10 November 2021

I’ve tried the first open62541 tutorial server, Now the second tutorial example in open62541 project is a server with a scalar variable and a matrix variable.

Firstly, generate the single file distribution of open62541:

cd ~/tutorials/open62541
cmake --build .

Then copy files to the tutorials folder:

cp open62541.c open62541.h examples/tutorial_server_variable.c ~/tutorials/

To use open62541.h, change the #include lines:

--- #<buffer examples/tutorial_server_variable.c>
+++ #<buffer tutorials/tutorial_server_variable.c>
@@ -14,9 +14,7 @@
-#include <open62541/plugin/log_stdout.h>
-#include <open62541/server.h>
-#include <open62541/server_config_default.h>
+#include "open62541.h"

Then compile the example:

gcc -std=c99 open62541.c -lws2_32 tutorial_server_variables.c -o srv_var.exe

Execute the variable example:

# ./srv_var.exe
[2021-11-10 13:55:48.424 (UTC+0800)] warn/server        AccessControl: Unconfigured AccessControl. Users have all permissions.
[2021-11-10 13:55:48.424 (UTC+0800)] info/server        AccessControl: Anonymous login is enabled
[2021-11-10 13:55:48.424 (UTC+0800)] info/server        AccessControl: x509 certificate user authentication is enabled
[2021-11-10 13:55:48.424 (UTC+0800)] warn/server        Username/Password configured, but no encrypting SecurityPolicy. This can leak credentials on the network.
[2021-11-10 13:55:48.424 (UTC+0800)] warn/userland      AcceptAll Certificate Verification. Any remote certificate will be accepted.
[2021-11-10 13:55:48.424 (UTC+0800)] info/session       SecureChannel 0 | Session g=00000001-0000-0000-0000-000000000000 | WriteRequest returned status code BadTypeMismatch
Writing a string returned statuscode BadTypeMismatch
[2021-11-10 13:55:48.431 (UTC+0800)] info/network       TCP network layer listening on opc.tcp://CN-L-7386623:4840/
[2021-11-10 13:55:50.669 (UTC+0800)] info/server        received ctrl-c
[2021-11-10 13:55:50.716 (UTC+0800)] info/network       Shutting down the TCP network layer

As expected, it will report this error:

Writing a string returned statuscode BadTypeMismatch

Which is printed inside writeWrongVariable function:

static void
writeWrongVariable(UA_Server *server) {
    UA_NodeId myIntegerNodeId = UA_NODEID_STRING(1, "the.answer");

    /* Write a string */
    UA_String myString = UA_STRING("test");
    UA_Variant myVar;
    UA_Variant_setScalar(&myVar, &myString, &UA_TYPES[UA_TYPES_STRING]);
    UA_StatusCode retval = UA_Server_writeValue(server, myIntegerNodeId, myVar);
    printf("Writing a string returned statuscode %s\n", UA_StatusCode_name(retval));

This function set a UA_STRING to an UA_Variant, and then try to write this UA_Variant myVar to the integer node the.answer. Because the datatype mismatch, the status code name is BadTypeMismatch.

To use different data type, modify these lines in addVariable:

    UA_VariableAttributes attr = UA_VariableAttributes_default;
-   UA_Int32 myInteger = 42;
+   UA_Float myFloat = 3.1415926;
-   UA_Variant_setScalar(&attr.value, &myInteger, &UA_TYPES[UA_TYPES_INT32]);
+   UA_Variant_setScalar(&attr.value, &myFloat, &UA_TYPES[UA_TYPES_FLOAT]);
    attr.description = UA_LOCALIZEDTEXT("en-US","the answer");
    attr.displayName = UA_LOCALIZEDTEXT("en-US","the answer");
-   attr.dataType = UA_TYPES[UA_TYPES_INT32].typeId;
+   attr.dataType = UA_TYPES[UA_TYPES_FLOAT].typeId;