# Protobuf Contracts

The contracts project contains the public gRPC API and the gateway-to-worker
IPC messages. The `.proto` files are the source of truth; generated C# files are
recreated by the contracts project build.

## Files

`src/MxGateway.Contracts/Protos/mxaccess_gateway.proto` defines the public
`MxAccessGateway` gRPC service, command payloads, command replies, event DTOs,
`MxValue`, `MxArray`, and `MxStatusProxy`.

The public command model includes bulk subscription command kinds for
`AddItemBulk`, `AdviseItemBulk`, `RemoveItemBulk`, `UnAdviseItemBulk`,
`SubscribeBulk`, and `UnsubscribeBulk`. These commands are normal unary
`Invoke` payloads. They do not add separate gRPC methods, and they return a
`BulkSubscribeReply` containing per-item `SubscribeResult` records with
`ServerHandle`, `TagAddress`, `ItemHandle`, `WasSuccessful`, and
`ErrorMessage`.

The gateway forwards each bulk command as one worker command. The worker runs
the corresponding MXAccess `AddItem`, `Advise`, `UnAdvise`, and `RemoveItem`
calls sequentially on the session STA and preserves input order in the result
list.

The command model also includes bulk write/read command kinds:
`WriteBulk`, `Write2Bulk`, `WriteSecuredBulk`, `WriteSecured2Bulk`, and
`ReadBulk`. They are unary `Invoke` payloads on the same `MxAccessGateway`
surface (not separate gRPC methods) and exist so a caller can submit one list
of items per round trip while preserving MXAccess parity per entry.

- `WriteBulkCommand` / `Write2BulkCommand` / `WriteSecuredBulkCommand` /
  `WriteSecured2BulkCommand` each carry a `server_handle` and a `repeated`
  list of entries (`WriteBulkEntry`, `Write2BulkEntry`,
  `WriteSecuredBulkEntry`, `WriteSecured2BulkEntry`). Each entry mirrors the
  single-item command shape — `item_handle` + `value` (+ `timestamp_value` on
  the `*2` variants, + `current_user_id` / `verifier_user_id` on the secured
  variants). All four replies use `BulkWriteReply`, which carries
  `repeated BulkWriteResult`. A `BulkWriteResult` has `server_handle`,
  `item_handle`, `was_successful`, `optional int32 hresult`, `repeated
  MxStatusProxy statuses`, and `error_message`. Per-entry failures populate
  `error_message` + `hresult` and never raise — callers iterate and inspect
  each entry. The credential-sensitive redaction rules for `WriteSecured` /
  `WriteSecured2` apply to every `value` inside `WriteSecuredBulkEntry` and
  `WriteSecured2BulkEntry`.

- `ReadBulkCommand` carries `server_handle`, `repeated string tag_addresses`,
  and `uint32 timeout_ms` (0 means use the gateway-configured default). The
  reply is `BulkReadReply` carrying `repeated BulkReadResult`. A
  `BulkReadResult` has `server_handle`, `tag_address`, `item_handle`,
  `was_successful`, `was_cached`, `value`, `quality`, `source_timestamp`,
  `repeated MxStatusProxy statuses`, and `error_message`. MXAccess has no
  synchronous `Read`, so `ReadBulk` is dual-mode per entry: when a tag is
  already advised in the session the worker returns the cached
  `OnDataChange` payload without touching the subscription
  (`was_cached = true`); otherwise the worker takes a full
  `AddItem` + `Advise` + wait-for-first-`OnDataChange` + `UnAdvise` +
  `RemoveItem` snapshot lifecycle and returns the result
  (`was_cached = false`). The asymmetry that `BulkReadResult` has no
  `hresult` field is intentional — `ReadBulk` outcomes are timeout / cache
  / lifecycle states rather than MXAccess COM return codes.

See `gateway.md` for the full cached-vs-snapshot `ReadBulk` lifecycle and the
per-command scope requirements, and `docs/DesignDecisions.md` "Bulk Command
Family" for the rationale behind the per-entry result shape (independent
success tracking, input-order preservation, no partial-failure exceptions).

`src/MxGateway.Contracts/Protos/mxaccess_worker.proto` defines the named-pipe
worker IPC envelope and control messages. It imports
`mxaccess_gateway.proto` so the worker and gateway use the same command, reply,
event, value, and status shapes.

`src/MxGateway.Contracts/Protos/galaxy_repository.proto` defines the
`GalaxyRepository` service used by clients to browse the Galaxy Repository
(deployed object hierarchy and dynamic attributes). The service is metadata-
only and does not share types with `mxaccess_gateway.proto`. See
[Galaxy Repository Browse](./GalaxyRepository.md) for the RPC catalog and
behavior.

Generated C# output is written to `src/MxGateway.Contracts/Generated/`. Do not
hand-edit generated files.

Client generation inputs are published through
`clients/proto/proto-inputs.json` and the descriptor set under
`clients/proto/descriptors/`. See
[Client Proto Generation](./ClientProtoGeneration.md) for language-specific
generation inputs, output directories, and golden protobuf JSON fixtures.

## Generation

Run the contracts build to regenerate C# protobuf and gRPC code:

```bash
dotnet build src/MxGateway.Contracts/MxGateway.Contracts.csproj
```

Run the focused contract tests after changing either `.proto` file:

```bash
dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter ProtobufContractRoundTripTests
```

The full solution build also regenerates the C# contracts before compiling
gateway and test projects:

```bash
dotnet build src/MxGateway.sln
```

Regenerate the client descriptor after changing either `.proto` file:

```bash
powershell -ExecutionPolicy Bypass -File scripts/publish-client-proto-inputs.ps1
```

## Related Documentation

- [Client Proto Generation](./ClientProtoGeneration.md)
- [Gateway Process Detailed Design](./GatewayProcessDesign.md)
- [MXAccess Worker Instance Detailed Design](./MxAccessWorkerInstanceDesign.md)
- [Protobuf Style Guide](./style-guides/ProtobufStyleGuide.md)
