LD_PRELOAD hook for vaurien proof of concept

README.md

1. compile shared library:

$ cc -shared -fPIC -Wl,--no-as-needed -ldl -lpthread -Wl,-soname=forward.so -o forward.so forward.c

2. Run standard redis server in separate terminal

$ redis-server

3. Start vaurien with 10000 port offset

$ vaurien --proxy 127.0.0.1:16379 --backend 127.0.0.1:6379 --protocol redis --behavior 100:delay

4. Test code without vaurien

$ python test.py 
12
0.00104689598083

5. Test code WITH vaurien but without changing any configuration

LD_PRELOAD=./forward.so python test.py 
Proxy: 6379 -> 16379
Proxy: 6379 -> 16379
12
2.00729990005

5. Don't use it in production :-)

KUDOS and inspiration: proxychains library

forward.c

#undef _GNU_SOURCE
#define _GNU_SOURCE

#include <stdio.h>
#include <dlfcn.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>

typedef int (*connect_t)(int, const struct sockaddr *, socklen_t);

int connect(int sock, const struct sockaddr *addr, socklen_t len) {

    struct sockaddr_in* addrin = ((struct sockaddr_in *) addr);
    int orig_port = ntohs(addrin->sin_port);
    addrin->sin_port = htons(ntohs(addrin->sin_port) + 10000);

    printf("Proxy: %d -> %d\n", orig_port, ntohs(((struct sockaddr_in *) addr)->sin_port));
    connect_t true_connect = dlsym(RTLD_NEXT, "connect");

    return true_connect(sock, addr, len);

}

test.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from __future__ import with_statement, division, absolute_import, print_function

import redis
import time
red = redis.StrictRedis()
start = time.time()
red.set("hi", 12)
print(red.get("hi"))
print (time.time() - start)