UDP 與 TCP 的核心區別

1. 無連接：不需要建立/維護連接

2. 不可靠：不保證數據包順序和到達

3. 高效：頭部開銷小，沒有連接管理負擔

4. 支持廣播/多播：可以向多個目標同時發送數據

一、基礎UDP服務器實現

1. 創建 UDP 套接字

#include <event2/event.h>
#include <event2/listener.h>
#include <event2/bufferevent.h>
#include <arpa/inet.h>int create_udp_socket(int port) {int fd = socket(AF_INET, SOCK_DGRAM, 0);if (fd < 0) {perror("socket");return -1;}struct sockaddr_in sin;memset(&sin, 0, sizeof(sin));sin.sin_family = AF_INET;sin.sin_port = htons(port);sin.sin_addr.s_addr = htonl(INADDR_ANY);if (bind(fd, (struct sockaddr*)&sin, sizeof(sin)) < 0) {perror("bind");close(fd);return -1;}// 設置非阻塞evutil_make_socket_nonblocking(fd);return fd;
}

2. UDP 事件處理

void udp_read_cb(evutil_socket_t fd, short events, void *arg) {struct sockaddr_in client_addr;socklen_t addr_len = sizeof(client_addr);char buf[1500]; // 標準MTU大小ssize_t n;while ((n = recvfrom(fd, buf, sizeof(buf), 0,(struct sockaddr*)&client_addr, &addr_len)) > 0) {// 處理接收到的數據printf("Received %zd bytes from %s:%d\n", n, inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));// 簡單回顯sendto(fd, buf, n, 0, (struct sockaddr*)&client_addr, addr_len);}if (n < 0 && errno != EAGAIN && errno != EWOULDBLOCK) {perror("recvfrom");}
}int main() {int udp_fd = create_udp_socket(8080);if (udp_fd < 0) return 1;struct event_base *base = event_base_new();struct event *udp_event = event_new(base, udp_fd, EV_READ | EV_PERSIST, udp_read_cb, NULL);event_add(udp_event, NULL);printf("UDP server started on port 8080\n");event_base_dispatch(base);event_free(udp_event);close(udp_fd);event_base_free(base);return 0;
}

3. UDP 服務器示例代碼

#include <event2/event.h>
#include <event2/bufferevent.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
#include <time.h>#define MAX_CLIENTS 10000
#define MAX_PACKET_SIZE 1500struct udp_client {struct sockaddr_in addr;time_t last_active;
};struct udp_server {struct event_base *base;int sockfd;struct event *ev;struct udp_client clients[MAX_CLIENTS];
};void udp_read_cb(evutil_socket_t fd, short events, void *arg) {struct udp_server *server = arg;char buf[MAX_PACKET_SIZE];struct sockaddr_in client_addr;socklen_t addr_len = sizeof(client_addr);ssize_t n = recvfrom(fd, buf, sizeof(buf), 0,(struct sockaddr*)&client_addr, &addr_len);if (n <= 0) return;// 查找或創建客戶端記錄struct udp_client *client = NULL;for (int i = 0; i < MAX_CLIENTS; i++) {if (memcmp(&server->clients[i].addr, &client_addr, addr_len) == 0) {client = &server->clients[i];break;}}if (!client) {// 查找空閑槽位for (int i = 0; i < MAX_CLIENTS; i++) {if (server->clients[i].last_active == 0) {client = &server->clients[i];memcpy(&client->addr, &client_addr, addr_len);break;}}}if (client) {client->last_active = time(NULL);// 業務處理printf("Received %zd bytes from %s:%d\n", n, inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));// 回顯sendto(fd, buf, n, 0, (struct sockaddr*)&client_addr, addr_len);} else {printf("Client limit reached, dropping packet\n");}
}struct udp_server* udp_server_create(int port) {struct udp_server *server = malloc(sizeof(struct udp_server));memset(server, 0, sizeof(*server));// 創建socketserver->sockfd = socket(AF_INET, SOCK_DGRAM, 0);if (server->sockfd < 0) {perror("socket");free(server);return NULL;}// 綁定地址struct sockaddr_in sin;memset(&sin, 0, sizeof(sin));sin.sin_family = AF_INET;sin.sin_port = htons(port);sin.sin_addr.s_addr = htonl(INADDR_ANY);if (bind(server->sockfd, (struct sockaddr*)&sin, sizeof(sin)) < 0) {perror("bind");close(server->sockfd);free(server);return NULL;}// 設置非阻塞evutil_make_socket_nonblocking(server->sockfd);// 創建事件基server->base = event_base_new();if (!server->base) {close(server->sockfd);free(server);return NULL;}// 創建事件server->ev = event_new(server->base, server->sockfd, EV_READ | EV_PERSIST, udp_read_cb, server);event_add(server->ev, NULL);return server;
}void udp_server_run(struct udp_server *server) {event_base_dispatch(server->base);
}void udp_server_free(struct udp_server *server) {if (!server) return;if (server->ev) event_free(server->ev);if (server->base) event_base_free(server->base);if (server->sockfd > 0) close(server->sockfd);free(server);
}int main() {struct udp_server *server = udp_server_create(8080);if (!server) return 1;printf("UDP server started on port 8080\n");udp_server_run(server);udp_server_free(server);return 0;
}

4. UDP 客戶器示例代碼 

#include <event2/event.h>
#include <event2/dns.h>
#include <event2/bufferevent.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>struct udp_client {struct event_base *base;struct evdns_base *dns;int sockfd;struct sockaddr_in server_addr;int connected;pthread_mutex_t lock;
};void udp_read_cb(evutil_socket_t fd, short events, void *arg) {struct udp_client *client = arg;char buf[1500];struct sockaddr_in from_addr;socklen_t addr_len = sizeof(from_addr);ssize_t n = recvfrom(fd, buf, sizeof(buf), 0,(struct sockaddr*)&from_addr, &addr_len);if (n > 0) {buf[n] = '\0';pthread_mutex_lock(&clie