fields: preserve containers when copying fields

scapy/fields.py

@@ -312,6 +312,30 @@ class _FieldContainer(object):
     """
     __slots__ = ["fld"]
 
+    def copy(self):
+        # type: () -> Any
+        other = self.__class__.__new__(self.__class__)
+        for slot in self.__slots__:
+            val = object.__getattribute__(self, slot)
+            if hasattr(val, "copy"):
+                val = val.copy()
+            object.__setattr__(other, slot, val)
+        return other
+
+    def __setattr__(self, attr, value):
+        # type: (str, Any) -> None
+        try:
+            object.__setattr__(self, attr, value)
+        except AttributeError as ex:
+            for cls in type(self).__mro__:
+                if attr in cls.__dict__:
+                    raise ex
+            try:
+                fld = object.__getattribute__(self, "fld")
+            except AttributeError:
+                raise ex
+            setattr(fld, attr, value)
+
     def __getattr__(self, attr):
         # type: (str) -> Any
         return getattr(self.fld, attr)

test/fields.uts

@@ -15,6 +15,34 @@
 #Field("foo", None, fmt="I").getfield(None, b"\x12\x34\x56\x78ABCD")
 #assert  _ == ("ABCD",0x12345678) 
 
+= FieldContainer copy
+~ core field
+
+field_container = Emph(ByteField("foo", 0))
+field_container_copy = field_container.copy()
+
+assert type(field_container_copy) is Emph
+assert type(field_container_copy.fld) is ByteField
+assert field_container_copy.fld is not field_container.fld
+assert field_container_copy.name == "foo"
+assert field_container_copy.default == 0
+
+class TEST_FIELD_CONTAINER_COPY_SOURCE(Packet):
+    fields_desc = [Emph(ByteField("foo", 0))]
+
+class TEST_FIELD_CONTAINER_COPY_TARGET(Packet):
+    fields_desc = [TEST_FIELD_CONTAINER_COPY_SOURCE, ByteField("bar", 0)]
+    foo = 7
+
+source_field = TEST_FIELD_CONTAINER_COPY_SOURCE.fields_desc[0]
+target_field = TEST_FIELD_CONTAINER_COPY_TARGET.fields_desc[0]
+
+assert type(target_field) is Emph
+assert type(target_field.fld) is ByteField
+assert target_field.fld is not source_field.fld
+assert target_field.default == 7
+assert source_field.default == 0
+
 
 = ConditionnalField class
 ~ core field