环回接口上的客户端服务器连接
我正在尝试使用localhost地址测试客户端 – 服务器简单实现。 这是代码。
服务器：
/* * Sequential busy-waiting */ int main(int argc, char** argv) { int opt, client_addr_l, errsv; unsigned short port; struct sockaddr_in server_addr, client_addr; /* ... */ printf("Port number retrieved (%d), server is starting ...\n", port); /*TCP Socket creation*/ sock_ds = socket(AF_INET, SOCK_STREAM, 0); if(sock_ds == -1){ fprintf(stderr, "Socket creation error: %s\n", strerror(errno)); exit(EXIT_FAILURE); } /*Server address binding*/ memset(&server_addr, 0, sizeof(server_addr)); server_addr.sin_family = AF_INET; server_addr.sin_port = htons(port); server_addr.sin_addr.s_addr = INADDR_ANY; /*!!!! */ int optval = 1; if( (setsockopt(sock_ds,SOL_SOCKET,SO_REUSEADDR,&optval,sizeof(optval))) == -1 ) { printf("Error on setsockopt\n"); exit(EXIT_FAILURE); } /*????*/ if(bind(sock_ds, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1){ fprintf(stderr, "Address binding error\n"); exit(EXIT_FAILURE); } /*Server with passive socket*/ if(listen(sock_ds, SOMAXCONN) == -1){ fprintf(stderr, "Listen call error: %s\n", strerror(errno)); exit(EXIT_FAILURE); } while(1){ memset(&client_addr, 0, sizeof(client_addr)); acc_sock_ds = accept(sock_ds, (struct sockaddr *)&client_addr, &client_addr_l); printf("DEBUG: LINE201, acc_sock_ds = %d\n", acc_sock_ds); /*Connect error management*/ if(acc_sock_ds == -1){ fprintf(stderr, "Fatal error on accept %d(%s)\n" , errsv, strerror(errsv)); exit(EXIT_FAILURE); } //sin_addr to ASCII (string) ); printf("Connected with: %s\n", inet_ntoa(client_addr.sin_addr)); /*...*/ close(acc_sock_ds); /*...*/ } /*...*/ } 客户：
int main(){ int sock_ds; struct sockaddr_in remote_addr; struct hostent *hp; /*TCP Socket creation*/ sock_ds = socket(AF_INET, SOCK_STREAM, 0); if(sock_ds == -1){ fprintf(stderr, "Socket creation error\n"); exit(EXIT_FAILURE); } remote_addr.sin_family = AF_INET; remote_addr.sin_port = htons(25556); hp = gethostbyname("localhost"); bcopy(hp -> h_addr, &remote_addr.sin_addr, hp -> h_length); //fills address entry if(connect(sock_ds, (struct sockaddr*)&remote_addr, sizeof(remote_addr)) == -1){ //connection attempt fprintf(stderr, "Connect failure(%s)\n", strerror(errno)); exit(EXIT_FAILURE); } /*...*/ }
当我在两个不同的终端上运行它们服务器返回我：
Port number retrieved (25556), server is starting ... Server is ready. Waiting for client connections. DEBUG: LINE201, acc_sock_ds = 4 Connected with: 0.0.0.0
我的问题是：为什么服务器检索的客户端地址是0.0.0.0。 它不应该是127.0.0.1？
看起来你将第三个参数传递给accept（）未初始化，它应该设置为第二个参数的大小。 除此之外，它应该是一个socklen_t，而不是一个int，请参阅http://pubs.opengroup.org/onlinepubs/009695399/functions/accept.html
可以尝试将client_addr_l声明为socklen_t，然后在传递给accept（）之前将其设置为sizeof（struct sockaddr_in）吗？
我猜它的单位化值为零，所以accept（）无法将远程地址设置为client_addr，因为它的大小为零。 因此，client_addr不受影响，并且在您之前将其归零时，您将获得0.0.0.0。
0.0.0.0表示您的服务器接受来自设备中任何接口的连接
所以包含地址127.0..0.1的环回接口
这似乎是一种特殊情况。 所有可能的地址都在监听您的连接。 这是一个线程。
引用：
0.0.0.0, in this context, means "all IP addresses on the local machine" (in fact probably, "all IPv4 addresses on the local machine"). So, if your webserver machine has two ip addresses, 192.168.1.1 and 10.1.2.1, and you allow a webserver daemon like apache to listen on 0.0.0.0, it will be reachable at both of those IPs. But only to what can contact those IPs and the web port(s).
server_addr.sin_addr.s_addr = INADDR_ANY;
可能应该是
server_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);