发送/接收UDP数据包的帮助-C套接字 [英] Help with Sending/ Receiving UDP packets - C Sockets
本文介绍了发送/接收UDP数据包的帮助-C套接字的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
好吧，如果您看过我以前的一些问题，我一直在努力建立简单的连接并使用C套接字运行(我对程序的整个网络方面还是很陌生，但是每个人都有开始某个地方，对吧?).到目前为止，我已经包含了下面的代码，当我执行它时，没有任何错误，但是与此同时，另一端没有得到该数据包.顺便说一句，我在Objective-C中编程多播套接字，"msgStatus"只是GUI中的一个标签(它已正确连接，因此没有问题).我只是不知道我要去哪里错了.有人可能会帮助我或为我指明正确的方向吗?谢谢！
Ok, if you look at some of my previous questions, I've been working on getting a simple connection up and running with C sockets (I'm still fairly new to the whole networking aspect of an program, but everyone has to start somewhere, right?). I've included the code below that I have so far and when I execute it, I get no errors, but at the same time, I don't get the packet on the other end. By the way, I'm programming multicast sockets in objective-C and "msgStatus" is just a label in my GUI (it's hooked up correctly, so there's no problem there). I'm just not seeing where I'm going wrong. Could someone possibly help me or point me in the right direction? Thanks!
#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IP地址的代码.
Here is the code I'm using to extract my IP Address.
-(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;
}
推荐答案
在侦听器中，我认为您需要设置
In the listener, I think you need to set
listeningMc_req.imr_interface.s_addr = htonl(INADDR_ANY);
...，因为这也是绑定套接字的接口.根据您是否在单个主机上运行所有内容，您可能需要考虑回送接口，并绑定到INADDR_ANY即可做到这一点.
... since that is also the interface on which you bind the socket. Depending on whether you run everything on a single host, you might need to consider the loopback interface and binding to INADDR_ANY will do that.
这篇关于发送/接收UDP数据包的帮助-C套接字的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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