ReplayKit2 有线投屏项目-反向Socket实现
一、需求
我们在使用RTMP协议进行推流的时候,底层仍然采用的是TCP协议或者QUICK协议,有客户端主动发起请求。但是在有线投屏中,需要PC端向手机发起请求建立连接
二、实现
在客户端主动发起请求之前,我们首先启动一个socket监听来自PC的连接,如果连接成功,那么我们使用这个已经建立好的连接,继续后面的流程
在实现中,我们需要设计一个超时的机制,一般socket可以对send和recv设置超时,当然超时都是对同步的socket生效的。
正常设置如下:
struct timeval tv, recv_timeout; tv.tv_sec = timeout / 1000; tv.tv_usec = static_cast<int>(timeout % 1000 * 1000); int ret = ::setsockopt(m_nRealServerSocket, SOL_SOCKET, SO_RCVTIMEO, (const char*) &tv, sizeof(tv)); ret = ::setsockopt(m_nRealServerSocket, SOL_SOCKET, SO_SNDTIMEO, (const char*) &tv, sizeof(tv));
但是这个设置对accept在iOS平台是不生效的,必须采用select的方式
select监听描述符如下所示
#define MYPORT 1937 // the port users will be connecting to #define BACKLOG 1 // how many pending connections queue will hold #define BUF_SIZE 200 int fd_A[BACKLOG]; // accepted connection fd int conn_amount; // current connection amount - (void)startSelectDemo2 { int sock_fd, new_fd; // listen on sock_fd, new connection on new_fd struct sockaddr_in server_addr; // server address information struct sockaddr_in client_addr; // connector's address information socklen_t sin_size; int yes = 1; char buf[BUF_SIZE]; int ret; int i; if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) { NSLog(@"socket"); exit(1); } if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) { NSLog(@"setsockopt"); exit(1); } server_addr.sin_family = AF_INET; // host byte order server_addr.sin_port = htons(MYPORT); // short, network byte order server_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP memset(server_addr.sin_zero, '\0', sizeof(server_addr.sin_zero)); if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) { NSLog(@"bind"); exit(1); } if (listen(sock_fd, BACKLOG) == -1) { NSLog(@"listen"); exit(1); } NSLog(@"listen port %d\n", MYPORT); fd_set fdsr; int maxsock; struct timeval tv; conn_amount = 0; sin_size = sizeof(client_addr); maxsock = sock_fd; while (1) { // initialize file descriptor set FD_ZERO(&fdsr); FD_SET(sock_fd, &fdsr); // timeout setting tv.tv_sec = 5; tv.tv_usec = 0; // add active connection to fd set for (i = 0; i < BACKLOG; i++) { if (fd_A[i] != 0) { FD_SET(fd_A[i], &fdsr); } } ret = select(maxsock + 1, &fdsr, NULL, NULL, &tv); if (ret < 0) { NSLog(@"select"); break; } else if (ret == 0) { NSLog(@"timeout\n"); continue; } // check every fd in the set for (i = 0; i < conn_amount; i++) { if (FD_ISSET(fd_A[i], &fdsr)) { ret = recv(fd_A[i], buf, sizeof(buf), 0); if (ret <= 0) { // client close NSLog(@"client[%d] close\n", i); close(fd_A[i]); FD_CLR(fd_A[i], &fdsr); fd_A[i] = 0; } else { // receive data if (ret < BUF_SIZE) memset(&buf[ret], '\0', 1); NSLog(@"client[%d] send:%s\n", i, buf); } } } // check whether a new connection comes if (FD_ISSET(sock_fd, &fdsr)) { new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size); if (new_fd <= 0) { NSLog(@"accept"); continue; } else { const char *hello = "hello from clent"; send(new_fd, hello, strlen(hello), 0); char recvbuf[4096]; int retry = 0; while (retry++ < 3) { memset(recvbuf, 0, 4096); int ret = recv(new_fd, recvbuf, 4096 - 1, 0); if(ret > 0) { NSLog(@"app recv:%s\n",recvbuf); } else { NSLog(@"app recv error ret = %d\n",ret); } } } // add to fd queue if (conn_amount < BACKLOG) { fd_A[conn_amount++] = new_fd; NSLog(@"new connection client[%d] %s:%d\n", conn_amount, inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port)); if (new_fd > maxsock) maxsock = new_fd; } else { NSLog(@"max connections arrive, exit\n"); send(new_fd, "bye", 4, 0); close(new_fd); break; } } int i; NSLog(@"client amount: %d\n", conn_amount); for (i = 0; i < BACKLOG; i++) { NSLog(@"[%d]:%d ", i, fd_A[i]); } NSLog(@"\n\n"); } // close other connections for (i = 0; i < BACKLOG; i++) { if (fd_A[i] != 0) { close(fd_A[i]); } } exit(0); }
在成功收到连接之后,我们确保连接变成同步方式
unsigned long ul = 0; ioctl(Sock, FIONBIO, &ul)
并且在recv的时候,最后一个参数也可以决定是否是同步还是异步的方式,0 表示默认方式 ; 0x80表示异步的方式
ssize_t recv(int, void *, size_t, int) __DARWIN_ALIAS_C(recv);
三、总结
对于理解网络底层的编程,理解select的工作原理还需要继续加深。
四、代码
https://github.com/liqiushui/iOSSocketAcceptTimeout