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Author SHA1 Message Date
Joseph Doherty 1db900edef mbproxy: add opt-in response cache (Phase 11) 
Layers a per-PLC, per-tag response cache on top of Phase 10's coalescing.
Cache is OFF by default per tag (CacheTtlMs = 0); a fresh deployment with no
TTL config behaves identically to Phase 10. Operators opt tags in by setting
CacheTtlMs > 0 on a BcdTagOptions entry (or DefaultCacheTtlMs > 0 on a
PlcOptions entry), explicitly acknowledging the staleness window.

Cache lookup order: cache -> coalesce -> backend. A cache hit short-circuits
both Phase 10's coalescing path and Phase 9's backend send. Cache stores
POST-rewriter PDU bytes so hits never re-invoke the BCD rewriter. FC06/FC16
write responses invalidate every cached entry whose address range overlaps
the write (half-open interval math).

New types (Mbproxy.Proxy.Cache, all internal):
- CacheKey (record-struct, same shape as CoalescingKey but kept SEPARATE so
  the two phases evolve independently).
- CacheEntry, ResponseCache (IDisposable; LRU + PeriodicTimer eviction
  loop), CacheInvalidator (pure overlap matcher), CacheLogEvents (stable
  mbproxy.cache.* names).

Multi-tag range TTL = min(TTLs); any tag with TTL = 0 in the range disables
caching for the whole read (conservative-by-design).

Options surface:
- BcdTagOptions.CacheTtlMs (nullable int; null = fall through to PLC default)
- PlcOptions.DefaultCacheTtlMs
- MbproxyOptions.Cache.{AllowLongTtl, MaxEntriesPerPlc, EvictionIntervalMs}
- TTL > 60_000 ms requires Cache.AllowLongTtl = true (reload validation).

Admin counters (Tier 1.8 + Tier 2 cache-memory KPIs from docs/kpi.md):
- CacheHitCount, CacheMissCount, CacheInvalidations on ProxyCounters.
- CacheEntryCount, CacheBytes via a new ICacheStatsProvider snapshot path.
- /status.json and the HTML page surface a new Cache cell per PLC row.

Hot-reload: any tag-list change to a PLC reseats the per-PLC context with a
fresh cache; the old cache is disposed inside ReplaceContextAsync. Per-tag
flush granularity is intentionally not implemented in v1.

PLCs with no cache-eligible tags (every resolved tag has CacheTtlMs = 0)
get Cache = null on the context and skip the eviction timer entirely, so
the no-cache path is byte-identical to Phase 10.

Tests (32 new unit + 5 new E2E = 37 new; suite now 314 unit + 48 E2E):
- CacheKeyTests, CacheEntryTests (records + boundary semantics).
- CacheInvalidatorTests: full overlap, both partials, adjacent-not-
  overlapping, disjoint, different unit ID + auxiliary FC-filter / zero-qty.
- ResponseCacheTests: round-trip, lazy expiry, range invalidation,
  unit-id filter, LRU bound, LRU access tracking, concurrent get/set,
  dispose, clear, approximate-bytes accounting.
- ResponseCacheMultiplexerTests (stub-backend): hit short-circuits
  coalescing, BCD-decoded bytes are cached not raw, FC06 invalidates
  overlapping, non-overlapping write does not invalidate, multi-tag
  TTL=min rule, regression-cache-disabled-by-default-is-Phase-10, hit
  works even when backend unreachable.
- ResponseCacheE2ETests (pymodbus DL205 sim, sequential reads):
  * Headline: 10 reads with TTL=1000 ms -> 9 hits, 1 miss, 1 backend trip.
  * TTL expiry path with sleep > TTL.
  * Write invalidation through the proxy on a scratch register.
  * BCD-decoded bytes are cached, not raw BCD nibbles.
  * Regression: Cache disabled by default -> behaviour byte-identical to
    Phase 10.

Pre-existing flake hardened: BackendDisconnect_CascadesToAllUpstreams now
polls briefly for the cascade counter to absorb the inherent scheduling
gap between "upstream EOF observed" and "counter incremented inside
TearDownBackendAsync." Counter semantics unchanged.

Phase doc updated with implementation clarifications discovered during
this work (CacheKey kept separate from CoalescingKey, LastUsedTick is
long, FC06/FC16 startAddr/qty parsing extension, cache-pre-connect
short-circuit, write-invalidation only on successful responses).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
 2026-05-14 03:08:51 -04:00
Joseph Doherty 892b10baf4 mbproxy/docs: pivot design contract for Phase 11 response cache 
Lands the design-contract pivot ahead of any cache implementation code so
reviewers can evaluate the change to the "purely transparent proxy" stance
independently of the Phase-11 code that depends on it.

- docs/design.md: rewrite "What this is" / Read-coalescing / Failure-modes
  sections to acknowledge the opt-in cache; add new "Response cache (Phase
  11)" section covering lookup order (cache -> coalesce -> backend), multi-
  tag range TTL = min, post-rewriter storage, address-range-overlap write
  invalidation, hot-reload PLC-wide flush, no-persistence, AllowLongTtl gate,
  and LRU-bounded capacity. Extend log event table with mbproxy.cache.*
  events. Extend per-PLC status field table with cacheHitCount /
  cacheMissCount / cacheInvalidations / cacheEntryCount / cacheBytes.
  Extend hot-reload propagation table with CacheTtlMs / Cache.* rows.
- docs/kpi.md: graduate Tier 1.8 (response cache) from "requires Phase 11"
  to "shipped in Phase 11" and add Tier 2.4a cache-memory section.
- CLAUDE.md (mbproxy): update Purpose paragraph and the Architecture
  headline bullets to reflect the transparent-by-default + opt-in-cache
  contract; flip "Implementation complete through Phase 10" to "through
  Phase 11".
- install/mbproxy.config.template.json: add a fully-commented Mbproxy.Cache
  block and a CacheTtlMs example on a BcdTags.Global entry, with prominent
  staleness commentary documenting the design contract.

No code changes in this commit - implementation lands in a follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
 2026-05-14 02:35:35 -04:00
Joseph Doherty a2dba4bd07 mbproxy: add in-flight read coalescing (Phase 10) 
When two or more upstream clients send the same FC03/FC04 read while a
matching request is already in flight on the same PLC's multiplexed
backend socket, attach the late arrivals to the existing InFlightRequest
.InterestedParties list instead of opening a second backend round-trip.
The single backend response fans out to every attached party with each
party's original MBAP TxId restored individually. Zero post-response
staleness — coalescing operates entirely within the in-flight window
(microseconds to ~10 ms typical); the proxy is NOT a cache layer.

Headline mechanism:

- New record struct CoalescingKey(UnitId, Fc, StartAddress, Qty) keys
  the per-PLC InFlightByKeyMap. FC03 and FC04 are separate Modbus
  tables and never share a key; different unit IDs never coalesce;
  writes (FC06/FC16) bypass the coalescing path entirely.
- InFlightByKeyMap uses a simple lock around a Dictionary; atomic
  TryAttachOrCreate either appends a new party to the in-flight
  request's mutable List<InterestedParty> or invokes a factory to
  build a fresh entry. Per-entry MaxParties cap (default 32) bounds
  fan-out cost; past the cap, the next arrival opens a new entry.
- PlcMultiplexer.OnUpstreamFrameAsync takes the coalescing path for
  FC03/FC04 when Mbproxy.Resilience.ReadCoalescing.Enabled. The
  factory closure does the Phase-9 work (allocate TxId, add to
  CorrelationMap); the channel send happens AFTER returning from
  TryAttachOrCreate so the map lock is not held across the async send.
- Response fan-out in RunBackendReaderAsync removes the entry from
  InFlightByKeyMap before iterating InterestedParties, ensuring no
  concurrent attach can mutate the list during iteration.
- Cascade + watchdog paths also drain the key map so a stale entry
  cannot outlive its backend round-trip.

Counter accounting balance (per snapshot): CoalescedHitCount +
CoalescedMissCount equals total FC03 + FC04 requests since startup.
Even with coalescing disabled, every read still bumps Miss so dashboard
math stays balanced.

New surface (additive only):
- src/Mbproxy/Proxy/Multiplexing/CoalescingKey.cs
- src/Mbproxy/Proxy/Multiplexing/InFlightByKeyMap.cs
- src/Mbproxy/Proxy/Multiplexing/CoalescingLogEvents.cs
- ReadCoalescingOptions on ResilienceOptions
- CoalescedHitCount / CoalescedMissCount /
  CoalescedResponseToDeadUpstream counters surfaced on /status.json
  per PLC and as a compact "Coal" cell on the HTML status page.

Phase 9 test patch: TwoUpstreams_ProxyTxIds_AreDistinct_OnTheWire
previously read the same register from both clients (which now
coalesces). Patched to read two different addresses so the test still
proves distinct backend TxIds without violating the coalescing
contract.

Tests added: 24 new (19 unit + 5 E2E):
- CoalescingKeyTests (5)
- InFlightByKeyMapTests (6, includes concurrent stress)
- ReadCoalescingTests (8, stub-backend with deterministic delay)
- ReadCoalescingE2ETests (5, pymodbus simulator; coalescing-active
  during overlap is proven against the stub, not the sim, due to
  pymodbus 3.13's known concurrent-frame bug)

Total: 325 tests passing (282 unit + 43 E2E).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
 2026-05-14 02:26:06 -04:00
Joseph Doherty 56eee3c563 mbproxy: initial commit through Phase 9 (TxId multiplexing) 
Adds the mbproxy service end-to-end. Phases 00-08 implement the
production-ready single-listener / 1:1-backend transparent Modbus TCP
proxy with bidirectional BCD rewriting for the ~54-PLC DL205/DL260
fleet. Phase 9 replaces the connection layer with a single backend
socket per PLC plus MBAP TxId rewriting, lifting the H2-ECOM100's
4-concurrent-client cap as an operational ceiling.

Phase 9 additions of note:
- PlcMultiplexer + UpstreamPipe + TxIdAllocator + CorrelationMap
- InFlightRequest with IReadOnlyList<InterestedParty> (load-bearing
  for Phase 10 read coalescing — do not collapse to a single field)
- Per-request watchdog: surfaces Modbus exception 0x0B to upstream
  on BackendRequestTimeoutMs, defending against lost responses,
  dead-PLC paths, and pymodbus 3.13.0's concurrent-multiplexed-
  request bug (its ServerRequestHandler.last_pdu state race)
- Status DTO + HTML gain inFlight / maxInFlight / txIdWraps /
  disconnectCascades / queueDepth (Tier 1.6 in docs/kpi.md)

Tests: 263 unit + 38 E2E. Multiplexer correctness under truly
concurrent backend traffic is proved against a stub backend in
PlcMultiplexerTests; MultiplexerE2ETests paces requests so pymodbus
3.13's single-PDU framer stays in known-good mode.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
 2026-05-14 01:49:35 -04:00