Why are there no scm_timestamping control messages coming up? - c++

Question

My code consists of two programs: a TCP server and a TCP client. The goal of the project is to get timestamping for TCP working. I consulted this piece of linux documentation, and I can't seem to find anything that would indicate that my code shouldn't work. It says SO_TIMESTAMPING works with stream sockets. I'm really lost here. Or am I misunderstanding how this should work? I have never worked with linux and never done any networking, so there might be an obvious error on my part, but I don't see it.
client.cpp:
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
#include <linux/errqueue.h>
#include <linux/net_tstamp.h>
int port = 8989;
const char *address = "127.0.0.1";
int main(int argc, char *argv[])
{
int sockfd = 0, n = 0;
char recvBuff[1024];
struct sockaddr_in serv_addr;
memset(recvBuff, '0',sizeof(recvBuff));
if((sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
{
fprintf(stderr, "\n Error : Could not create socket \n");
return 1;
}
// Enable timestamping:
int timestampingFlags = SOF_TIMESTAMPING_RX_SOFTWARE | SOF_TIMESTAMPING_SOFTWARE;
int optRet = setsockopt(sockfd, SOL_SOCKET, SO_TIMESTAMPING, &timestampingFlags, sizeof(timestampingFlags));
if(optRet < 0)
{
printf("Unable to set socket option for timestamping");
} // OK
memset(&serv_addr, '0', sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(port);
if(inet_pton(AF_INET, address, &serv_addr.sin_addr)<=0)
{
fprintf(stderr, "\n inet_pton error occured\n");
return 1;
}
if(connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
{
fprintf(stderr, "\n Error : Connect Failed \n");
perror(0);
return 1;
}
// Receive responses
while ((n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) > 0)
{
recvBuff[n] = 0;
if(fputs(recvBuff, stdout) == EOF)
{
fprintf(stderr, "\n Error : Fputs error\n");
}
// Get and print the time stamp
struct msghdr msgh;
struct cmsghdr *cmsg;
struct scm_timestamping *timeStamp;
int flags = MSG_WAITALL | MSG_PEEK;
int recvRet = recvmsg(sockfd, &msgh, flags);
/* Receive auxiliary data in msgh */
// There are no messages here
for(cmsg = CMSG_FIRSTHDR(&msgh);
cmsg != NULL;
cmsg = CMSG_NXTHDR(&msgh, cmsg))
{
printf("A control message arrived!\n");
if (cmsg->cmsg_level == SOL_SOCKET &&
cmsg->cmsg_type == SCM_TIMESTAMPING)
{
timeStamp = (struct scm_timestamping *)CMSG_DATA(cmsg);
printf("Timestamp received: %ld.09%ld\n", timeStamp->ts[0].tv_sec, timeStamp->ts[0].tv_nsec);
break;
}
}
}
if(n < 0)
{
fprintf(stderr, "\n Read error \n");
}
return 0;
}
-server.cpp:
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>
#include <signal.h>
// call this function to start a nanosecond-resolution timer
struct timespec timer_start()
{
struct timespec start_time;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start_time);
return start_time;
}
// call this function to end a timer, returning microseconds elapsed as a long
long timer_end(struct timespec start_time)
{
struct timespec end_time;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end_time);
long diffInNanos = (end_time.tv_sec - start_time.tv_sec) * (long)1e9 + (end_time.tv_nsec - start_time.tv_nsec);
return diffInNanos / 1000;
}
int port = 8989;
int main(int argc, char *argv[])
{
int listenfd = 0, connfd = 0;
struct sockaddr_in serv_addr;
char sendBuff[1025];
time_t ticks;
listenfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
memset(&serv_addr, '0', sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(port);
bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
printf("Now listening for a connection!\n");
listen(listenfd, 1);
// Wait for a connection from a client socket
connfd = accept(listenfd, (struct sockaddr*)NULL, NULL);
printf("Connected!\n");
// Once connection is established, start sending messagess in a regular time interval
long timeBetweenSendsUS = 1000*1000;
for(struct timespec startTime = timer_start();
true;
startTime = timer_start())
{
memset(sendBuff, '0', sizeof(sendBuff));
ticks = time(NULL);
snprintf(sendBuff, sizeof(sendBuff), "%.24s\r\n", ctime(&ticks));
long elapsedUS = timer_end(startTime);
usleep(timeBetweenSendsUS - elapsedUS);
printf("Sending message!\n");
write(connfd, sendBuff, strlen(sendBuff));
}
close(connfd);
return 0;
}
I then compile each file separately using g++ <filename> -o <filename> and run the server binary first and the client binary second while the server is running. So, to repeat my question: Why are there no control messages in the ancillary data?