/*把监听socket和可读socket三个一起放入select的可读句柄列表里*/
nfds = max (nfds, h);
if (fd1 > 0 && buf1_avail < BUF_SIZE) {
FD_SET (fd1, &rd);
nfds = max (nfds, fd1);
}
if (fd2 > 0 && buf2_avail < BUF_SIZE) {
FD_SET (fd2, &rd);
nfds = max (nfds, fd2);
}
/*把可写socket两个一起放入select的可写句柄列表里*/
if (fd1 > 0 && buf2_avail - buf2_written > 0) {
FD_SET (fd1, &wr);
nfds = max (nfds, fd1);
}
if (fd2 > 0 && buf1_avail - buf1_written > 0) {
FD_SET (fd2, &wr);
nfds = max (nfds, fd2);
}
/*把有异常数据的socket两个一起放入select的异常句柄列表里*/
if (fd1 > 0) {
FD_SET (fd1, &er);
nfds = max (nfds, fd1);
}
if (fd2 > 0) {
FD_SET (fd2, &er);
nfds = max (nfds, fd2);
}
/*开始select*/
r = select (nfds + 1, &rd, &wr, &er, NULL);
if (r == -1 && errno == EINTR) continue;
if (r < 0) {
perror ("select()");
exit (1);
}
/*处理新连接*/
if (FD_ISSET (h, &rd)) {
unsigned int l;
struct sockaddr_in client_address;
memset (&client_address, 0, l = sizeof (client_address));
r = accept (h, (struct sockaddr *)&client_address, &l);
if (r < 0) {
perror ("accept()");
} else {
/*关闭原有连接，把新连接作为fd1，同时连接新的目标fd2*/
SHUT_FD1;
SHUT_FD2;
buf1_avail = buf1_written = 0;
buf2_avail = buf2_written = 0;
fd1 = r;
fd2 = connect_socket (forward_port, argv[3]);
if (fd2 < 0) {
SHUT_FD1;
} else
printf ("connect from %s\n", inet_ntoa(client_address.sin_addr));
}
}
/* NB: read oob data before normal reads */
if (fd1 > 0)
if (FD_ISSET (fd1, &er)) {
char c;
errno = 0;
r = recv (fd1, &c, 1, MSG_OOB);
if (r < 1) {
SHUT_FD1;
} else
send (fd2, &c, 1, MSG_OOB);
}
if (fd2 > 0)
if (FD_ISSET (fd2, &er)) {
char c;
errno = 0;
r = recv (fd2, &c, 1, MSG_OOB);
if (r < 1) {
SHUT_FD1;
} else
send (fd1, &c, 1, MSG_OOB);
}
/* NB: read data from fd1 */
if (fd1 > 0)
if (FD_ISSET (fd1, &rd)) {
r = read (fd1, buf1 + buf1_avail, BUF_SIZE - buf1_avail);
if (r < 1) {
SHUT_FD1;
} else
buf1_avail += r;
}
/* NB: read data from fd2 */
if (fd2 > 0)
if (FD_ISSET (fd2, &rd)) {
r = read (fd2, buf2 + buf2_avail, BUF_SIZE - buf2_avail);
if (r < 1) {
SHUT_FD2;
} else
buf2_avail += r;
}
/* NB: write data to fd1 */
if (fd1 > 0)
if (FD_ISSET (fd1, &wr)) {
r = write (fd1, buf2 + buf2_written, buf2_avail - buf2_written);
if (r < 1) {
SHUT_FD1;
} else
buf2_written += r;
}
/* NB: write data to fd1 */
if (fd2 > 0)
if (FD_ISSET (fd2, &wr)) {
r = write (fd2, buf1 + buf1_written, buf1_avail - buf1_written);
if (r < 1) {
SHUT_FD2;
} else
buf1_written += r;
}
/* check if write data has caught read data */
if (buf1_written == buf1_avail) buf1_written = buf1_avail = 0;
if (buf2_written == buf2_avail) buf2_written = buf2_avail = 0;
/* one side has closed the connection, keep writing to the other side until empty */
if (fd1 < 0 && buf1_avail - buf1_written == 0) {
SHUT_FD2;
}
if (fd2 < 0 && buf2_avail - buf2_written == 0) {
SHUT_FD1;
}
}
return 0;
}
/*----------------------源代码结束--------------------------------------------*/
[/CODE]
--------------------------------------------------------------------------------
zhoulifa 回复于：2006-07-05 23:13:33
用gcc tcpforwardport.c -o MyProxy编译此程序后运行效果如下：
引用:
./MyProxy 8000 80 172.16.100.218
accepting connections on port 8000
connect from 127.0.0.1
当有用户访问本机的8000端口时，MyProxy程序将把此请求转发到172.16.100.218主机的80端口，即实现了一个http代理。
关于select函数：
其函数原型为：
int select(int n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
此函数的功能是由内核检测在timeout时间内，是否有readfds，writefds，exceptfds三个句柄集(file descriptors)里的某个句柄（file descriptor)的状态符合寻求，即readfds句柄集里有句柄可读或writefds句柄集里有可写或exceptfds句柄集里有例外发生，任何一个有变化函数就立即返回，返回值为timeout发生状态变化的句柄个数。
n是所有readfds，writefds，exceptfds三个句柄集(file descriptors)里编号最大值加1。比如：要检测两个socket句柄fd1和fd2在timeout时间内是否分别可读和可写就可以这样：
先把两个句柄集(file descriptors)清零：
FD_ZERO (&readfds);
FD_ZERO (&writefds);
然后把fd1加入读检测集：
FD_SET (fd1, &readfds);
然后把fd2加入写检测集：
FD_SET (fd2, &writefds);
再给timeout设置值，timeout是这样的一个结构：
struct timeval {
long tv_sec; /* seconds */
long tv_usec; /* microseconds */
};
你可以这样赋值：
timeout.tv_sec=1;
timeout.tv_uec=0;
表示检测在1秒钟内是否有句柄状态发生变化。
如果有句柄发生变化，就可以用FD_ISSET检测各个句柄，比如：
FD_ISSET (fd1, &readfds);//检测是否fd1变成可读的了
FD_ISSET (fd2, &writefds);//检测是否fd2变成可写的了
示意程序代码如下：
[CODE]
/*----------------------示意代码开始--------------------------------------------*/
fd1 = socket();//创建一个socket
fd2 = socket();//创建一个socket
while(1) {
FD_ZERO (&readfds);
FD_ZERO (&writefds);
FD_SET (fd1, &readfds);
FD_SET (fd2, &writefds);
timeout.tv_sec=1;
timeout.tv_uec=0;
ret = select(fd1>fd2?(fd1+1)
fd2+1), &readfds, &writefds, NULL, &timeout);
if(ret < 0) {printf("系统错误，select出错，错误代码：%d, 错误信息：%s", errno, strerror(errno));}
else if(ret == 0) {printf("select超时返回，没有任何句柄状态发生变化！");}
//有句柄状态发生了变化
if(FD_ISSET(fd1, &readfds)) {
fd1有数据可读;
fd1里的数据被读出来;
}
if(FD_ISSET(fd2, &writefds)) {
fd2可写;
fd2里发送数据给对方;
}
}
/*----------------------示意代码结束--------------------------------------------*/
