private String tryFetchConfig()

in apm-agent-core/src/main/java/co/elastic/apm/agent/configuration/ApmServerConfigurationSource.java [185:235]
50 lines of code
12 McCabe index (conditional complexity)

    private String tryFetchConfig(ConfigurationRegistry configurationRegistry, HttpURLConnection connection) throws IOException, DslJsonSerializer.UninitializedException {
        if (logger.isDebugEnabled()) {
            logger.debug("Reloading configuration from APM Server {}", connection.getURL());
        }
        connection.setRequestProperty("Content-Type", "application/json");
        connection.setRequestMethod("POST");
        connection.setDoOutput(true);
        if (etag != null) {
            connection.setRequestProperty("If-None-Match", etag);
        }
        payloadSerializer.setOutputStream(connection.getOutputStream());
        payloadSerializer.appendMetadataToStream();
        payloadSerializer.fullFlush();
        etag = connection.getHeaderField("ETag");

        final int status = connection.getResponseCode();
        switch (status) {
            case SC_OK:
                InputStream is = connection.getInputStream();
                final JsonReader<Object> reader = dslJson.newReader(is, buffer);
                reader.startObject();
                config = MapConverter.deserialize(reader);
                configurationRegistry.reloadDynamicConfigurationOptions();
                logger.info("Received new configuration from APM Server: {}", config);
                for (Map.Entry<String, String> entry : config.entrySet()) {
                    ConfigurationOption<?> conf = configurationRegistry.getConfigurationOptionByKey(entry.getKey());
                    if (IGNORED_REMOTE_KEYS.contains(entry.getKey())) {
                        logger.debug("Received ignored remote configuration key {}", entry.getKey());
                    } else if (conf == null) {
                        logger.warn("Received unknown remote configuration key {}", entry.getKey());
                    } else if (!conf.isDynamic()) {
                        logger.warn("Can't apply remote configuration {} as this option is not dynamic (aka. reloadable)", entry.getKey());
                    }
                }
                break;
            case SC_NOT_MODIFIED:
                logger.debug("Configuration did not change");
                break;
            case SC_NOT_FOUND:
                logger.debug("This APM Server does not support central configuration. Update to APM Server 7.3+");
                break;
            case SC_FORBIDDEN:
                logger.debug("Central configuration is disabled. Set kibana.enabled: true in your APM Server configuration.");
                break;
            case SC_SERVICE_UNAVAILABLE:
                throw new IllegalStateException("Remote configuration is not available. Check the connection between APM Server and Kibana.");
            default:
                throw new IllegalStateException("Unexpected status " + status + " while fetching configuration");
        }
        return connection.getHeaderField("Cache-Control");
    }