Simple TCP pair
This page describes step-by-step how to play with TCP dumping and restoring.
Compile and run simple TCP client and server
The below program is a simple echo server and a client, that pings server with increasing numbers once a second. In this howto we will dump and restore the client part.
| tcp-howto.c: |
|---|
#include <sys/socket.h>
#include <linux/types.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
static int serve_new_conn(int sk)
{
int rd, wr;
char buf[1024];
printf("New connection\n");
while (1) {
rd = read(sk, buf, sizeof(buf));
if (!rd)
break;
if (rd < 0) {
perror("Can't read socket");
return 1;
}
wr = 0;
while (wr < rd) {
int w;
w = write(sk, buf + wr, rd - wr);
if (w <= 0) {
perror("Can't write socket");
return 1;
}
wr += w;
}
}
printf("Done\n");
return 0;
}
static int main_srv(int argc, char **argv)
{
int sk, port, ret;
struct sockaddr_in addr;
/*
* Let kids die themselves
*/
signal(SIGCHLD, SIG_IGN);
sk = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sk < 0) {
perror("Can't create socket");
return -1;
}
port = atoi(argv[1]);
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_ANY);
addr.sin_port = htons(port);
printf("Binding to port %d\n", port);
ret = bind(sk, (struct sockaddr *)&addr, sizeof(addr));
if (ret < 0) {
perror("Can't bind socket");
return -1;
}
ret = listen(sk, 16);
if (ret < 0) {
perror("Can't put sock to listen");
return -1;
}
printf("Waiting for connections\n");
while (1) {
int ask, pid;
ask = accept(sk, NULL, NULL);
if (ask < 0) {
perror("Can't accept new conn");
return -1;
}
pid = fork();
if (pid < 0) {
perror("Can't fork");
return -1;
}
if (pid > 0)
close(ask);
else {
close(sk);
ret = serve_new_conn(ask);
exit(ret);
}
}
}
static int main_cl(int argc, char **argv)
{
int sk, port, ret, val = 1, rval;
struct sockaddr_in addr;
sk = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sk < 0) {
perror("Can't create socket");
return -1;
}
port = atoi(argv[2]);
printf("Connecting to %s:%d\n", argv[1], port);
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
ret = inet_aton(argv[1], &addr.sin_addr);
if (ret < 0) {
perror("Can't convert addr");
return -1;
}
addr.sin_port = htons(port);
ret = connect(sk, (struct sockaddr *)&addr, sizeof(addr));
if (ret < 0) {
perror("Can't connect");
return -1;
}
while (1) {
write(sk, &val, sizeof(val));
rval = -1;
read(sk, &rval, sizeof(rval));
printf("PP %d -> %d\n", val, rval);
sleep(2);
val++;
}
}
int main(int argc, char **argv)
{
if (argc == 2)
return main_srv(argc, argv);
else if (argc == 3)
return main_cl(argc, argv);
printf("Bad usage\n");
return 1;
}
|
So compile it and run server
# ./tcp-howto <some-port>
and on another terminal (for better output readability) -- the client
# ./tcp-howto 127.0.0.1 <some-port>
Try to dump the client
Create a directory for images (img-dir/ below) and dump the client
# crtools dump --tree <tcp-howto-client-pid> --images-dir img-dir/ -v 4 -o dump.log --shell-job --tcp-established
The --tcp-established option is a must, since client have active TCP connection and we should explicitly inform crtools about it.
The --shell-job option is also required, as the client was launched from shell and uses shell's session and terminal.
Then restore the client
It's done like this
# crtools restore --tree <tcp-howto-client-pid> --images-dir img-dir/ -v 4 -o rst.log --shell-job --tcp-established
That's it. After this in the terminal you launched crtools from you should see the contunuing output of the tcp client.