[dwdunwetter] should handle properly response messages

[UrsusS]

The binding should handle properly the non-XML response messages.
In this case: "This service is not available due to technical problems!" The warning message "Exception occurred while parsing the XML response: Unexpected character 'T' (code 84) in prolog; expected '<' at [row,col {unknown-source}]: [1,1]" is not really helpful.

2023-03-27 07:33:07.918 [DEBUG] [er.internal.dto.DwdWarningDataAccess] - Refreshing Data for cell 809xxxxxx
2023-03-27 07:33:07.995 [TRACE] [er.internal.dto.DwdWarningDataAccess] - Raw request: https://maps.dwd.de/geoserver/dwd/ows?service=WFS&version=2.0.0&request=GetFeature&typeName=dwd:Warnungen_Gemeinden&CQL_FILTER=WARNCELLID+LIKE+%27809xxxxxx%27
2023-03-27 07:33:07.995 [TRACE] [er.internal.dto.DwdWarningDataAccess] - Raw response: This service is not available due to technical problems!
2023-03-27 07:33:07.996 [WARN ] [nwetter.internal.dto.DwdWarningsData] - Exception occurred while parsing the XML response: Unexpected character 'T' (code 84) in prolog; expected '<'
 at [row,col {unknown-source}]: [1,1]
2023-03-27 07:33:07.997 [DEBUG] [nwetter.internal.dto.DwdWarningsData] - Exception trace
com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character 'T' (code 84) in prolog; expected '<'
 at [row,col {unknown-source}]: [1,1]
	at com.ctc.wstx.sr.StreamScanner.throwUnexpectedChar(StreamScanner.java:666) ~[?:?]
	at com.ctc.wstx.sr.BasicStreamReader.nextFromProlog(BasicStreamReader.java:2148) ~[?:?]
	at com.ctc.wstx.sr.BasicStreamReader.next(BasicStreamReader.java:1180) ~[?:?]
	at com.ctc.wstx.evt.WstxEventReader.nextEvent(WstxEventReader.java:283) ~[?:?]
	at org.openhab.binding.dwdunwetter.internal.dto.DwdWarningsData.refresh(DwdWarningsData.java:127) ~[?:?]
	at org.openhab.binding.dwdunwetter.internal.handler.DwdUnwetterHandler.refresh(DwdUnwetterHandler.java:96) ~[?:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) [?:?]
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:305) [?:?]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:305) [?:?]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
	at java.lang.Thread.run(Thread.java:829) [?:?]
2023-03-27 07:33:08.001 [DEBUG] [.internal.handler.DwdUnwetterHandler] - Failed to retrieve new data from the server.

This behavior exists since a long time. Currently observed with OH 3.4.1.

[lsiepel]

The method responsible for the data access is not very smart. It just calls an url and returns its body:

openhab-addons/bundles/org.openhab.binding.dwdunwetter/src/main/java/org/openhab/binding/dwdunwetter/internal/dto/DwdWarningDataAccess.java

Lines 42 to 65 in 6115cd3

	public String getDataFromEndpoint(String cellId) {
	try {
	if (cellId == null || cellId.isBlank()) {
	logger.warn("No cellId provided");
	return "";
	}
	StringBuilder stringBuilder = new StringBuilder();
	stringBuilder.append(DWD_URL);
	stringBuilder.append("&CQL_FILTER=");
	stringBuilder.append(URLEncoder.encode("WARNCELLID LIKE '" + cellId + "'", StandardCharsets.UTF_8));
	logger.debug("Refreshing Data for cell {}", cellId);
	String rawData = HttpUtil.executeUrl("GET", stringBuilder.toString(), 5000);
	logger.trace("Raw request: {}", stringBuilder);
	logger.trace("Raw response: {}", rawData);
	return rawData;
	} catch (IOException e) {
	logger.warn("Communication error occurred while getting data: {}", e.getMessage());
	logger.debug("Communication error trace", e);
	}
	return "";
	}

I could not find any documentation regarding this API and errors. It could have been nice if we could react to the http response code. But at this moment the only thing i can think of is performing a check to see if the body is (valid) xml and if not, raise an IOException. Maybe @limdul79 as codeowner can give some advise?

[lsiepel]

Made a fix. Test jar 4.x is here: https://1drv.ms/u/s!AnMcxmvEeupwjrMmX76PHq61-JUHFQ?e=K0E0TR

Please let me know your test results.