Add POC OPC-UA server.

coupler/opc-ua-server/server.c

+/*
+ * POC OPC-UA server based on https://github.com/open62541
+ */
+#include <open62541/plugin/log_stdout.h>
+#include <open62541/server.h>
+#include <open62541/server_config_default.h>
+
+#include <signal.h>
+#include <stdlib.h>
+
+static volatile UA_Boolean running = true;
+static void stopHandler(int sig) {
+    UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "received ctrl-c");
+    running = false;
+}
+
+int main(void) {
+    signal(SIGINT, stopHandler);
+    signal(SIGTERM, stopHandler);
+
+    UA_Server *server = UA_Server_new();
+    UA_ServerConfig_setDefault(UA_Server_getConfig(server));
+
+    UA_StatusCode retval = UA_Server_run(server, &running);
+
+    UA_Server_delete(server);
+    return retval == UA_STATUSCODE_GOOD ? EXIT_SUCCESS : EXIT_FAILURE;
+}