feat: add SMPSerialRawTransport for Zephyr raw UART SMP

[JPHutchins]

Summary

Adds SMPSerialRawTransport for Zephyr 4.4's CONFIG_MCUMGR_TRANSPORT_RAW_UART — the raw (unencoded) SMP-over-UART transport that sends each SMP message as [8-byte header][payload] bytes with no framing, base64, or CRC. Smaller code size and faster transfers than the historical "SMP over console" framing, at the cost of being unable to share the UART with shell or log output.

The existing serial.py file is split into a package so the two serial transports share connection management via a common base class:

serial/
  __init__.py    re-exports SMPSerialTransport, SMPSerialRawTransport,
                 and the Auto / BufferSize / BufferParams / FragmentationStrategy API
  common.py      _SerialTransportBase: pyserial holder, the open/retry connect loop
                 (overridable for non-serial-port byte pipes), disconnect,
                 SerialException -> SMPTransportDisconnected translation, TX drain, RX poll
  encoded.py     SMPSerialTransport: base64 + CRC + delimiter framing and its
                 Auto/BufferSize/BufferParams sizing, now on the shared base (behavior unchanged)
  unencoded.py   SMPSerialRawTransport (new): writes bytes verbatim, reads the SMP header
                 then exactly its payload, raises on overrun / oversized header length

from smpclient.transport.serial import SMPSerialTransport (and the strategy exports) continues to work, so no migration is required for existing users of the encoded transport.

Rebased onto main after the FragmentationStrategy (Auto/BufferSize/BufferParams) and camas/integration-suite work merged; encoded.py carries that sizing logic on the new shared base. connect is a normal (non-final) method so the integration suite's socket-backed QemuSocketSerialTransport can swap the byte pipe.

Integration tests

The manifest-driven SMP-server suite already described a native_sim serial_raw fixture and skipped it ("smpclient has no raw-UART transport yet"). This PR makes it live:

• Vendors native_sim_serial_raw.exe from the pinned smp-server-fixtures release (0eae053d, sha256-verified against SHA256SUMS).
• Drops the client_supported skip in servers.py and builds SMPSerialRawTransport for serial_raw fixtures in conftest._build_transport, so the raw transport runs the generic echo / enumeration / MCUmgr-params suite.
• test_serial_raw.py adds a raw-specific check: after _initialize reads the server's params, the transport adopts buf_size as max_unencoded_size (the chunk size SMPClient.upload fills) — with no on-wire frame to subtract, unlike the encoded transport's buf_size - 4.

Note: there is deliberately no echo-at-max_unencoded_size round-trip. A full-buf_size echo returns MGMT_ERR_EMSGSIZE because the echo response mirrors the request and overflows the response netbuf — an echo-symmetry artifact, not a transport limit. The 384-byte request is received and parsed, so max_unencoded_size == buf_size is correct for the upload direction (large request, small response).

Related

• Upstream: mgmt: mcumgr: transport: uart: Add support for non-console raw mode zephyrproject-rtos/zephyr#101821 — mgmt: mcumgr: transport: uart: Add support for non-console raw mode (the Zephyr PR this transport speaks to)
• Kconfig context: RFC: Breaking API Change: mgmt: mcumgr: transport: uart: Change Kconfig to depends on zephyrproject-rtos/zephyr#102242 — RFC for the UART_MCUMGR_RAW_PROTOCOL Kconfig split that determines which transport applies
• Downstream RFC: RFC: Use URIs for transport selection and config smpmgr#35 — transport URI selection in smpmgr will need to expose the new transport

Test plan

• camas check (ruff + pydoclint + mypy + unit tests) — 363 passed, 14 skipped
• camas test_integration — 207 passed, 91 skipped, incl. the native_sim.serial_raw fixture across echo / enumeration / MCUmgr-params and the raw-specific buf_size test
• New raw transport unit tests (test_smp_serial_raw_transport.py) + an MTU-parametrized SMPClient.upload() chunking test over the raw transport
• Existing SMPSerialTransport suite passes unchanged (behavior-preserving refactor onto the shared base)
• Manual smoke test against a physical CONFIG_MCUMGR_TRANSPORT_RAW_UART=y target

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a new raw (unencoded) SMP-over-UART transport for Zephyr’s CONFIG_MCUMGR_TRANSPORT_RAW_UART, while refactoring the existing base64/framed serial transport into a package with shared connection management.

Changes:

• Introduces SMPSerialRawTransport implementing Zephyr “raw UART” SMP message exchange ([8-byte header][payload]) with MTU-based send limiting.
• Refactors existing SMPSerialTransport to share connect/disconnect/TX drain/read helpers via a _SerialTransportBase in serial/common.py.
• Updates and expands the test suite, including a new end-to-end MTU-parametrized upload test for the raw transport.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/test_smp_serial_transport.py	Updates serial mocking target to the new serial.common.Serial location.
tests/test_smp_serial_raw_transport.py	Adds unit tests for the new raw serial transport behavior.
tests/test_smp_client.py	Adds an MTU-parametrized upload test exercising chunking with the raw transport.
tests/test_base64.py	Updates internal base64 helper imports to the new serial.encoded module.
src/smpclient/transport/serial/init.py	Re-exports SMPSerialTransport and SMPSerialRawTransport from the new package layout.
src/smpclient/transport/serial/common.py	Adds shared serial connection management and SerialException translation utilities.
src/smpclient/transport/serial/encoded.py	Moves encoded transport onto the shared serial base class; behavior largely preserved.
src/smpclient/transport/serial/unencoded.py	Implements the new raw SMP serial transport.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

[JPHutchins]

This needs rebase since a lot has changed with serial transport capabilities and integration tests.

[JPHutchins]

After rebase, would be nice to add some integration tests for the MCUBoot raw transport: mcu-tools/mcuboot#2755

[JPHutchins]

Support for: zephyrproject-rtos/zephyr#101821