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Folks,
I’m trying (for tests of third party hardware) to set up a very simple ‘UDP parrot’. It receives a packet, and returns it to the source with a '*' prefixed.
Can’t get it work. The following code works like a charm on FreeBSD, but won’t work on MacOS:
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <sys/errno.h>
#include <string.h>
int main(int argc, const char * argv[]) {
struct sockaddr_in myAddr;
struct sockaddr_in rmtAddr;
socklen_t rmtAddrLength;
char buffer [2048];
char src [256];
printf ("Opening socket…\n");
int sock;
if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
printf("Cannot open UDP socket. Bailing!\n");
return -1;
}
int opt = 1;
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
myAddr.sin_family = AF_INET;
myAddr.sin_addr.s_addr = INADDR_ANY;
myAddr.sin_port = htons(5522);
if (bind(sock, (struct sockaddr *) &myAddr, sizeof(myAddr))) {
printf ("Error binding socket -> %d\n", errno);
return -1;
}
printf ("Listening…\n");
while (1) {
ssize_t dataLength = recvfrom(sock, buffer + 1, sizeof(buffer) - 1,
0, (struct sockaddr *)& rmtAddr, & rmtAddrLength);
printf ("Received %zd bytes: %s\n", dataLength, buffer);
printf ("addrLength: %d\n", rmtAddrLength);
inet_ntop(AF_INET, & rmtAddr.sin_addr, src, sizeof(src));
printf("From %s port %d\n", src, ntohs (rmtAddr.sin_port));
if (! strncmp (buffer + 1, "STOP", 4)) {
sendto (sock, "Terminated\n", 11, 0,
(struct sockaddr *)& rmtAddr, sizeof(rmtAddr));
break;}
buffer [0] = '*';
dataLength = sendto(sock, buffer, dataLength + 1, 0,
(struct sockaddr *)& rmtAddr, sizeof(rmtAddr));
}
return 0;
}
The problem is, the rmtAddr structure, which is supposed to contain the IP address of the remote sender, well, does not. I always get 1.0.0.0 instead. As I said before, I have no such problem with the exact same code on FreeBSD. Also, rmtAddrLength, which is 8 on FreeBSD, is 16 on MacOS apparently.
I've dumped the memory starting at &rmtAddr and did not see a hint of a possible IP address.
Any idea what could be wrong?
Thanks !
V.
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Vingt-Cent.
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Vingt-Cent.
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