为什么没有收到（UDP组播）数据包？ [英] Why are (UDP multicast) packets not being received?

问题描述

所以，我一直试图弄清楚为什么这不起作用但我没有线索。我已经设法从iPhone发送数据包并在我的Mac上接收它们。根据tcpdump我的mac正确发送数据包。另外，如果我在模拟器中运行它，它工作正常。这让我相信这是一个网络问题，但我不知道那可能是什么，所以我希望（！）它是下面的东西。

So, I've been trying to figure out exactly why this isn't working but I haven't a clue. I've managed to send packets from the iPhone and receive them on my Mac. And according to tcpdump my mac is correctly sending the packets. Additionally, if I run this in the simulator it works fine. This leads me to believe that it's a network problem, but I have no idea what that could be, so I was hoping(!) that it's something below.

CFSocketContext socketContext = {0, self, NULL, NULL, NULL};
advertiseSocket = CFSocketCreate(kCFAllocatorDefault, PF_INET, SOCK_DGRAM, IPPROTO_UDP, kCFSocketDataCallBack, (CFSocketCallBack)&advertiseCallBack, &socketContext);

int yes = 1;
setsockopt(CFSocketGetNative(advertiseSocket), SOL_SOCKET, SO_REUSEADDR, (void *)&yes, sizeof(yes));

u_char loop = 0;
setsockopt(CFSocketGetNative(advertiseSocket), IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop)); 

unsigned char ttl = 64;
setsockopt(CFSocketGetNative(advertiseSocket), IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));        

struct sockaddr_in addressData;
memset(&addressData, 0, sizeof(addressData));
addressData.sin_len = sizeof(addressData);
addressData.sin_family = AF_INET;
addressData.sin_port = htons(broadcastPort);
addressData.sin_addr.s_addr = htonl(INADDR_ANY);
NSData *address = [NSData dataWithBytes:&addressData length:sizeof(addressData)];
CFSocketSetAddress(advertiseSocket, (CFDataRef)address);

struct ip_mreq mreq;
mreq.imr_multiaddr.s_addr = inet_addr(broadcastIP);         
mreq.imr_interface.s_addr = INADDR_ANY;

setsockopt(CFSocketGetNative(advertiseSocket), IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));

// set up the run loop sources for the sockets
CFRunLoopRef cfrl = CFRunLoopGetCurrent();
CFRunLoopSourceRef source = CFSocketCreateRunLoopSource(kCFAllocatorDefault, advertiseSocket, 0);
CFRunLoopAddSource(cfrl, source, kCFRunLoopCommonModes);
CFRelease(source);

编辑：

上面的代码是对于iPhone上的接收端。

The code above is for the receiving end on the iPhone.

我正在使用下面的java代码与iPhone交谈（这是浓缩的）。 iPhone不会收到发送的数据包，但mac会收到iPhone发送的数据包。

I'm using the java code below to talk to the iPhone (this is condensed). The packet that gets sent is not received by the iPhone but the mac receives the packet that the iPhone sends.

String ident = broadcastKey;
MulticastSocket socket = new MulticastSocket(broadcastPort);
InetAddress group = InetAddress.getByName(broadcastIP);
socket.joinGroup(group);
socket.setTimeToLive(64);
socket.setLoopbackMode(true);
byte [] key = ident.getBytes("UTF-16BE");
byte [] request = Arrays.copyOf(key,key.length+2);
System.out.println(Arrays.toString(request));
DatagramPacket packet = new DatagramPacket(request, request.length, group, broadcastPort);
socket.send(packet);
byte [] res = new byte[1024];
packet = new DatagramPacket(res, res.length);
socket.receive(packet);
System.out.println(Arrays.toString(res));

这是我用来从iPhone发送的代码

This is the code I'm using to send from the iPhone

NSData *toSend = [broadcastIdentifier dataUsingEncoding:NSUTF16BigEndianStringEncoding];
struct in_addr        localInterface;
struct sockaddr_in    groupSock;
int                   sd;
int                   datalen;

sd = socket(AF_INET, SOCK_DGRAM, 0);
memset((char *) &groupSock, 0, sizeof(groupSock));
groupSock.sin_family = AF_INET;
groupSock.sin_addr.s_addr = inet_addr(broadcastIP);
groupSock.sin_port = htons(broadcastPort);
localInterface.s_addr = INADDR_ANY;
setsockopt(sd, IPPROTO_IP, IP_MULTICAST_IF, (char *)&localInterface, sizeof(localInterface));
sendto(sd, [toSend bytes], [toSend length], 0, (struct sockaddr*)&groupSock, sizeof(groupSock));

因此，为了澄清这个问题，我想知道为什么iPhone没有收到数据包。此外，Robert完全正确，因为它在模拟器上工作的原因是由于环回。

So, to clarify the question, I want to know why the iPhone isn't receiving the packet. Also, Robert is completely right that the reason it was working on the simulator is due to the loopback.

推荐答案

我需要改变INADDR_ANY到broadcastIP ...

I needed to change the INADDR_ANY to the broadcastIP...

struct sockaddr_in addressData;
memset(&addressData, 0, sizeof(addressData));
addressData.sin_len = sizeof(addressData);
addressData.sin_family = AF_INET;
addressData.sin_port = htons(broadcastPort);
addressData.sin_addr.s_addr = inet_addr(broadcastIP);
NSData *address = [NSData dataWithBytes:&addressData length:sizeof(addressData)];
if (kCFSocketSuccess != CFSocketSetAddress(advertiseSocket, (CFDataRef)address)) {
    [self stopBeforeStart];
    [self connectionFailed];
    return;
}

struct ip_mreq mreq;
mreq.imr_multiaddr.s_addr = inet_addr(broadcastIP);         
mreq.imr_interface.s_addr = INADDR_ANY;

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