c ++发送UDP广播

Question

For a project i need to send a UDP broadcast every second to 87.255.255.255 and port 4448 with the values of my project. I have writen some code in c++ but i got always the error:

Assertion `::bind(s, (sockaddr *)&si_me, sizeof(sockaddr))!=-1' failed

with this line:

//assert(::bind(s, (sockaddr *)&si_me, sizeof(sockaddr))!=-1);

When i delete this line the code runs but i find nothing on wireshark.

Does anyone have a solution or some extra info to build a broadcast sender?

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <assert.h>
#include <string.h>
#include <ctime>

int main(int argc, char const *argv[]) {

  sockaddr_in si_me, si_other;
  int s;
  printf("Making socket\n");
  assert((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))!=-1);
  fprintf(stderr,"usage %s hostname port\n", argv[0]);
  int port=4448;
  int broadcast=1;
  setsockopt(s, SOL_SOCKET, SO_BROADCAST,
        &broadcast, sizeof broadcast);

        memset(&si_me, 0, sizeof(si_me));
        si_me.sin_family = AF_INET;
        si_me.sin_port = htons(port);
        si_me.sin_addr.s_addr = INADDR_ANY;

  assert(::bind(s, (sockaddr *)&si_me, sizeof(sockaddr))!=-1);

  while(1)
  {
     printf("Send message to broadcast\n");
     char buf[10000];
     strcpy(buf, "test for wireshark");
     unsigned slen=sizeof(sockaddr);
     send(s, buf, sizeof(buf)-1, 0);
     //recvfrom(s, buf, sizeof(buf)-1, 0, (sockaddr *)&si_other, &slen);
     printf("recv: %s\n", buf);
     sleep(1);
  }
}

Answer 1

Apparently there's some weirdness with broadcasting under UNIX. So this may or may not work as expected.

void errno_abort(const char* header)
{
    perror(header);
    exit(EXIT_FAILURE);
}

int main(int argc, char* argv[])
{
#define SERVERPORT 4567
    struct sockaddr_in send_addr, recv_addr;
    int trueflag = 1, count = 0;
    int fd;
    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
        errno_abort("socket");
#ifndef RECV_ONLY
    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST,
                   &trueflag, sizeof trueflag) < 0)
        errno_abort("setsockopt");

    memset(&send_addr, 0, sizeof send_addr);
    send_addr.sin_family = AF_INET;
    send_addr.sin_port = (in_port_t) htons(SERVERPORT);
    // broadcasting address for unix (?)
    inet_aton("127.255.255.255", &send_addr.sin_addr);
    // send_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
#endif // ! RECV_ONLY

#ifndef SEND_ONLY
    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
                   &trueflag, sizeof trueflag) < 0)
        errno_abort("setsockopt");

    memset(&recv_addr, 0, sizeof recv_addr);
    recv_addr.sin_family = AF_INET;
    recv_addr.sin_port = (in_port_t) htons(SERVERPORT);
    recv_addr.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(fd, (struct sockaddr*) &recv_addr, sizeof recv_addr) < 0)
        errno_abort("bind");
#endif // ! SEND_ONLY

    while ( 1 ) {
#ifndef RECV_ONLY
        char sbuf[256] = {};
        snprintf(sbuf, sizeof(sbuf), "Hello(%d)!", count++);
        if (sendto(fd, sbuf, strlen(sbuf)+1, 0,
                   (struct sockaddr*) &send_addr, sizeof send_addr) < 0)
            errno_abort("send");
        printf("send: %s\n", sbuf);
        usleep(1000000/2);
#endif // ! RECV_ONLY

#ifndef SEND_ONLY
        char rbuf[256] = {};
        if (recv(fd, rbuf, sizeof(rbuf)-1, 0) < 0)
            errno_abort("recv");
        printf("recv: %s\n", rbuf);
#endif // ! SEND_ONLY
    }
    close(fd);
    return 0;
}

Hope this helps. Good luck.

Answer 2

Sending a UDP packet with size 10000 is probably a bad idea. Try using strlen(buffer) instead when calling send(). This might be a reason why you don't see anything on shark.

To find a reason why bind() fails, you need to eval errno.

BTW: I remember one TCP stack implementation, which did not like IPPROTO_UDP as third parameter to the socket() call even though it is supposed to work according to the standard. Try using 0 instead.