思路：

UDP服務器端：服務器維護一個client鏈表，當有client連接創建新節點保存客戶主機名和地址，并保存心跳時間heart_beat_time。

當客戶端發起一次心跳，服務器收到心跳包更新client節點的心跳時間。服務定時去檢測client鏈表里的每個client的心跳時間，如果心跳時間和當前時間的時間差超過一定的時間間隔，就認為該client已經掉線。

UDP客戶端：定時發送心跳包。

服務端代碼:

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/socket.h> #include <arpa/inet.h> #include <unistd.h> #include <signal.h> #include <time.h> #include <sys/timerfd.h> #include <pthread.h> #include <sys/epoll.h>#define UDP_PORT_NUM (8888)#define CLIENT_LOGIN 100 #define CLIENT_CHAT 200 #define CLIENT_QUIT 300 #define SERVER_CHAT 400 #define SERVER_QUIT 500 #define PRINT_ONLINE 600 #define PRIVATE_CHAT 700#define HEART_BEAT 800static int s_epoll_fd = -1;typedef enum {E_CLIENT_OFF_LINE = 0,E_CLIENT_ON_LINE }eClientSatus;struct node { char name[20]; // client namestruct sockaddr_in client_addr; // client addreClientSatus client_status; // client statusstruct timespec heart_beat_time; // each heart beat update this timestruct node *next; }; struct message { long type; char name[20]; char peer_name[20]; char mtext[512]; }; struct node *create_list(void); void insert_list(struct node *, char *, struct sockaddr_in *); void delete_list(struct node *, char *); void recv_message(int , struct node *); void send_message(int , struct sockaddr_in *, pid_t ); void client_login(int , struct node *, struct message *, struct sockaddr_in *); void client_chat(int , struct node *, struct message *); void client_quit(int , struct node *, struct message *); void server_chat(int , struct node *, struct message *); void server_quit(int , struct node *, struct message *); void brocast_msg(int , struct node *, struct message *); void print_online(int , struct node *, struct message *); void private_chat(int , struct node *, struct message *); void father_func(int sig_no) { return ; }/* return ms */ static int calcProcessTime(int *pStartMs) {struct timespec endTime;clock_gettime(CLOCK_REALTIME, &endTime);if(pStartMs){return endTime.tv_sec * 1000 + endTime.tv_nsec / 1000000 - *pStartMs;}return endTime.tv_sec * 1000 + endTime.tv_nsec / 1000000; }static void epollAddEvent(int epollFd, int addFd, int state) {struct epoll_event ev;ev.events = state;ev.data.fd = addFd;epoll_ctl(epollFd, EPOLL_CTL_ADD, addFd, &ev);return; }void* monitor_thread(void* user) {struct node *head = (struct node *)user;struct epoll_event events[1] = {0};int cnt = 0;while(1){int ms = 0;ms = calcProcessTime(NULL);int fireEvents = epoll_wait(s_epoll_fd, events, 1, -1);ms = calcProcessTime(&ms);if(fireEvents > 0){printf("monitor time out: %d ms\n", ms);uint64_t exp;ssize_t size = read(events[0].data.fd, &exp, sizeof(uint64_t));if(size != sizeof(uint64_t)) {printf("read error!\n");}struct node *p = head;struct timespec nowTime;clock_gettime(CLOCK_REALTIME, &nowTime);while (p != NULL){/* if 10 second not receive client heart beat, we think the client is offline */if(p->client_status == E_CLIENT_ON_LINE) {int duration = (nowTime.tv_sec * 1000 + nowTime.tv_nsec / 1000000) - (p->heart_beat_time.tv_sec * 1000 + p->heart_beat_time.tv_nsec / 1000000);if (duration > 10000) {p->client_status = E_CLIENT_OFF_LINE;printf("client: %s had off line\n", p->name);}}p = p->next;} printf("All client check finished\n");}else{printf("fireEvents = %d", fireEvents);}} }int main(int argc, const char *argv[]) { int socket_fd; pid_t pid; struct sockaddr_in server_addr; struct node *head; if (argc < 2){ fprintf(stderr, "usages : %s ip\n", argv[0]); exit(-1); } /* create UDP socket */if ((socket_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){ perror("failed to create socket"); exit(-1); } /* create client list */head = create_list(); server_addr.sin_family = AF_INET; server_addr.sin_port = htons(UDP_PORT_NUM); server_addr.sin_addr.s_addr = inet_addr(argv[1]); if (bind(socket_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0){ perror("failed to bind"); exit(-1); } if ((pid = fork()) < 0){ perror("failed to fork pid"); exit(-1); } if (pid == 0){/* create epoll */int epollFd = -1;epollFd = epoll_create(1);s_epoll_fd = epollFd;/* create timer */int timerFd = -1;timerFd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC | TFD_NONBLOCK);/* add timer fd to epoll monitor event */epollAddEvent(epollFd, timerFd, EPOLLIN);/* create thread to monitor */pthread_t threadId = -1;pthread_create(&threadId, NULL, &monitor_thread, (void*)head);/* create timer, time out is 10 seconds */struct itimerspec its;its.it_interval.tv_sec = 10; // 10 secondsits.it_interval.tv_nsec = 0;its.it_value.tv_sec = 10;its.it_value.tv_nsec = 0;if (timerfd_settime(timerFd, 0, &its, NULL) < 0) {fprintf(stderr, "timerfd_settime error\n");}printf("udp server <receive message> running......\n");recv_message(socket_fd, head); }else{printf("udp server <send message> running......\n");send_message(socket_fd, &server_addr, pid); }return 0; } struct node *create_list(void) { struct node *head; head = (struct node *)malloc(sizeof(struct node)); head->next = NULL; return head; } void insert_list(struct node *head, char *name, struct sockaddr_in *client_addr) { if(!head) return;struct node *new; new = (struct node *)malloc(sizeof(struct node)); strcpy(new->name, name); new->client_addr = *client_addr; new->client_status = E_CLIENT_ON_LINE;clock_gettime(CLOCK_REALTIME, &new->heart_beat_time);new->next = head->next; head->next = new; return ; } void delete_list(struct node *head, char *name) { if(!head) return;struct node *p = head->next; struct node *q = head; while (p != NULL){ if (strcmp(p->name, name) == 0) break; p = p->next; q = q->next; } q->next = p->next; p->next = NULL; free(p); return ; } void recv_message(int socket_fd, struct node *head) { struct message msg; struct sockaddr_in client_addr; int client_addrlen = sizeof(struct sockaddr); while (1) { memset(&msg, 0, sizeof(msg)); if (recvfrom(socket_fd, &msg, sizeof(msg), 0, (struct sockaddr *)&client_addr, &client_addrlen) < 0){ perror("failed to recvform client"); exit(-1); } switch(msg.type) { case CLIENT_LOGIN: client_login(socket_fd, head, &msg, &client_addr); break; case CLIENT_CHAT: client_chat(socket_fd, head, &msg); break; case CLIENT_QUIT: client_quit(socket_fd, head, &msg); break; case SERVER_CHAT: server_chat(socket_fd, head, &msg); break; case SERVER_QUIT: server_quit(socket_fd, head, &msg); break; case PRINT_ONLINE: print_online(socket_fd, head, &msg); break; case PRIVATE_CHAT: private_chat(socket_fd, head, &msg); break; case HEART_BEAT:heart_beat(socket_fd, head, &msg);break;default: break; } } return ; } void send_message(int socket_fd, struct sockaddr_in *server_addr, pid_t pid) { struct message msg; char buf[512]; signal(getppid(), father_func); while (1) { usleep(500); printf(">"); fgets(buf, sizeof(buf), stdin); buf[strlen(buf) - 1] = 0; strcpy(msg.mtext, buf); strcpy(msg.name , "server"); msg.type = SERVER_CHAT; if (strncmp(buf, "quit", 4) == 0){ msg.type = SERVER_QUIT; printf("udp server will quit, socket_fd = %d!!!!!\n", socket_fd);if (sendto(socket_fd, &msg, sizeof(msg), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send server_quit message"); exit(-1); } //pause(); kill(pid, SIGKILL); waitpid(pid, NULL, 0); close(socket_fd); exit(-1); } if (sendto(socket_fd, &msg, sizeof(msg), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send server_chat message"); exit(-1); } } return ; } void client_login(int socket_fd, struct node *head, struct message *msg, struct sockaddr_in *client_addr) { printf("********Login In Notice********\n"); printf("%s has Login In, you can talk to him/her.\n", msg->name); printf("****************************\n"); insert_list(head, msg->name, client_addr); brocast_msg(socket_fd, head, msg); return ; } void client_chat(int socket_fd, struct node *head, struct message *msg) { printf("********Group Chat********\n"); printf("name: %s\n", msg->name); printf("msg: %s\n", msg->mtext); printf("**************************\n"); brocast_msg(socket_fd, head, msg); return ; } void client_quit(int socket_fd, struct node *head, struct message *msg) { printf("*********Quit Msg********\n"); printf("%s is Quit\n", msg->name); printf("*************************\n"); delete_list(head, msg->name); brocast_msg(socket_fd, head, msg); return ; } void server_chat(int socket_fd, struct node *head, struct message *msg) { printf("********Server Msg*********\n"); printf("msg: %s\n", msg->mtext); printf("***************************\n"); brocast_msg(socket_fd, head, msg); return ; } void server_quit(int socket_fd, struct node *head, struct message *msg) { brocast_msg(socket_fd, head, msg); kill(getppid(), SIGUSR1); return ; } void print_online(int socket_fd, struct node *head, struct message *msg) { struct node *p = head->next; struct sockaddr_in my_addr; char buf[512]; printf("%s is request to print online client\n", msg->name); memset(buf, 0, sizeof(buf)); while (p != NULL) { if (strcmp(p->name, msg->name) == 0){ my_addr = p->client_addr; p = p->next;continue;}strcat(buf, p->name); strcat(buf, " "); p = p->next; } strcpy(msg->mtext, buf); msg->type = PRINT_ONLINE; if (sendto(socket_fd, msg, sizeof(struct message), 0, (struct sockaddr *)&my_addr, sizeof(my_addr)) < 0){ perror("failed to send print_online message"); exit(-1); } return ; } void private_chat(int socket_fd, struct node *head, struct message *msg) { struct node *p = head->next; struct sockaddr_in *peer_addr = NULL; printf("******** Private Msg ********\n"); printf("from %s\n", msg->name); printf("to %s\n", msg->peer_name); printf("msg: %s\n", msg->mtext); printf("*****************************\n"); while (p != NULL) { if (strcmp(p->name, msg->peer_name) == 0){ peer_addr = &(p->client_addr); break; } p = p->next; } if(!peer_addr){printf("[Udp server] user %s is not in online list!!\n", msg->peer_name);msg->type = SERVER_CHAT;sprintf(msg->mtext, "The one of %s who you want to talk is not exist!!!\n", msg->peer_name);p = head->next;while (p != NULL){ if (strcmp(p->name, msg->name) == 0){ peer_addr = &(p->client_addr); break; } p = p->next; }}if(peer_addr){if (sendto(socket_fd, msg, sizeof(struct message), 0, (struct sockaddr *)peer_addr, sizeof(struct sockaddr_in)) < 0){ perror("failed to send private message"); exit(-1); } }return ; } void heart_beat(int socket_fd, struct node *head, struct message *msg) { struct node *p = head->next; printf("%s heart beat ^^^\n", msg->name); while (p != NULL) { if (strcmp(p->name, msg->name) == 0){p->client_status = E_CLIENT_ON_LINE;clock_gettime(CLOCK_REALTIME, &p->heart_beat_time);}p = p->next; } return ; } void brocast_msg(int socket_fd, struct node *head, struct message *msg) { struct node *p = head->next; while(p != NULL) { if (msg->type == CLIENT_LOGIN){ if (strcmp(p->name, msg->name) == 0){ p = p->next; continue; } } sendto(socket_fd, msg, sizeof(struct message), 0, (struct sockaddr *)&(p->client_addr), sizeof(struct sockaddr)); p = p->next; } return ; }

客戶端代碼：

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/socket.h> #include <arpa/inet.h> #include <unistd.h> #include <signal.h> #include <pthread.h> #include <sys/timerfd.h> #include <sys/epoll.h>#define UDP_PORT_NUM (8888)#define CLIENT_LOGIN 100 #define CLIENT_CHAT 200 #define CLIENT_QUIT 300 #define SERVER_CHAT 400 #define SERVER_QUIT 500 #define PRINT_ONLINE 600 #define PRIVATE_CHAT 700#define HEART_BEAT 800static char s_my_name[20]; static int s_server_fd; static int s_epoll_fd = -1;struct message { long type; char name[20]; char peer_name[20]; char mtext[512]; }; void recv_message(int ); void send_message(int , struct sockaddr_in *, char *, pid_t); void login_msg(struct message *); void group_msg(struct message *); void quit_msg(struct message *); void server_msg(struct message *); void server_quit(void); void online_msg(struct message *); void private_msg(struct message *); void print_online(int , struct message *, struct sockaddr_in *); void group_chat(int , struct message *, struct sockaddr_in *); void private_chat(int ,struct message *, struct sockaddr_in *); void client_quit(int , struct message *, struct sockaddr_in *, pid_t ); static void epollAddEvent(int epollFd, int addFd, int state) {struct epoll_event ev;ev.events = state;ev.data.fd = addFd;epoll_ctl(epollFd, EPOLL_CTL_ADD, addFd, &ev);return; }void heart_beat(struct sockaddr_in *server_addr) { struct message msg; msg.type = HEART_BEAT; strcpy(msg.name, s_my_name); if (sendto(s_server_fd, &msg, sizeof(struct message), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send online message"); return; } return ; }void* heart_beat_thread(void* user) {struct sockaddr_in *server_addr = (struct sockaddr_in*)user;struct epoll_event events[1] = {0};int cnt = 0;while(1){int fireEvents = epoll_wait(s_epoll_fd, events, 1, -1);if(fireEvents > 0){printf("I heart beat\n");uint64_t exp;ssize_t size = read(events[0].data.fd, &exp, sizeof(uint64_t));if(size != sizeof(uint64_t)) {printf("read error!\n");}heart_beat(server_addr);}else{printf("fireEvents = %d", fireEvents);}}return NULL; }int main(int argc, char *argv[]) { pid_t pid; int server_fd; struct sockaddr_in server_addr; if (argc < 4){ fprintf(stderr, "usages: %s ip name heart_beat(seconds)\n", argv[0]); exit(-1); } int heart_beat_period = atoi(argv[3]);if ((server_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){ perror("failed to create server_fd"); exit(-1); }s_server_fd = server_fd;server_addr.sin_family = AF_INET; server_addr.sin_port = htons(UDP_PORT_NUM); server_addr.sin_addr.s_addr = inet_addr(argv[1]); if ((pid = fork()) < 0){ perror("failed to fork pid"); exit(-1); } memset(s_my_name, '\0', 20);memcpy(s_my_name, argv[2], sizeof(char) * (strlen(argv[2]) + 1));if (pid == 0) { /* create epoll */int epollFd = -1;epollFd = epoll_create(1);s_epoll_fd = epollFd;/* create timer */int timerFd = -1;timerFd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC | TFD_NONBLOCK);/* add timer fd to epoll monitor event */epollAddEvent(epollFd, timerFd, EPOLLIN);/* create heart beat thread */pthread_t threadId = -1;pthread_create(&threadId, NULL, &heart_beat_thread, (void*)&server_addr);/* create timer, time out is heart beat seconds */struct itimerspec its;its.it_interval.tv_sec = heart_beat_period;its.it_interval.tv_nsec = 0;its.it_value.tv_sec = heart_beat_period;its.it_value.tv_nsec = 0;if (timerfd_settime(timerFd, 0, &its, NULL) < 0) {fprintf(stderr, "timerfd_settime error\n");}recv_message(server_fd); }else {send_message(server_fd, &server_addr, argv[2], pid); }return 0; } void recv_message(int server_fd) { struct message msg; while (1) { memset(&msg, 0, sizeof(msg)); int nbytes = 0;if ((nbytes = recvfrom(server_fd, &msg, sizeof(msg), 0, NULL, NULL)) < 0){ perror("failed to recv server message"); exit(-1); } switch(msg.type) { case CLIENT_LOGIN: login_msg(&msg); break; case CLIENT_CHAT: group_msg(&msg); break; case CLIENT_QUIT: quit_msg(&msg); break; case SERVER_CHAT: server_msg(&msg); break; case SERVER_QUIT: server_quit(); break; case PRINT_ONLINE: online_msg(&msg); break; case PRIVATE_CHAT: private_msg(&msg); break; default: break; } } return ; } void send_message(int server_fd, struct sockaddr_in *server_addr, char *name, pid_t pid) { struct message msg; char buf[512]; int c; msg.type = CLIENT_LOGIN; strcpy(msg.name, name); if (sendto(server_fd, &msg, sizeof(msg), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send login message"); exit(-1); } while(1) { usleep(500); printf("#####################################\n"); printf("the following options can be choose:\n"); printf("input 1 is to print online client\n"); printf("input 2 is to chat to all the client\n"); printf("input 3 is to chat to only one client\n"); printf("input q is to quit\n"); printf("#####################################\n"); printf(">"); c = getchar(); while (getchar() != '\n'); switch(c) { case '1': print_online(server_fd, &msg, server_addr); break; case '2':printf("[Notice:]you can input <quit> cmd to close group chat....\n");group_chat(server_fd, &msg, server_addr); break; case '3': printf("[Notice:]you can input <quit> cmd to close private chat....\n");private_chat(server_fd, &msg, server_addr); break; case 'q': client_quit(server_fd, &msg, server_addr, pid); break; default: break; } } return ; } void login_msg(struct message *msg) { printf("********Login In Notice********\n"); printf("%s has Login In, you can talk to him/her.\n", msg->name); printf("****************************\n"); return ; } void group_msg(struct message *msg) { printf("******** Group Msg ********\n"); printf("name: %s\n", msg->name); printf("msg: %s\n", msg->mtext); printf("******** Group Msg ********\n"); return ; } void quit_msg(struct message *msg) { printf("######## Quit Msg ########\n"); printf("%s is Quit\n", msg->name); printf("######## Quit Msg ########\n"); return ; } void server_msg(struct message *msg) { printf("******** Server Msg ********\n"); printf("msg: %s\n", msg->mtext); printf("******** Server Msg ********\n"); return ; } void server_quit(void ) { kill(getppid(), SIGKILL); exit(0); } void online_msg(struct message *msg) { printf("******** Clients you can talk to. ********\n"); printf("Clients: %s\n", msg->mtext); printf("******** Clients you can talk to. ********\n"); return ; } void private_msg(struct message *msg) { printf("******** Private Msg ********\n"); printf("[%s] say: %s\n", msg->name, msg->mtext); printf("******** Private Msg ********\n"); return ; } void print_online(int server_fd, struct message *msg, struct sockaddr_in *server_addr) { msg->type = PRINT_ONLINE; if (sendto(server_fd, msg, sizeof(struct message), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send online message"); exit(-1); } return ; } void group_chat(int server_fd, struct message *msg, struct sockaddr_in *server_addr) { char buf[512]; memset(buf, 0, sizeof(buf)); printf("*********** Group Chat Room ***********\n"); printf("****** Welcome to group chat room ******\n"); printf("* if you want to quit, please input quit\n"); printf("****************************************\n"); while(1) { memset(buf, 0, sizeof(buf)); usleep(500); printf(">"); fgets(buf, sizeof(buf), stdin); buf[strlen(buf) - 1] = 0; msg->type = CLIENT_CHAT; strcpy(msg->mtext, buf); if (strncmp(buf, "quit", 4) == 0) break; if (sendto(server_fd, msg, sizeof(struct message), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send group message"); exit(-1); } } return ; } void private_chat(int server_fd, struct message *msg, struct sockaddr_in *server_addr) { char name[20]; char buf[512]; memset(name, 0, sizeof(name)); printf("please input the peer_name\n"); printf(">"); fgets(name, sizeof(name), stdin); name[strlen(name) - 1] = 0; if(strncmp(s_my_name, name, strlen(name)) == 0){printf("you can not talk with yourself!!!!!\n");return;}strcpy(msg->peer_name, name); msg->type = PRIVATE_CHAT; printf("you want to talk to %s!\n", msg->peer_name); while(1) { usleep(500); printf(">"); fgets(buf, sizeof(buf), stdin); buf[strlen(buf) - 1] = 0; strcpy(msg->mtext, buf); if (strncmp(buf, "quit", 4) == 0) break; if (sendto(server_fd, msg, sizeof(struct message), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send private message"); exit(-1); } } return ; } void client_quit(int server_fd, struct message *msg, struct sockaddr_in *server_addr, pid_t pid) { msg->type = CLIENT_QUIT; if (sendto(server_fd, msg, sizeof(struct message), 0, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) < 0){ perror("failed to send quit message"); exit(-1); } kill(pid, SIGKILL); waitpid(pid, NULL, 0); exit(0); }

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