server side which missing verifyClientVersion method get too many zombie connections

[iiibui]

Invalid connection didn't close immediately when ping failed cause by verifyClientVersion method missing exception(connect to nebula graph < 2.6):

nebula-java/client/src/main/java/com/vesoft/nebula/client/graph/net/RoundRobinLoadBalancer.java

Lines 75 to 88 in 453064d

	public boolean ping(HostAddress addr) {
	try {
	Connection connection = new SyncConnection();
	if (enabledSsl) {
	connection.open(addr, this.timeout, sslParam);
	} else {
	connection.open(addr, this.timeout);
	}
	connection.close();
	return true;
	} catch (IOErrorException | ClientServerIncompatibleException e) {
	return false;
	}
	}

Also see:

nebula-java/client/src/main/java/com/vesoft/nebula/client/graph/net/SyncConnection.java

Lines 86 to 108 in 453064d

	public void open(HostAddress address, int timeout)
	throws IOErrorException, ClientServerIncompatibleException {
	try {
	this.serverAddr = address;
	this.timeout = timeout <= 0 ? Integer.MAX_VALUE : timeout;
	this.transport = new TSocket(
	address.getHost(), address.getPort(), this.timeout, this.timeout);
	this.transport.open();
	this.protocol = new TCompactProtocol(transport);
	client = new GraphService.Client(protocol);
	// check if client version matches server version
	VerifyClientVersionResp resp =
	client.verifyClientVersion(new VerifyClientVersionReq());
	if (resp.error_code != ErrorCode.SUCCEEDED) {
	client.getInputProtocol().getTransport().close();
	throw new ClientServerIncompatibleException(new String(resp.getError_msg(),
	Charsets.UTF_8));
	}
	} catch (TException e) {
	throw new IOErrorException(IOErrorException.E_UNKNOWN, e.getMessage());
	}
	}

client.verifyClientVersion will have no response but exception.

[Nicole00]

Great catch, thanks for raising this issue.
#402