iPhone 无法使用 UDP recvfrom 接收数据

Question

我正在编写一个连续发送和接收数据的应用程序。我的初始发送/接收运行成功，但是当我期望接收中的数据大小为 512 字节时，我得到的返回值为 -1，即“资源暂时不可用”。并且 errno 设置为 EAGAIN。如果我使用阻塞调用，即没有超时，应用程序只会卡在recvfrom中。 iPhone 上的recvfrom 有最大限制吗？下面是从服务器接收数据的函数。我无法弄清楚出了什么问题。

{   struct timeval tv;

tv.tv_sec = 3;
tv.tv_usec = 100000;

    setsockopt (mSock, SOL_SOCKET, SO_RCVTIMEO, (char   *)&tv, sizeof tv);

    NSLog(@"Receiving.. sock:%d",mSock);

    recvBuff = (unsigned char *)malloc(1024);
    if(recvBuff == NULL)
        NSLog(@"Cannot allocate memory to recvBuff");

    fromlen = sizeof(struct sockaddr_in);
    n = recvfrom(mSock,recvBuff,1024,0,(struct sockaddr *)&from, &fromlen);

    if (n == -1) {
        [self error:@"Recv From"];
        return;
    }
    else
    {
        NSLog(@"Recv Addr: %s Recv Port: %d",inet_ntoa(from.sin_addr), ntohs(from.sin_port));
        strIPAddr = [[NSString alloc] initWithFormat:@"%s",inet_ntoa(from.sin_addr)];
        portNumber = ntohs(from.sin_port);
        lIPAddr = [KDefine StrIpToLong:strIPAddr];
        write(1,recvBuff,n);
        bcopy(recvBuff, data, n);
        actualRecvBytes = n;
        free(recvBuff);
    }

}

Answer 1

阅读the manpage :

If no messages are available at the socket, the receive call waits for a message to arrive, unless the socket is nonblocking (see fcntl(2)) in which case the value -1 is returned and the external variable errno set to EAGAIN.