# OPC UA Discovery

A small C project that demonstrates OPC UA server discovery using the
[open62541](https://www.open62541.org/) library. Three programs work together:

- **ServerLDS** — Local Discovery Server that other servers register with
- **ServerRegister** — a server that periodically registers itself with the LDS
- **Client** — queries the LDS for servers, lists endpoints, or reads the current time from a server

## Prerequisites

- CMake 4.0+
- A C11 compiler (GCC or Clang)
- OpenSSL development libraries (`libssl-dev` / `openssl-devel`)
- `openssl` CLI (for generating certificates)

## Getting started

Clone the repository with its submodule:

```sh
git clone --recursive https://git.tvcloud.fr/opcua_c
cd opcua_c
```

### Generate certificates

The programs use TLS certificates for mutual authentication. Four identities
are needed — run these from the project root:

```sh
tools/generate_certificate.sh certs ServerLDS
tools/generate_certificate.sh certs ServerRegister
tools/generate_certificate.sh certs ServerRegisterClient
tools/generate_certificate.sh certs ClientFindServers
```

### Populate the trust stores

Each program trusts a specific set of peers. Copy the certificates into the
trust store directories so they can find each other:

```sh
mkdir -p certs/trust/{server_lds,server_register,server_register_client,client}

cp certs/ServerRegisterClient_cert.der certs/ClientFindServers_cert.der \
   certs/trust/server_lds/

cp certs/ServerLDS_cert.der certs/ClientFindServers_cert.der \
   certs/trust/server_register/

cp certs/ServerLDS_cert.der \
   certs/trust/server_register_client/

cp certs/ServerLDS_cert.der certs/ServerRegister_cert.der \
   certs/trust/client/
```

### Build

```sh
cmake -B build
cmake --build build --parallel
```

open62541 is fetched from the submodule and built automatically — the first
build takes a bit longer.

## Running

Start the programs in order, each in its own terminal, from the project root:

```sh
# 1. Local Discovery Server
build/ServerLDS config/server_lds.conf

# 2. Register Server (connects to the LDS on port 4840)
build/ServerRegister config/server_register.conf \
  config/server_register_client.conf opc.tcp://localhost:4840

# 3. Find registered servers via the LDS
build/Client config/client.conf find-servers opc.tcp://localhost:4840

# 4. List endpoints on the registered server
build/Client config/client.conf get-endpoints opc.tcp://localhost:4841

# 5. Read the current time from the registered server
build/Client config/client.conf read-time opc.tcp://localhost:4841
```

All three programs accept an optional log level as the last argument
(`trace`, `debug`, `info`, `warning`, `error`, `fatal`). The default is `info`.

## Tests

Integration tests exercise four combinations of security and authentication:

| Test | Security | Auth |
|------|----------|------|
| `none_anon` | None | anonymous |
| `none_user` | None | user/password |
| `basic256sha256_anon` | SignAndEncrypt / Basic256Sha256 | anonymous |
| `aes128_user` | SignAndEncrypt / Aes128_Sha256_RsaOaep | user/password |

Run them:

```sh
ctest --test-dir build --output-on-failure
```

### Memory leak check

Rebuild with AddressSanitizer, run the tests, then switch back:

```sh
# ASan build
cmake -B build \
  -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer" \
  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address"
cmake --build build --parallel

ASAN_OPTIONS="detect_leaks=1" ctest --test-dir build --output-on-failure

# Restore normal build
cmake -B build -DCMAKE_C_FLAGS="" -DCMAKE_EXE_LINKER_FLAGS=""
cmake --build build --parallel
```

## Configuration

Programs are configured through plain text files (`key = value`, one per line).
Example configs are in `config/`.