As per much tinkering, re-designs and preceding rubber-ducking via many
"commit msg novelas", **finally** this adds the (hopefully) final
missing layer for typed msg safety: `tractor.msg._ops.PldRx`
(or `PayloadReceiver`? haven't decided how verbose to go..)
Design justification summary:
------ - ------
- need a way to be as-close-as-possible to the `tractor`-application
such that when `MsgType.pld: PayloadT` validation takes place, it is
straightforward and obvious how user code can decide to handle any
resulting `MsgTypeError`.
- there should be a common and optional-yet-modular way to modify
**how** data delivered via IPC (possibly embedded as user defined,
type-constrained `.pld: msgspec.Struct`s) can be handled and processed
during fault conditions and/or IPC "msg attacks".
- support for nested type constraints within a `MsgType.pld` field
should be simple to define, implement and understand at runtime.
- a layer between the app-level IPC primitive APIs
(`Context`/`MsgStream`) and application-task code (consumer code of
those APIs) should be easily customized and prove-to-be-as-such
through demonstrably rigorous internal (sub-sys) use!
-> eg. via seemless runtime RPC eps support like `Actor.cancel()`
-> by correctly implementing our `.devx._debug.Lock` REPL TTY mgmt
dialog prot, via a dead simple payload-as-ctl-msg-spec.
There are some fairly detailed doc strings included so I won't duplicate
that content, the majority of the work here is actually somewhat of
a factoring of many similar blocks that are doing more or less the same
`msg = await Context._rx_chan.receive()` with boilerplate for
`Error`/`Stop` handling via `_raise_from_no_key_in_msg()`. The new
`PldRx` basically provides a shim layer for this common "receive msg,
decode its payload, yield it up to the consuming app task" by pairing
the RPC feeder mem-chan with a msg-payload decoder and expecting IPC API
internals to use **one** API instead of re-implementing the same pattern
all over the place XD
`PldRx` breakdown
------ - ------
- for now only expects a `._msgdec: MsgDec` which allows for
override-able `MsgType.pld` validation and most obviously used in
the impl of `.dec_msg()`, the decode message method.
- provides multiple mem-chan receive options including:
|_ `.recv_pld()` which does the e2e operation of receiving a payload
item.
|_ a sync `.recv_pld_nowait()` version.
|_ a `.recv_msg_w_pld()` which optionally allows retreiving both the
shuttling `MsgType` as well as it's `.pld` body for use cases where
info on both is important (eg. draining a `MsgStream`).
Dirty internal changeover/implementation deatz:
------ - ------
- obvi move over all the IPC "primitives" that previously had the duplicate recv-n-yield
logic:
- `MsgStream.receive[_nowait]()` delegating instead to the equivalent
`PldRx.recv_pld[_nowait]()`.
- add `Context._pld_rx: PldRx`, created and passed in by
`mk_context()`; use it for the `.started()` -> `first: Started`
retrieval inside `open_context_from_portal()`.
- all the relevant `Portal` invocation methods: `.result()`,
`.run_from_ns()`, `.run()`; also allows for dropping `_unwrap_msg()`
and `.Portal_return_once()` outright Bo
- rename `Context.ctx._recv_chan` -> `._rx_chan`.
- add detailed `Context._scope` info for logging whether or not it's
cancelled inside `_maybe_cancel_and_set_remote_error()`.
- move `._context._drain_to_final_msg()` -> `._ops.drain_to_final_msg()`
since it's really not necessarily ctx specific per say, and it does
kinda fit with "msg operations" more abstractly ;)
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