Rust OPC Classic

Rust bindings and ownership-aware client/server facades for OPC Classic on Windows. The workspace targets Rust 1.97, edition 2024.

Workspace

• opc_classic_types: dependency-free public Guid, Timestamp, Value, ComObject, and OPC error types.
• opc_classic_abi: unpublished shared ABI definitions used only to compose multiple OPC interfaces on one private COM identity.
• opc_classic_utils: COM apartment, task-memory ownership, transactional output builders, panic-safe ABI helpers, class factory and local-server class registration.
• opc_comn_bindings: generated OPC Common ABI plus safe common/server-list clients and server adapters.
• opc_da_bindings: generated Data Access ABI plus safe server/group/property clients and IOPCServer/group adapters.
• opc_ae_bindings: generated Alarms & Events ABI plus safe query/subscription clients and an IOPCEventServer adapter.
• opc_hda_bindings: generated Historical Data Access ABI plus safe metadata, handle and raw-read clients and IOPCHDA_Server/IOPCHDA_SyncRead adapters.

Each bindings crate keeps generated code in a private src/bindings.rs module. Application code uses its client or server module. Their public signatures contain only opc_classic_types, core, and std types; Windows ABI values are converted inside private boundary modules.

This private visibility is a 0.4.0 breaking change: applications that imported generated IOPC*, tagOPC*, or OPC* symbols must use the safe facades or maintain a separate ABI layer. DA, AE, and HDA server adapters expose their domain interfaces and IOPCCommon from the same COM identity; the new_with_common constructors attach application-defined common behavior.

Ownership model

Input strings and arrays are Rust-owned borrowed values. COM output memory is adopted by an explicit owner:

• OwnedPwstr owns one task-allocated string.
• CoTaskMemArray<T, C> owns a task-allocated array and a cleanup policy for nested values.
• CoTaskMemArrayOut<T, C> distinguishes fixed, trusted lengths from lengths reported by a foreign call. Reported lengths are committed only after a successful HRESULT; failure cleanup never walks an untrusted count.
• CoTaskMemObjectOut<T, C> owns one task-allocated object returned through T**, including its nested cleanup policy.
• CoTaskMemOut<T> null-initializes a single-allocation out pointer.
• CoTaskMemArrayBuilder<T, C> constructs server outputs transactionally and rolls back the initialized prefix after an error or panic.

Owners are not shallow-cloneable. VARIANT values use Rust drop glue, string arrays free each string, and HDA item arrays use method-specific nested cleanup.

Minimal client setup

use opc_classic_utils::ComApartment;use opc_da_bindings::client::DaClient;fnexample() -> opc_classic_utils::Result<()>{let apartment = ComApartment::mta()?;let client = DaClient::connect_prog_id(&apartment,"Vendor.OPC.Server")?;let status = client.status()?;println!("{}", status.vendor_info);Ok(())}

OPC Classic integration test

The real COM integration test is isolated from the normal test suite because it requires a registered local OPC DA server. On Windows, set the server ProgID and run the ignored test explicitly:

$env:OPC_TEST_PROG_ID="OPCLabs.KitServer.2"
cargo test -p opc_da_bindings --test opc_kit ----ignored --nocapture

The GitHub Actions integration job downloads and verifies the OPC Labs Kit Server, registers it for the job, and always unregisters it during cleanup.

Minimal local-server activation

use opc_classic_utils::{ComApartment,ComObject,Guid,Result};use opc_classic_utils::server::{ClassFactory,LocalClassRegistration};fnmake_server() -> Result<ComObject>{unimplemented!()}fnexample() -> Result<()>{let apartment = ComApartment::mta()?;let class_id = Guid::new(0x1234_5678,0x1234,0x1234,[0x12,0x34,0x12,0x34,0x56,0x78,0x9a,0xbc],);let factory = ClassFactory::new(make_server);let registration = LocalClassRegistration::register(&apartment,&class_id, factory)?;// Run the application's shutdown/message loop while `registration` is alive.
registration.revoke()?;Ok(())}

The higher-level adapters intentionally return the COM equivalent of ErrorCode::NOT_IMPLEMENTED for capabilities not represented by their current Rust service traits. Extend the private ABI boundary when adding another interface instead of leaking Windows types into the public facade.

License notice

This personal project is not affiliated with the OPC Foundation. Files under the bindings crates' .metadata directories originate from the OPC Foundation and remain subject to its license terms.