【发布时间】：2017-01-25 12:10:59
【问题描述】：
我一直在尝试 TCP 打孔有一段时间了，对于基于 TCP 的方法和 C 编程语言，论坛似乎没有多大帮助。以下是来自互联网的主要参考资料，
一个。 http://www.brynosaurus.com/pub/net/p2pnat/
湾。 https://wuyongzheng.wordpress.com/2013/01/31/experiment-on-tcp-hole-punching/
我的设置是
客户端 A -- NAT-A -- 互联网 -- NAT-B -- 客户端 B。
假设客户端 A 知道 B 的公共和私有端点，并且 B 知道 A 的端点（我已经编写了一个服务器“S”，它在对等点之间交换端点信息），并且假设两个 NAT 都不是对称的，这就足够了（以实现 TCP 打孔），如果两个客户端都尝试连接（）到彼此的公共端点（对于上述设置）重复？
如果没有，具体要怎么做才能实现tcp打孔？
我在每个客户端上有两个线程，一个对其他客户端重复进行连接调用，另一个监听来自其他客户端的传入连接。我确保两个线程中的套接字都绑定到提供给对等方的本地端口。此外，我看到两个 NAT 都保留端口映射，即本地和公共端口是相同的。然而，我的程序不工作。
是不是我上面提到的集合服务器“S”在打孔或创建允许 SYN 请求通过的 NAT 映射中发挥作用，到达对等点。如果是，需要做什么？
附上代码的相关部分。
connect_with_peer() 是入口点，在服务器“S”提供对等方的公共 ip:port 元组之后，该元组与完成绑定的本地端口一起提供给此函数。该函数生成一个线程（accept_handler()），该线程也绑定到本地端口并侦听来自对等方的传入连接。
connect_with_peer() 返回一个套接字，如果 connect() [主线程] 或 accept() [子线程] 成功。
谢谢，
丁卡
volatile int quit_connecting=0;
void *accept_handler(void *arg)
{
int i,psock,cnt=0;
int port = *((int *)arg);
ssize_t len;
int asock,opt,fdmax;
char str[BUF_SIZE];
struct sockaddr_in peer,local;
socklen_t peer_len = sizeof(peer);
fd_set master,read_fds; // master file descriptor list
struct timeval tv = {10, 0}; // 10 sec timeout
int *ret_sock = NULL;
struct linger lin;
lin.l_onoff=1;
lin.l_linger=0;
opt=1;
//Create socket
asock = socket(AF_INET , SOCK_STREAM, IPPROTO_TCP);
if (asock == -1)
{
fprintf(stderr,"Could not create socket");
goto quit_ah;
}
else if (setsockopt(asock, SOL_SOCKET, SO_LINGER, &lin,
(socklen_t) sizeof lin) < 0)
{
fprintf(stderr,"\nTCP set linger socket options failure");
goto quit_ah;
}
else if (setsockopt(asock, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt,
(socklen_t) sizeof opt) < 0)
{
fprintf(stderr,"\nTCP set csock options failure");
goto quit_ah;
}
local.sin_family = AF_INET; /* host byte order */
local.sin_port = htons(port); /* short, network byte order */
local.sin_addr.s_addr = INADDR_ANY; /* auto-fill with my IP */
bzero(&(local.sin_zero), 8); /* zero the rest of the struct */
fprintf(stderr,"\naccept_handler: binding to port %d",port);
if (bind(asock, (struct sockaddr *)&local, sizeof(struct sockaddr)) == -1) {
perror("accept_handler bind error :");
goto quit_ah;
}
if (listen(asock, 1) == -1) {
perror(" accept_handler listen");
goto quit_ah;
}
memset(&peer, 0, sizeof(peer));
peer.sin_addr.s_addr = inet_addr(peer_global_address);
peer.sin_family = AF_INET;
peer.sin_port = htons( peer_global_port );
FD_ZERO(&master); // clear the master and temp sets
FD_SET(asock, &master);
fdmax = asock; // so far, it's this one
// Try accept
fprintf(stderr,"\n listen done; accepting next ... ");
while(quit_connecting == 0){
read_fds = master; // copy it
if (select(fdmax+1, &read_fds, NULL, NULL, &tv) == -1) {
perror("accept_handler select");
break;
}
// run through the existing connections looking for data to read
for(i = 0; i <= fdmax; i++) {
if (FD_ISSET(i, &read_fds)) { // we got one!!
if (i == asock) {
// handle new connections
psock = accept(asock, (struct sockaddr *)&peer, (socklen_t*)&peer_len);
if (psock == -1) {
perror("accept_handler accept");
} else {
fprintf(stderr,"\n Punch accept in thread succeeded soc=%d....",psock);
quit_connecting = 1;
ret_sock = malloc(sizeof(int));
if(ret_sock){
*ret_sock = psock;
}
}
}
}
} // end for
}
quit_ah:
if(asock>=0) {
shutdown(asock,2);
close(asock);
}
pthread_exit((void *)ret_sock);
return (NULL);
}
int connect_with_peer(char *ip, int port, int lport)
{
int retval=-1, csock=-1;
int *psock=NULL;
int attempts=0, cnt=0;
int rc=0, opt;
ssize_t len=0;
struct sockaddr_in peer, apeer;
struct sockaddr_storage from;
socklen_t peer_len = sizeof(peer);
socklen_t fromLen = sizeof(from);
char str[64];
int connected = 0;
pthread_t accept_thread;
long arg;
struct timeval tv;
fd_set myset;
int so_error;
struct linger lin;
lin.l_onoff=1;
lin.l_linger=0;
opt=1;
//Create socket
csock = socket(AF_INET , SOCK_STREAM, IPPROTO_TCP);
if (csock == -1)
{
fprintf(stderr,"Could not create socket");
return -1;
}
else if (setsockopt(csock, SOL_SOCKET, SO_LINGER, &lin,
(socklen_t) sizeof lin) < 0)
{
fprintf(stderr,"\nTCP set linger socket options failure");
}
#if 1
else if (setsockopt(csock, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt,
(socklen_t) sizeof opt) < 0)
{
fprintf(stderr,"\nTCP set csock options failure");
}
#endif
quit_connecting = 0;
///////////
if( pthread_create( &accept_thread , NULL , accept_handler , &lport) < 0)
{
perror("could not create thread");
return 1;
}
sleep(2); // wait for listen/accept to begin in accept_thread.
///////////
peer.sin_family = AF_INET; /* host byte order */
peer.sin_port = htons(lport); /* short, network byte order */
peer.sin_addr.s_addr = INADDR_ANY; /* auto-fill with my IP */
bzero(&(peer.sin_zero), 8); /* zero the rest of the struct */
fprintf(stderr,"\n connect_with_peer: binding to port %d",lport);
if (bind(csock, (struct sockaddr *)&peer, sizeof(struct sockaddr)) == -1) {
perror("connect_with_peer bind error :");
goto quit_connect_with_peer;
}
// Set non-blocking
arg = fcntl(csock, F_GETFL, NULL);
arg |= O_NONBLOCK;
fcntl(csock, F_SETFL, arg);
memset(&peer, 0, sizeof(peer));
peer.sin_addr.s_addr = inet_addr(ip);
peer.sin_family = AF_INET;
peer.sin_port = htons( port );
//Connect to remote server
fprintf(stderr,"\n Attempting to connect/punch to %s; attempt=%d",ip,attempts);
rc = connect(csock , (struct sockaddr *)&peer , peer_len);
if(rc == 0){ //succeeded
fprintf(stderr,"\n Punch Connect succeeded first time....");
} else {
if (errno == EINPROGRESS) {
while((attempts<5) && (quit_connecting==0)){
tv.tv_sec = 10;
tv.tv_usec = 0;
FD_ZERO(&myset);
FD_SET(csock, &myset);
if (select(csock+1, NULL, &myset, NULL, &tv) > 0) {
len = sizeof(so_error);
getsockopt(csock, SOL_SOCKET, SO_ERROR, &so_error, (socklen_t *)&len);
if (so_error == 0) {
fprintf(stderr,"\n Punch Connect succeeded ....");
// Set it back to blocking mode
arg = fcntl(csock, F_GETFL, NULL);
arg &= ~(O_NONBLOCK);
fcntl(csock, F_SETFL, arg);
quit_connecting=1;
retval = csock;
} else { // error
fprintf(stderr,"\n Punch select error: %s\n", strerror(so_error));
goto quit_connect_with_peer;
}
} else {
fprintf(stderr,"\n Punch select timeout: %s\n", strerror(so_error));
}
attempts++;
}// end while
} else { //errorno is not EINPROGRESS
fprintf(stderr, "\n Punch connect error: %s\n", strerror(errno));
}
}
quit_connect_with_peer:
quit_connecting=1;
fprintf(stderr,"\n Waiting for accept_thread to close..");
pthread_join(accept_thread,(void **)&psock);
if(retval == -1 ) {
if(psock && ((*psock) != -1)){
retval = (*psock); // Success from accept socket
}
}
fprintf(stderr,"\n After accept_thread psock = %d csock=%d, retval=%d",psock?(*psock):-1,csock,retval);
if(psock) free(psock); // Free the socket pointer , not the socket.
if((retval != csock) && (csock>=0)){ // close connect socket if accept succeeded
shutdown(csock,2);
close(csock);
}
return retval;
}
【问题讨论】：
标签： c tcp hole-punching