review(Driver.S7.Contracts): first review; gate stringLength check to String type
First review at 7286d320. -002 (Low): stringLength range check now only fires for
S7DataType.String (was rejecting valid non-String equipment-tag blobs). -001 ArrayCount=1
doc fix. -003 (driver-specs.md CpuType omissions) deferred. Consuming Driver.S7.Tests green.
This commit is contained in:
Joseph Doherty
@@ -0,0 +1,83 @@
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# Code Review — Driver.S7.Contracts
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| Field | Value |
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|---|---|
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| Module | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Contracts` |
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| Reviewer | Claude Code |
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| Review date | 2026-06-19 |
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| Commit reviewed | `a19b0f86` |
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| Status | Reviewed |
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| Open findings | 0 |
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## Checklist coverage
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A comprehensive review completes every category, recording "No issues found" where
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a category produced nothing rather than leaving it blank.
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| # | Category | Result |
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|---|---|---|
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| 1 | Correctness & logic bugs | Driver.S7.Contracts-002 |
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| 2 | OtOpcUa conventions | No issues found |
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| 3 | Concurrency & thread safety | No issues found |
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| 4 | Error handling & resilience | No issues found |
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| 5 | Security | No issues found |
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| 6 | Performance & resource management | No issues found |
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| 7 | Design-document adherence | Driver.S7.Contracts-003 |
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| 8 | Code organization & conventions | No issues found |
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| 9 | Testing coverage | No issues found |
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| 10 | Documentation & comments | Driver.S7.Contracts-001 |
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## Findings
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<!-- One ### entry per finding. IDs are Driver.S7.Contracts-NNN, sequential within the module,
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never reused. Findings are never deleted — close them by changing Status and
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completing Resolution. -->
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### Driver.S7.Contracts-001
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| Field | Value |
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|---|---|
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| Severity | Low |
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| Category | Documentation & comments |
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| Location | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Contracts/S7DriverOptions.cs:107` |
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| Status | Resolved |
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**Description:** The `ArrayCount` XML doc on `S7TagDefinition` stated "null (or `<= 1`) for a scalar", which is inaccurate. The driver and the OPC UA materializer both use `ArrayCount is >= 1` as the array gate (in `RejectUnsupportedTagConfigs`, `ReadOneAsync`, `WriteOneAsync`, and `DiscoverAsync`), meaning `ArrayCount = 1` surfaces as a 1-element OPC UA array node, not a scalar. The `<= 1` phrasing would lead a caller to pass `ArrayCount = 1` expecting scalar behaviour and instead receive an array node.
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**Recommendation:** Change the doc to "null for a scalar; any value >= 1 (including 1) surfaces as a 1-D OPC UA array node."
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**Resolution:** Fixed in this review (2026-06-19, commit `a19b0f86`) — updated `S7TagDefinition.ArrayCount` XML doc to accurately state "null for a scalar; any value >= 1 (including 1) surfaces as a 1-D OPC UA array node." Verified by build (no test project).
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---
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### Driver.S7.Contracts-002
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| Field | Value |
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|---|---|
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| Severity | Low |
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| Category | Correctness & logic bugs |
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| Location | `src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Contracts/S7EquipmentTagParser.cs:38` |
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| Status | Resolved |
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**Description:** `TryParse` validated the `stringLength` range (`< 0 || > 254`) unconditionally for all `DataType` values. A non-String tag blob that carries an out-of-range `stringLength` field (e.g., from copy-paste or manual edit: `{"address":"DB1.DBD0","dataType":"Float32","stringLength":300}`) caused `TryParse` to return `false`, silently failing to resolve the equipment tag. The driver would then return `BadNodeIdUnknown` on every read/write for that tag, with no config error at init — exactly the hard-to-diagnose failure mode that init-time validation was meant to prevent. The `stringLength` field is only meaningful when `DataType == String`; for all other types it is stored in the record but never consumed by the driver.
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**Recommendation:** Gate the range check on `dataType == S7DataType.String`, leaving non-String blobs unaffected regardless of any `stringLength` value they carry.
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**Resolution:** Fixed in this review (2026-06-19, commit `a19b0f86`) — added `dataType == S7DataType.String &&` guard before the out-of-range check. Non-String blobs now parse correctly regardless of their `stringLength` value; String blobs with an out-of-range length are still correctly rejected. Verified by build (no test project).
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---
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### Driver.S7.Contracts-003
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| Field | Value |
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|---|---|
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| Severity | Low |
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| Category | Design-document adherence |
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| Location | `docs/v2/driver-specs.md:369` |
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| Status | Deferred |
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**Description:** The `CpuType` table in `docs/v2/driver-specs.md` (§5, "Connection Settings") lists only four values: `S7300`, `S7400`, `S71200`, `S71500`. The `S7CpuType` enum in this module defines seven values — `S7200 = 0`, `Logo0BA8 = 1`, `S7200Smart = 2`, `S7300 = 10`, `S7400 = 20`, `S71200 = 30`, `S71500 = 40` — all mapped through `S7CpuTypeMap.ToS7Net` in the driver. `docs/drivers/S7.md` mentions S7-200 / S7-200 Smart / LOGO! 0BA8 in prose but gives no enum string names or rack/slot conventions. An operator targeting a LOGO! 0BA8 has no documentation reference for the `CpuType` JSON string to use.
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**Recommendation:** Add `S7200`, `S7200Smart`, `Logo0BA8` rows to the `driver-specs.md` CpuType table (or note limited S7comm support for these legacy families) and add their enum names to `docs/drivers/S7.md`'s rack/slot table.
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**Resolution:** Deferred — the fix is in `docs/v2/driver-specs.md` and `docs/drivers/S7.md`, outside this module's source files. No code impact. Tracked as a documentation-only follow-up.
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@@ -105,7 +105,8 @@ public sealed class S7ProbeOptions
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/// coils that drive edge-triggered routines in the PLC program.
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/// </param>
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/// <param name="ArrayCount">
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/// Element count when the tag is a 1-D array; <c>null</c> (or <c><= 1</c>) for a scalar.
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/// Element count when the tag is a 1-D array; <c>null</c> for a scalar. Any value <c>>= 1</c>
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/// (including 1) surfaces as a 1-D OPC UA array node.
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/// For an equipment tag this is threaded from the <c>TagConfig</c> JSON's <c>arrayLength</c>
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/// (honoured only when <c>isArray</c> is true) by <see cref="S7EquipmentTagParser"/>. When
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/// set, the driver issues a single contiguous block read of
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@@ -33,9 +33,10 @@ public static class S7EquipmentTagParser
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if (string.IsNullOrWhiteSpace(address)) return false;
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var dataType = ReadEnum(root, "dataType", S7DataType.Int16);
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var stringLength = ReadInt(root, "stringLength");
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// Range-guard rather than truncate: an S7 string can't exceed 254 chars, and a
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// negative length is meaningless — reject so a malformed blob can't slip through.
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if (stringLength < 0 || stringLength > MaxStringLength) return false;
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// Range-guard applies only to String tags: an S7 string can't exceed 254 chars, and a
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// negative length is meaningless. For non-String types stringLength is irrelevant and any
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// authored value (including an out-of-range remnant from copy-paste) must not block parsing.
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if (dataType == S7DataType.String && (stringLength < 0 || stringLength > MaxStringLength)) return false;
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// Array intent: the canonical sink-side parse (DeploymentArtifact.ExtractTagArray)
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// honours arrayLength ONLY when isArray is true AND the prop is a JSON number — mirror
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// that here so the driver's transient def agrees byte-for-byte with the materialised
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