mxaccessgw/docs/Contracts.md

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/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto defines the public MxAccessGateway gRPC service, command payloads, command replies, event DTOs, MxValue, MxArray, MxSparseArray, and MxStatusProxy.

MxValue carries a kind oneof with arms for all scalar and array types. One arm is sparse_array_value = 19 (field number 19), which carries an MxSparseArray. MxSparseArray is a write-only value type: the gateway accepts it on every write variant (Write, Write2, WriteSecured, WriteSecured2, and the corresponding *BulkEntry shapes), expands it into a full, default-filled MxArray before forwarding to the worker, and rejects it on read or event paths. The worker never receives or produces it.

MxSparseArray has three fields: element_data_type (1, the MxDataType of every element), total_length (2, the length of the expanded full array), and elements (3, repeated MxSparseElement). Each MxSparseElement has index (1, zero-based position in the expanded array) and value (2, a scalar MxValue). Indices not mentioned in elements take the element type's default value — they are reset, not preserved. See gateway.md section "MxSparseArray — default-fill partial array writes" for the expansion rules, validation constraints, and the scope requirements per write variant.

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/ZB.MOM.WW.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/ZB.MOM.WW.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 for the RPC catalog and behavior.

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

The Generated/ C# is tracked and must be committed after any .proto change. The contracts project Compile Removes Generated/**/*.cs and has Grpc.Tools regenerate them, but Grpc.Tools skips regeneration when the committed output looks up to date. On the net10 build the freshly regenerated code is compiled, so a stale Generated/ is invisible there — but the net48 worker consumes the committed Generated/ and fails to build with CS0246 on any new type when the checked-in code lags the .proto. So after editing a .proto you must regenerate and commit Generated/. If a build does not pick up your proto change, delete the stale output to force a full regeneration:

rm src/ZB.MOM.WW.MxGateway.Contracts/Generated/*.cs
dotnet build src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj

scripts/check-codegen.ps1 enforces this in CI (it force-regenerates and fails on any git diff against the committed Generated/); the Windows CI job's net48 worker build is the definitive guard.

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

Generation

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

dotnet build src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj

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

dotnet test src/ZB.MOM.WW.MxGateway.Tests/ZB.MOM.WW.MxGateway.Tests.csproj --filter ProtobufContractRoundTripTests

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

dotnet build src/ZB.MOM.WW.MxGateway.slnx

Regenerate the client descriptor after changing either .proto file, using the pinned protoc (34.1, see Toolchain Links):

pwsh -File scripts/publish-client-proto-inputs.ps1

Freshness is guarded two ways so a skipped regeneration cannot ship silently:

• ClientProtoInputTests.Descriptor_ContainsEveryContractMessageAndField (gateway test project) reflects over the in-process contract descriptors and fails if any message or field is missing from the committed protoset. It is semantic (symbol presence), needs no protoc, and runs in the Linux CI. A red test means "regenerate and commit the protoset."
• pwsh -File scripts/publish-client-proto-inputs.ps1 -Check rebuilds the descriptor and compares it to the committed one. The comparison normalizes both sides through the same protoc with source_code_info stripped, so it does not false-fail across protoc releases.
• pwsh scripts/check-codegen.ps1 runs both the descriptor check and the Generated/-clean check together; it is the single guard the CI pipeline invokes.

Related Documentation

• Client Proto Generation
• Gateway Process Detailed Design
• MXAccess Worker Instance Detailed Design
• Protobuf Style Guide