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tcp_repair.c
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tcp_repair.c
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//: ----------------------------------------------------------------------------
//: includes
//: ----------------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
//: ----------------------------------------------------------------------------
//: constants
//: ----------------------------------------------------------------------------
#define BUFFER_SIZE 1024
#ifndef STATUS_OK
#define STATUS_OK 0
#endif
#ifndef STATUS_ERROR
#define STATUS_ERROR -1
#endif
//: ----------------------------------------------------------------------------
//: macros
//: ----------------------------------------------------------------------------
#ifndef ERROR
#define ERROR(...) \
do { \
fprintf(stderr, "%s:%s.%d: error: ", __FILE__, __FUNCTION__, __LINE__); \
fprintf(stderr, __VA_ARGS__); \
fflush(stderr); \
} while(0)
#endif
//#define ERROR(...) { fprintf(stderr, __VA_ARGS__); fflush(stderr); exit(1); }
//: ----------------------------------------------------------------------------
//: silently drop connection using TCP_REPAIR
//: ref: https://oroboro.com/dealing-with-network-port-abuse-in-sockets-in-c/
//: ----------------------------------------------------------------------------
static int tcp_repair_close(int a_fd)
{
int l_s;
(void)l_s;
// -------------------------------------------------
// use TCP_REPAIR to "freeze" socket state
// -------------------------------------------------
#ifdef TCP_REPAIR
int l_opt = 1;
l_s = setsockopt(a_fd, SOL_TCP, TCP_REPAIR, &l_opt, sizeof(l_opt));
if(l_s < 0)
{
ERROR("socket: %s\n", strerror(errno));
return STATUS_ERROR;
}
#endif
// -------------------------------------------------
// std close
// -------------------------------------------------
close(a_fd);
return STATUS_OK;
}
//: ----------------------------------------------------------------------------
//: run echo server
//: ----------------------------------------------------------------------------
int main(int argc, char **argv)
{
int l_s;
// -------------------------------------------------
// args
// -------------------------------------------------
if (argc < 3)
{
fprintf(stderr, "usage: %s (port) (freeze)\n", argv[0]);
return STATUS_ERROR;
}
// -------------------------------------------------
// get port...
// -------------------------------------------------
int l_port = 0;
l_port = atoi(argv[1]);
// -------------------------------------------------
// get freeze...
// -------------------------------------------------
int l_freeze = 0;
l_freeze = atoi(argv[2]);
// -------------------------------------------------
// create server socket
// -------------------------------------------------
int l_server_fd;
l_server_fd = socket(AF_INET, SOCK_STREAM, 0);
if(l_server_fd < 0)
{
ERROR("socket: %s\n", strerror(errno));
return STATUS_ERROR;
}
// -------------------------------------------------
// create sockaddr_in
// -------------------------------------------------
struct sockaddr_in l_server_sockaddr;
bzero( &l_server_sockaddr, sizeof(l_server_sockaddr));
l_server_sockaddr.sin_family = AF_INET;
l_server_sockaddr.sin_addr.s_addr = htonl(INADDR_ANY);
l_server_sockaddr.sin_port = htons(l_port);
// -------------------------------------------------
// set reuse...
// -------------------------------------------------
int l_opt = 1;
setsockopt(l_server_fd, SOL_SOCKET, SO_REUSEADDR, &l_opt, sizeof(l_opt));
// -------------------------------------------------
// bind...
// -------------------------------------------------
l_s = bind(l_server_fd, (struct sockaddr *) &l_server_sockaddr, sizeof(l_server_sockaddr));
if(l_s < 0)
{
ERROR("bind: %s\n", strerror(errno));
return STATUS_ERROR;
}
// -------------------------------------------------
// listen...
// -------------------------------------------------
l_s = listen(l_server_fd, 16);
if(l_s < 0)
{
ERROR("listen: %s\n", strerror(errno));
return STATUS_ERROR;
}
// -------------------------------------------------
// accept loop
// -------------------------------------------------
while(1)
{
int l_clnt_fd;
struct sockaddr_in l_clnt;
socklen_t l_client_len = sizeof(l_clnt);
// -----------------------------------------
// client accept...
// -----------------------------------------
l_clnt_fd = accept(l_server_fd, (struct sockaddr *) &l_clnt, &l_client_len);
if(l_clnt_fd < 0)
{
ERROR("accept: %s\n", strerror(errno));
return STATUS_ERROR;
}
// -----------------------------------------
// read loop
// -----------------------------------------
while(1)
{
char l_buf[BUFFER_SIZE];
int l_read;
// ---------------------------------
// recv data...
// ---------------------------------
l_read = recv(l_clnt_fd, l_buf, BUFFER_SIZE, 0);
if(!l_read)
{
// done reading
break;
}
else if(l_read < 0)
{
ERROR("recv: %s\n", strerror(errno));
return STATUS_ERROR;
}
// ---------------------------------
// echo back
// ---------------------------------
l_s = send(l_clnt_fd, l_buf, l_read, 0);
if(l_s < 0)
{
ERROR("send: %s\n", strerror(errno));
return STATUS_ERROR;
}
// ---------------------------------
// shut down...
// ---------------------------------
if(l_freeze)
{
tcp_repair_close(l_clnt_fd);
l_clnt_fd = -1;
break;
}
else
{
close(l_clnt_fd);
l_clnt_fd = -1;
break;
}
}
}
// -------------------------------------------------
// cleanup
// -------------------------------------------------
close(l_server_fd);
return STATUS_OK;
}