有关发送/接收UDP数据包的帮助 - C Sockets

Question

好的，如果你看看我以前的一些问题，我一直在努力获得一个简单的连接并使用C套接字运行（我对于一个程序的整个网络方面，但每个人都必须从某个地方开始，对吧？）。我已经包含了我目前为止的代码，当我执行它时，我没有遇到任何错误，但是同时，我没有在另一端获得数据包。顺便说一句，我在Objective-C中编程多播套接字，“msgStatus”只是我的GUI中的一个标签（它正确连接，所以没有问题）。我只是没有看到我要出错的地方。有人可能帮助我或指出我朝着正确的方向吗？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

在听者，我想你需要设置

listeningMc_req.imr_interface.s_addr = htonl(INADDR_ANY); 

...因为这也是您在其上绑定套接字接口。根据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，并且绑定到INADDR_ANY将执行此操作。

Answer 2

您和目的地之间是否有路由器？如果是这样，那么需要做一些工作来告诉路由器您要订阅订阅源，并告诉路由器您将发送订阅源。

我会从tcpdump-ing连接开始，确保数据包首先离开你的机器。