Add single layer UDS configuration mode

doc/scapy/layers/automotive.rst

@@ -1081,6 +1081,64 @@ to the Scapy interpreter::
 
 .. image:: ../graphics/animations/animation-scapy-uds3.svg
 
+
+Single Layer Mode
+-----------------
+
+UDS, KWP, OBD, and GMLAN all support a *single layer mode* that makes each
+service packet a standalone ``Packet`` rather than a nested sublayer.  The
+feature is backed by the generic helpers in
+:mod:`scapy.contrib.automotive.utils` and works identically for every protocol.
+
+**Default (multi-layer) mode**
+
+.. code-block:: python
+
+    >>> pkt = UDS() / UDS_DSC(diagnosticSessionType=0x01)
+    >>> UDS(b'\x10\x01')
+    <UDS  service=DiagnosticSessionControl |<UDS_DSC  diagnosticSessionType=defaultSession |>>
+
+**Single layer mode**
+
+To enable before loading a module::
+
+    >>> conf.contribs['UDS'] = {'treat-response-pending-as-answer': False,
+    ...                          'single_layer_mode': True}
+    >>> load_contrib('automotive.uds')
+
+To toggle at runtime after loading::
+
+    >>> conf.contribs['UDS']['single_layer_mode'] = True
+    >>> UDS(b'\x10\x01')
+    <UDS_DSC  service=DiagnosticSessionControl diagnosticSessionType=defaultSession |>
+    >>> bytes(UDS_DSC(diagnosticSessionType=0x01))
+    b'\x10\x01'
+    >>> conf.contribs['UDS']['single_layer_mode'] = False   # revert to multi-layer mode
+
+The same API is available for the other protocols — use the ``single_layer_mode``
+config key in the corresponding ``conf.contribs`` entry:
+
++----------+-----------------------------------------------+
+| Protocol | Config entry                                  |
++==========+===============================================+
+| UDS      | ``conf.contribs['UDS']['single_layer_mode']`` |
++----------+-----------------------------------------------+
+| KWP      | ``conf.contribs['KWP']['single_layer_mode']`` |
++----------+-----------------------------------------------+
+| OBD      | ``conf.contribs['OBD']['single_layer_mode']`` |
++----------+-----------------------------------------------+
+| GMLAN    | ``conf.contribs['GMLAN']['single_layer_mode']`` |
++----------+-----------------------------------------------+
+
+In single layer mode:
+
+- The base class (e.g. ``KWP``) acts as a dispatcher via ``dispatch_hook``:
+  it reads the first byte and returns the correct service class directly.
+- Each service packet has a conditional ``service`` field that is present
+  (for building and dissection) only when single layer mode is active.
+- Service packets' ``answers()`` and ``hashret()`` methods work correctly in
+  both modes.
+
 GMLAN
 =====