After the accept() on a socket, I'm trying to configure the TCP keepalive.
SockConnected = accept(SockListen, &RemoteAddr,
&RemoteLen);
/* A bit of checking goes here */
if (setsockopt (SockConnected , SOL_SOCKET, SO_KEEPALIVE,
(ST_CHAR *) &sockopt_on, sizeof (int) ) )
{
/* Error logging */
}
if (setsockopt(SockConnected , IPPROTO_TCP, TCP_KEEPIDLE, (char*)&(sockopt_tcp_keep_idle), sizeof(sockopt_tcp_keep_idle)))
{
/* Error logging */
}
if (setsockopt(SockConnected, IPPROTO_TCP, TCP_KEEPINTVL, (char*)&(sockopt_tcp_keep_intvl), sizeof(sockopt_tcp_keep_intvl)))
{
/* Error logging */
}
if (setsockopt(SockConnected, IPPROTO_TCP, TCP_KEEPCNT, (char*)&(sockopt_tcp_keep_cnt), sizeof(sockopt_tcp_keep_cnt)))
{
/* Error logging */
}
After calling getsockopt() for all four properties, everything seems alright. I've checked in Wireshark and there are no Keep alive packets being sent. I had to change SOL_TCP to IPPROTO_TCP, because when calling setsockopt() for TCP_KEEPIDLE it was returning errno 92 (Protocol not found).
I'm doing the same thing after calling socket() for an outgoing connection, and it's working perfectly.
I'm using C and Linux.
Is there any reason why setsockopt may not be working after an accept?
Here is a minimal working example. If it works for you, you can use it as a reference.
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/signal.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#define check(expr) if (!(expr)) { perror(#expr); kill(0, SIGTERM); }
void enable_keepalive(int sock) {
int yes = 1;
check(setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &yes, sizeof(int)) != -1);
int idle = 1;
check(setsockopt(sock, IPPROTO_TCP, TCP_KEEPIDLE, &idle, sizeof(int)) != -1);
int interval = 1;
check(setsockopt(sock, IPPROTO_TCP, TCP_KEEPINTVL, &interval, sizeof(int)) != -1);
int maxpkt = 10;
check(setsockopt(sock, IPPROTO_TCP, TCP_KEEPCNT, &maxpkt, sizeof(int)) != -1);
}
int main(int argc, char** argv) {
check(argc == 2);
struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_port = htons(12345);
check(inet_pton(AF_INET, argv[1], &addr.sin_addr) != -1);
int server = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
check(server != -1);
int yes = 1;
check(setsockopt(server, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) != -1);
check(bind(server, (struct sockaddr*)&addr, sizeof(addr)) != -1);
check(listen(server, 1) != -1);
if (fork() == 0) {
int client = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
check(client != -1);
check(connect(client, (struct sockaddr*)&addr, sizeof(addr)) != -1);
printf("connected\n");
pause();
}
else {
int client = accept(server, NULL, NULL);
check(client != -1);
enable_keepalive(client);
printf("accepted\n");
wait(NULL);
}
return 0;
}
Example output (tcpdump reports keepalive packets every second):
$ ./a.out 127.0.0.1 &
[1] 14010
connected
accepted
$ tcpdump -n -c4 -ilo port 12345
dropped privs to tcpdump
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
18:00:35.173892 IP 127.0.0.1.12345 > 127.0.0.1.60998: Flags [.], ack 510307430, win 342, options [nop,nop,TS val 389745775 ecr 389745675], length 0
18:00:35.173903 IP 127.0.0.1.60998 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 389745775 ecr 389745075], length 0
18:00:36.173886 IP 127.0.0.1.12345 > 127.0.0.1.60998: Flags [.], ack 1, win 342, options [nop,nop,TS val 389745875 ecr 389745775], length 0
18:00:36.173898 IP 127.0.0.1.60998 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 389745875 ecr 389745075], length 0
4 packets captured
8 packets received by filter
0 packets dropped by kernel
SO_KEEPALIVE should be used with SOL_SOCKET, not IPPROTO_TCP or SOL_TCP. See socket(7) and tcp(7).
So try this:
int val = 1;
setsockopt(SockConnected, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof(val));
I guess TCP_KEEPIDLE and similar options are just ignored if SO_KEEPALIVE was not set correctly, and SOL_TCP is a synonym for IPPROTO_TCP.
If it does not help, consider posting a minimal example that reproduces the problem.