refactor: S11.03 rename NullBuffer to PassthroughBuffer

[DavidCozens]

Purpose

Closes #397.

SolidSyslogNullBuffer is misnamed — it isn't a GoF Null Object. Its Write forwards directly into an injected SolidSyslogSender; its purpose is single-task targets where the application thread is willing to block on transport I/O. Calling it Null* has confused readers (the iec62443.md SR 6.1 row had to spell out "single-task / synchronous Send" because the name didn't). E11 already plans to migrate every stateful Created class onto SolidSyslogPoolAllocator; the rename belongs at some point in that work. Splitting it off from the Core sweep (S11.04) keeps both review surfaces small — the cross-tree identifier rename here, the pool semantics there.

Change Description

Purely mechanical rename observing docs/NAMING.md:

• Files (git mv): Core/Interface/SolidSyslogNullBuffer.h, Core/Source/SolidSyslogNullBuffer.c, Tests/SolidSyslogNullBufferTest.cpp → corresponding PassthroughBuffer paths. The test rename is detected at the 50% similarity threshold; the .h/.c pair fall under it because every line carries an identifier swap, but git history is intact via --find-renames.
• Tier 1: SolidSyslogNullBuffer_Create, _Destroy, struct SolidSyslogNullBuffer, include guard SOLIDSYSLOGNULLBUFFER_H → SolidSyslogPassthroughBuffer_* / SOLIDSYSLOGPASSTHROUGHBUFFER_H.
• Tier 2: file-scope statics NullBuffer_Read, _Write, _SelfFromBase, _Instance → PassthroughBuffer_* per the strip-only rule.
• Tests: TEST_GROUP(SolidSyslogPassthroughBuffer). Individual TEST names left alone — they describe behaviour.
• Call sites: Tests/SolidSyslogTest.cpp (include + two Create/Destroy calls), two CMakeLists.txt source entries.
• Docs: CLAUDE.md audience-table row, README.md (two prose), SKILL.md (one prose), docs/iec62443.md (three SR rows), Core/Interface/SolidSyslogBlockStore.h recursion-gotcha comment, Bdd/features/tcp_singletask.feature Feature description, Bdd/features/steps/syslog_steps.py historical-context block.
• MISRA: misra_suppressions.txt 11.3 entry path updated (line number unchanged — same content).

Three adjacent doc honesty corrections forced by the rename (substantive edits in an otherwise mechanical story — calling them out explicitly):

1. CLAUDE.md Design Patterns null-object bullet dropped PassthroughBuffer from the list. Not a null object — keeping it would propagate the false framing the rename is trying to fix. NullSecurityPolicy + NullStore remain (genuine no-ops).
2. SKILL.md Architecture line "Null object pattern throughout (NullBuffer is the buffer null object)" — parenthetical struck. The remaining "Null object pattern throughout" stands (NullMutex / NullStore / NullSecurityPolicy genuinely are).
3. Core/Source/SolidSyslog.c nil-collaborators comment block "(e.g. NullBuffer is a direct-send shim)" caveat removed. With the misleading example gone, the caveat no longer applies.

Three deliberate non-renames to keep visible:

• Tests/SolidSyslogTest.cpp::TEST(SolidSyslogLifecycle, CreateWithNullBufferReportsError) — NULL pointer, not the class.
• Tests/SolidSyslogUdpSenderTest.cpp::TEST(SolidSyslogUdpSenderBadSetup, SendWithNullBufferReportsErrorAndDoesNotSend) — NULL pointer, not the class.
• Bdd/Targets/FreeRtos/main.c:6 historical S08.04 comment — preserved as historical narrative.

Test Evidence

• No new tests, no behaviour change. The eight existing tests (now TEST_GROUP(SolidSyslogPassthroughBuffer)) carry over byte-for-byte except for the group identifier.
• Gates run locally: debug, clang-debug, sanitize, coverage, tidy, cppcheck, clang-format.
• Full suite green on both gcc and clang containers.
• Coverage: SolidSyslogPassthroughBuffer.c at 100% line (matches SolidSyslogNullBuffer.c's prior coverage — identical code, different name).
• cppcheck-misra: 88 hits on this branch, 88 on main — zero new findings, zero entries against SolidSyslogPassthroughBuffer.c. (Side-note: S11.02's closing notes recorded the baseline as "60". Re-running the identical CI command on main in isolation produces 88 — the earlier number was non-deterministic or a partial run. The true invariant — "no new findings introduced by the rename" — is met. The story body's AC E01: Core Syslog Formatting #3 inherits the same stale number; the real bar is "unchanged from main".)

Areas Affected

• Core/Interface/, Core/Source/ — the renamed pair plus three small touches (SolidSyslogBlockStore.h recursion comment, SolidSyslog.c nil-collaborators comment, CMakeLists.txt).
• Tests/ — renamed test file, group rename, two call sites in SolidSyslogTest.cpp, CMakeLists.txt.
• Bdd/features/ — feature description + step file historical-context comment.
• Root docs — CLAUDE.md, README.md, SKILL.md.
• docs/iec62443.md.
• misra_suppressions.txt.

Out of scope (carrying forward to S11.04): the Instance singleton, the void _Destroy(void) signature, the existing 11.3 storage-cast suppression on the SelfFromBase helper, the absence of a SOLIDSYSLOG_PASSTHROUGHBUFFER_POOL_SIZE tunable. S11.04 migrates this class onto SolidSyslogPoolAllocator and retires the cast in the same move.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Documentation

  • Updated architecture documentation, deployment guides, and compliance materials to reflect buffer implementation changes.

• Refactor

  • Replaced buffer implementation to optimize single-task system deployments.

• Tests

  • Updated test suite to validate new buffer implementation behavior and maintain full coverage.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7d26d7cd-d572-4f63-8f9f-474287d5c9be

📥 Commits

Reviewing files that changed from the base of the PR and between 4829dfc and 77b7c8e.

📒 Files selected for processing (18)

• Bdd/features/steps/syslog_steps.py
• Bdd/features/tcp_singletask.feature
• CLAUDE.md
• Core/Interface/SolidSyslogBlockStore.h
• Core/Interface/SolidSyslogNullBuffer.h
• Core/Interface/SolidSyslogPassthroughBuffer.h
• Core/Source/CMakeLists.txt
• Core/Source/SolidSyslog.c
• Core/Source/SolidSyslogNullBuffer.c
• Core/Source/SolidSyslogPassthroughBuffer.c
• DEVLOG.md
• README.md
• SKILL.md
• Tests/CMakeLists.txt
• Tests/SolidSyslogPassthroughBufferTest.cpp
• Tests/SolidSyslogTest.cpp
• docs/iec62443.md
• misra_suppressions.txt

💤 Files with no reviewable changes (2)

• Core/Interface/SolidSyslogNullBuffer.h
• Core/Source/SolidSyslogNullBuffer.c

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📝 Walkthrough

Walkthrough

A mechanical symbol rename of SolidSyslogNullBuffer to SolidSyslogPassthroughBuffer across public headers, implementation, build system, tests, and documentation. The buffer's behavior—write-through forwarding to a sender—is unchanged; the rename fixes a naming confusion between the actual "passthrough" semantics and the GoF Null Object pattern.

Changes

NullBuffer → PassthroughBuffer Symbol Rename

Layer / File(s)	Summary
PassthroughBuffer public API contract Core/Interface/SolidSyslogPassthroughBuffer.h	New header declares SolidSyslogPassthroughBuffer_Create(struct SolidSyslogSender* sender) and SolidSyslogPassthroughBuffer_Destroy(void) in place of the prior NullBuffer public functions.
PassthroughBuffer implementation and write-through semantics Core/Source/SolidSyslogPassthroughBuffer.c	New implementation defines the singleton buffer with create/destroy lifecycle wiring and PassthroughBuffer_Write that forwards all data to SolidSyslogSender_Send, and PassthroughBuffer_Read that always returns failure (reads unsupported).
Build system and test infrastructure updates Core/Source/CMakeLists.txt, Tests/CMakeLists.txt, Tests/SolidSyslogPassthroughBufferTest.cpp, Tests/SolidSyslogTest.cpp, misra_suppressions.txt	CMake source lists swap SolidSyslogNullBuffer.c for SolidSyslogPassthroughBuffer.c; test group renamed and setup/teardown fixture calls updated to SolidSyslogPassthroughBuffer_Create/_Destroy; MISRA suppression path updated to reference the new implementation file.
Documentation, comments, and semantic updates Core/Source/SolidSyslog.c, README.md, CLAUDE.md, SKILL.md, Core/Interface/SolidSyslogBlockStore.h, docs/iec62443.md, Bdd/features/tcp_singletask.feature, Bdd/features/steps/syslog_steps.py	All architecture tables, design-pattern guidance, recursion notes, and compliance docs updated to reference PassthroughBuffer; internal comment in SolidSyslog.c clarifies that file-static Nil collaborators are distinct from the public SolidSyslogNull* family; PassthroughBuffer removed from the "no null-pointer checks" design rule (it is not a true Null Object).
Devlog entry DEVLOG.md	New entry documents S11.03 scope, adjacent doc corrections, deliberate non-renames (e.g., CreateWithNullBuffer* test names that refer to NULL pointers), and verification gates (cppcheck-misra counts unchanged, coverage equivalence).

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• DavidCozens/solid-syslog#382: Prior refactoring of Core/Source/SolidSyslogNullBuffer.c internals; this PR removes and replaces that file with the renamed PassthroughBuffer implementation.
• DavidCozens/solid-syslog#378: Earlier changes to the NullBuffer implementation surface; this PR completes the rename and removes the old API entirely.
• DavidCozens/solid-syslog#368: MISRA suppression curation; this PR updates the suppression path from SolidSyslogNullBuffer.c:54 to SolidSyslogPassthroughBuffer.c:54.

🐰 A buffer renamed, no longer null,
PassthroughBuffer shines, candid and full—
Write-through it sends, with synchronous grace,
No more confusion in single-task space! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: a refactoring that renames NullBuffer to PassthroughBuffer, which is the primary objective of the PR.
Description check	✅ Passed	The PR description comprehensively covers Purpose (links #397), Change Description (detailed mechanical rename with tiers, file moves, call sites, docs, and three doc honesty corrections), Test Evidence (existing tests carry over, gates green, coverage parity, cppcheck-misra unchanged), and Areas Affected.
Linked Issues check	✅ Passed	The PR fully meets issue #397's requirements: all symbol renames across tiers (Tier 1 functions/struct/include guard, Tier 2 file-scope statics) are implemented, files renamed via git mv, call sites updated, docs/comments corrected, MISRA suppression path updated, three doc honesty edits applied, and three deliberate non-renames preserved.
Out of Scope Changes check	✅ Passed	All changes are scoped to the mechanical rename objective. No unrelated refactoring, no pool allocator migration, no structural improvements—only identifier renames, file moves, call-site updates, and doc rewrites directly tied to the rename purpose.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/s11-03-passthrough-buffer-rename

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[github-actions]

☀️   Quality Summary

   🚦   build-linux-gcc: 100% successful (✔️ 1145 passed, 🙈 2 skipped)
   🚦   build-freertos-host-tdd: 100% successful (✔️ 1265 passed, 🙈 2 skipped)
   🚦   build-linux-clang: 100% successful (✔️ 1097 passed, 🙈 2 skipped)
   🚦   sanitize-linux-gcc: 100% successful (✔️ 1097 passed, 🙈 2 skipped)
   🚦   integration-linux-openssl: 100% successful (✔️ 9 passed)
   🚦   integration-windows-openssl: 100% successful (✔️ 9 passed)
   🚦   bdd-linux-syslog-ng: 94% successful (✔️ 46 passed, 🙈 3 skipped)
   🚦   bdd-windows-otel: 90% successful (✔️ 44 passed, 🙈 5 skipped)
   🚦   bdd-freertos-qemu: 73% successful (✔️ 36 passed, 🙈 13 skipped)
   🚦   build-windows-msvc: 100% successful (✔️ 1001 passed, 🙈 1 skipped)
   🚦   build-linux-tunable-override: 100% successful (✔️ 1097 passed, 🙈 2 skipped)
   ⚠️   Clang-Tidy: 9 warnings (normal: 9)
   ⚠️   CPPCheck: No warnings

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Created by Quality Monitor v1.14.0 (#f3859fd). More details are shown in the GitHub Checks Result.