Question

I have a code which receives packets from the Ethernet and sends it via wireless network. This works on a wireless box which uses OpenWrt. The code is written below. It gives me the following error at runtime. Based on the printf statements I feel the error is somewhere on this syntax, but I cant figure out whats wrong.

Probable region of error:

  if(sendto(b_sock, buf, sizeof(v2vmessage), 0, (struct sockaddr *)&tx_addr, sizeof(tx_addr)) < 0)

Error:

Receving packets
Packets received
Sending packet started
Variables initialized
Send test
./dsrc_dsrc: can't resolve symbol 'sendto' in lib './dsrc_dsrc'.

Code:

#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <netdb.h>
#include <stdio.h>

#include <fcntl.h>
#include <string.h>
#include <sys/time.h>
#include <arpa/inet.h>  /* for sockaddr_in */

#define BROADCAST_IP "192.168.255.255"
#define BROADCAST_PORT 4545

struct v2vmessage
{
  ...
  ...
};

int b_sock=-1;

void init_socket()
{
  unsigned short b_port = BROADCAST_PORT;
  struct sockaddr_in b_addr;
  int broadcastPermission;
  char* rx_ip = BROADCAST_IP;

  if ((b_sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
    perror("socket() failed");

  /* Set socket to allow broadcast */
  broadcastPermission = 1;
  if (setsockopt(b_sock, SOL_SOCKET, SO_BROADCAST, (void *) &broadcastPermission, sizeof(broadcastPermission)) < 0)
    perror("setsockopt() failed");

  int opts;
  opts = fcntl(b_sock,F_GETFL);
  if(opts < 0)
    perror("fcntl get failed");

  opts = (opts | O_NONBLOCK);
  if(fcntl(b_sock,F_SETFL,opts) < 0)
    perror("fcntl set failed");

  memset(&b_addr, 0, sizeof(b_addr));   /* Zero out structure */
  b_addr.sin_family = AF_INET;                 /* Internet address family */
  b_addr.sin_addr.s_addr = inet_addr(rx_ip);/* Broadcast IP address */
  b_addr.sin_port = htons(b_port);         /* Broadcast port */

  if (bind(b_sock, (struct sockaddr *) &b_addr, sizeof(b_addr)) < 0)
    perror("rx bind() failed");
}


void send_thread_body(v2vmessage *buf)
{
  printf("Sending packet started\n");
  char *tx_ip = BROADCAST_IP;
  unsigned short tx_port = BROADCAST_PORT;
  struct sockaddr_in tx_addr;

  printf("Variables initialized\n");

  memset(&tx_addr, 0, sizeof(tx_addr));   /* Zero out structure */
  tx_addr.sin_family = AF_INET;                 /* Internet address family */
  tx_addr.sin_addr.s_addr = inet_addr(tx_ip);/* Broadcast IP address */
  tx_addr.sin_port = htons(tx_port);         /* Broadcast port */

  printf("Send test\n");

  if(sendto(b_sock, buf, sizeof(v2vmessage), 0, (struct sockaddr *)&tx_addr, sizeof(tx_addr)) < 0)
    perror("tx sent diff num bytes than expected");
}

int main(int argc, char *argv[])
{
  init_socket();
  {
    int sock, length, n,p;
    socklen_t fromlen;
    struct sockaddr_in server;
    struct sockaddr_in from;

    if (argc < 2)
    {
      fprintf(stderr, "ERROR, no port provided\n");
      exit(0);
    }

    sock=socket(AF_INET, SOCK_DGRAM, 0);
    if (sock < 0)
      perror("Opening socket");
    length = sizeof(server);
    bzero(&server,length);
    server.sin_family=AF_INET;
    server.sin_addr.s_addr=INADDR_ANY;
    server.sin_port=htons(atoi(argv[1]));
    if (bind(sock,(struct sockaddr *)&server,length)<0) 
      perror("binding");
    fromlen = sizeof(struct sockaddr_in);
    v2vmessage *buf;

    while (1)
    {
      printf("Receving packets\n");
      n = recvfrom(sock,buf,sizeof(v2vmessage),0,(struct sockaddr *)&from,&fromlen);
      if (n < 0)
        perror("recvfrom");
      printf("Packets received\n");
      send_thread_body(buf);
      printf("Packets sent\n");
    }
  }
  return 0;
}

Answer 1

In the main(), replace v2vmessage* buf by v2vmessage buf and in the following while(1), replace the buf by &buf to solve the problem. Since, no memory was allocated to the pointer, hence it gave an error at runtime.