Adding and reading/writing variables

In this tutorial, we will add three variables to an open62541 server. The first variable will contain a floating point number, the second an array of floating point numbers and the third will be an array of two strings.

Configuring the server

This will detail how to add the variables mentioned above to the server. The code block is commented line by line.

using Open62541

#configure the open62541 server; we choose a default config on port 4840.
server = JUA_Server()
config = JUA_ServerConfig(server)
JUA_ServerConfig_setDefault(config)

#Define NodeIds that will contain the variables we are adding later. We define 
#NodeIds with nameSpaceIndex = 1 and string identifiers
name1 = "scalar float"
name2 = "array of floats"
name3 = "array of strings"
id1 = JUA_NodeId(1, name1)
id2 = JUA_NodeId(1, name2)
id3 = JUA_NodeId(1, name3)

#Now define variable attributes

accesslevel = UA_ACCESSLEVEL(read = true, write = true) #allows clients to read/write the value of a variable
writemask = UA_WRITEMASK(arraydimensions = true) #allows clients to change the array dimensions of a variable

attr1 = JUA_VariableAttributes(value = 42.0,
    displayname = name1,
    description = "this is a $name1 variable",
    accesslevel = accesslevel)
attr2 = JUA_VariableAttributes(value = [42.0, 80.0],
    displayname = name2,
    description = "this is a $name2 variable",
    accesslevel = accesslevel, writemask = writemask)

attr3 = JUA_VariableAttributes(value = ["Maria", "Peter"],
    displayname = name3,
    description = "this is a $name3 variable",
    accesslevel = accesslevel)

#Define parent nodes, references, typedefinitions, etc. (same for all three variables)
parentnodeid = JUA_NodeId(0, UA_NS0ID_OBJECTSFOLDER)
parentreferencenodeid = JUA_NodeId(0, UA_NS0ID_ORGANIZES)
typedefinition = JUA_NodeId(0, UA_NS0ID_BASEDATAVARIABLETYPE)
nodecontext = JUA_NodeId()
outnewnodeid = JUA_NodeId()

#Define browsenames for the three variables:
browsename1 = JUA_QualifiedName(1, name1)
browsename2 = JUA_QualifiedName(1, name2)
browsename3 = JUA_QualifiedName(1, name3)

#Add the variables to the server
retval1 = JUA_Server_addNode(server, id1, parentnodeid,
    parentreferencenodeid, browsename1, attr1, nodecontext, outnewnodeid,
    typedefinition)

retval2 = JUA_Server_addNode(server, id2, parentnodeid,
    parentreferencenodeid, browsename2, attr2, nodecontext, outnewnodeid,
    typedefinition)

retval3 = JUA_Server_addNode(server, id3, parentnodeid,
    parentreferencenodeid, browsename3, attr3, nodecontext, outnewnodeid,
    typedefinition)

#retval1-3 should all be UA_STATUSCODE_GOOD (== 0)

#start up the server - interrupt server by pressing CTRL + C multiple times when 
#you are done.
JUA_Server_runUntilInterrupt(server)

Using the client

Start a new Julia session and run the program shown below. Once you are finished, you may want to return to the first Julia session and stop the server (press CTRL + C repeatedly).

using Open62541

#initiate client, configure it and connect to server
client = JUA_Client()
config = JUA_ClientConfig(client)
JUA_ClientConfig_setDefault(config)
JUA_Client_connect(client, "opc.tcp://localhost:4840")

#create the relevant nodeids (note that we are in a new Julia session, therefore,
#we have to redefine these variables)
name1 = "scalar float"
name2 = "array of floats"
name3 = "array of strings"
id1 = JUA_NodeId(1, name1)
id2 = JUA_NodeId(1, name2)
id3 = JUA_NodeId(1, name3)

#read values from the nodeids specified above
value_id1 = JUA_Client_readValueAttribute(client, id1)
value_id2 = JUA_Client_readValueAttribute(client, id2)
value_id3 = JUA_Client_readValueAttribute(client, id3)

#now write something new into the variables
new1 = 43.0
new2 = [1.0, 2.0, 3.0]
new3 = ["Maria", "Wuffi"]
retval1 = JUA_Client_writeValueAttribute(client, id1, new1)
retval2 = JUA_Client_writeValueAttribute(client, id2, new2)
retval3 = JUA_Client_writeValueAttribute(client, id3, new3)

Inspecting the return values (retval1,2,3) and the log and error messages in the terminal (both server and client), you will see that writing new2 to id2 failed with the statuscode "BadTypeMismatch" (retval2).

This is because in open62541 arrays are statically sized, both in terms of the number of dimensions, as well as the number of elements along each dimension. In order for this to work, one first has to specify the new array dimensions (and the write mask property of the variable has to allow altering this value; see the server code above!).

#Try again, but properly this time
retval4 = UA_Client_writeArrayDimensionsAttribute(client, id2, 1, [3])
retval5 = JUA_Client_writeValueAttribute(client, id2, new2)

#disconnect the client (good housekeeping practice)
JUA_Client_disconnect(client)

Note that changing the dimensionality of the array additionally requires setting the valuerank attribute either to UA_VALUERANK_ONE_OR_MORE_DIMENSIONS when defining the variable attributes in the server setup code above, or, one can use UA_Client_writeValueRankAttribute (and the writemask of the variable attributes has to allow changing the valuerank property) to first change the valuerank of the variable, before proceeding to change the array dimensions and then finally setting the variable.