How to get user_data passed from client while creating endpoint in server ?

[PrateekJoshi]

I see that there is a parameter called user_data in ucp_ep_params_t stuct which can be passed while creating an endpoint. I am passing a unique id in this parameter as below in my client :

    ucp_ep_params_t ep_params;
    ep_params.field_mask = UCP_EP_PARAM_FIELD_FLAGS |
                           UCP_EP_PARAM_FIELD_SOCK_ADDR |
                           UCP_EP_PARAM_FIELD_ERR_HANDLER |
                           UCP_EP_PARAM_FIELD_ERR_HANDLING_MODE ;
    ep_params.err_mode = UCP_ERR_HANDLING_MODE_PEER;
    ep_params.err_handler.cb = ErrorHandlingCb;
    ep_params.err_handler.arg = this;
    ep_params.flags = UCP_EP_PARAMS_FLAGS_CLIENT_SERVER | UCP_EP_PARAM_FIELD_USER_DATA;  // USER DATA is set 
    ep_params.sockaddr.addr = (struct sockaddr *)&connect_addr;
    ep_params.sockaddr.addrlen = sizeof(connect_addr);
    ::ucp::common::client_metadata_t client_data;
    client_data.client_id = 12345; // Unique client ID
    ep_params.user_data = &client_data;                              // Pass client metadata as user data

    // Create an endpoint to the client
    auto status = ucp_ep_create(m_UcpWorker, &ep_params, &m_UcpServerEp);

I want to know how can I get this user_data in my server during connection establishment?

[bosilca]

ucp_ep_attr_t attr;
attr.field_mask = UCP_EP_ATTR_FIELD_USER_DATA;
auto status = ucp_ep_query(ep, &attr);
if (UCS_OK == status) ...

[PrateekJoshi]

Thanks @bosilca for getting back. I tried this but I see empty user data at server side. Below is my client and server code snipper

Client :

    struct application_header
    {
        uint8_t eventType;
        uint8_t clientid[16]; 
    };
    
     ucp_ep_params_t ep_params;
    ep_params.field_mask = UCP_EP_PARAM_FIELD_FLAGS |
                           UCP_EP_PARAM_FIELD_SOCK_ADDR |
                           UCP_EP_PARAM_FIELD_ERR_HANDLER |
                           UCP_EP_PARAM_FIELD_ERR_HANDLING_MODE ;
    ep_params.err_mode = UCP_ERR_HANDLING_MODE_PEER;
    ep_params.err_handler.cb = ErrorHandlingCb;
    ep_params.err_handler.arg = this;
    ep_params.flags = UCP_EP_PARAMS_FLAGS_CLIENT_SERVER | UCP_EP_PARAM_FIELD_USER_DATA;
    ep_params.sockaddr.addr = (struct sockaddr *)&connect_addr;
    ep_params.sockaddr.addrlen = sizeof(connect_addr);
    ::ucp::common::application_header connect_header = {};
    connect_header.eventType = static_cast<uint8_t>(::ucp::common::EventType::CONNECT);
    memcpy(connect_header.clientid, "12345", strlen("12345"));
    ep_params.user_data = &connect_header; 

    // Create an endpoint to the client
    auto status = ucp_ep_create(m_UcpWorker, &ep_params, &m_UcpServerEp);
   ...

Server :

...
    ucp_ep_attr_t ep_attr;
    ::ucp::common::application_header connect_header = {};
    ep_attr.field_mask = UCP_EP_ATTR_FIELD_USER_DATA;
    ep_attr.user_data = &connect_header;
    status = ucp_ep_query(pServer->m_mapUcpClientEp[clientIp], &ep_attr);
    if (status != UCS_OK)
    {
        LOG_AND_THROW(std::runtime_error,
                      std::format("Failed to query endpoint attributes: {}", ucs_status_string(status)));
    }
    LOG(std::format("Queried user_data from endpoint: {}",std::string( (char*) connect_header.clientid, sizeof( connect_header.clientid))));
    LOG(std::format("Queried user_data from endpoint: {}", connect_header.eventType));
...

Sever Log :

message: Queried user_data from endpoint: 
message: Queried user_data from endpoint: 0

What I am doing wrong ? How can I fix it ?

[bosilca]

As far as I know the user_data is local, you can only retrieve it on the same process that sets it.

[PrateekJoshi]

Ok, got it. My use case is to maintain a unique client id to endpoint mapping at the server. I need it because I need to call UCX operation ( send,recv,disconnect) on specific clients. Please let me know if there is any mechanism to send some metadata with client connection request.

[bosilca]

You can establish a connection handshake, where the client is not considered connected until it provides the server with his unique client id and maybe some other security key (to validate that the connecting process is really intended for your server and it is not just scanning ports).