一个简易的UDP Proxy程序
作为<<一个简易的proxy程序的开发过程>>的补充
1、为什么开发这个UDP程序
网络状况如上文<<一个简易的proxy程序的开发过程>>。我们的socks代理是有权限的（相信很多公司
都有这种情况存在）。写这个程序的时候，我还没有socks代理的权限，所以不能上OICQ。这让我感到
很不方便。所以，我决定写一个UDP的代理程序来实现我上OICQ的愿望。原理同上文是一样的。只是在
具体实现上略有所不同。
先看看源代码，稍后再来解释。(由于这个版本是一个完全功能版，所以提供了很多sp.c没有提供的功
能。）上文中提到过的部分，这里就不再次一一解释了。
-----------------------------------------------------------------------------------------
/***************************************************
Program: pu.c
Description: a smart UDP proxy
Author: Alan Chen ( ariesram@may10.ca )
Date: Dec 1, 2000
***************************************************/
#include
#include
#include
#include
#include
#include
#include
#include
#define MAX_ID_LEN 12
#define LOGFILE "/usr/tmp/.pu.log"
#define ERRLOG "/usr/tmp/.pu.err"
void sig_int(int sig);
void do_receive(int fd_tran);
void p_error(const char * err_msg);
void p_log(const char * buffer, int len);
int
main(int argc, char ** argv)
{
int fd_listen, fd_tran;
struct sockaddr_in sin, out;
struct sockaddr_in r_in, r_out;
struct sockaddr_in stmp;
int port = 1250;
int pid;
char * ip;
int i;
fd_set fdset;
char buffer[2048*2];
int data_len, alen;
struct timeval val;
#ifndef _DEBUG
signal(SIGINT, SIG_IGN);
#endif
signal(SIGHUP, SIG_IGN);
/* signal(SIGTERM, SIG_IGN); */
signal(SIGABRT, SIG_IGN);
signal(SIGSTOP, SIG_IGN);
signal(SIGCHLD, SIG_IGN);
#ifndef _DEBUG
if (fork() != 0)
exit(0);
setsid();
for (i = 256; i >= 0; i --)
#endif
#ifdef _DEBUG
for (i = 256; i >= 3; i --)
#endif
close(i);
chdir("/usr/tmp");
bzero(&sin, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_port = htons(8000);
sin.sin_addr.s_addr = INADDR_ANY;
bzero(&out, sizeof(out));
out.sin_family = AF_INET;
/* out.sin_port = htons(5000); */
out.sin_port = htons(4000);
out.sin_addr.s_addr = INADDR_ANY;
/* remote server */
bzero(&r_out, sizeof(r_out));
r_out.sin_family = AF_INET;
r_out.sin_port = htons(8000);
r_out.sin_addr.s_addr = inet_addr("202.96.170.164");
/* remote client */
bzero(&r_in, sizeof(r_in));
r_in.sin_family = AF_INET;
r_in.sin_port = htons(4000);
r_in.sin_addr.s_addr = inet_addr("192.168.103.97");
fd_listen = socket(PF_INET, SOCK_DGRAM, 0);
if (fd_listen < 0) {
p_error("socket1 error");
exit(1);
}
fd_tran = socket(PF_INET, SOCK_DGRAM, 0);
if (fd_tran < 0) {
p_error("socket2 error");
exit(1);
}
if (bind(fd_listen, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
p_error("bind error1: ");
exit(1);
}
if (bind(fd_tran, (struct sockaddr *)&out, sizeof(out)) < 0) {
p_error("bind error2: ");
exit(1);
}
fcntl(fd_listen, F_SETFL, O_NONBLOCK);
fcntl(fd_tran, F_SETFL, O_NONBLOCK);
while (1) {
FD_ZERO(&fdset);
FD_SET(fd_tran, &fdset);
FD_SET(fd_listen, &fdset);
val.tv_sec = 1;
val.tv_usec = 0;
if (select(fd_tran + 1, &fdset, NULL, NULL, &val) < 0) {
p_error("select error: ");
continue;
}
if (FD_ISSET(fd_listen, &fdset)) {
alen = sizeof(r_in);
data_len = recvfrom (fd_listen, buffer, sizeof(buffer), 0,
(struct sockaddr *)&r_in, &alen);
if (data_len <= 0) {
p_error("socket closed by remote client");
close(fd_listen);
close(fd_tran);
exit(0);
}
#ifdef _DEBUG
ip = inet_ntoa(r_in.sin_addr.s_addr);
printf("received from %s , socket id: %d
", ip, fd_listen);
p_log("
received from inner:
", 23);
/* sizeof("
received from inner:
"); */
p_log(buffer, data_len);
#endif
if (sendto(fd_tran, (char *)buffer, data_len, 0,
(struct sockaddr *)&r_out, sizeof(r_out)) <=0 ) {
p_error("cann't send to remote server");
close(fd_tran);
close(fd_listen);
exit(0);
}
#ifdef _DEBUG
ip = inet_ntoa(r_out.sin_addr.s_addr);
printf("send to %s
", ip);
#endif
}
else if (FD_ISSET(fd_tran, &fdset)) {
alen = sizeof(stmp);
data_len = recvfrom (fd_tran, buffer, sizeof(buffer), 0,
(struct sockaddr *)&stmp, &alen);
if (data_len <= 0) {
p_error("socket closed by remote server");
close(fd_listen);
close(fd_tran);
exit(0);
}
#ifdef _DEBUG
ip = inet_ntoa(stmp.sin_addr.s_addr);
printf("received from %s , socket id: %d
", ip, fd_tran);
p_log("
received from outer:
", 23);
/* sizeof("
received from outer:
"); */
p_log(buffer, data_len);
#endif
if (sendto(fd_listen, (char *)buffer, data_len, 0,
(struct sockaddr *)&r_in,
sizeof(r_in)) <=0 ) {
p_error("cann't send to remote server");
close(fd_tran);
close(fd_listen);
exit(0);
}
#ifdef _DEBUG
ip = inet_ntoa(r_in.sin_addr.s_addr);
printf("send to %s
", ip);
#endif
}
}
return 0;
}
void
sig_int(int sig)
{
signal(SIGINT, sig_int);
exit(1);
}
void
p_error(const char * err_msg)
{
FILE * fp;
#ifdef _DEBUG
printf("%s
", err_msg);
#endif
fp = fopen(ERRLOG, "a");
if (fp == NULL)
return;
fprintf(fp, "%s
", err_msg);
fclose(fp);
}
void
p_log(const char * buffer, int len)
{
FILE * fp;
fp = fopen(LOGFILE, "ab");
if (fp == NULL)
return;
fwrite(buffer, len, 1, fp);
fclose(fp);
}
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编译，运行是同上文所述相同的。
但是，要注意UDP是没有连接的，所以程序的具体实现方式有所不同。
来看程序。
#ifndef _DEBUG
signal(SIGINT, SIG_IGN);
#endif
signal(SIGHUP, SIG_IGN);
/* signal(SIGTERM, SIG_IGN); */
signal(SIGABRT, SIG_IGN);
signal(SIGSTOP, SIG_IGN);
signal(SIGCHLD, SIG_IGN);
忽略上述信号，使程序以后台方式运行。
#ifndef _DEBUG
if (fork() != 0)
exit(0);
setsid();
for (i = 256; i >= 0; i --)
#endif
如果不是DEBUG方式，程序以前台方式运行。
#ifdef _DEBUG
for (i = 256; i >= 3; i --)
#endif
close(i);
关闭描述字。
bzero(&r_in, sizeof(r_in));
r_in.sin_family = AF_INET;
r_in.sin_port = htons(4000);
r_in.sin_addr.s_addr = inet_addr("192.168.103.97");
192.168.103.97 是我机器的局域网IP地址。由于这个程序只是给我一个人使用的，所以没有在这上面处理
得更灵活一些。:-)
fd_listen = socket(PF_INET, SOCK_DGRAM, 0);
if (fd_listen < 0) {
p_error("socket1 error");
exit(1);
}
UDP的socket描述字是这样子建立的。
fcntl(fd_listen, F_SETFL, O_NONBLOCK);
fcntl(fd_tran, F_SETFL, O_NONBLOCK);
将这两个监听端口的socket方式设置为非阻塞的。
if (FD_ISSET(fd_listen, &fdset)) {
alen = sizeof(r_in);
data_len = recvfrom (fd_listen, buffer, sizeof(buffer), 0,
(struct sockaddr *)&r_in, &alen);
if (data_len <= 0) {
p_error("socket closed by remote client");
close(fd_listen);
close(fd_tran);
exit(0);
}
#ifdef _DEBUG
ip = inet_ntoa(r_in.sin_addr.s_addr);
printf("received from %s , socket id: %d
", ip, fd_listen);
p_log("
received from inner:
", 23);
/* sizeof("
received from inner:
"); */
p_log(buffer, data_len);
#endif
if (sendto(fd_tran, (char *)buffer, data_len, 0,
(struct sockaddr *)&r_out, sizeof(r_out)) <=0 ) {
p_error("cann't send to remote server");
close(fd_tran);
close(fd_listen);
exit(0);
}
#ifdef _DEBUG
ip = inet_ntoa(r_out.sin_addr.s_addr);
printf("send to %s
", ip);
#endif
}
对于UDP来说，用的是recvfrom和sendto. 在程序中同时加入了recvfrom时的客户端地址，便于在调试的
时候来检查。同时，这里面也有一些调试的信息，比如，输出接收到的字符串，客户端地址等等。
else if (FD_ISSET(fd_tran, &fdset)) {
alen = sizeof(stmp);
data_len = recvfrom (fd_tran, buffer, sizeof(buffer), 0,
(struct sockaddr *)&stmp, &alen);
if (data_len <= 0) {
p_error("socket closed by remote server");
close(fd_listen);
close(fd_tran);
exit(0);
}
#ifdef _DEBUG
ip = inet_ntoa(stmp.sin_addr.s_addr);
printf("received fro
