feat(plc4j/slmp): add Batch Write (0x1401) support

[LivingLikeKrillin]

What & why

The SLMP (MELSEC Communication Protocol) driver merged in #2640 is read-only. This adds write
support via the 3E-frame Batch Write command 0x1401 in word units (subcommand 0x0000),
mirroring the existing Batch Read (0x0401) path: same 3E framing, same word-device addressing
(D / W / R), the same typed-value layer, the same single-frame constraints, and the same per-tag
error isolation. The only genuinely new pieces are a request-data type that carries the payload words
and a value encode that is the mirror of the existing decode.

Changes

• mspec (protocols/slmp/slmp.mspec) — add a SlmpWriteRequest case (0x1401) to the
  SlmpRequestData typeSwitch: the same device addressing as SlmpReadRequest
  (uint 24 headDeviceNumber + SlmpDeviceCode + uint 16 numberOfPoints) followed by
  byte[] writeData count 'numberOfPoints * 2'. The payload is carried as raw bytes; typed encoding
  stays in the driver layer, symmetric with how the read response leaves responseData raw. The
  generated readwrite model (SlmpWriteRequest, updated SlmpRequestData) is regenerated and
  committed. No response-type change is needed — Batch Write success is endCode 0x0000 with an
  empty payload, which the existing SlmpResponseFrame3E already handles.
• SlmpDataType.encode(PlcValue, quantity) — the mirror of decode: little-endian, same buffer
  options, per-type WORD/UINT → writeUnsignedInt(16), INT → writeSignedShort(16),
  DINT → writeSignedInt(32), UDINT → writeUnsignedLong(32), REAL → writeFloat(32). Returns
  null on a type/arity mismatch (the caller maps that to INVALID_DATA), symmetric with decode
  returning null on a short buffer.
• SlmpResponseMapper.mapWriteTag — endCode 0x0000 → OK, otherwise log + REMOTE_ERROR.
• SlmpConnection.onWrite / writeSingleTag — structurally mirror onRead / readSingleTag:
  per-tag sequential dispatch, executeThrottled + the single-slot request/response correlation,
  allOf(...).handle(...) partial-failure isolation (timeout → REMOTE_ERROR, other → INTERNAL_ERROR),
  building a 0x1401 frame. An un-encodable value short-circuits to INVALID_DATA without sending a frame.
• SlmpDriver.canWrite() → true — declare the capability alongside the existing canRead().
• Housekeeping (no behavior change): the shared SlmpTag single-frame ceiling is unchanged at 960
  words, but its javadoc and the PlcInvalidTagException message it throws are generalized from
  "Batch Read" to "Batch Read/Write" (the ceiling now guards both paths); the driver module's POM
  <description> and the mspec header comments drop the now-inaccurate "read-only" wording; and the
  SH-080008 section references are corrected against the manual (device access is chapter 8; §8.1 is
  the device data spec, §8.2 is "Batch Read and Write" — the comments previously mislabelled
  batch read as §8.1).

Data types & devices

Word devices D (decimal), W (hex), R (decimal) and data types WORD, INT, UINT, DINT,
UDINT, REAL — the same set the reader supports. Multi-element writes (quantity ≥ 1) are bounded by
the existing 960-word single-frame ceiling, enforced in the shared SlmpTag validation for both read
and write (the numeric limit is unchanged).

Out of scope

Random Write (0x1402), bit-unit writes (subcommand 0x0001), bit devices (M/X/Y/B), and multi-frame
splitting — consistent with the read driver's current scope.

Review follow-ups (commits after the initial review)

• Echo builder error items — a tag the request builder had already rejected (bad address →
  INVALID_ADDRESS, un-coercible value → INVALID_DATA) reached onWrite as a null tag/value and
  NPE'd into a misleading INTERNAL_ERROR. Both onWrite and onRead now check
  getTagResponseCode(...) first and echo the builder's code (the pattern SimulatedConnection
  uses); nothing is sent on the wire for rejected tags. onRead had the same pre-existing flaw and
  is fixed symmetrically.
• Unexpected-payload tripwire — per SH-080008 a Batch Write success carries no response data, so
  endCode 0x0000 with a non-empty payload (e.g. a late, mis-attributed read response under the
  documented no-correlation-id caveat) now maps to REMOTE_ERROR instead of a silent OK.
• Timed-out-write semantics documented — a timed-out write may nevertheless have been applied by
  the device (3E carries no correlation id, so the driver cannot tell); noted on sendRequest/onWrite
  so callers don't blindly retry side effects.
• Quieter logging for un-coercible values (expected caller error → DEBUG, no stack trace), a
  reflection-free capability test, and message-casing/naming cleanups from the first review round.

Testing (hardware-free, mirrors the reader)

• New unit tests: SlmpDataTypeEncodeTest (11 — per-type little-endian encoding, high-bit unsigned,
  two's-complement, DINT low-word-first, IEEE754, list encoding, the three null-return guard paths,
  and encode → decode round-trips), SlmpConnectionWritePathTest (4 — OK / device-error →
  REMOTE_ERROR / timeout → REMOTE_ERROR / builder-error echo with per-tag isolation),
  SlmpDriverTest (1 — the driver reports canRead/canWrite), plus write cases in
  SlmpErrorMappingTest (3) and SlmpRequestBuildTest (1), and a read-side builder-error echo test.
• The connection-level encode()==null → INVALID_DATA short-circuit is a two-line branch over the
  same null the encode-level guard tests pin directly; the builder rejects un-coercible values
  before the driver sees them (now covered by the builder-error echo tests).
• New end-to-end driver-testsuite case: a PlcWriteRequest for D350 = 0x1234 is driven through
  the real driver, the exact 0x1401 frame bytes are checked, an empty-payload success response is fed
  back, and the api response code is asserted OK.
• Full plc4j-driver-slmp module suite green: 62 unit tests + the 2 driver-testsuite IT cases (read + write).

Notes for reviewers

• Wire field layouts and the 0x1401 command come from the public Mitsubishi manual SH(NA)-080008
  (§8.2, "Batch Read and Write") — the same source and citation discipline as the merged reader; a
  fact/spec, not copyrightable expression. encode / onWrite / mapWriteTag are mechanical mirrors
  of the existing decode/read path. The request layout ([head device 3B][device code 1B][points 2B]
  [write data]) and "there is no response data for this command" were checked against §8.2 (p.92).
• Beyond the committed tests, I validated the full write→read round-trip end-to-end over TCP against an
  independent SLMP 3E server built from the manual: writing WORD / INT / DINT / REAL / WORD[3] and
  reading them back all matched, with the expected little-endian, low-word-first multi-word ordering.
• This touches only the SLMP driver + its protocol mspec — no change to AbstractBuffer or the shared
  buffers.

[Copilot]

Pull request overview

This PR adds SLMP 3E-frame Batch Write (0x1401) support (word units, subcommand 0x0000) to the PLC4J SLMP driver, mirroring the existing Batch Read path while keeping the protocol layer payload as raw bytes and doing typed value encoding/decoding in the driver.

Changes:

• Extend the SLMP protocol mspec + generated model to support SlmpWriteRequest (0x1401) with [headDevice][deviceCode][points][writeData].
• Implement driver-side typed encode (SlmpDataType.encode) and the write execution path (SlmpConnection.onWrite / writeSingleTag) including per-tag error isolation and endCode mapping.
• Add unit + integration tests (including driver-testsuite XML) to validate request bytes and response handling; update docs/comments/POM wording to remove “read-only”.

Reviewed changes

Copilot reviewed 14 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
protocols/slmp/src/test/resources/protocols/slmp/ParserSerializerTestsuite.xml	Updates manual section reference in protocol testsuite comments.
protocols/slmp/src/main/resources/protocols/slmp/slmp.mspec	Adds Batch Write request layout to the protocol model and updates header comments/scope.
plc4j/drivers/slmp/src/test/resources/slmp/slmp-driver-testsuite.xml	Adds an end-to-end driver-testsuite testcase covering Batch Write bytes + OK mapping.
plc4j/drivers/slmp/src/test/java/org/apache/plc4x/java/slmp/SlmpRequestBuildTest.java	Adds a unit test asserting the exact serialized 0x1401 request frame bytes.
plc4j/drivers/slmp/src/test/java/org/apache/plc4x/java/slmp/SlmpErrorMappingTest.java	Adds unit tests for write endCode → response code mapping.
plc4j/drivers/slmp/src/test/java/org/apache/plc4x/java/slmp/SlmpDriverTest.java	Adds a driver capability test for canRead/canWrite.
plc4j/drivers/slmp/src/test/java/org/apache/plc4x/java/slmp/SlmpDataTypeEncodeTest.java	Adds unit tests for typed value encoding and encode↔decode round-trips.
plc4j/drivers/slmp/src/test/java/org/apache/plc4x/java/slmp/SlmpConnectionWritePathTest.java	Adds write-path tests for OK/device-error/timeout mappings via scripted transport.
plc4j/drivers/slmp/src/main/java/org/apache/plc4x/java/slmp/tag/SlmpTag.java	Generalizes single-frame word ceiling messaging/docs from read-only to read/write.
plc4j/drivers/slmp/src/main/java/org/apache/plc4x/java/slmp/SlmpResponseMapper.java	Adds mapWriteTag for endCode-only Batch Write responses.
plc4j/drivers/slmp/src/main/java/org/apache/plc4x/java/slmp/SlmpDriver.java	Declares canWrite() -> true.
plc4j/drivers/slmp/src/main/java/org/apache/plc4x/java/slmp/SlmpDataType.java	Adds encode(...) to mirror existing typed decode logic.
plc4j/drivers/slmp/src/main/java/org/apache/plc4x/java/slmp/SlmpConnection.java	Implements onWrite and request building/sending for 0x1401.
plc4j/drivers/slmp/src/main/generated/org/apache/plc4x/java/slmp/readwrite/SlmpWriteRequest.java	Generated request type for Batch Write payload.
plc4j/drivers/slmp/src/main/generated/org/apache/plc4x/java/slmp/readwrite/SlmpRequestData.java	Updates discriminated parsing to include the new 0x1401 case.
plc4j/drivers/slmp/pom.xml	Updates module description to no longer claim “read-only”.

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 17 changed files in this pull request and generated no new comments.