tcpstate.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <poll.h>
#include <signal.h>

#define CLIENT_PORT 9999
#define SERVER_PORT 10000

#define CHECK(cond) {				 \
	if (!(cond)) {					 \
		printf("Failed at tcpstat.c:%d (%d): %s\n", __LINE__, errno, #cond); \
		exit(1);				     \
	}							     \
}

int main() {
	printf("PID id %d\n", getpid());

	int sock = socket(AF_INET, SOCK_STREAM, 0);
	CHECK(sock >= 0);
	int yes = 1;

	struct sockaddr_in addr;
	addr.sin_family = AF_INET;
	addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
	addr.sin_port = htons(CLIENT_PORT);
	CHECK(0 == bind(sock, &addr, sizeof(addr)));

	// Create a connection and leave it in TIME_WAIT state
	if (fork() == 0) {
		close(sock);
		int server = socket(AF_INET, SOCK_STREAM, 0);
		CHECK(server >= 0);
	    setsockopt(server, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));

		addr.sin_port = htons(SERVER_PORT);
		CHECK(0 == bind(server, &addr, sizeof(addr)));
		CHECK(0 == listen(server, 3));

		int client = accept(server, NULL, 0);
		close(client);
		return 0;
	}

	sleep(1);
	addr.sin_port = htons(SERVER_PORT);
	CHECK(0 == connect(sock, &addr, sizeof(addr)));

	// Make sure the client connection ends up in CLOSE_WAIT
	sleep(3);
	close(sock);
	// Wait for transition to CLOSED
	sleep(1);

	sock = socket(AF_INET, SOCK_STREAM, 0);
	CHECK(sock >= 0);

	addr.sin_port = htons(CLIENT_PORT);
	CHECK(0 == bind(sock, &addr, sizeof(addr)));

	pid_t pid;
	if ((pid = fork()) == 0) {
		close(sock);
		int server = socket(AF_INET, SOCK_STREAM, 0);
		CHECK(server >= 0);
	    CHECK(0 == setsockopt(server, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)));
		addr.sin_port = htons(SERVER_PORT);
		printf("Binding...\n");
		CHECK(0 == bind(server, &addr, sizeof(addr)));
		CHECK(0 == listen(sock, 3));

		printf("Waiting...\n");
		int client = accept(server, NULL, 0);
		close(client);
		return 0;
	}

	sleep(5);

	addr.sin_port = htons(SERVER_PORT);
	printf("Attempting to connect\n");
	int err = connect(sock, &addr, sizeof(addr));
	if (err == 0) {
		printf("Ok\n");
	} else {
		printf("Failed %d\n", errno);
		kill(pid, SIGKILL);
	}

	// Make sure the client connection ends up in CLOSE_WAIT
	sleep(3);
	close(sock);

	return 0;
}