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](https://github.com/open62541/open62541/releases/download/v0.1.1/open62541.h) and [source](https://github.com/open62541/open62541/releases/download/v0.1.1/open62541.c) files, that can be easily dropped into your project. An example server and client implementation can be found in the [/examples](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](plugins/), as well as the server and client [examples](examples/) are in the public domain (CC0 license). They can be used under any license and changes don't have to be published.

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### 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](https://ci.appveyor.com/project/Stasik0/open62541/build/artifacts).


For discussion and help, you can use
- the [mailing list](https://groups.google.com/d/forum/open62541)
- our [IRC channel](http://webchat.freenode.net/?channels=%23open62541)
- the [bugtracker](https://github.com/open62541/open62541/issues)

### 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](https://github.com/open62541/open62541/issues)
- Improve the [documentation](http://open62541.org/doc/current)
- Work on issues marked as "[easy hacks](https://github.com/open62541/open62541/labels/easy%20hack)"

### 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```.
```c
#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
```c
#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;
}
```