From 159afb7b7c4235263f610f7c7e7bdd5f46f022e9 Mon Sep 17 00:00:00 2001
From: "Teppei.F" <37261985+T3pp31@users.noreply.github.com>
Date: Mon, 1 Jun 2026 23:34:28 +0900
Subject: [PATCH] fields: preserve containers when copying fields

AI-Assisted: yes (Codex)
---
 scapy/fields.py | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 test/fields.uts | 28 ++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/scapy/fields.py b/scapy/fields.py
index 46064b726e2..8b9a9be6407 100644
--- a/scapy/fields.py
+++ b/scapy/fields.py
@@ -312,6 +312,54 @@ class _FieldContainer(object):
     """
     __slots__ = ["fld"]
 
+    def copy(self):
+        # type: () -> Any
+        def _copy_attr(attr):
+            # type: (Any) -> Any
+            if hasattr(attr, "copy"):
+                return attr.copy()
+            return attr
+
+        cls = self.__class__
+        other = cls.__new__(cls)
+
+        if hasattr(self, "__dict__"):
+            other.__dict__ = {
+                key: _copy_attr(value)
+                for key, value in self.__dict__.items()
+            }
+
+        copied_slots = set()
+        for base in cls.__mro__:
+            slots = base.__dict__.get("__slots__", ())
+            if isinstance(slots, str):
+                slots = (slots,)
+            for slot in slots:
+                if slot in ("__dict__", "__weakref__") or slot in copied_slots:
+                    continue
+                slot_descriptor = base.__dict__.get(slot)
+                if getattr(cls, slot, None) is not slot_descriptor:
+                    continue
+                copied_slots.add(slot)
+                try:
+                    value = getattr(self, slot)
+                except AttributeError:
+                    continue
+                setattr(other, slot, _copy_attr(value))
+
+        return other
+
+    def __setattr__(self, attr, value):
+        # type: (str, Any) -> None
+        try:
+            object.__setattr__(self, attr, value)
+        except AttributeError as 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)
diff --git a/test/fields.uts b/test/fields.uts
index 38263f2a49f..a127056a1aa 100644
--- a/test/fields.uts
+++ b/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