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--- sk2:multicast_example [2021/12/20 13:49]
jkonczak
+++ sk2:multicast_example [2025/11/27 19:49] (aktualna)
jkonczak
@@ Linia 1: / Linia 1: @@
 ==== Przykład użycia UDP multicast ====
 <code cpp multicast_example.cpp>
+#include <csignal>
+#include <cstdio>
 #include <cstdlib>
-#include <cstdio>
-#include <csignal>
-#include <thread>
 #include <atomic>
+#include <thread>
-#include <unistd.h>
 #include <errno.h>
 #include <error.h>
+#include <unistd.h>
-#include <sys/socket.h>
-#include <netinet/ip.h>
 #include <arpa/inet.h>
+#include <netinet/ip.h>
+#include <sys/socket.h>
 /* UDP multicast example. Compile with threads and C++11 (g++ -pthread --std=c++11)
  *
  * Sending to multicast group MCASTIP:MCASTPORT
  *   - create a UDP socket
  *   - send a datagram to MCASTIP:MCASTPORT
  *
  * Receiving datagrams sent to a multicast group MCASTIP:MCASTPORT
  *   - create a UDP socket
@@ Linia 28: / Linia 28: @@
  *   - call setsockopt to set option IP_ADD_MEMBERSHIP on level IPPROTO_IP to the aforementioned structure
  *   - receive datagrams
  *
  * setsockopt of IP_ADD_MEMBERSHIP sends an IGMP message "join group" and tells OS that the program waits for messages for the group.
  *
  * More info at: https://tldp.org/HOWTO/Multicast-HOWTO-6.html
  */
+const sockaddr_in groupSockaddr{
-const sockaddr_in groupSockaddr {
+    .sin_family = AF_INET,
-	.sin_family = AF_INET,
+    .sin_port = htons(6789),
-	.sin_port = htons(6789),
+    .sin_addr = {.s_addr = inet_addr("239.255.123.45")}
-	.sin_addr = {inet_addr("239.255.123.45")}
 };
-std::atomic<bool> quitting {false};
+std::atomic<bool> quitting{false};
-void ctrl_c(int){
+void ctrl_c(int) {
-	if(quitting)
+    if (quitting)
-		exit(-1);
+        exit(-1);
-	quitting = true;
+    quitting = true;
 }
 void setupSignals();
-int main(int argc, char **argv) {
+int main() {
-	// create socket
+    // create socket
-	int sockfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
+    int sockfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
-	if(sockfd==-1) error(1,errno, "socket");
+    if (sockfd == -1)
+        error(1, errno, "socket");
-	// set SO_REUSEADDR (or only one app will be allowed to receive multicast messages from the groupIP:port pair)
-	// this is one of very few cases when SO_REUSEADDR on UDP has any use
+    // set SO_REUSEADDR (or only one app will be allowed to receive multicast messages from the groupIP:port pair)
-	const int one = 1;
+    const int one = 1;
-	int res = setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+    int res = setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
-	if(res) error(1,errno, "setsockopt SO_REUSEADDR");
+    if (res)
+        error(1, errno, "setsockopt SO_REUSEADDR");
-	// bind
-	sockaddr_in myAddress {
+    // bind
-		.sin_family = AF_INET,
+    sockaddr_in myAddress{
-		.sin_port = groupSockaddr.sin_port,
+        .sin_family = AF_INET,
-		.sin_addr = {INADDR_ANY}
+        .sin_port = groupSockaddr.sin_port,
-	};
+        .sin_addr = {INADDR_ANY}
-	res = bind(sockfd, (sockaddr*) &myAddress, sizeof(myAddress));
+    };
-	if(res) error(1, errno, "bind");
+    res = bind(sockfd, (sockaddr *)&myAddress, sizeof(myAddress));
+    if (res)
-	// send IGMP join group
+        error(1, errno, "bind");
-	ip_mreqn groupDescription{
-		.imr_multiaddr = groupSockaddr.sin_addr,
+    // send IGMP join group
-		.imr_address =  {INADDR_ANY},
+    ip_mreqn groupDescription{
-		.imr_ifindex = 0
+        .imr_multiaddr = groupSockaddr.sin_addr,
-	};
+        .imr_address = {INADDR_ANY},
-	auto ret = setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &groupDescription, sizeof(groupDescription));
+        .imr_ifindex = 0
-	if(ret) error(1, errno, "setsockopt IP_ADD_MEMBERSHIP");
+    };
+    auto ret = setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &groupDescription, sizeof(groupDescription));
-	// handle ctrl+c for gracefull exit
+    if (ret)
-	setupSignals();
+        error(1, errno, "setsockopt IP_ADD_MEMBERSHIP");
-	// receive and display ANY packet that arrives
+    // handle ctrl+c for gracefull exit
-	std::thread readerThread([&]{
+    setupSignals();
-		sockaddr_in peerAddr;
-		socklen_t peerAddrSize;
+    // receive and display ANY packet that arrives
-		char buffer[255];
+    std::thread readerThread([&] {
-		while(true){
+        sockaddr_in peerAddr;
-			peerAddrSize = sizeof(peerAddr);
+        socklen_t peerAddrSize;
-			auto readSize = recvfrom(sockfd, buffer, 254, MSG_TRUNC, (sockaddr*) &peerAddr, &peerAddrSize);
+        char buffer[255];
-			if(quitting) break;
+        while (true) {
-			if(readSize==-1) error(1,errno, "recvfrom");
+            peerAddrSize = sizeof(peerAddr);
-			if(readSize>254) { error(0,0,"UDP packet too long - truncated from %ld to %d", readSize, 254); readSize=254;}
+            auto readSize = recvfrom(sockfd, buffer, 254, MSG_TRUNC, (sockaddr *)&peerAddr, &peerAddrSize);
-			buffer[readSize] = 0;
+            if (quitting)
-			printf("<%s:%hu> %s", inet_ntoa(peerAddr.sin_addr), ntohs(peerAddr.sin_port), buffer);
+                break;
-		}
+            if (readSize == -1)
-	});
+                error(1, errno, "recvfrom");
+            if (readSize > 254) {
-	// read standard input and send it to the group
+                error(0, 0, "UDP packet too long - truncated from %ld to %d", readSize, 254);
-	char buffer[255];
+                readSize = 254;
-	while(true){
+            }
-		auto readSize = read(0, buffer, 254);
+            buffer[readSize] = 0;
-		if(quitting || !readSize) break;
+            printf("<%s:%hu> %s", inet_ntoa(peerAddr.sin_addr), ntohs(peerAddr.sin_port), buffer);
-		if(readSize<0) { error(0, errno, "reading stdin"); break; }
+        }
+    });
-		auto res = sendto(sockfd, buffer, readSize, 0, (sockaddr*) &groupSockaddr, sizeof(groupSockaddr));
-		if(res!=readSize) { error(0,  errno, "sendto"); break; }
+    // read standard input and send it to the group
-	}
+    char buffer[255];
+    while (true) {
-	quitting = true;
+        auto readSize = read(0, buffer, 254);
-	// leave group
+        if (quitting || !readSize)
-	setsockopt(sockfd, IPPROTO_IP, IP_DROP_MEMBERSHIP, &groupDescription, sizeof(groupDescription));
+            break;
-	// close socket AND interrupt all blocked recvfrom
+        if (readSize < 0) {
-	shutdown(sockfd, SHUT_RDWR);
+            error(0, errno, "reading stdin");
-	close(sockfd);
+            break;
-	// wait for child
+        }
-	readerThread.join();
+        auto res = sendto(sockfd, buffer, readSize, 0, (sockaddr *)&groupSockaddr, sizeof(groupSockaddr));
-	return 0;
+        if (res != readSize) {
+            error(0, errno, "sendto");
+            break;
+        }
+    }
+    quitting = true;
+    // leave group
+    setsockopt(sockfd, IPPROTO_IP, IP_DROP_MEMBERSHIP, &groupDescription, sizeof(groupDescription));
+    // close socket AND interrupt all blocked recvfrom
+    shutdown(sockfd, SHUT_RDWR);
+    close(sockfd);
+    // wait for child
+    readerThread.join();
+    return 0;
 }
-void setupSignals(){
+void setupSignals() {
-	struct sigaction action;
+    struct sigaction action;
-	// read sigint handler description
+    // read sigint handler description
-	auto res = sigaction(SIGINT, nullptr, &action);
+    auto res = sigaction(SIGINT, nullptr, &action);
-	if(res) error(1, errno, "sigaction read");
+    if (res)
+        error(1, errno, "sigaction read");
-	// set new interrupt handler
-	action.sa_handler = ctrl_c;
+    // set new interrupt handler
-	// disable SA_RESTART flag to exit blocking IO upon a signal
+    action.sa_handler = ctrl_c;
-	action.sa_flags &= ~SA_RESTART;
+    // disable SA_RESTART flag to exit blocking IO upon a signal
+    action.sa_flags &= ~SA_RESTART;
-	// update sigint handler description
-	res = sigaction(SIGINT, &action, nullptr);
+    // update sigint handler description
-	if(res) error(1, errno, "sigaction modify");
+    res = sigaction(SIGINT, &action, nullptr);
+    if (res)
+        error(1, errno, "sigaction modify");
 }
 </code>

Jan Kończak

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