Fail to create service with labelSelector.

[Xezeloh]

Describe the bug
I tried to create a service with labelSelector but got this:

ErrCode:400, ErrMsg:failed to req API:/api//nacos/v1/ns/service after all servers([127.0.0.1:8848]) tried: caused: specified service already exists, serviceName : DEFAULT_GROUP@@cross-site-server;
	at com.alibaba.nacos.client.naming.net.NamingProxy.reqAPI(NamingProxy.java:490)
	at com.alibaba.nacos.client.naming.net.NamingProxy.reqAPI(NamingProxy.java:395)
	at com.alibaba.nacos.client.naming.net.NamingProxy.reqAPI(NamingProxy.java:391)
	at com.alibaba.nacos.client.naming.net.NamingProxy.createService(NamingProxy.java:276)
	at com.alibaba.nacos.client.naming.NacosNamingMaintainService.createService(NacosNamingMaintainService.java:133)
	at com.alibaba.nacos.client.naming.NacosNamingMaintainService.createService(NacosNamingMaintainService.java:128)
	at com.alibaba.nacos.spring.factory.DelegatingNamingMaintainService.createService(DelegatingNamingMaintainService.java:89)
...

My code is as below:

@SpringBootApplication
public class CrossSiteServerApplication {

	@NacosInjected
	private NamingMaintainService namingMaintainService;

	@NacosInjected
	private NamingService namingService;

	@Value("${spring.application.name}")
	private String applicationName;

	@Value("${service.provider.ip}")
	private String ip;

	@Value("${service.provider.port}")
	private Integer port;

	@PostConstruct
	private void registerInstance() throws NacosException {
		System.out.println(namingMaintainService);

		Service service = new Service();
		service.setAppName(applicationName);
		service.setGroupName(Constants.DEFAULT_GROUP);
		try {
			namingMaintainService.createService(
					applicationName,
					Constants.DEFAULT_GROUP,
					0,
					"CONSUMER.label.site = PROVIDER.label.site"
			);
		} catch (NacosException e) {
			e.printStackTrace();
			return;
		}

		try {
			namingService.registerInstance(applicationName, ip, port);
		} catch (NacosException e) {
			e.printStackTrace();
		}
	}

	public static void main(String[] args) {
		SpringApplication.run(CrossSiteServerApplication.class, args);
	}
}

Expected behavior
Service created successfully.

Acutally behavior
Fail to create the service.

How to Reproduce
Steps to reproduce the behavior:

1. Run the code.
2. See the error.

Desktop (please complete the following information):

• OS: Windows 10
• Version: nacos-server 1.3.2
• Module: naming
• SDK: nacos-discovery-spring-boot-starter

Additional context
FYI, here's another way to see a related error on the console:

1. Click the “Create Service” button.
2. Type "Dragonborn" in "Service Name" box.
3. Type "0" in "Protect Threshold" box.
4. Choose “Label” in the drop-down box "Type".
5. Type "CONSUMER.label.site = PROVIDER.label.site" in the "Selector" box.
6. Click the "OK" button.
7. See the error "caused: parsed expression failed!;"

I try to locate the error and find this:

nacos/naming/src/main/java/com/alibaba/nacos/naming/selector/LabelSelector.java

Lines 170 to 176 in 7fd4d9a

	int index = 0;
	index = checkInnerSyntax(elements, index);
	if (index == -1) {
	throw new NacosException(NacosException.INVALID_PARAM, "parse expression failed!");
	}

nacos/naming/src/main/java/com/alibaba/nacos/naming/selector/LabelSelector.java

Lines 247 to 267 in 7fd4d9a

	private static int checkInnerSyntax(List<String> elements, int start) {
	int index = start;
	index = skipEmpty(elements, index);
	if (index >= elements.size()) {
	return -1;
	}
	if (!elements.get(index).startsWith(CONSUMER_PREFIX)) {
	return -1;
	}
	index = skipEmpty(elements, index);
	if (index >= elements.size()) {
	return -1;
	}
	if (!SUPPORTED_INNER_CONNCETORS.contains(elements.get(index++))) {
	return -1;
	}

第一段代码在172行调用了一次checkInnerSyntax方法，并且给形参start赋了0值。而在checkInnerSyntax方法中，第265行，这里用了一个index++来作为索引。结合前后代码，我推测这里或许是想表达“确认下一个元素是否在SUPPORTED_INNER_CONNCETORS”中这样一个逻辑，但却错误地使用了index++，导致了错误的出现。

[horizonzy]

I will trace it.

[horizonzy]

It's really a bug, I will fix it.