/* File: message.c */

/*
 *********************************************************************
   ALTERNATING BIT AND GO-BACK-N NETWORK EMULATOR

   Revised version of code by J.F. Kurose

   From the companion website for 
   _Computer Networking: A Top-Down Approach Featuring the Internet_
   by J.F. Kurose and K. W. Ross
   (c) 2001 by Addison Wesley Longman

   Based on document at <URL:http://occawlonline.pearsoned.com/
   bookbind/pubbooks/kurose-ross1/chapter4/custom12/deluxe-content.html>
   (as of 02 July 2002)
 *********************************************************************
*/

#include <strings.h>
#include <stdlib.h>
#include "payload.h"
#include "message.h"

  /* struct msg 
     a "msg" is the data unit passed from layer 5 (teacher's code) to
     layer 4 (student's code).  It contains the data (characters) to
     be delivered to layer 5 via the student's transport level protocol
     entities.
  */
  struct msg {
    char data[PAYLOAD_SZ];
  };


/* create a message */
message_t 
new_msg(void) {
  message_t M;

  if (NULL != (M = malloc(sizeof(struct msg)))) {
    init_msg(M);
  }
  return M;
} /* new_msg() */


/* destroy a message */
void
dispose_msg(message_t M) {
  free(M);
} /* dispose_msg() */


/* initialize value of message data field (make it empty) */
void
init_msg(message_t M) {
  M->data[0] = '\0';
} /* init_msg() */


/* set value of message data field */
void
set_msg_data (message_t M,
              char      *data) {
  (void)strncpy(M->data, data, PAYLOAD_SZ - 1);
} /* set_msg_data() */


/* append data to message's data field */
void
append_msg_data (message_t M,
                 char      datum) {
  char str[2] = {'\0','\0'};
  str[0] = datum;
  (void)strncat(M->data, str, PAYLOAD_SZ - strlen(M->data) - 1);
} /* append_msg_data() */


/* get copy of message's data field */
char *
msg_data (message_t M) {
  return M->data;
} /* msg_data() */


/* display copy of message's data field */
int
print_msg (FILE *    where,
           char *    before, 
           message_t M,
           char *    after) {
  return
    fprintf(where, "%s%s%s",
            before, M->data, after);
} /* print_msg() */

/* EOF (message.c) */