The DL205/DL260 ECOM emits no TCP keepalives, so an idle backend socket
can be silently dropped by a middlebox (switch, firewall, NAT) after
2-5 minutes. Enable OS SO_KEEPALIVE on backend and accepted upstream
sockets, and drive a periodic synthetic FC03 heartbeat on each idle
backend socket so a dead path is detected before a real client request
hits it. Controlled by Connection.Keepalive (ON by default).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Comments described the *history* of how the code arrived (phase numbers,
wave IDs, review IDs, dated TODOs) instead of what it does today. That
scaffolding rotted as the codebase evolved. Cleaned 60 source files +
.gitignore; behaviour unchanged (387/387 tests still pass).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Resolves the 21 Major findings catalogued in
codereviews/2026-05-14/RemediationPlan.md (Wave 2). Tests: 370 pass / 0 fail
(baseline 363 + 7 new W2 regression tests).
Multiplexer / concurrency:
W2.1 ConfigReconciler.Attach now threads the live coalescingAccessor through
to add/restart-built supervisors so a hot-reload of
ReadCoalescing.{Enabled,MaxParties} propagates to PLCs added or
restarted via reload.
W2.2 PlcMultiplexer._disposed and UpstreamPipe._disposed are now volatile
for ARM/portability defense.
W2.3 ProxyWorker._supervisors / ConfigReconciler._supervisors switched from
Dictionary to ConcurrentDictionary; reconciler uses TryRemove. The
outer Apply is serialised by a semaphore but the inner Add/Remove/
Restart Task.WhenAll continuations run in parallel.
W2.4 Counter parity for cache miss + coalescing-saturation miss documented
inline (per-design contract; behavior unchanged).
W2.5 _disposeCts.Dispose() and _connectGate.Dispose() guarded against late
watchdog ticks.
W2.6 _connectGate disposed in DisposeAsync.
W2.7 Inline doc clarifying the post-rewriter FC byte read.
Cache / hot-reload:
W2.8 PlcListenerSupervisor.ReplaceContextAsync now calls Clear() to capture
the entry count, emits mbproxy.cache.flushed, then disposes the old
cache. Previously the event was defined but never emitted.
W2.9 Inline doc explaining the implicit "skip cache invalidation while
recovering" gating (no backend reader during recovery → no FC06/FC16
response → no invalidation).
W2.10 ReloadValidator now re-checks resolved per-tag CacheTtlMs against
Cache.AllowLongTtl after BcdTagMapBuilder folds the per-PLC default.
BCD rewriter:
W2.11 Duplicate addresses detected within Global itself and within the per-PLC
Add list itself, BEFORE the working dictionary collapses keys. Cross-list
collisions (Global vs Add) remain the documented width-override pattern.
Previously the DuplicateAddress error was unreachable dead code.
W2.12 OverlappingHighRegister reports each colliding pair exactly once
(canonicalised low/high pair tracked in a HashSet).
W2.13 FC16 32-bit write rejects clientLow > 9999 or clientHigh > 9999 BEFORE
the high*10000+low reconstruction. Without this guard, (high=9999,
low=9999) silently re-encoded as (high=9998, low=9999), losing 1 from
the high word.
W2.14 FC16 validates pdu.Length >= 6 + qty*2 upfront — no half-rewritten
requests when a malformed client claims more registers than it ships.
Supervisor:
W2.15 WaitForInitialBindAttemptAsync now backed by TaskCompletionSource
instead of 10ms busy-poll. Resolves race against fast Stopped→Bound→
Stopped transitions and hangs when the supervisor task throws.
W2.16 StartAsync refuses re-entry on a non-Stopped supervisor (was leaking
the previous _supervisorCts).
W2.17 New TransitionTo helper writes _state, _lastBindError, and (optionally)
_recoveryAttempts under one lock. Snapshot() reads under the same lock
so the status page never reports an inconsistent triple. Truncate
helper extracted (was copy-pasted across three sites).
W2.18 MbproxyOptionsValidator + ReloadValidator reject Connection.{Backend
ConnectTimeoutMs, BackendRequestTimeoutMs, GracefulShutdownTimeoutMs}
<= 0. Misconfigured 0 produces immediate CancelAfter(0) failures.
Hosting / diagnostics:
W2.20 ProxyWorker.StopAsync supervisor-stop deadline now reads from
IOptionsMonitor.CurrentValue.Connection.GracefulShutdownTimeoutMs
(was hard-coded 5s).
W2.21 src/Mbproxy/appsettings.json deleted; the published file is now a Link
to install/mbproxy.config.template.json so the binary ships with a
usable, fully-commented example config instead of an empty stub. Tests
strip the inherited file from their bin via an AfterTargets="Build"
Target so they don't pick up the template's example PLCs.
W2.22 invalidBcdWarnings (PlcPdusStatus) and codeOther (ExceptionCounts)
added to StatusDto, plumbed through StatusSnapshotBuilder, surfaced
in StatusHtmlRenderer table cells.
W2.23 EventLogBridge caches EventLog.SourceExists at construction so Emit
doesn't hit the registry on every Error+ log line.
New regression tests:
ReloadValidatorTests:
Validate_PerTagCacheTtl_Above60s_Without_AllowLongTtl_Fails
Validate_PerTagCacheTtl_Above60s_With_AllowLongTtl_Passes
Validate_ResolvedTtl_FromPerPlcDefault_AboveCap_Fails
Validate_ZeroBackendConnectTimeoutMs_Fails
Validate_NegativeGracefulShutdownTimeoutMs_Fails
BcdPduPipelineTests:
FC16_32Bit_ClientHighOrLowAbove9999_PassesThroughRaw_WithInvalidBcdWarning
FC16_TruncatedRegisterData_PassesThroughRaw_NoPartialRewrite
Reworked tests in BcdTagMapBuilderTests for the W2.11 contract (Global dup,
Add dup, Add-overrides-Global accepted as width override).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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>
Joseph Doherty