objective-c - 帮助发送/接收 UDP 数据包 - C 套接字

Question

好吧，如果你看看我之前的一些问题，我一直在努力建立一个简单的连接并使用 C 套接字运行(我对程序的整个网络方面还很陌生，但每个人都有从某个地方开始，对吧？)。到目前为止，我已经包含了下面的代码，当我执行它时，我没有收到任何错误，但与此同时，我没有在另一端收到数据包。顺便说一句，我在 objective-C 中编写多播套接字，“msgStatus”只是我 GUI 中的一个标签(它已正确连接，所以没有问题)。我只是没有看到我要去哪里错了。有人可以帮助我或指出正确的方向吗？谢谢!

#define MAX_LEN  1024    /* maximum string size to send */
#define MIN_PORT 1024    /* minimum port allowed */
#define MAX_PORT 65535   /* maximum port allowed */
#define MYPORT 5673      /* port we will be using for our multicast socket */

    -(void)broadcastMessage {//(NSString*)msg {
        NSLog(@"broadcastMessage - Stage 1");
        NSString *msg = @"From Master";
        mc_ttl = 3; // number of node hops the message is allowed to travel across the network

        // define the port we will be using
        mc_port = MYPORT;

        /* create a socket for sending to the multicast address  */
    if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
        NSLog(@"ERROR: broadcastMessage - socket() failed");
        return;
    }

    mc_addr.sin_family      = AF_INET;
    mc_addr.sin_addr.s_addr = inet_addr("225.0.0.37");
    mc_addr.sin_port        = htons(mc_port);

    if (bind(sock, (struct sockaddr *) &mc_addr, sizeof(struct sockaddr_in)) < 0) {
        NSLog(@"ERROR: bind not successful");
        return;
    }

    NSLog(@"broadcastMessage - Stage 2");
    /* set the TTL (time to live/hop count) for the send */
    if ((setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (void*) &mc_ttl, sizeof(mc_ttl))) < 0) {
        NSLog(@"ERROR: broadcastMessage - setsockopt() failed");
        return;
    }

    NSLog(@"broadcastMessage - Stage 3");
    /* construct a multicast address structure - erase everything in the structure first*/
    memset(&mc_addr, 0, sizeof(mc_addr));

    // prepare the message to be sent
    char send_str[MAX_LEN];

    /* clear send buffer */
    memset(send_str, 0, sizeof(send_str));

    // convert the message to a C string to send
    [msg getCString:send_str maxLength:MAX_LEN encoding:NSASCIIStringEncoding];

    //while (fgets(send_str, MAX_LEN, stdin)) {
        NSLog(@"broadcastMessage - Stage 4");
    //  send_len = strlen(send_str);

    /* send string to multicast address */
    if ((sendto(sock, send_str, sizeof(send_str), 0, (struct sockaddr *) &mc_addr, sizeof(mc_addr))) != sizeof(send_str)) {
        NSLog(@"ERROR: broadcastMessage - sendto() sent incorrect number of bytes");
        return;
    }

    NSLog(@"broadcastMessage - Stage 5");


    /* clear send buffer */
    memset(send_str, 0, sizeof(send_str));

    NSLog(@"broadcastMessage - Stage 6");
    close(sock);
}


-(void)listenForPackets {
    listeningFlag_on = 1;

    NSLog(@"listenForPackets - Stage 1");
    if ((listeningSock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
        NSLog(@"ERROR: listenForPackets - socket() failed");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    // set reuse port to on to allow multiple binds per host
    if ((setsockopt(listeningSock, SOL_SOCKET, SO_REUSEADDR, &listeningFlag_on, sizeof(listeningFlag_on))) < 0) {
        NSLog(@"ERROR: listenForPackets - setsockopt() failed");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    NSLog(@"listenForPackets - Stage 2");
    // construct a multicast address structure after erasing anything in the listeningmc_addr structure
    memset(&listeningmc_addr, 0, sizeof(listeningmc_addr));
    listeningmc_addr.sin_family      = AF_INET;
    listeningmc_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    listeningmc_addr.sin_port        = htons(mc_port);

    // bind multicast address to socket
    if ((bind(listeningSock, (struct sockaddr *) &listeningmc_addr, sizeof(listeningmc_addr))) < 0) {
        NSLog(@"ERROR: listenForPackets - bind() failed");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    //******************************************************************************************************************************
    //******************************************************************************************************************************
    NSString *ipAddress = [[NSString alloc] initWithString:self.getIPAddress];
    const char *tmp = [ipAddress UTF8String];
    listeningMc_addr_str = tmp;

    printf("%s\n", listeningMc_addr_str);

    listeningMc_req.imr_multiaddr.s_addr = inet_addr("225.0.0.37");
    listeningMc_req.imr_interface.s_addr = htonl(INADDR_ANY);


    // send an ADD MEMBERSHIP message via setsockopt
    if ((setsockopt(listeningSock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void*) &listeningMc_req, sizeof(listeningMc_req))) < 0) {
        NSLog(@"ERROR: listenForPackets - setsockopt() failed");
        int err = errno;
        NSLog(@"errno - %i", err);
        NSLog(@"Error = %s", strerror(err));
        perror("ERROR");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    NSLog(@"listenForPackets - Stage 3");
    for (;;) {          // loop forever

        // clear the receive buffers & structs
        memset(listeningRecv_str, 0, sizeof(listeningRecv_str));
        listeningFrom_len = sizeof(listeningFrom_addr);
        memset(&listeningFrom_addr, 0, listeningFrom_len);

        // block waiting to receive a packet
        if ((listeningRecv_len = recvfrom(listeningSock, listeningRecv_str, MAX_LEN, 0, (struct sockaddr*)&listeningFrom_addr, &listeningFrom_len)) < 0) {
            NSLog(@"ERROR: listenForPackets - recvfrom() failed");
            return;                     // make the method return an int instead of void and use this statement to check for errors
        }
        NSLog(@"listenForPackets - Stage 4");

        NSString *tmpy = [[NSString alloc] initWithCString:listeningRecv_str encoding:NSASCIIStringEncoding];
            msgStatus.text = tmpy;
            NSLog(@"ERROR");
        }
        // received string
        printf("Received %d bytes from %s: ", listeningRecv_len, inet_ntoa(listeningFrom_addr.sin_addr));
        printf("%s", listeningRecv_str);
    }

    // send a DROP MEMBERSHIP message via setsockopt
    if ((setsockopt(listeningSock, IPPROTO_IP, IP_DROP_MEMBERSHIP, (void*) &listeningMc_req, sizeof(listeningMc_req))) < 0) {
        NSLog(@"ERROR: listenForPackets - setsockopt() failed");
        //return 1;                         // make the method return an int instead of void and use this statement to check for errors
    }

    close(listeningSock);
    NSLog(@"listenForPackets - Stage 5 - Complete");    
}

这是我用来提取我的 IP 地址的代码。

-(NSString *)getIPAddress {
    NSString *address = @"error";
    struct ifaddrs *interfaces; // = NULL;
    struct ifaddrs *temp_addr; // = NULL;
    int success = 0;

    // retrieve the current interfaces - returns 0 on success
    success = getifaddrs(&interfaces);
    if (success == 0)  
    {
        // Loop through linked list of interfaces
        temp_addr = interfaces;
        while(temp_addr != NULL)  
        {
            if(temp_addr->ifa_addr->sa_family == AF_INET)
            {
                // Check if interface is en0 which is the wifi connection on the iPhone  
                if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"])  
                {
                    // Get NSString from C String
                    address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];
                }
            }
            temp_addr = temp_addr->ifa_next;
        }
    }

    // Free memory
    freeifaddrs(interfaces); 
    return address; 
}

Answer 1

在监听器中，我觉得你需要设置

listeningMc_req.imr_interface.s_addr = htonl(INADDR_ANY);

... 因为这也是您绑定(bind)套接字的接口(interface)。根据您是否在单个主机上运行所有内容，您可能需要考虑环回接口(interface)并绑定(bind)到 INADDR_ANY 即可。