MTConnectDriver now implements IWritable over the Task-1 agent-client seam
(WriteObservationAsync -> the Agent's AllowPut POST surface). A write is
OBSERVATION INJECTION, not machine command: it sets what the Agent reports for
a DataItem, is visible to every consumer of that Agent, and is overwritten by
the next adapter/SHDR update. Off at two independent gates, both off by default
- the Agent's own AllowPut and the driver's write.enabled (Task 0).
Per-slot refusal order (never throws, strict N-in/N-out batch shape):
write disabled -> BadNotWritable
no live client -> BadNotConnected (ReadAsync's existing convention)
reference unresolved -> BadNodeIdUnknown
no resolvable device -> BadNodeIdUnknown
CONDITION category -> BadNotWritable
null / non-scalar value -> BadTypeMismatch
agent refusal OR throw -> BadCommunicationError
OperationCanceledException fills the remaining slots and returns. The Agent's
refusal text is logged at Warning and never enters DriverHealth.LastError
(type-only discipline); a refused write leaves health untouched.
Device-name resolution: TagBinding gains WriteTargetsByDataItemId, built in
BuildBinding from a probe-model walk that remembers which device each DataItem
was declared under (name, or id when nameless) plus its category. Falls back to
options.DeviceName; unresolvable -> BadNodeIdUnknown rather than a guess.
Values render via Convert.ToString(..., InvariantCulture) - so a Boolean writes
the invariant string "True"/"False", NOT "1"/"0". Arrays are refused rather
than rendered: Convert.ToString would emit the literal "System.Double[]", which
the Agent stores happily and which is invisible until read-back.
FINDING - the CurrentWrite bit does NOT key on SecurityClassification, and the
discovery stamping below is therefore cosmetic. Traced end to end: a browsed
leaf's SecurityClass survives into the browse session's AttributeInfo
(CapturedTreeBrowseSession.cs:53) and stops there - RawBrowseModal never reads
it, RawBrowseCommitMapper.MapLeaf hardcodes TagAccessLevel.Read, and Tag has no
SecurityClass column. AddressSpaceComposer:746/:809 sets Writable purely from
Tag.AccessLevel == ReadWrite; AddressSpaceApplier ANDs !IsArray;
OtOpcUaNodeManager.ComposeAccessLevel:2002 composes CurrentWrite from that
alone. Driver capability is never consulted at compose time either - IWritable
is checked only at runtime in DriverInstanceActor:755. Consequences: (a) raw
tags already committed keep their authored AccessLevel, so nothing this commit
does makes an existing node writable; (b) an operator must still set the tag to
ReadWrite for an MTConnect write to be reachable over OPC UA; (c) conversely a
ReadWrite tag on a non-IWritable driver has always advertised CurrentWrite and
failed only at the actor - pre-existing, not touched here.
Discovery stamps CanWrite(writeEnabled, dataItem) = write.enabled && !CONDITION
-> Operate, else ViewOnly - kept honest so the browse never advertises a tier
the write path would refuse (MQTT's CanWrite principle), with the caveat above
recorded verbatim at the call site.
Status-code constants are spelled WITHOUT MqttDriver's "Status" prefix, to
match the two this file already declares (BadCommunicationError,
BadNotConnected). StatusCodeParityTests strips either spelling and passes.
TDD: WriteAsync landed first as a NotImplementedException scaffold - 19 of 20
new tests red on behaviour, 1 (the capability assertion) green on the scaffold
- then implemented. MTConnectFactoryTests' "not_writable" characterization test
is rewritten to pin the new truth, and is the guard for the concrete-return
contract the factory remark explains.
Tests: 532 passed / 0 failed (was ~509). Full solution build: 0 errors,
0 warnings; OTOPCUA0001 clean.
- docs/drivers/MTConnect.md: getting-started guide for the P1 Agent MVP —
config keys read off MTConnectDriverOptions/ConfigDto, capability surface,
RawPath->dataItemId coercion precedence, UNAVAILABLE->BadNoCommunication +
the rest of the quality-code table, CONDITION-as-String, browse-via-the-
universal-browser, the fixture recipe (links the existing IntegrationTests
Docker README instead of duplicating it), and a Known limitations section
covering the two pre-existing fleet-wide gaps this build surfaced
(IRediscoverable/IHostConnectivityProbe have no server consumer; no driver
form blocks Save on validation). Records write-back (MTConnect Interfaces),
P1.5 (native alarms, TIME_SERIES arrays, EVENT->enum), and P2 (SHDR ingest)
as deferred per design doc SS3.6/SS9. Documents where the build diverged
from the design: TrakHound MTConnect.NET was dropped entirely (no XML
formatter in the pinned packages, no injectable HTTP handler) in favor of
a hand-rolled System.Xml.Linq client, namespace-agnostic on LocalName.
- docs/drivers/README.md: adds MTConnect to the ground-truth driver table,
the per-driver doc list, and the fixture coverage-map list.
- docs/plans/2026-07-24-driver-expansion-tracking.md: marks the MTConnect
Wave-2 row Done (22/23 tasks; Task 21 live gate tracked separately in the
plan file, not touched here), corrects mtconnect/cppagent -> mtconnect/agent
in the fixture note, and links the new driver guide.
Deferred-cleanup decision (Task 1 review follow-up): removed
GenerateDocumentationFile/NoWarn CS1591 from Driver.MTConnect.Contracts's
csproj to match all eight sibling .Contracts projects, none of which carry
it. Verified both the Contracts project alone and the full solution still
build clean (0 warnings, 0 errors) with the flags gone — the existing XML
doc comments don't depend on GenerateDocumentationFile to compile.
The driver could not receive data after a real deploy. The runtime hands every
driver its authored tags as a RawTags array (RawPath identity + TagConfig blob,
injected by DriverDeviceConfigMerger) and then subscribes, reads, and routes
published values by RawPath. MTConnectDriverConfigDto declared no RawTags
property, so System.Text.Json silently dropped the array, and every reference
the server passed missed an index keyed by DataItem id: every value came back
BadNodeIdUnknown, with the whole suite green because every test handed the
driver its own Tags array directly.
- MTConnectDriverOptions gains RawTags; the config DTO binds it (verbatim — a
bad blob is skipped per-tag at binding time, never fails the deployment).
- A new TagBinding, derived from the options and swapped with them in one write,
carries RawPath -> dataItemId, its one-to-many reverse, and the definition set
the observation index coerces against. Subscribe/Read resolve through it; the
fan-out expands each touched dataItemId into every RawPath bound to it and
publishes under THAT reference — the line the blocker turned on.
- Coercion type precedence: the blob's driverDataType/dataType (both spellings —
the AdminUI's MTConnectTagConfigModel writes the latter), else a Tags entry for
the same DataItem, else the Agent's own /probe declaration via
MTConnectDataTypeInference (what makes a browse-committed {"address": id} blob
publish as a number), else String. A present-but-invalid type rejects that tag.
- An unmapped reference falls through unchanged, so the dataItemId-keyed CLI
surface and every existing test keep working, and an unclaimed RawPath reports
Bad rather than throwing.
15 new tests build their config through the real DriverDeviceConfigMerger; all
four mutations (publish the dataItemId, drop the RawTags binding, drop the
derived coercion type, drop the reverse-map expansion) are caught.
Joseph Doherty