[GitHub] [dubbo] vergilyn commented on issue #5885: nacos v1.1.4, dubbo v2.7.6.SNAPSHOT "No provider available from registry xxx"

["vergilyn (GitHub)" <gi...@apache.org>]

> 这个应该不是empty协议的问题，因为ZookeepRergistry里也是这么做的

理解不能..😅
debug 确实是因为 dubbo 2.7.6为了兼容历史，创建了一个未被提供的 serviceName = "providers:org.apache.dubbo.samples.api.GreetingService:1.0.0"。（被正确提供的 serviceName 后面多一个 冒号）
```
// org.apache.dubbo.registry.nacos.NacosRegistry#getServiceNames0
private Set<String> getServiceNames0(URL url) {
        NacosServiceName serviceName = createServiceName(url);

        final Set<String> serviceNames;

        if (serviceName.isConcrete()) { // is the concrete service name
            serviceNames = new LinkedHashSet<>();
            serviceNames.add(serviceName.toString());

            /* vergilyn-question, 2020-03-18 >>>> 注释，由于"no provider available"
             *   https://github.com/apache/dubbo/issues/5871
             *   https://github.com/apache/dubbo/issues/5885
             */
            // Add the legacy service name since 2.7.6
            // serviceNames.add(getLegacySubscribedServiceName(url));
        } else {
            serviceNames = filterServiceNames(serviceName);
        }

        return serviceNames;
    }
``
然后由于nacos确实不存在这个serviceName，其 instances == empty，刚好满足创建 empty protocol的条件。接着也满足 `integration.RegistryDirectory#refreshInvoker(...)` forbidden 的条件，所以最终并没有可用的invokers.

ps. 大佬通过 dubbo-sample 修改dubbo版本复现bug了吗？

[ Full content available at: https://github.com/apache/dubbo/issues/5885 ]
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