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/*
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 * rebind: Intercept bind calls and bind to a different port
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 * Copyright 2010 Joel Martin
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 * Licensed under LGPL version 3 (see docs/LICENSE.LGPL-3)
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 *
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 * Overload (LD_PRELOAD) bind system call. If REBIND_PORT_OLD and
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 * REBIND_PORT_NEW environment variables are set then bind on the new
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 * port (of localhost) instead of the old port. 
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 *
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 * This allows a proxy (such as wsproxy) to run on the old port and translate
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 * traffic to/from the new port.
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 *
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 * Usage:
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 *     LD_PRELOAD=./rebind.so \
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 *     REBIND_PORT_OLD=23 \
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 *     REBIND_PORT_NEW=2023 \
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 *     program
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 */
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//#define DO_DEBUG 1
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#include <stdio.h>
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#include <stdlib.h>
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#define __USE_GNU 1  // Pull in RTLD_NEXT
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#include <dlfcn.h>
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#include <string.h>
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#include <netinet/in.h>
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#if defined(DO_DEBUG)
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#define DEBUG(...) \
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    fprintf(stderr, "wswrapper: "); \
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    fprintf(stderr, __VA_ARGS__);
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#else
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#define DEBUG(...)
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#endif
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int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
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{
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    static void * (*func)();
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    int do_move = 0;
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    struct sockaddr_in * addr_in = (struct sockaddr_in *)addr;
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    struct sockaddr_in addr_tmp;
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    socklen_t addrlen_tmp;
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    char * PORT_OLD, * PORT_NEW, * end1, * end2;
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    int ret, oldport, newport, askport = htons(addr_in->sin_port);
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    uint32_t askaddr = htons(addr_in->sin_addr.s_addr);
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    if (!func) func = (void *(*)()) dlsym(RTLD_NEXT, "bind");
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    DEBUG(">> bind(%d, _, %d), askaddr %d, askport %d\n",
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          sockfd, addrlen, askaddr, askport);
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    /* Determine if we should move this socket */
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    if (addr_in->sin_family == AF_INET) {
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        // TODO: support IPv6
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        PORT_OLD = getenv("REBIND_OLD_PORT");
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        PORT_NEW = getenv("REBIND_NEW_PORT");
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        if (PORT_OLD && (*PORT_OLD != '\0') &&
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            PORT_NEW && (*PORT_NEW != '\0')) {
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            oldport = strtol(PORT_OLD, &end1, 10);
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            newport = strtol(PORT_NEW, &end2, 10);
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            if (oldport && (*end1 == '\0') &&
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                newport && (*end2 == '\0') &&
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                (oldport == askport)) {
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                do_move = 1;
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            }
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        }
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    }
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    if (! do_move) {
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        /* Just pass everything right through to the real bind */
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        ret = (int) func(sockfd, addr, addrlen);
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        DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
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        return ret;
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    }
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    DEBUG("binding fd %d on localhost:%d instead of 0x%x:%d\n",
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        sockfd, newport, ntohl(addr_in->sin_addr.s_addr), oldport);
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    /* Use a temporary location for the new address information */
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    addrlen_tmp = sizeof(addr_tmp);
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    memcpy(&addr_tmp, addr, addrlen_tmp);
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    /* Bind to other port on the loopback instead */
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    addr_tmp.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
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    addr_tmp.sin_port = htons(newport);
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    ret = (int) func(sockfd, &addr_tmp, addrlen_tmp);
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    DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
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    return ret;
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}