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 distributions (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.* header and source files. With the GCC compiler, just run gcc -std=c99 <server.c> open62541.c -o server.

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

#define PORT 16664

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

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

    /* init the server */
    UA_ServerNetworkLayer nl = UA_ServerNetworkLayerTCP(UA_ConnectionConfig_standard, PORT);
    UA_ServerConfig config = UA_ServerConfig_standard;
    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 retval = UA_Server_run(server, &running);
    UA_Server_delete(server);
    nl.deleteMembers(&nl);
    return retval;
}

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 retval = UA_Client_connect(client, "opc.tcp://localhost:16664");
    if(retval != UA_STATUSCODE_GOOD) {
        UA_Client_delete(client);
        return retval;
    }

    /* create a readrequest with one entry */
    UA_ReadRequest req;
    UA_ReadRequest_init(&req);
    req.nodesToRead = UA_Array_new(1, &UA_TYPES[UA_TYPES_READVALUEID]);
    req.nodesToReadSize = 1;

    /* define the node and attribute to be read */
    req.nodesToRead[0].nodeId = UA_NODEID_STRING_ALLOC(1, "the.answer");
    req.nodesToRead[0].attributeId = UA_ATTRIBUTEID_VALUE;

    /* call the service and print the result */
    UA_ReadResponse resp = UA_Client_Service_read(client, req);
    if(resp.responseHeader.serviceResult == UA_STATUSCODE_GOOD &&
       resp.resultsSize > 0 && resp.results[0].hasValue &&
       UA_Variant_isScalar(&resp.results[0].value) &&
       resp.results[0].value.type == &UA_TYPES[UA_TYPES_INT32]) {
           UA_Int32 *value = (UA_Int32*)resp.results[0].value.data;
           printf("the value is: %i\n", *value);
   }

    UA_ReadRequest_deleteMembers(&req);
    UA_ReadResponse_deleteMembers(&resp);
    UA_Client_disconnect(client);
    UA_Client_delete(client);
    return UA_STATUSCODE_GOOD;
}