# Code Review — Driver.AbLegacy.Contracts

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| Field | Value |
|---|---|
| Module | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts` |
| Reviewer | Claude Code |
| Review date | 2026-06-19 |
| Commit reviewed | `a19b0f86` |
| Status | Reviewed |
| Open findings | 0 |

## Checklist coverage

A comprehensive review completes every category, recording "No issues found" where
a category produced nothing rather than leaving it blank.

| # | Category | Result |
|---|---|---|
| 1 | Correctness & logic bugs | No issues found |
| 2 | OtOpcUa conventions | 1 finding (Driver.AbLegacy.Contracts-003) |
| 3 | Concurrency & thread safety | No issues found |
| 4 | Error handling & resilience | No issues found |
| 5 | Security | No issues found |
| 6 | Performance & resource management | No issues found |
| 7 | Design-document adherence | No issues found |
| 8 | Code organization & conventions | 1 finding (Driver.AbLegacy.Contracts-004) |
| 9 | Testing coverage | No issues found (contracts exercised by Driver.AbLegacy.Tests and AdminUI.Tests) |
| 10 | Documentation & comments | 2 findings (Driver.AbLegacy.Contracts-001 fixed, Driver.AbLegacy.Contracts-002 open) |

## Findings

<!-- One ### entry per finding. IDs are <Module>-NNN, sequential within the module,
     never reused. Findings are never deleted -- close them by changing Status and
     completing Resolution. -->

### Driver.AbLegacy.Contracts-001

| Field | Value |
|---|---|
| Severity | Low |
| Category | Documentation & comments |
| Location | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts/AbLegacyDriverOptions.cs:48` |
| Status | Resolved |

**Description:** The `<param name="ArrayLength">` XML doc on `AbLegacyTagDefinition` stated
`<c>1</c> reads as a scalar.` This was incorrect. Both the parser (`AbLegacyEquipmentTagParser`,
line 44: `if (rawLength >= 1)`) and the driver (`AbLegacyDriver.IsArrayTag`, checks `len >= 1`)
treat `ArrayLength: 1` as a valid one-element array, exposing a `[1]` OPC UA array node -- not a
scalar. The in-source comment at `AbLegacyEquipmentTagParser.cs:36` correctly stated
"A 1-element array (isArray:true, arrayLength:1) is a valid [1] array." The XML doc contradicted this.

**Recommendation:** Change the offending sentence from `<c>1</c> reads as a scalar.` to
`<c>1</c> is a valid one-element array exposed as a <c>[1]</c> OPC UA array node.`

**Resolution:** Fixed in same review session, 2026-06-19. Changed the misleading sentence in
`AbLegacyDriverOptions.cs:48` to correctly describe ArrayLength 1 as a one-element array;
verified by build (no test project in this module).

---

### Driver.AbLegacy.Contracts-002

| Field | Value |
|---|---|
| Severity | Low |
| Category | Documentation & comments |
| Location | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts/AbLegacyEquipmentTagParser.cs:15` |
| Status | Resolved |

**Description:** `AbLegacyEquipmentTagParser.TryParse` has an undocumented edge case: when
`isArray` is the JSON literal `true` but `arrayLength` is absent, zero, or negative,
`ReadInt` returns `0`, the `rawLength >= 1` guard fails, and `arrayLength` stays
`null` -- producing a scalar tag despite `isArray:true`. This is intentional (the in-source
comment at lines 33-39 references "review C-2"), but it is invisible from the public
`<summary>` and `<returns>` XML docs, and there is no unit test covering this case.
An operator who hand-edits the raw TagConfig JSON with `{"isArray":true}` and no
`arrayLength` will silently get a scalar OPC UA node instead of the expected array shape.

**Recommendation:** Add a `<remarks>` element to the XML doc noting that `isArray:true`
without a valid positive `arrayLength` silently produces a scalar (null `ArrayLength`).
Optionally add a unit test to `AbLegacyEquipmentTagTests` covering
`isArray:true, arrayLength:0/absent -> null` for regression protection.

**Resolution:** Resolved 2026-06-20. Added a `<remarks>` block to `TryParse` in
`AbLegacyEquipmentTagParser.cs` documenting that `isArray:true` without a valid positive
`arrayLength` silently produces a scalar (`ArrayLength` is `null`), referencing the
in-source review C-2 rationale. Added three regression unit tests to
`AbLegacyEquipmentTagTests`: `IsArray_true_with_arrayLength_zero_produces_scalar`,
`IsArray_true_with_no_arrayLength_produces_scalar`, and
`IsArray_true_with_negative_arrayLength_produces_scalar`. Suite: 199 passed, 0 failed.

---

### Driver.AbLegacy.Contracts-003

| Field | Value |
|---|---|
| Severity | Low |
| Category | OtOpcUa conventions |
| Location | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts/AbLegacyPlcFamilyProfile.cs:10` |
| Status | Resolved |

**Description:** `AbLegacyPlcFamilyProfile.MaxTagBytes` is a record constructor parameter
populated with distinct values per family (240/232/240/240), but a global search finds zero
call sites that read this property anywhere in the codebase -- not in `AbLegacyDriver.cs`,
the probe, the CLI, or any test. The field is dead weight in the public contract surface.
Keeping it may mislead future implementors into assuming it is enforced: a caller that adds
array-size clamping logic on `MaxTagBytes` without knowing the values are approximate
(e.g. SLC 5/05 240 is the PCCC packet payload cap, not a libplctag fragment limit) could
produce off-by-one sizing. If reserved for future clamping, the intent is undocumented.

**Recommendation:** Either (a) add XML doc noting it is reserved for future array-length
clamping and is not currently enforced, or (b) remove the field and its four initialisers
in a dedicated cleanup PR (signature change is out of scope for this review).

**Resolution:** Resolved 2026-06-20. Applied option (a): added XML doc on the `MaxTagBytes`
constructor parameter in `AbLegacyPlcFamilyProfile.cs` noting it is reserved for future
array-length clamping, is NOT currently enforced anywhere in the driver, and that the values
are approximate PCCC packet payload caps (not libplctag fragment limits). Field and
initialisers unchanged.

---

### Driver.AbLegacy.Contracts-004

| Field | Value |
|---|---|
| Severity | Low |
| Category | Code organization & conventions |
| Location | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts/AbLegacyPlcFamilyProfile.cs:22` |
| Status | Resolved |

**Description:** `AbLegacyPlcFamilyProfile.ForFamily` has a catch-all arm `_ => Slc500`
that silently returns the SLC 500 profile for any unrecognised `AbLegacyPlcFamily` value
(e.g. an integer cast). The XML doc on `ForFamily` does not mention the fallback. A
misconfigured device (or a future enum member added without updating the switch) will
silently receive SLC 500 libplctag attributes (`plc="slc500"`, `path="1,0"`) and a
`MaxTagBytes` of 240, which may produce libplctag session errors or wrong data only at
runtime, far from where the enum value was set. The parallel FOCAS driver throws on
unexpected values.

**Recommendation:** Either (a) document the silent fallback in the XML doc and note it is
intentional (e.g. for forward-compatibility with configs authored before a new family was
added), or (b) replace `_ => Slc500` with
`_ => throw new ArgumentOutOfRangeException(nameof(family), family, null)` and apply it
in a cleanup PR. Semantic change -- defer.

**Resolution:** Resolved 2026-06-20. Applied option (a): added a `<remarks>` block to the
`ForFamily` XML doc in `AbLegacyPlcFamilyProfile.cs` documenting that any unrecognised
`family` value silently returns the `Slc500` profile, and noting this is intentional for
forward-compatibility with configs authored before a new family enum member is added. The
switch body is unchanged.
