You can use shutdown(2) in order to shutdown reception part of the socket.
See shutdown man page
EDIT : I found that shutdown only works on connected (ie TCP) sockets.
With Raw socket, there are 2 possibilities :
- Receive data into a temporary buffer (with recv) and discard them (perhaps in an other thread)
- If I remember well, when the socket buffer is full, incoming data are automatically discarded (and data in the buffer aren't modified), so you can set the socket reception buffer size to 0 (and increase it later if needed).
Here's how to set reception buffer size to 0 :
int opt = 0;
setsockopt(sock_fd, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt));
TEST
/**
* @file raw_print_pkt.c
* @brief
* @author Airead Fan <fgh1987168@gmail.com>
* @date 2012/08/22 12:35:22
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
int main(int argc, char *argv[])
{
int s;
ssize_t rn; /* receive number */
struct sockaddr_in saddr;
char packet[4096];
int count;
if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) < 0) {
perror("error:");
exit(EXIT_FAILURE);
}
memset(packet, 0, sizeof(packet));
socklen_t *len = (socklen_t *)sizeof(saddr);
int fromlen = sizeof(saddr);
int opt = 0;
count = 0;
while(1) {
if ((rn = recvfrom(s, (char *)&packet, sizeof(packet), 0,
(struct sockaddr *)&saddr, &fromlen)) < 0)
perror("packet receive error:");
if (rn == 0) {
printf("the peer has performed an orderly shutdown\n");
break;
}
printf("[%d] rn = %lu \n", count++, rn);
if (count == 16) {
if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt)) < 0) {
perror("setsocketopt failed");
} else {
fprintf(stdout, "setsocketopt successful\n");
}
// int shutdown(int sockfd, int how);
/* if (shutdown(s, SHUT_RD) < 0) {
* perror("shutdown failed");
* } */
}
}
return 0;
}
TEST 2 (same includes):
int main(int argc, char *argv[])
{
int s;
ssize_t rn; /* receive number */
char packet[4096];
int count;
if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) < 0) {
perror("error:");
exit(EXIT_FAILURE);
}
memset(packet, 0, sizeof(packet));
int opt = 0;
count = 0;
//Set recv buffer size
if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt)) < 0) {
perror("setsocketopt failed");
} else {
fprintf(stdout, "setsocketopt successful\n");
}
//10 seconds countdown
int i = 10;
while(i > 0)
{
printf("\r%d ", i);
fflush(stdout);
i--;
sleep(1);
}
printf("\n");
while(1) {
if ((rn = recv(s, (char *)&packet, sizeof(packet), 0)) <= 0)
perror("packet receive error:");
printf("[%d] rn = %lu \n", count++, rn);
}
return 0;
}
Here's how to proceed with test 2 :
First of all, set the buffer size to 4096 (or bigger if you have a lot of traffic on your network). Compile and launch. During the 10 seconds before starting receiving data, send a lot of data to the socket. After the 10 seconds, the program will receive everything you sent during the countdown.
After that, set the buffer size to 0. Proceed as previously. After the 10 seconds, the program won't receive the data you sent during the countdown. But if you send data while it's in recvfrom, it will read them normally.
