  float, which carried 23:59:59 and 65535/65536 past the year's end.
- The mutation sweep's known crashes and the maker sweep's unparsed maximum go.

New tests fail on 57a6c36 without the pcapkit/ change; MH and guard modules pass.

Author: JarryShaw

pcapkit/protocols/data/internet/mh.py

@@ -10,7 +10,7 @@
 if TYPE_CHECKING:
     from datetime import datetime as dt_type
     from datetime import timedelta
-    from ipaddress import IPv4Address, IPv6Address, IPv6Network
+    from ipaddress import IPv4Address, IPv6Address
     from typing import Optional
 
     from pcapkit.const.mh.access_type import AccessType as Enum_AccessType
@@ -932,15 +932,28 @@ class MobileNetworkPrefixOption(Option):
 
        New required field ``reserved`` (:issue:`1437`).
 
+    .. versionchanged:: 1.6.0
+
+       New required field ``prefix_length``, and :attr:`prefix` is the
+       :class:`~ipaddress.IPv6Address` captured rather than an
+       :class:`~ipaddress.IPv6Network`, which cannot hold a prefix with bits set
+       past its length or a length past 128 (:issue:`2702`).
+
     """
 
     #: The reserved octet, as captured.
     reserved: 'bytes'
-    #: Mobile Network Prefix.
-    prefix: 'IPv6Network'
+    #: Prefix length, as captured.
+    prefix_length: 'int'
+    #: Mobile Network Prefix. Kept apart from :attr:`prefix_length` rather than
+    #: fused into an :class:`~ipaddress.IPv6Network`, so that bits past
+    #: :attr:`prefix_length`, which :rfc:`3963#section-6.2` reads as given, survive a
+    #: round trip. Same reasoning as :class:`HomeNetworkPrefixOption`.
+    prefix: 'IPv6Address'
 
     if TYPE_CHECKING:
-        def __init__(self, type: 'Enum_Option', length: 'int', reserved: 'bytes', prefix: 'IPv6Network') -> 'None': ...
+        def __init__(self, type: 'Enum_Option', length: 'int', reserved: 'bytes', prefix_length: 'int',
+                     prefix: 'IPv6Address') -> 'None': ...
 
 
 @info_final
@@ -1310,17 +1323,26 @@ def __init__(self, seconds: 'int', fraction: 'int') -> 'None': ...
 
 @info_final
 class TimestampOption(Option):
-    """Data model for MH Timestamp option."""
+    """Data model for MH Timestamp option.
 
-    #: Timestamp.
-    timestamp: 'dt_type'
+    .. versionchanged:: 1.6.0
+
+       :attr:`timestamp` is :data:`None` for a time past the year 9999, which
+       :class:`~datetime.datetime` cannot hold, rather than the read raising
+       :exc:`ValueError` (:issue:`2702`).
+
+    """
+
+    #: Timestamp, or :data:`None` past the year 9999, which the 48-bit second
+    #: count reaches and :class:`~datetime.datetime` cannot hold.
+    timestamp: 'Optional[dt_type]'
     #: Timestamp in the fixed-point format of :rfc:`5213#section-8.8`, kept
     #: alongside :attr:`timestamp` so that the 1/65536-second resolution of the
     #: wire format survives a round trip.
     pmip_timestamp: 'PMIPv6Timestamp'
 
     if TYPE_CHECKING:
-        def __init__(self, type: 'Enum_Option', length: 'int', timestamp: 'dt_type',
+        def __init__(self, type: 'Enum_Option', length: 'int', timestamp: 'Optional[dt_type]',
                      pmip_timestamp: 'PMIPv6Timestamp') -> 'None': ...
 
 

pcapkit/protocols/internet/mh.py

@@ -3350,14 +3350,16 @@ def _read_opt_mnp(self, schema: 'Schema_MobileNetworkPrefixOption', *,
         if schema.length != 18:
             raise ProtocolError(f'{self.alias}: [Opt {schema.type}] invalid format')
 
-        prefix = cast('IPv6Network',
-                      ipaddress.ip_network((schema.prefix, schema.prefix_length)))
-
+        # NOTE: The prefix and its length stay apart, as captured: an IPv6Network
+        # holds neither bits set past the length nor a length past 128. RFC 3963
+        # section 6.2 reads both fields as given, and answers a prefix the home
+        # agent cannot use with a status rather than discarding the option (#2702).
         data = Data_MobileNetworkPrefixOption(
             type=schema.type,
             length=self._mh_option_length(schema.length),
             reserved=schema.reserved,
-            prefix=prefix,
+            prefix_length=schema.prefix_length,
+            prefix=schema.prefix,
         )
         return data
 
@@ -4237,12 +4239,23 @@ def _read_opt_timestamp(self, schema: 'Schema_TimestampOption', *,
         seconds = schema.timestamp['seconds']
         fraction = schema.timestamp['fraction']
 
+        try:
+            # NOTE: Not the stdlib's ``fromtimestamp``, which takes no time
+            # after 3000 on Windows (#2099). The whole seconds go in as an int
+            # and the fraction as a timedelta, which rounds it to microseconds
+            # half to even as one float did, but loses no precision to the
+            # seconds, so the last second of 9999 is not carried past it.
+            timestamp = (fromtimestamp(seconds, datetime.timezone.utc)
+                         + datetime.timedelta(seconds=fraction / 65536))  # type: Optional[dt_type]
+        except ValueError:
+            # past the year 9999, which the 48-bit count reaches and datetime
+            # cannot hold, so pmip_timestamp alone keeps it (#2702)
+            timestamp = None
+
         data = Data_TimestampOption(
             type=schema.type,
             length=self._mh_option_length(schema.length),
-            # not the stdlib's ``fromtimestamp``, which takes no time after 3000
-            # on Windows (#2099)
-            timestamp=fromtimestamp(seconds + fraction / 65536, datetime.timezone.utc),
+            timestamp=timestamp,
             pmip_timestamp=Data_PMIPv6Timestamp(seconds=seconds, fraction=fraction),
         )
         return data
@@ -8258,32 +8271,62 @@ def _make_opt_bad(self, type: 'Enum_Option', option: 'Optional[Data_Authorizatio
         )
 
     def _make_opt_mnp(self, type: 'Enum_Option', option: 'Optional[Data_MobileNetworkPrefixOption]' = None, *,
-                      prefix: 'bytes | str | IPv6Network' = '::/0',
+                      prefix: 'bytes | str | int | IPv6Address | IPv6Network' = '::/0',
+                      prefix_length: 'Optional[int]' = None,
                       reserved: 'bytes' = b'\x00',
                       **kwargs: 'Any') -> 'Schema_MobileNetworkPrefixOption':
         """Make MH mobile network prefix option.
 
         Args:
             type: Option type.
             option: Option data model.
-            prefix: Mobile network prefix.
+            prefix: Mobile network prefix, an IPv6 address or network, whose
+                bits past ``prefix_length`` are written as given.
+            prefix_length: Prefix length; defaults to that of a network or of
+                text ending in ``/<length>``, and to 128 for an address.
             reserved: The reserved octet as captured, truncated or zero-filled to 1
                 octet.
             **kwargs: Arbitrary keyword arguments.
 
         Returns:
             Constructed option schema.
 
+        Raises:
+            ProtocolError: If ``prefix`` is not an IPv6 address or network, or
+                ``prefix_length`` is negative, a :obj:`bool`, or does not fit in
+                one octet.
+
+        Note:
+            The prefix length is checked against its 8-bit field alone, as
+            :rfc:`3963#section-6.2` has a home agent answer a prefix it cannot
+            use with a status rather than discard the option, so whatever the
+            reader keeps is written back.
+
+        .. versionchanged:: 1.6.0
+
+           New argument ``prefix_length``. ``prefix`` keeps the bits set past
+           its length, rather than raising :exc:`ValueError`, and a prefix
+           length past 128 is written (:issue:`2702`).
+
         """
         if option is not None:
             reserved = getattr(option, 'reserved', b'\x00')
-            prefix = option.prefix
-
-        prefix_val = ipaddress.ip_network(prefix)
-        if prefix_val.version != 6:
-            raise ProtocolError(f'{self.alias}: [OptNo {type}] invalid mobile network prefix: {prefix!r}')
-        prefix_length = prefix_val.prefixlen
-        prefix_addr = prefix_val.network_address
+            prefix_length = option.prefix_length
+            prefix_addr = option.prefix
+        else:
+            try:
+                # NOTE: An interface, unlike a network, keeps the bits past its
+                # length, and takes an address, a network or text alike. A bool
+                # is refused first, as it would pass for the address ``::1``.
+                prefix_val = None if isinstance(prefix, bool) else ipaddress.IPv6Interface(prefix)
+            except ValueError:
+                prefix_val = None
+            if prefix_val is None:
+                raise ProtocolError(f'{self.alias}: [OptNo {type}] invalid mobile network prefix: {prefix!r}')
+            if prefix_length is None:
+                prefix_length = prefix_val.network.prefixlen
+            prefix_addr = prefix_val.ip
+        prefix_length = self._make_uint(prefix_length, bits=8, name='prefix length')
 
         return Schema_MobileNetworkPrefixOption(
             type=type,

tests/protocols/internet/test_internet_maker_ranges_2614_unit.py

@@ -447,6 +447,7 @@ class MHMakerTests(_Case):
         'bra': ('Binding_Refresh_Advice', {}, {'interval': (0xFFFF, 'refresh interval')}),
         'ni': ('Nonce_Indices', {}, {'home': (0xFFFF, 'home nonce index'),
                                      'careof': (0xFFFF, 'care-of nonce index')}),
+        'mnp': ('Mobile_Network_Prefix_Option', {}, {'prefix_length': (0xFF, 'prefix length')}),
         'auth': ('AUTH_OPTION_TYPE', {'data': b'\x00\x00'}, {'spi': (0xFFFFFFFF, 'SPI')}),
         'badf': ('Binding_Authorization_Data_for_FMIPv6', {'data': b'\x00'},
                  {'spi': (0xFFFFFFFF, 'SPI')}),
@@ -562,11 +563,6 @@ class MHMakerTests(_Case):
          'maximum retransmissions'),
     )
 
-    UNPARSED_MAXIMA = {
-        '_make_opt_timestamp.seconds': 'MH._read_opt_timestamp turns the seconds into a '
-                                       'datetime, which cannot hold the 48-bit maximum',
-    }
-
     #: Integer arguments outside the sweep, and why.
     EXEMPT = {
         # The CGA extension makers are reached only through a CGA parameter

tests/protocols/internet/test_mh_option_mutation_2684_unit.py

@@ -31,13 +31,9 @@
 LONG_KEY = b'\x30\x81\x9f' + bytes(range(159))
 
 #: Options a one-octet change makes the reader raise an error that is not
-#: pcapkit's, by the reader: its data model has no form for the octets, a prefix
-#: with host bits set or a time past datetime.MAXYEAR. Inside IPv6 the header is
-#: then Raw, so the round trip holds. Found by this sweep, not fixed here.
-KNOWN_CRASHES = {
-    'Mobile_Network_Prefix_Option': '_read_opt_mnp',
-    'Timestamp_Option': '_read_opt_timestamp',
-}
+#: pcapkit's, by the reader whose data model has no form for the octets. Inside
+#: IPv6 the header is then Raw, so the round trip holds.
+KNOWN_CRASHES = {}  # type: dict[str, str]
 
 
 def _ipv6(body: bytes) -> bytes:

tests/protocols/internet/test_mh_unit.py

@@ -2,7 +2,7 @@
 
 import datetime
 import io
-from ipaddress import ip_address, ip_network
+from ipaddress import ip_address
 import importlib.util
 from types import SimpleNamespace
 import unittest
@@ -353,12 +353,13 @@ def test_mh_option_readers_cover_known_options_and_guards(self) -> None:
             schema.AuthorizationDataOption(type=Option.Authorization_Data, length=8, data=b'12345678'),
             options=options,
         ).data, b'12345678')
-        self.assertEqual(str(proto._read_opt_mnp(
+        mnp = proto._read_opt_mnp(
             schema.MobileNetworkPrefixOption(type=Option.Mobile_Network_Prefix_Option,
                                              length=18, prefix_length=64,
                                              prefix='2001:db8::'),
             options=options,
-        ).prefix), '2001:db8::/64')
+        )
+        self.assertEqual((mnp.prefix_length, str(mnp.prefix)), (64, '2001:db8::'))
         self.assertEqual(proto._read_opt_lla(
             schema.LinkLayerAddressOption(type=Option.Mobility_Header_Link_Layer_Address_option,
                                           length=7, code=LLACode.MN, lla=b'abcdef'),
@@ -789,8 +790,8 @@ def make_extension(code: CGAExtension, extension: data.UnknownExtension | None =
             self.assertEqual(proto._make_opt_mnp(
                 Option.Mobile_Network_Prefix_Option,
                 data.MobileNetworkPrefixOption(type=Option.Mobile_Network_Prefix_Option,
-                                               length=18, reserved=b'\x00',
-                                               prefix=ip_network('2001:db8:1::/64')),
+                                               length=18, reserved=b'\x00', prefix_length=64,
+                                               prefix=ip_address('2001:db8:1::')),
             ).prefix_length, 64)
             self.assertEqual(proto._make_opt_lla(
                 Option.Mobility_Header_Link_Layer_Address_option,