52 lines
4.6 KiB
Markdown
52 lines
4.6 KiB
Markdown
# LmxProxy v2 Rebuild — Deviations & Key Technical Decisions
|
||
|
||
Decisions made during implementation that differ from or extend the original plan.
|
||
|
||
## 1. Grpc.Tools downgraded to 2.68.1
|
||
|
||
**Plan specified**: Grpc.Tools 2.71.0
|
||
**Actual**: 2.68.1
|
||
**Why**: protoc.exe from 2.71.0 crashes with access violation (exit code 0xC0000005) on windev (Windows 10, x64). The 2.68.1 version works reliably.
|
||
**How to apply**: If upgrading Grpc.Tools in the future, test protoc on windev first.
|
||
|
||
## 2. STA Dispatch Thread replaced with Task.Run
|
||
|
||
**Plan specified**: Dedicated STA thread with `BlockingCollection<Action>` dispatch queue and `Application.DoEvents()` message pump for all COM operations.
|
||
**Actual**: `Task.Run` on thread pool (MTA) for all COM operations, matching the v1 pattern.
|
||
**Why**: The STA thread's message pump (`Application.DoEvents()`) between work items was insufficient — when a COM call like `AdviseSupervisory` was dispatched and the thread blocked waiting for the next work item, COM event callbacks (`OnDataChange`, `OnWriteComplete`) never fired because there was no active message pump during the wait. MxAccess works from MTA threads because COM marshaling handles cross-apartment calls, and events fire on their own threads.
|
||
**How to apply**: Do not reintroduce STA threading for MxAccess. The `System.Windows.Forms` reference was removed from the Host csproj.
|
||
|
||
## 3. TypedValue property-level `_setCase` tracking
|
||
|
||
**Plan specified**: `GetValueCase()` heuristic checking non-default values (e.g., `if (BoolValue) return BoolValue`).
|
||
**Actual**: Each property setter records `_setCase = TypedValueCase.XxxValue`, and `GetValueCase()` returns `_setCase` directly.
|
||
**Why**: protobuf-net code-first has no native `oneof` support. The heuristic approach can't distinguish "field not set" from "field set to default value" (e.g., `BoolValue = false`, `DoubleValue = 0.0`, `Int32Value = 0`). Since protobuf-net calls property setters during deserialization, tracking in the setter correctly identifies which field was deserialized.
|
||
**How to apply**: Always use `GetValueCase()` to determine which TypedValue field is set, never check for non-default values directly.
|
||
|
||
## 4. API key sent via HTTP header (DelegatingHandler)
|
||
|
||
**Plan specified**: API key sent in `ConnectRequest.ApiKey` field (request body).
|
||
**Actual**: API key sent as `x-api-key` HTTP header on every gRPC request via `ApiKeyDelegatingHandler`, in addition to the request body.
|
||
**Why**: The Host's `ApiKeyInterceptor` validates the `x-api-key` gRPC metadata header before any RPC handler executes. protobuf-net.Grpc's `CreateGrpcService<T>()` doesn't expose per-call metadata, so the header must be added at the HTTP transport level. A `DelegatingHandler` wrapping the `SocketsHttpHandler` adds it to all outgoing requests.
|
||
**How to apply**: The `GrpcChannelFactory.CreateChannel()` accepts an optional `apiKey` parameter. The `LmxProxyClient` passes it during channel creation in `ConnectAsync`.
|
||
|
||
## 5. v2 test deployment on port 50100
|
||
|
||
**Plan specified**: Port 50052 for v2 test deployment.
|
||
**Actual**: Port 50100.
|
||
**Why**: Ports 50049–50060 are used by MxAccess internal COM connections (established TCP pairs between the COM client and server). Port 50052 was occupied by an ephemeral MxAccess connection from the v1 service.
|
||
**How to apply**: When deploying alongside v1, use ports above 50100 to avoid MxAccess ephemeral port range.
|
||
|
||
## 6. CheckApiKey validates request body key
|
||
|
||
**Plan specified**: Not explicitly defined — the interceptor validates the header key.
|
||
**Actual**: `CheckApiKey` RPC validates the key from the *request body* (`request.ApiKey`) against `ApiKeyService`, not the header key.
|
||
**Why**: The `x-api-key` header always carries the caller's valid key (for interceptor auth). The `CheckApiKey` RPC is designed for clients to test whether a *different* key is valid, so it must check the body key independently.
|
||
**How to apply**: `ScadaGrpcService` receives `ApiKeyService` as an optional constructor parameter.
|
||
|
||
## 7. Write integration tests pending
|
||
|
||
**Status**: 2 of 17 integration tests fail (WriteAndReadBack, WriteBatchAndWait).
|
||
**Why**: The `OnWriteComplete` COM callback from MxAccess doesn't fire within the timeout. This may be because MxAccess completes writes synchronously without invoking the callback, or the callback event subscription (`OperationCompleted` event) requires different wiring. The v1 code had the same pattern but may have relied on different MxAccess COM object initialization.
|
||
**How to apply**: Investigate whether MxAccess `Write` returns synchronously (check HRESULT) and bypass the callback wait if so. Alternatively, check if `OperationCompleted` needs explicit COM event subscription via `IConnectionPoint`.
|