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# 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. ServerLDS and
ServerRegister can also run without certificates (SecurityPolicy#None only) by
omitting the `certificate`, `privateKey`, and `trustStore` keys from their
config files. For encrypted operation, 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. Create symlinks to the
certificates in the trust store directories so they can find each other:
```sh
mkdir -p certs/trust/{server_lds,server_register,server_register_client,client}
ln -s ../../ServerRegisterClient_cert.der ../../ClientFindServers_cert.der \
certs/trust/server_lds/
ln -s ../../ServerLDS_cert.der ../../ClientFindServers_cert.der \
certs/trust/server_register/
ln -s ../../ServerLDS_cert.der \
certs/trust/server_register_client/
ln -s ../../ServerLDS_cert.der ../../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 five combinations of security and authentication:
| Test | Security | Auth |
|------|----------|------|
| `nosec_anon` | LDS + ServerRegister unsecured / None | anonymous |
| `none_user` | None | user/password |
| `basic256sha256_anon` | SignAndEncrypt / Basic256Sha256 | anonymous |
| `aes256_anon` | SignAndEncrypt / Aes256_Sha256_RsaPss | 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/`.
|
