// How to compile:
// gcc -shared  -fPIC -ldl -o lowermss.so lowermss.c
// How to use:
// LD_PRELOAD=./lowermss.so <command>
#define _GNU_SOURCE
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <dlfcn.h>

static void __attribute__((constructor)) lowermss_init();
static int (*real_socket)(int, int, int);
static int new_mss = 1460;

void lowermss_init() {
  real_socket = dlsym(RTLD_NEXT, "socket");
}


int socket(int domain, int type, int protocol) {
  int s = real_socket(domain, type, protocol);
  if(type == SOCK_STREAM) {
    setsockopt(s, IPPROTO_TCP, TCP_MAXSEG, &new_mss, sizeof(&new_mss));
  }
  return s;
}