Andy Grebe created PLC4X-341:
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Summary: PLC4J GIP/CIP Read STRING tag returns null w/error
Key: PLC4X-341
URL: https://issues.apache.org/jira/browse/PLC4X-341
Project: Apache PLC4X
Issue Type: Bug
Components: Driver-Ethernet/IP, PLC4J
Affects Versions: 0.9.1
Reporter: Andy Grebe
Attachments: eipcipstringread.pcapng
STRING tag reads in plc4j using eip are not returning the string. The error
returned is:
java.lang.NullPointerException: Cannot invoke
"org.apache.plc4x.java.api.value.PlcValue.getString()" because the return value
of "org.apache.plc4x.java.api.messages.PlcReadResponse.getPlcValue(String)" is
null
It looks like plc4j is considering it a structure or array. If I read with
{code:java}
%MyString[{index}]:STRING:1 {code}
I can get the individual characters in the string by placing the actual index
in \{index}. So it knows where to start reading the data from.
When running a wireshark cap, I can see the returned string in the response
from the PLC. Attached is a pcap of the transaction.
Code Snippet:
{code:java}
try (PlcConnection plcConnection = new
PlcDriverManager().getConnection("eip://127.0.0.1")) { if
(!plcConnection.getMetadata().canRead()) {
logger.error("PLC connection doesn't support reading.");
return;
} logger.info("PLC connector connected"); // Create a new read
request:
PlcReadRequest.Builder builder = plcConnection.readRequestBuilder();
logger.info("Created Builder"); builder.addItem("value-1",
"%MyString:STRING:1"); PlcReadRequest readRequest = builder.build(); //
Register a callback executed as soon as a response arrives.
logger.info("Make sync request for PLC data");
PlcReadResponse readResponse = readRequest.execute().get(5000,
TimeUnit.MILLISECONDS);
if (readResponse != null) {
printPlcResponse(readResponse);
} else {
logger.error("An error reading PLC, response is NULL");
}
for (String field : readResponse.getFieldNames()){
rtnArray.add(new PlcReadResponseData(field,
readResponse.getPlcValue(field).getString()) ); // Exception is
thrown here
}
} catch (PlcConnectionException e) {
e.printStackTrace();
} {code}
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