"Cannot open null host" log by com.vesoft.nebula.client.meta.MetaManager

[iiibui]

It should be check if the leader address is empty when E_LEADER_CHANGED:

nebula-java/client/src/main/java/com/vesoft/nebula/client/meta/MetaClient.java

Lines 195 to 197 in d487480

	if (response.getCode() == ErrorCode.E_LEADER_CHANGED) {
	freshClient(response.getLeader());
	} else {

Also see:

nebula-java/client/src/main/java/com/vesoft/nebula/client/meta/MetaClient.java

Lines 164 to 172 in d487480

	private void freshClient(HostAddr leader)
	throws TTransportException {
	close();
	try {
	getClient(leader.getHost(), leader.getPort());
	} catch (ClientServerIncompatibleException e) {
	LOGGER.error(e.getMessage());
	}
	}

nebula-java/client/src/main/java/com/vesoft/nebula/client/meta/MetaClient.java

Lines 130 to 162 in d487480

	private void getClient(String host, int port)
	throws TTransportException, ClientServerIncompatibleException {
	if (enableSSL) {
	SSLSocketFactory sslSocketFactory;
	if (sslParam.getSignMode() == SSLParam.SignMode.CA_SIGNED) {
	sslSocketFactory = SslUtil.getSSLSocketFactoryWithCA((CASignedSSLParam) sslParam);
	} else {
	sslSocketFactory =
	SslUtil.getSSLSocketFactoryWithoutCA((SelfSignedSSLParam) sslParam);
	}
	try {
	transport = new TSocket(sslSocketFactory.createSocket(host, port), timeout,
	timeout);
	} catch (IOException e) {
	throw new TTransportException(IOErrorException.E_UNKNOWN, e);
	}
	} else {
	transport = new TSocket(host, port, timeout, timeout);
	transport.open();
	}
	protocol = new TCompactProtocol(transport);
	client = new MetaService.Client(protocol);
	// check if client version matches server version
	VerifyClientVersionResp resp =
	client.verifyClientVersion(new VerifyClientVersionReq());
	if (resp.getCode() != ErrorCode.SUCCEEDED) {
	client.getInputProtocol().getTransport().close();
	throw new ClientServerIncompatibleException(new String(resp.getError_msg(),
	Charsets.UTF_8));
	}
	}

It may be fine to process like C++ meta client: MetaClient.cpp#L701-L702, MetaClient.h#L689-L696, since metad should response empty leader address when it's role is CANDIDATE:RaftPart.cpp#L960-L972.

Response call stack: handleErrorCode->handleLeaderChanged->partLeader->getStoreAddr->getStoreAddrFromRaftAddr.

[iiibui]

By the way, MetaManager should do some refactor since fillMetaInfo caught the TException then the caller like getSpace and so on know nothing about it. And the MetaClient stays in a strange state(transport has closed but the user know nothing about it) when getClient fail:

nebula-java/client/src/main/java/com/vesoft/nebula/client/meta/MetaClient.java

Lines 164 to 172 in d487480

	private void freshClient(HostAddr leader)
	throws TTransportException {
	close();
	try {
	getClient(leader.getHost(), leader.getPort());
	} catch (ClientServerIncompatibleException e) {
	LOGGER.error(e.getMessage());
	}
	}