Net-SNMP Single API use

saviour_q

Author: Tony Qian
Date: May 1st, 2006
Contact: tonyqian@gmail.com

Net-SNMP provide traditional API usage and Single API Usage, however their example online only provide tradition usage, thereby I change the code a little to make it a single api usage.

The advantage for single api use is thread-safe.
You can enable mutiple thread for get set and query.

In this example I use asynchr sending with select and call back support . This is the original post and please mention the original when you post anywhere else

Here is the command to compile
gcc -I/usr/local/include -g   -c -o snmp1.o snmp1.c
gcc -o snmp1 snmp1.o  -L/usr/local/lib -lm -lnetsnmp -lssl -lcrypto


Here is the code
#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>


int active_hosts = 1;

int print_result (int status, struct snmp_session *sp, struct snmp_pdu *pdu)
{
  char buf[1024];
  struct variable_list *vp;
  int ix;
  struct timeval now;
  struct timezone tz;
  struct tm *tm;

  gettimeofday(&now, &tz);
  tm = localtime(&now.tv_sec);
  fprintf(stdout, "%.2d:%.2d:%.2d.%.6li ", tm->tm_hour, tm->tm_min, tm->tm_sec, now.tv_usec);
  switch (status) {
  case STAT_SUCCESS:
    vp = pdu->variables;
    if (pdu->errstat == SNMP_ERR_NOERROR) {
      while (vp) {
        snprint_variable(buf, sizeof(buf), vp->name, vp->name_length, vp);
        fprintf(stdout, "%s: %s\n", sp->peername, buf);
        vp = vp->next_variable;
      }
    }
    else {
      for (ix = 1; vp && ix != pdu->errindex; vp = vp->next_variable, ix++)
        ;
      if (vp) snprint_objid(buf, sizeof(buf), vp->name, vp->name_length);
      else strcpy(buf, "(none)");
      fprintf(stdout, "%s: %s: %s\n",
              sp->peername, buf, snmp_errstring(pdu->errstat));
    }
    return 1;
  case STAT_TIMEOUT:
    fprintf(stdout, "%s: Timeout\n", sp->peername);
    return 0;
  case STAT_ERROR:
    snmp_perror(sp->peername);
    return 0;
  }
  return 0;
}

int asynch_response(int operation, struct snmp_session *sp, int reqid, struct snmp_pdu *pdu, void *magic)
{
  struct snmp_session *sess = (struct snmp_session *)magic;

  if (operation == NETSNMP_CALLBACK_OP_RECEIVED_MESSAGE) {
    if (print_result(STAT_SUCCESS, sess, pdu)) {
    }
  }else{
    print_result(STAT_TIMEOUT, sess, pdu);
  }
  /* something went wrong (or end of variables)
   * this host not active any more
   */
  active_hosts--;
  return 1;
}

int main(int argc, char **argv)
{

  int liberr, syserr;
  char *errstr;
  void *sessp;  /* <-- an opaque pointer, not a struct pointer */
  struct snmp_session Session;
  struct snmp_session *sptr;
  struct snmp_pdu *pdu;

  oid anOID[MAX_OID_LEN];
  size_t anOID_len = MAX_OID_LEN;
  //struct variable_list *vars;
  
  /*
   * Initialize the SNMP library
   */
  init_snmp("snmputil");

  /*
   * Initialize a "session" defines who we're going to talk to
   */  
  snmp_sess_init(&Session);

  Session.peername = strdup("10.255.51.2");
  Session.version = SNMP_VERSION_2c;
  Session.callback = asynch_response;
  //Session.callback_magic = sptr;
  Session.community = strdup("public");
  //Session.community_len = strlen(Session.community);
  sessp = snmp_sess_open(&Session);
  if (sessp == NULL) {
      /* Error codes found in open calling argument */
      snmp_error(&Session, &liberr, &syserr, &errstr);
      printf("SNMP create error %s.\n", errstr);
      free(errstr);
      return 0;
  }
  sptr = snmp_sess_session(sessp); /* <-- get the snmp_session pointer */

  /* Pass sptr to snmp_sess_error from here forward */
  /* Change the community name */
  //printf("TEST:%s\n",sptr->peername);
  free(sptr->community);
  sptr->community = strdup("public");
  sptr->community_len = strlen("public");
  sptr->callback_magic = sptr;
  /*
   * Create the PDU for the data for our request.
   *   1) We're going to GET the system.sysDescr.0 node.
   */
  pdu = snmp_pdu_create(SNMP_MSG_GET);
  read_objid(".1.3.6.1.2.1.1.1.0", anOID, &anOID_len);

#if OTHER_METHODS
  get_node("sysDescr.0", anOID, &anOID_len);
  read_objid("system.sysDescr.0", anOID, &anOID_len);
#endif

  snmp_add_null_var(pdu, anOID, anOID_len);
  
  if (0 == snmp_sess_send(sessp, pdu)) {
      snmp_sess_error(sessp, &liberr, &syserr, &errstr);
      printf("SNMP write error %s.\n", errstr);
      free(errstr);
      return 0;
  }

  while (active_hosts) {
    int fds = 0, block = 1;
    fd_set fdset;
    struct timeval timeout;

    FD_ZERO(&fdset);
    snmp_sess_select_info(sessp, &fds, &fdset, &timeout, &block);
    fds = select(fds, &fdset, NULL, NULL, block ? NULL : &timeout);
    if (fds < 0) {
        perror("select failed");
        exit(1);
    }
    if (fds)
        snmp_sess_read(sessp, &fdset);
    else
        snmp_sess_timeout(sessp);
  }

  snmp_sess_close(sessp);
  SOCK_CLEANUP;
  return (0);
}

Sample Text