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RL-ARM User's Guide (MDK v4)

RL-RTX RL-FlashFS RL-TCPnet TCP Socket Opening TCP Connection TCP Active Open TCP Passive Open Sending TCP Data Example for Sending Data Multiple TCP Connections UDP Socket Opening UDP Connection Sending UDP Data When DHCP Enabled When ARP Cache Empty Example for Sending Data IP Multicasting Multiple UDP Connections Configuring RL-TCPnet Static Configuration System Definitions Ethernet Network Interface PPP Network Interface SLIP Network Interface UDP Socket TCP Socket BSD Socket HTTP Server Telnet Server TFTP Server TFTP Client FTP Server FTP Client DNS Client SMTP Client SNMP Agent SNTP Client Error Function Runtime Configuration Library Files Using RL-TCPnet Stand Alone With RTX Kernel Event Driven Operation IP Address Assignment Ethernet Interface PPP Interface SLIP Interface Localhost Applications HTTP Server Script Language CGI Functions Ajax Support Using XML XML Example How it works SOAP Support SOAP Interface Large POST Messages Web Pages Default Page Error Pages Web on SD Card Web Update File System Interface Http Caching How it works Internal Web External Web Multi-user Authentication Using RAM File System FCARM File Converter PRINT Directive NOPRINT Directive PAGEWIDTH Directive PAGELENGTH Directive ROOT Directive Telnet Server Command Line Interface Multi-user Authentication Sending Reply Message Short Reply Long Reply Continuous Screen Update TFTP Server File System Interface TFTP Client File System Interface FTP Server File System Interface Multi-user Authentication Supported Commands FTP Client File System Interface SMTP Client SNMP Agent MIB Database MIB Interface MIB Entry MIB Table DNS Resolver Starting DNS Device Drivers Ethernet Driver Interrupt Mode Modem Driver Serial Driver Using Serial Link Cable Connection Modem Connection Windows Dial-up Add Direct Serial Link New Dial-up Connection Configure PPP Dial-up Configure SLIP Dial-up Debugging Enabling Debug Debug Level Redirecting Output Function Overview BSD Routines CGI Routines Ethernet Routines FTP Routines HTTP Routines IGMP Routines Miscellaneous Routines Modem Routines PPP Routines Serial Routines SLIP Routines SMTP Routines SNMP Routines System Functions TCP Routines Telnet Routines TFTP Routines UDP Routines RL-CAN RL-USB Example Programs Library Reference Appendix

Multiple UDP Connections

It is often required for the server applications to be able to accept several UDP connections from clients on the same port. Such application is for example a TFTP server. The multiplex handling must be implemented in the session layer of the user application.

Because UDP socket is a connectionless service, it is able to accept several concurrent connections from different remote hosts. The packet multiplexing must be done in user application.

The framework of the user application shall contain the following basic functions:

  1. The user_init() function to initialize all user application sessions at startup.
    void user_init () {
      USER_INFO *user_s;
      int i;
    
      for (i = 0; i < user_num_sess; i++) {
        user_s = &user_session[i];
        mem_set (user_s->RemIp, 0, IP_ADRLEN);
        user_s->RemPort = 0;
        user_s->Flags   = 0;
        user_s->Retries = 0;
        user_s->Tout    = 0;
        user_s->File    = NULL;
        user_s->State   = USER_STATE_IDLE;
      }
      /* Allocate one UDP socket for all sessions. */
      user_Socket = udp_get_socket (0, UDP_OPT_SEND_CS | UDP_OPT_CHK_CS,
                                    user_listener);
      if (user_Socket != 0) {
        udp_open (user_Socket, USER_SERVER_PORT);
      }
    }
    
    All user sessions are now initialized. A common UDP socket is opened for communication on selected USER_SERVER_PORT port.
  2. The user_listener() callback function for UDP socket.
    static U16 user_listener (U8 socket, U8 *remip, U16 port,
                              U8 *buf, U16 len) {
      USER_INFO *user_s;
      U8 session;
      int i;
    
      if (socket != user_Socket)) {
        return (__FALSE);
      }
    
      session = user_map_session (remip, port);
      if (session == 0) {
        return (__FALSE);
      }
      user_s = &user_session[session-1];
      switch (user_s->State) {
        case USER_STATE_IDLE:
          /* A new connection established. */
           ..
          user_s->State = USER_STATE_ACTIVE;
          break;
    
        case USER_STATE_ACTIVE:
          /* Process UDP data. */
           ..
          break;
      }
      return (__TRUE);
    }
    
  3. The user_map_session() function to map the UDP packet, which has generated a callback event, to it's owner session.
    static U8 user_map_session (U8 *remip, U16 port) {
      USER_INFO *user_s;
      int i;
    
      /* Check if this is an existing connection. */
      for (i = 1; i <= user_num_sess; i++) {
        user_s = &user_session[i-1];
        if ((user_s->State > USER_STATE_IDLE) &&
            (mem_comp (remip, user_s->RemIp, IP_ADRLEN) == __TRUE) &&
            (port == user_s->RemPort)) {
          return (i);
        }
      }
      /* Check if this is a new connection. */
      for (i = 1; i <= user_num_sess; i++) {
        user_s = &user_session[i-1];
        if (user_s->State == USER_STATE_IDLE) {
          mem_copy (user_s->RemIp, remip, IP_ADRLEN);
          user_s->RemPort = port;
          return (i);
        }
      }
      return (0);
    }
    
  4. The user_kill_session() function to initialize the session to a default state, close any eventually opened files and release any eventually allocated buffers.
    static void user_kill_session (USER_INFO *user_s) {
    
      user_s->State = USER_STATE_IDLE;
      if (user_s->File != NULL) {
        user_fclose (user_s->File);
        user_s->File = NULL;
      }
      mem_set (user_s->RemIp, 0, IP_ADRLEN);
      user_s->RemPort = 0;
      user_s->Flags   = 0;
      user_s->Retries = 0;
      user_s->Tout    = 0;
    }
    
  5. The user_run_server() function to maintain the application jobs, timeouts, etc. This function shall be frequently called from the main loop.
    void user_run_server () {
      USER_INFO *user_s;
      int i;
    
      for (i = 0; i < user_num_sess; i++) {
        user_s = &user_session[i];
    
        switch (user_s->State) {
          case USER_STATE_ACTIVE:
            if (sec_tick == __TRUE) {
              if (--user_s->Tout == 0) {
                /* A timeout expired. */
                user_kill_session (user_s);
              }
            }
            break;
        }
      }
    }
    

Note

  • There is only one socket used for all user sessions.
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