tcp_redir.c

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/** @file tcp_redir.c
    @brief xfrp tcp redirect service implemented
    @author Copyright (C) 2023 Dengfeng Liu <liu_df@qq.com>
*/

#include <pthread.h>
#include <arpa/inet.h>

#include "common.h"
#include "debug.h"
#include "config.h"
#include "utils.h"
#include "tcp_redir.h"


// define a struct for tcp_redir which include proxy_service and event_base
struct tcp_redir_service {
    struct event_base *base;
    struct proxy_service *ps;
    struct sockaddr_in server_addr;
};             

static struct bufferevent *current_bev = NULL; // Global variable to hold the current connection

// define a callback function for read event
static void read_cb(struct bufferevent *bev, void *arg)
{
    struct bufferevent *bev_out = (struct bufferevent *)arg;
    struct evbuffer *input = bufferevent_get_input(bev);
    struct evbuffer *output = bufferevent_get_output(bev_out);
    evbuffer_add_buffer(output, input);
}

// define a callback function for event event
static void event_cb(struct bufferevent *bev, short events, void *arg)
{
    struct bufferevent *partner = (struct bufferevent *)arg;
    if (events & BEV_EVENT_CONNECTED) {
        debug(LOG_INFO, "connected");
    } else if (events & BEV_EVENT_ERROR) {
        debug(LOG_ERR, "connection error");
        bufferevent_free(bev);
        bufferevent_free(partner);
        current_bev = NULL;
    } else if (events & BEV_EVENT_EOF) {
        debug(LOG_INFO, "connection closed");
        bufferevent_free(bev);
        bufferevent_free(partner);
        current_bev = NULL;
    }
}

// define a callback function for accept event
static void accept_cb(struct evconnlistener *listener, evutil_socket_t fd,
    struct sockaddr *address, int socklen, void *arg)
{
     if (current_bev) {
        // Already have a connection, reject new connection
        debug(LOG_INFO, "Rejecting new connection. Only one connection allowed at a time.");
        evutil_closesocket(fd);
        return;
    }

    // the argument is the proxy_service
    struct tcp_redir_service *trs = (struct tcp_redir_service *)arg;
    struct event_base *base = trs->base;

    // read the data from the local port
    struct bufferevent *bev_in = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE|BEV_OPT_DEFER_CALLBACKS);
    if (!bev_in) {
        debug(LOG_ERR, "create bufferevent for local port failed!");
        evutil_closesocket(fd); 
        return;
    }

     // connect to the remote xfrpc service
    struct bufferevent *bev_out = bufferevent_socket_new(base, -1, BEV_OPT_CLOSE_ON_FREE|BEV_OPT_DEFER_CALLBACKS);
    if (!bev_out) {
        debug(LOG_ERR, "create bufferevent for remote xfrps service failed!");
        bufferevent_free(bev_in);
        return;
    }

    // connect to the remote port
    if (bufferevent_socket_connect(bev_out, (struct sockaddr *)&(trs->server_addr), sizeof(trs->server_addr)) < 0) {
        debug(LOG_ERR, "connect to remote port failed! %s", strerror(errno));
        bufferevent_free(bev_in);
        bufferevent_free(bev_out);
        return;
    }
    debug(LOG_INFO, "connect to remote xfrps service [%s:%d] success!", 
        get_common_config()->server_addr, trs->ps->remote_port);

    bufferevent_setcb(bev_in, read_cb, NULL, event_cb, (void *)bev_out);
    bufferevent_setcb(bev_out, read_cb, NULL, event_cb, (void *)bev_in);
    bufferevent_enable(bev_in, EV_READ|EV_WRITE);
    bufferevent_enable(bev_out, EV_READ|EV_WRITE);

    current_bev = bev_in;

    debug(LOG_INFO, "connect to remote port success!");
    return;
}

// define a thread worker function for tcp_redir
static void *tcp_redir_worker(void *arg)
{
    struct proxy_service *ps = (struct proxy_service *)arg;
    struct common_conf *c_conf = get_common_config();
    // the worker is based on libevent and bufferevent
    // it listens on the local port and forward the data to the remote port
    // the local port and remote port are defined in the proxy_service
    // the proxy_service as argument is passed to the worker function

    // create a event_base
    struct evconnlistener *listener;
    struct event_base *base = event_base_new();
    if (!base) {
        debug(LOG_ERR, "create event base failed!");
        exit(1);
    }

    // define listen address and port
    struct sockaddr_in sin;
    memset(&sin, 0, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_port = htons(ps->local_port);
    sin.sin_addr.s_addr = htonl(INADDR_ANY);
    
    struct tcp_redir_service trs;
    trs.base = base;
    trs.ps = ps;
    trs.server_addr.sin_family = AF_INET;
    trs.server_addr.sin_port = htons(ps->remote_port);
    // if c_conf->server_addr is ip address, use inet_addr to convert it
    // if c_conf->server_addr is domain name, use gethostbyname to convert it
    if (is_valid_ip_address(c_conf->server_addr))
        trs.server_addr.sin_addr.s_addr = inet_addr(c_conf->server_addr);
    else {
        struct hostent *host = gethostbyname(c_conf->server_addr);
        if (!host) {
            debug(LOG_ERR, "gethostbyname failed!");
            exit(1);
        }
        // only support ipv4
        if (host->h_addrtype != AF_INET) {
            debug(LOG_ERR, "only support ipv4!");
            exit(1);
        }
        trs.server_addr.sin_addr.s_addr = *(unsigned long *)host->h_addr_list[0];
    }
    
    // create a listener
    listener = evconnlistener_new_bind(base, accept_cb, (void *)&trs,
        LEV_OPT_CLOSE_ON_FREE | LEV_OPT_REUSEABLE, -1, (struct sockaddr *)&sin, sizeof(sin));
    if (!listener) {
        debug(LOG_ERR, "create listener failed!");
        exit(1);
    }

    // start the event loop
    event_base_dispatch(base);

    // free the listener
    evconnlistener_free(listener);
    // free the event base
    event_base_free(base);

    return NULL;
}

void start_tcp_redir_service(struct proxy_service *ps)
{
    // create a thread 
    pthread_t tid;
    if (pthread_create(&tid, NULL, tcp_redir_worker, (void *)ps) != 0) {
        debug(LOG_ERR, "create tcp_redir worker thread failed!");
        exit(1);
    }
    debug(LOG_INFO, "create tcp_redir worker thread success!");

    // detach the thread
    if (pthread_detach(tid) != 0) {
        debug(LOG_ERR, "detach tcp_redir worker thread failed!");
        exit(1);
    }
    debug(LOG_INFO, "detach tcp_redir worker thread success!");

    return;
}