Drop `MsgCodec.decoder()/.encoder()` design

Instead just instantiate `msgpack.Encoder/Decoder` instances inside
`mk_codec()` and assign them directly as `._enc/._dec` fields.
Explicitly take in named-args to both and proxy to the coder/decoder
instantiation calls directly.

Shuffling some codec internals:
- rename `mk_codec()` inputs as `ipc_msg_spec` and `ipc_pld_spec`, make
  them mutex such that a payload type spec can't be passed if the
  built-in msg-spec isn't used.
  => expose `MsgCodec.ipc_pld_spec` directly from `._dec.type`
  => presume input `ipc_msg_spec` is `Any` by default when no
    `ipc_pld_spec` is passed since we have no way atm to enable
    a similar type-restricted-payload feature without a wrapping
    "shuttle protocol" ;)

- move all the payload-sub-decoders stuff prototyped in GH#311
  (inside `.types`) to `._codec` as commented-for-later-maybe `MsgCodec`
  methods including:
  - `.mk_pld_subdec()` for registering
  - `.enc/dec_payload()` for sub-codec field loading.

- also comment out `._codec.mk_tagged_union_dec()` as the orig
  tag-to-decoder table factory, now mostly superseded by
  `.types.mk_msg_spec()` which takes the generic parameterizing approach
  instead.

- change naming to `types.mk_msg_spec(payload_type_union)` input, making
  it more explicit that it expects a `Union[Type]`.

Oh right, and start exposing all the `.types.Msg` subtypes in the `.msg`
subpkg in prep for usage throughout the runtime B)

tractor/msg/__init__.py

@@ -33,3 +33,40 @@ from ._codec import (
     MsgCodec as MsgCodec,
     current_msgspec_codec as current_msgspec_codec,
 )
+
+from .types import (
+    Msg as Msg,
+
+    Start,  # with pld
+    FuncSpec as FuncSpec,
+
+    StartAck, # with pld
+    IpcCtxSpec as IpcCtxSpec,
+
+    Started,
+    Yield,
+    Stop,
+    Return,
+
+    Error,  # with pld
+    ErrorData as ErrorData
+)
+
+
+# built-in SC shuttle protocol msg type set in
+# approx order of the IPC txn-state spaces.
+__spec__: list[Msg] = [
+
+    # inter-actor RPC initiation
+    Start,
+    StartAck,
+
+    # no-outcome-yet IAC (inter-actor-communication)
+    Started,
+    Yield,
+    Stop,
+
+    # termination outcomes
+    Return,
+    Error,
+]

tractor/msg/_codec.py

@@ -29,6 +29,7 @@ ToDo: backends we prolly should offer:
    - https://capnproto.org/language.html#language-reference
 
 '''
+from __future__ import annotations
 from contextvars import (
     ContextVar,
     Token,
@@ -54,18 +55,36 @@ from tractor.msg.types import (
 )
 
 
-# TODO: API changes towards being interchange lib agnostic!
+# TODO: overall IPC msg-spec features (i.e. in this mod)!
 #
-# -[ ] capnproto has pre-compiled schema for eg..
+# -[ ] API changes towards being interchange lib agnostic!
-#  * https://capnproto.org/language.html
+#   -[ ] capnproto has pre-compiled schema for eg..
-#  * http://capnproto.github.io/pycapnp/quickstart.html
+#    * https://capnproto.org/language.html
-#   * https://github.com/capnproto/pycapnp/blob/master/examples/addressbook.capnp
+#    * http://capnproto.github.io/pycapnp/quickstart.html
+#     * https://github.com/capnproto/pycapnp/blob/master/examples/addressbook.capnp
+#
+# -[ ] struct aware messaging coders as per:
+#   -[x] https://github.com/goodboy/tractor/issues/36
+#   -[ ] https://github.com/goodboy/tractor/issues/196
+#   -[ ] https://github.com/goodboy/tractor/issues/365
 #
 class MsgCodec(Struct):
     '''
     A IPC msg interchange format lib's encoder + decoder pair.
 
     '''
+    # post-configure-cached when prop-accessed (see `mk_codec()`
+    # OR can be passed directly as,
+    # `MsgCodec(_enc=<Encoder>,  _dec=<Decoder>)`
+    _enc: msgpack.Encoder|None = None
+    _dec: msgpack.Decoder|None = None
+
+    # struct type unions
+    # https://jcristharif.com/msgspec/structs.html#tagged-unions
+    @property
+    def ipc_pld_spec(self) -> Union[Type[Struct]]:
+        return self._dec.type
+
     lib: ModuleType = msgspec
 
     # ad-hoc type extensions
@@ -73,16 +92,8 @@ class MsgCodec(Struct):
     enc_hook: Callable[[Any], Any]|None = None  # coder
     dec_hook: Callable[[type, Any], Any]|None = None # decoder
 
-    # struct type unions
-    # https://jcristharif.com/msgspec/structs.html#tagged-unions
-    ipc_msg_spec: Union[Type[Struct]]|Any = Any
-    payload_msg_spec: Union[Type[Struct]] = Any
-
-    # post-configure cached props
-    _enc: msgpack.Encoder|None = None
-    _dec: msgpack.Decoder|None = None
-
     # TODO: a sub-decoder system as well?
+    # payload_msg_specs: Union[Type[Struct]] = Any
     # see related comments in `.msg.types`
     # _payload_decs: (
     #     dict[
@@ -91,42 +102,18 @@ class MsgCodec(Struct):
     #     ]
     #     |None
     # ) = None
+    # OR
+    # ) = {
+    #     # pre-seed decoders for std-py-type-set for use when
+    #     # `Msg.pld == None|Any`.
+    #     None: msgpack.Decoder(Any),
+    #     Any: msgpack.Decoder(Any),
+    # }
 
     # TODO: use `functools.cached_property` for these ?
     # https://docs.python.org/3/library/functools.html#functools.cached_property
     @property
     def enc(self) -> msgpack.Encoder:
-        return self._enc or self.encoder()
-
-    def encoder(
-        self,
-        enc_hook: Callable|None = None,
-        reset: bool = False,
-
-        # TODO: what's the default for this, and do we care?
-        # write_buffer_size: int
-        #
-        **kwargs,
-
-    ) -> msgpack.Encoder:
-        '''
-        Set or get the maybe-cached `msgspec.msgpack.Encoder`
-        instance configured for this codec.
-
-        When `reset=True` any previously configured encoder will
-        be recreated and then cached with the new settings passed
-        as input.
-
-        '''
-        if (
-            self._enc is None
-            or reset
-        ):
-            self._enc = self.lib.msgpack.Encoder(
-                enc_hook=enc_hook or self.enc_hook,
-                # write_buffer_size=write_buffer_size,
-            )
-
         return self._enc
 
     def encode(
@@ -139,40 +126,10 @@ class MsgCodec(Struct):
         on a tranport protocol connection.
 
         '''
-        return self.enc.encode(py_obj)
+        return self._enc.encode(py_obj)
 
     @property
     def dec(self) -> msgpack.Decoder:
-        return self._dec or self.decoder()
-
-    def decoder(
-        self,
-        ipc_msg_spec: Union[Type[Struct]]|None = None,
-        dec_hook: Callable|None = None,
-        reset: bool = False,
-        **kwargs,
-        # ext_hook: ext_hook_sig
-
-    ) -> msgpack.Decoder:
-        '''
-        Set or get the maybe-cached `msgspec.msgpack.Decoder`
-        instance configured for this codec.
-
-        When `reset=True` any previously configured decoder will
-        be recreated and then cached with the new settings passed
-        as input.
-
-        '''
-        if (
-            self._dec is None
-            or reset
-        ):
-            self._dec = self.lib.msgpack.Decoder(
-                type=ipc_msg_spec or self.ipc_msg_spec,
-                dec_hook=dec_hook or self.dec_hook,
-                **kwargs,
-            )
-
         return self._dec
 
     def decode(
@@ -185,60 +142,165 @@ class MsgCodec(Struct):
         determined by the 
 
         '''
-        return self.dec.decode(msg)
+        return self._dec.decode(msg)
+
+    # TODO: do we still want to try and support the sub-decoder with
+    # `.Raw` technique in the case that the `Generic` approach gives
+    # future grief?
+    #
+    # -[ ] <NEW-ISSUE-FOR-ThIS-HERE>
+    #
+    #def mk_pld_subdec(
+    #    self,
+    #    payload_types: Union[Type[Struct]],
+
+    #) -> msgpack.Decoder:
+    #    # TODO: sub-decoder suppor for `.pld: Raw`?
+    #    # => see similar notes inside `.msg.types`..
+    #    #
+    #    # not sure we'll end up needing this though it might have
+    #    # unforeseen advantages in terms of enabling encrypted
+    #    # appliciation layer (only) payloads?
+    #    #
+    #    # register sub-payload decoders to load `.pld: Raw`
+    #    # decoded `Msg`-packets using a dynamic lookup (table)
+    #    # instead of a pre-defined msg-spec via `Generic`
+    #    # parameterization.
+    #    #
+    #    (
+    #        tags,
+    #        payload_dec,
+    #    ) = mk_tagged_union_dec(
+    #        tagged_structs=list(payload_types.__args__),
+    #    )
+    #    # register sub-decoders by tag
+    #    subdecs: dict[str, msgpack.Decoder]|None = self._payload_decs
+    #    for name in tags:
+    #        subdecs.setdefault(
+    #            name,
+    #            payload_dec,
+    #        )
+
+    #    return payload_dec
+
+    # sub-decoders for retreiving embedded
+    # payload data and decoding to a sender
+    # side defined (struct) type.
+    # def dec_payload(
+    #     codec: MsgCodec,
+    #     msg: Msg,
+
+    # ) -> Any|Struct:
+
+    #     msg: Msg = codec.dec.decode(msg)
+    #     payload_tag: str = msg.header.payload_tag
+    #     payload_dec: msgpack.Decoder = codec._payload_decs[payload_tag]
+    #     return payload_dec.decode(msg.pld)
+
+    # def enc_payload(
+    #     codec: MsgCodec,
+    #     payload: Any,
+    #     cid: str,
+
+    # ) -> bytes:
+
+    #     # tag_field: str|None = None
+
+    #     plbytes = codec.enc.encode(payload)
+    #     if b'msg_type' in plbytes:
+    #         assert isinstance(payload, Struct)
+
+    #         # tag_field: str = type(payload).__name__
+    #         payload = msgspec.Raw(plbytes)
+
+    #     msg = Msg(
+    #         cid=cid,
+    #         pld=payload,
+    #         # Header(
+    #         #     payload_tag=tag_field,
+    #         #     # dialog_id,
+    #         # ),
+    #     )
+    #     return codec.enc.encode(msg)
 
 
-def mk_tagged_union_dec(
+ #def mk_tagged_union_dec(
-    tagged_structs: list[Struct],
+    # tagged_structs: list[Struct],
 
-) -> tuple[
+ #) -> tuple[
-    list[str],
+    # list[str],
-    msgpack.Decoder,
+    # msgpack.Decoder,
-]:
+ #]:
-    # See "tagged unions" docs:
+    # '''
-    # https://jcristharif.com/msgspec/structs.html#tagged-unions
+    # Create a `msgpack.Decoder` for an input `list[msgspec.Struct]`
+    # and return a `list[str]` of each struct's `tag_field: str` value
+    # which can be used to "map to" the initialized dec.
 
-    # "The quickest way to enable tagged unions is to set tag=True when
+    # '''
-    # defining every struct type in the union. In this case tag_field
+    # # See "tagged unions" docs:
-    # defaults to "type", and tag defaults to the struct class name
+    # # https://jcristharif.com/msgspec/structs.html#tagged-unions
-    # (e.g. "Get")."
-    first: Struct = tagged_structs[0]
-    types_union: Union[Type[Struct]] = Union[
-       first
-    ]|Any
-    tags: list[str] = [first.__name__]
 
-    for struct in tagged_structs[1:]:
+    # # "The quickest way to enable tagged unions is to set tag=True when
-        types_union |= struct
+    # # defining every struct type in the union. In this case tag_field
-        tags.append(struct.__name__)
+    # # defaults to "type", and tag defaults to the struct class name
+    # # (e.g. "Get")."
+    # first: Struct = tagged_structs[0]
+    # types_union: Union[Type[Struct]] = Union[
+    #    first
+    # ]|Any
+    # tags: list[str] = [first.__name__]
 
-    dec = msgpack.Decoder(types_union)
+    # for struct in tagged_structs[1:]:
-    return (
+    #     types_union |= struct
-        tags,
+    #     tags.append(
-        dec,
+    #         getattr(
-    )
+    #             struct,
+    #             struct.__struct_config__.tag_field,
+    #             struct.__name__,
+    #         )
+    #     )
+
+    # dec = msgpack.Decoder(types_union)
+    # return (
+    #     tags,
+    #     dec,
+    # )
 
-# TODO: struct aware messaging coders as per:
-# - https://github.com/goodboy/tractor/issues/36
-# - https://github.com/goodboy/tractor/issues/196
-# - https://github.com/goodboy/tractor/issues/365
 
 def mk_codec(
-    libname: str = 'msgspec',
+    ipc_msg_spec: Union[Type[Struct]]|Any|None = None,
-
-    # for codec-ing boxed `Msg`-with-payload msgs
-    payload_types: Union[Type[Struct]]|None = None,
-
-    # TODO: do we want to allow NOT/using a diff `Msg`-set?
     #
+    # ^TODO^: in the long run, do we want to allow using a diff IPC `Msg`-set?
+    # it would break the runtime, but maybe say if you wanted
+    # to add some kinda field-specific or wholesale `.pld` ecryption?
+
     # struct type unions set for `Decoder`
     # https://jcristharif.com/msgspec/structs.html#tagged-unions
-    ipc_msg_spec: Union[Type[Struct]]|Any = Any,
+    ipc_pld_spec: Union[Type[Struct]]|Any|None = None,
 
-    cache_now: bool = True,
+    # TODO: offering a per-msg(-field) type-spec such that
+    # the fields can be dynamically NOT decoded and left as `Raw`
+    # values which are later loaded by a sub-decoder specified
+    # by `tag_field: str` value key?
+    # payload_msg_specs: dict[
+    #     str,  # tag_field value as sub-decoder key
+    #     Union[Type[Struct]]  # `Msg.pld` type spec
+    # ]|None = None,
+
+    libname: str = 'msgspec',
 
     # proxy as `Struct(**kwargs)`
+    # ------ - ------
+    dec_hook: Callable|None = None,
+    enc_hook: Callable|None = None,
+    # ------ - ------
     **kwargs,
+    #
+    # Encoder:
+    # write_buffer_size=write_buffer_size,
+    #
+    # Decoder:
+    # ext_hook: ext_hook_sig
 
 ) -> MsgCodec:
     '''
@@ -247,75 +309,81 @@ def mk_codec(
     `msgspec` ;).
 
     '''
-    # (manually) generate a msg-payload-spec for all relevant
+    if (
-    # god-boxing-msg subtypes, parameterizing the `Msg.pld: PayloadT`
+        ipc_msg_spec is not None
-    # for the decoder such that all sub-type msgs in our SCIPP
+        and ipc_pld_spec
-    # will automatically decode to a type-"limited" payload (`Struct`)
+    ):
-    # object (set).
+        raise RuntimeError(
-    payload_type_spec: Union[Type[Msg]]|None = None
+            f'If a payload spec is provided,\n'
-    if payload_types:
+            "the builtin SC-shuttle-protocol's msg set\n"
+            f'(i.e. `{Msg}`) MUST be used!\n\n'
+            f'However both values were passed as => mk_codec(\n'
+            f'   ipc_msg_spec={ipc_msg_spec}`\n'
+            f'   ipc_pld_spec={ipc_pld_spec}`\n)\n'
+        )
+
+    elif (
+        ipc_pld_spec
+        and
+
+        # XXX required for now (or maybe forever?) until
+        # we can dream up a way to allow parameterizing and/or
+        # custom overrides to the `Msg`-spec protocol itself?
+        ipc_msg_spec is None
+    ):
+        # (manually) generate a msg-payload-spec for all relevant
+        # god-boxing-msg subtypes, parameterizing the `Msg.pld: PayloadT`
+        # for the decoder such that all sub-type msgs in our SCIPP
+        # will automatically decode to a type-"limited" payload (`Struct`)
+        # object (set).
         (
-            payload_type_spec,
+            ipc_msg_spec,
             msg_types,
         ) = mk_msg_spec(
-            payload_type=payload_types,
+            payload_type_union=ipc_pld_spec,
         )
-        assert len(payload_type_spec.__args__) == len(msg_types)
+        assert len(ipc_msg_spec.__args__) == len(msg_types)
+        assert ipc_msg_spec
 
-        # TODO: sub-decode `.pld: Raw`?
+        dec = msgpack.Decoder(
-        # see similar notes inside `.msg.types`..
+            type=ipc_msg_spec,  # like `Msg[Any]`
-        #
+        )
-        # not sure we'll end up wanting/needing this
+
-        # though it might have unforeseen advantages in terms
+    else:
-        # of enabling encrypted appliciation layer (only)
+        ipc_msg_spec = ipc_msg_spec or Any
-        # payloads?
+
-        #
+    enc = msgpack.Encoder(
-        # register sub-payload decoders to load `.pld: Raw`
+       enc_hook=enc_hook,
-        # decoded `Msg`-packets using a dynamic lookup (table)
+    )
-        # instead of a pre-defined msg-spec via `Generic`
+    dec = msgpack.Decoder(
-        # parameterization.
+        type=ipc_msg_spec,  # like `Msg[Any]`
-        #
+        dec_hook=dec_hook,
-        # (
+    )
-        #     tags,
-        #     payload_dec,
-        # ) = mk_tagged_union_dec(
-        #     tagged_structs=list(payload_types.__args__),
-        # )
-        # _payload_decs: (
-        #     dict[str, msgpack.Decoder]|None
-        # ) = {
-        #     # pre-seed decoders for std-py-type-set for use when
-        #     # `Msg.pld == None|Any`.
-        #     None: msgpack.Decoder(Any),
-        #     Any: msgpack.Decoder(Any),
-        # }
-        # for name in tags:
-        #     _payload_decs[name] = payload_dec
 
     codec = MsgCodec(
-        ipc_msg_spec=ipc_msg_spec,
+        _enc=enc,
-        payload_msg_spec=payload_type_spec,
+        _dec=dec,
-        **kwargs,
+        # payload_msg_specs=payload_msg_specs,
+        # **kwargs,
     )
-    assert codec.lib.__name__ == libname
 
-    # by default, config-n-cache the codec pair from input settings.
+    # sanity on expected backend support
-    if cache_now:
+    assert codec.lib.__name__ == libname
-        assert codec.enc
-        assert codec.dec
 
     return codec
 
 
 # instance of the default `msgspec.msgpack` codec settings, i.e.
 # no custom structs, hooks or other special types.
-_def_msgspec_codec: MsgCodec = mk_codec()
+_def_msgspec_codec: MsgCodec = mk_codec(ipc_msg_spec=Any)
 
 # NOTE: provides for per-`trio.Task` specificity of the
 # IPC msging codec used by the transport layer when doing
 # `Channel.send()/.recv()` of wire data.
 _ctxvar_MsgCodec: ContextVar[MsgCodec] = ContextVar(
     'msgspec_codec',
+
+    # TODO: move this to our new `Msg`-spec!
     default=_def_msgspec_codec,
 )
 
@@ -353,7 +421,7 @@ def limit_msg_spec(
     payload_types: Union[Type[Struct]],
 
     # TODO: don't need this approach right?
-    #
+    # -> related to the `MsgCodec._payload_decs` stuff above..
     # tagged_structs: list[Struct]|None = None,
 
     **codec_kwargs,

tractor/msg/types.py

@@ -22,9 +22,7 @@ that is,
 the "Structurred-Concurrency-Inter-Process-(dialog)-(un)Protocol".
 
 '''
-
 from __future__ import annotations
-# from contextlib import contextmanager as cm
 import types
 from typing import (
     Any,
@@ -36,14 +34,12 @@ from typing import (
 )
 
 from msgspec import (
-    msgpack,
-    Raw,
     Struct,
     UNSET,
 )
 
-
+# TODO: sub-decoded `Raw` fields?
-# TODO: can also remove yah?
+# -[ ] see `MsgCodec._payload_decs` notes
 #
 # class Header(Struct, tag=True):
 #     '''
@@ -70,7 +66,6 @@ class Msg(
     tree.
 
     '''
-    # header: Header
     # TODO: use UNSET here?
     cid: str|None  # call/context-id
 
@@ -94,9 +89,24 @@ class Msg(
     pld: PayloadT
 
 
-# TODO: better name, like `Call/TaskInput`?
+# TODO: caps based RPC support in the payload?
+#
+# -[ ] integration with our ``enable_modules: list[str]`` caps sys.
+#   ``pkgutil.resolve_name()`` internally uses
+#   ``importlib.import_module()`` which can be filtered by
+#   inserting a ``MetaPathFinder`` into ``sys.meta_path`` (which
+#   we could do before entering the ``Actor._process_messages()``
+#   loop)?
+#   - https://github.com/python/cpython/blob/main/Lib/pkgutil.py#L645
+#   - https://stackoverflow.com/questions/1350466/preventing-python-code-from-importing-certain-modules
+#   - https://stackoverflow.com/a/63320902
+#   - https://docs.python.org/3/library/sys.html#sys.meta_path
+#
+# -[ ] can we combine .ns + .func into a native `NamespacePath` field?
+#
+# -[ ]better name, like `Call/TaskInput`?
+#
 class FuncSpec(Struct):
-    # TODO: can we combine these 2 into a `NamespacePath` field?
     ns: str
     func: str
 
@@ -249,7 +259,7 @@ class Error(Msg):
 
 
 def mk_msg_spec(
-    payload_type: Union[Type] = Any,
+    payload_type_union: Union[Type] = Any,
     boxing_msg_set: set[Msg] = {
         Started,
         Yield,
@@ -261,10 +271,13 @@ def mk_msg_spec(
     list[Type[Msg]],
 ]:
     '''
-    Generate a payload-type-parameterized `Msg` specification such
+    Create a payload-(data-)type-parameterized IPC message specification.
-    that IPC msgs which can be `Msg.pld` (payload) type
+
-    limited/filterd are specified given an input `payload_type:
+    Allows generating IPC msg types from the above builtin set
-    Union[Type]`.
+    with a payload (field) restricted data-type via the `Msg.pld:
+    PayloadT` type var. This allows runtime-task contexts to use
+    the python type system to limit/filter payload values as
+    determined by the input `payload_type_union: Union[Type]`.
 
     '''
     submsg_types: list[Type[Msg]] = Msg.__subclasses__()
@@ -287,7 +300,7 @@ def mk_msg_spec(
         # -[ ] is there a way to get it to work at module level
         #   just using inheritance or maybe a metaclass?
         #
-        # index_paramed_msg_type: Msg = msgtype[payload_type]
+        # index_paramed_msg_type: Msg = msgtype[payload_type_union]
 
         # TODO: WHY do we need to dynamically generate the
         # subtype-msgs here to ensure the `.pld` parameterization
@@ -300,7 +313,7 @@ def mk_msg_spec(
             (
                 # XXX NOTE XXX this seems to be THE ONLY
                 # way to get this to work correctly!?!
-                Msg[payload_type],
+                Msg[payload_type_union],
                 Generic[PayloadT],
             ),
             {},
@@ -322,71 +335,3 @@ def mk_msg_spec(
         payload_type_spec,
         msg_types,
     )
-
-
-# TODO: integration with our ``enable_modules: list[str]`` caps sys.
-#
-# ``pkgutil.resolve_name()`` internally uses
-# ``importlib.import_module()`` which can be filtered by inserting
-# a ``MetaPathFinder`` into ``sys.meta_path`` (which we could do before
-# entering the ``Actor._process_messages()`` loop).
-# https://github.com/python/cpython/blob/main/Lib/pkgutil.py#L645
-# https://stackoverflow.com/questions/1350466/preventing-python-code-from-importing-certain-modules
-#   - https://stackoverflow.com/a/63320902
-#   - https://docs.python.org/3/library/sys.html#sys.meta_path
-
-# TODO: do we still want to try and support the sub-decoder with
-# `Raw` technique in the case that the `Generic` approach gives
-# future grief?
-#
-# sub-decoders for retreiving embedded
-# payload data and decoding to a sender
-# side defined (struct) type.
-_payload_decs:  dict[
-    str|None,
-    msgpack.Decoder,
-] = {
-    # default decoder is used when `Header.payload_tag == None`
-    None: msgpack.Decoder(Any),
-}
-
-
-def dec_payload(
-    msg: Msg,
-    msg_dec: msgpack.Decoder = msgpack.Decoder(
-        type=Msg[Any]
-    ),
-
-) -> Any|Struct:
-
-    msg: Msg = msg_dec.decode(msg)
-    payload_tag: str = msg.header.payload_tag
-    payload_dec: msgpack.Decoder = _payload_decs[payload_tag]
-    return payload_dec.decode(msg.pld)
-
-
-def enc_payload(
-    enc: msgpack.Encoder,
-    payload: Any,
-    cid: str,
-
-) -> bytes:
-
-    # tag_field: str|None = None
-
-    plbytes = enc.encode(payload)
-    if b'msg_type' in plbytes:
-        assert isinstance(payload, Struct)
-
-        # tag_field: str = type(payload).__name__
-        payload = Raw(plbytes)
-
-    msg = Msg(
-        cid=cid,
-        pld=payload,
-        # Header(
-        #     payload_tag=tag_field,
-        #     # dialog_id,
-        # ),
-    )
-    return enc.encode(msg)