open62541

open62541

open62541 (http://open62541.org) is an open source and free implementation of OPC UA (OPC Unified Architecture). open62541 is a C-based library (linking with C++ projects is possible) with all necessary tools to implement dedicated OPC UA clients and servers, or to integrate OPC UA-based communication into existing applications. The library is distributed as a single pair of header and source files, that can be easily dropped into your project. An example server and client implementation can be found in the /examples directory or further down on this page.

open62541 is licensed under the LGPL with static linking exception. That means open62541 can be used in commercial projects without affecting code that uses the library. However, changes to the open62541 library itself need to be released under the same license. The plugins, as well as the server and client examples are in the public domain (CC0 license). They can be used under any license and changes don't have to be published.

Using open62541

A general introduction to OPC UA and the open62541 documentation can be found at http://open62541.org/doc/current. Past releases of the library can be downloaded at https://github.com/open62541/open62541/releases. To use the latest improvements, download a recent build of the single-file distribution (the entire library merged into a single source and header file) from http://open62541.org/releases. Recent MSVC binaries of the library are available here.

For discussion and help, you can use

• the mailing list
• our IRC channel
• the bugtracker

Contribute to open62541

As an open source project, we invite new contributors to help improving open62541. If you are a developer, your bugfixes and new features are very welcome. Note that there are ways to begin contributing without deep knowledge of the OPC UA standard:

• Report bugs
• Improve the documentation
• Work on issues marked as "easy hacks"

Example Server Implementation

Compile the examples with the single-file distribution open62541.h/.c header and source file. Using the GCC compiler, just run gcc -std=c99 <server.c> open62541.c -o server.

#include <signal.h>
#include "open62541.h"

UA_Boolean running = true;
void signalHandler(int sig) {
    running = false;
}

int main(int argc, char** argv)
{
    signal(SIGINT, signalHandler); /* catch ctrl-c */

    /* create a server with one networklayer listening on port 4840 */
    UA_ServerConfig config = UA_ServerConfig_standard;
    UA_ServerNetworkLayer nl = UA_ServerNetworkLayerTCP(UA_ConnectionConfig_standard, 4840);
    config.networkLayers = &nl;
    config.networkLayersSize = 1;
    UA_Server *server = UA_Server_new(config);

    /* add a variable node */
    /* 1) set the variable attributes (no memory allocations here) */
    UA_Int32 myInteger = 42;
    UA_VariableAttributes attr;
    UA_VariableAttributes_init(&attr);
    UA_Variant_setScalar(&attr.value, &myInteger, &UA_TYPES[UA_TYPES_INT32]);
    attr.displayName = UA_LOCALIZEDTEXT("en_US", "the answer");

    /* 2) define where the variable shall be added with which browsename */
    UA_NodeId newNodeId = UA_NODEID_STRING(1, "the.answer");
    UA_NodeId parentNodeId = UA_NODEID_NUMERIC(0, UA_NS0ID_OBJECTSFOLDER);
    UA_NodeId parentReferenceNodeId = UA_NODEID_NUMERIC(0, UA_NS0ID_ORGANIZES);
    UA_NodeId variableType = UA_NODEID_NULL; /* no variable type defined */
    UA_QualifiedName browseName = UA_QUALIFIEDNAME(1, "the answer");

    /* 3) add the variable */
    UA_Server_addVariableNode(server, newNodeId, parentNodeId, parentReferenceNodeId,
                              browseName, variableType, attr, NULL, NULL);

    /* run the server loop */
    UA_StatusCode status = UA_Server_run(server, &running);
    UA_Server_delete(server);
    nl.deleteMembers(&nl);
    return status;
}

Example Client Implementation

#include <stdio.h>
#include "open62541.h"

int main(int argc, char *argv[])
{
    /* create a client and connect */
    UA_Client *client = UA_Client_new(UA_ClientConfig_standard);
    UA_StatusCode status = UA_Client_connect(client, "opc.tcp://localhost:4840");
    if(status != UA_STATUSCODE_GOOD) {
        UA_Client_delete(client);
        return status;
    }

    /* read the value attribute of the node into the val variable */
    UA_Variant *val = UA_Variant_new();
    status = UA_Client_readValueAttribute(client, UA_NODEID_STRING(1, "the.answer"), val);
    if(status == UA_STATUSCODE_GOOD && UA_Variant_isScalar(val) &&
       val->type == &UA_TYPES[UA_TYPES_INT32]) {
        printf("the value is: %i\n", *(UA_Int32*)val->data);
    }

    UA_Variant_delete(val);
    UA_Client_delete(client); /* disconnects the client first */
    return status;
}