tnet_cbfunc

#include <net_config.h>

U16 tnet_cbfunc (
    U8  code,        /* Type of message requested by the telnet server. */
    U8* buf,         /* Location where to write the requested message. */
    U16 buflen );    /* Number of bytes in the output buffer. */

The tnet_cbfunc function provides the connection and login messages to the telnet server running on TCPnet, when requested. The telnet server sends these messages to the telnet client.

The argument code specifies the type of message that the telnet server requires. This is shown in the table.

The argument buf points to the output buffer where the tnet_cbfunc must write the message. The argument buflen specifies the length of the output buffer in bytes.

The tnet_cbfunc function is part of RL-TCPnet. The prototype is defined in net_config.h. You must customize the function in telnet_uif.c.

note

• The length of the output buffer, buflen, might vary because buffer length is determined by the TCP socket Maximum Segment Size (MSS) negotiation. The buffer length is normally around 1400 bytes for local LAN. But this can be reduced to 500 bytes or even less.
• If the tnet_cbfunc function writes more bytes than buflen into the output buffer, then a system crash resulting from corruption of memory link pointers is highly likely.
• The telnet server does not automatically expand the carriage return (CR) character. The tnet_cbfunc function must write the carriage return and line feed (LF) characters into the the buffer to indicate the end of each message.

The tnet_cbfunc function returns the number of bytes written to the output buffer.

tnet_process_cmd

U16 tnet_cbfunc (U8 code, U8 *buf, U16 buflen) {
  U16 len = 0;

  switch (code) {
    case 0:
      /* Write initial header after login. */
      len = str_copy (buf, tnet_header);
      break;
    case 1:
      /* Write a prompt string. */
      len = str_copy (buf, "\r\nMcb2100> ");
      break;
    case 2:
      /* Write Login header. */
      len = str_copy (buf, CLS "\r\nKeil Embedded Telnet Server V1.00,"
                             " please login...\r\n");
      break;
    case 3:
      /* Write 'username' prompt. */
      len = str_copy (buf, "\r\nUsername: ");
      break;
    case 4:
      /* Write 'Password' prompt. */
      len = str_copy (buf, "\r\nPassword: ");
      break;
    case 5:
      /* Write 'Login incorrect'.message. */
      len = str_copy (buf, "\r\nLogin incorrect");
      break;
    case 6:
      /* Write 'Login Timeout' message. */
      len = str_copy (buf, "\r\nLogin timed out after 60 seconds.\r\n");
      break;
    case 7:
      /* Write Unsolicited messages from the Application Layer above. */
      len = sprintf ((S8 *)buf, "\r\nUnsolicited message nr. %d\r\n",
                                unsol_msg++);
      break;
  }
  return (len);
}