osip_message_get__property 函数剖析

当被返回1，说明当前的sip结构体已经正确转化为字符串报文

返回2，说明需要重新构建

 /* return values:
    1: structure and buffer "message" are identical.
    2: buffer "message" is not up to date with the structure info (call osip_message_to_str to update it).
    -1 on error.
  */
int
osip_message_get__property (const osip_message_t * sip)

该函数会影响到

int
osip_message_to_str (osip_message_t * sip, char **dest, size_t * message_length)
{
  return _osip_message_to_str (sip, dest, message_length, 0);
}

static int
_osip_message_to_str (osip_message_t * sip, char **dest, size_t * message_length, int sipfrag)
{
  size_t malloc_size;
  size_t total_length = 0;

  /* Added at SIPit day1 */
  char *start_of_bodies;
  char *content_length_to_modify = NULL;

  char *message;
  char *next;
  char *tmp;
  int pos;
  int i;
  char *boundary = NULL;

  malloc_size = SIP_MESSAGE_MAX_LENGTH;

  *dest = NULL;
  if (sip == NULL)
    return OSIP_BADPARAMETER;

  {
    if (1 == osip_message_get__property (sip)) {        /* message is already available in "message" */

      *dest = osip_malloc (sip->message_length + 1);
      if (*dest == NULL)
        return OSIP_NOMEM;
      memcpy (*dest, sip->message, sip->message_length);
      (*dest)[sip->message_length] = '\0';
      if (message_length != NULL)
        *message_length = sip->message_length;
      return OSIP_SUCCESS;
    }
    else {
      /* message should be rebuilt: delete the old one if exists. */
      osip_free (sip->message);
      sip->message = NULL;
    }
  }