CODEWITHSUNDEEP
linuxudp
Daniel Silveira
Daniel Silveira

Reputation: 42543

How to UDP Broadcast with C in Linux?

How to UDP Broadcast with C in Linux?

Upvotes: 38

Views: 112162

Answers (4)

shodanex
shodanex

Reputation: 15406

Unwind has it right, except you should use 'sendto'

Here is an example, that assumes you already have a socket. It was taken from clamav

static void
broadcast(const char *mess)
{
    #define BROADCAST_PORT 30000u
    struct sockaddr_in s;

    int broadcastSock = socket(AF_INET, SOCK_DGRAM, 0);
    
    if(broadcastSock < 0)
        return;

    memset(&s, '\0', sizeof(struct sockaddr_in));
    s.sin_family = AF_INET;
    s.sin_port = htons(BROADCAST_PORT)
    s.sin_addr.s_addr = INADDR_BROADCAST; /* This is not correct : htonl(INADDR_BROADCAST); */

    cli_dbgmsg("broadcast %s to %d\n", mess, broadcastSock);
    if(sendto(broadcastSock, mess, strlen(mess), 0, (struct sockaddr *)&s, sizeof(struct sockaddr_in)) < 0)
        perror("sendto");
}

Upvotes: 16

skoylu
skoylu

Reputation: 541

In many IP stack, such as Linux, this code does not work. Your socket must have broadcast permissions. Try this:

bcast_sock = socket(AF_INET, SOCK_DGRAM, 0);
int broadcastEnable=1;
int ret=setsockopt(bcast_sock, SOL_SOCKET, SO_BROADCAST, &broadcastEnable, sizeof(broadcastEnable));

/* Add other code, sockaddr, sendto() etc. */

Upvotes: 54

stefanB
stefanB

Reputation:

I wrote udp multicast server recently for testing. To subscribe to multicast you would subscribe your client to Multicast group 225.0.0.37 port 12346 and port 12345 (2 feeds - one feeds sends "Hello, World!" the other one "Bye, Office!").

I've been using it for testing my client, both client and server run on the same box so there might be bits that may not work but give it a try first.

#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <string.h>
#include <stdio.h>

#include <unistd.h>


#define BYE_OFFICE 12346
#define HELLO_PORT 12345
#define HELLO_GROUP "225.0.0.37"

int main(int argc, char *argv[])
{
    struct sockaddr_in addr;
    struct sockaddr_in addr2;
    int fd;
    int fd2;
    char *message = "Hello, World!";
    char *message2 = "Bye, Office!";

    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror("socket");
        exit(1);
    }

    if ((fd2 = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror("socket");
        exit(1);
    }

    /* set up destination address */
    memset(&addr,0,sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr(HELLO_GROUP);
    addr.sin_port=htons(HELLO_PORT);

    memset(&addr2,0,sizeof(addr2));
    addr2.sin_family = AF_INET;
    addr2.sin_addr.s_addr = inet_addr(HELLO_GROUP);
    addr2.sin_port=htons(BYE_OFFICE);

    while (1)
    {
        if (sendto(fd, message, strlen(message), 0,(struct sockaddr *) &addr, sizeof(addr)) < 0)
        {
            perror("sendto");
            exit(1);
        }
        sleep(3);
        if (sendto(fd2, message2, strlen(message2), 0,(struct sockaddr *) &addr2, sizeof(addr2)) < 0)
        {
            perror("sendto2");
            exit(1);
        }
        sleep(3);
    }
}

Upvotes: 3

unwind
unwind

Reputation: 399989

Typically using the Berkeley sockets API, to sendto() one or more datagrams to a known broadcast-class IP address.

Upvotes: 4

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