Libevent UDP开发指南
UDP 与 TCP 的核心区别
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无连接：不需要建立/维护连接
-
不可靠：不保证数据包顺序和到达
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高效：头部开销小，没有连接管理负担
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支持广播/多播：可以向多个目标同时发送数据
一、基础UDP服务器实现
1. 创建 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;
}
// 设置非阻塞
evutil_make_socket_nonblocking(fd);
return fd;
}2. UDP 事件处理
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]; // 标准MTU大小
ssize_t n;
while ((n = recvfrom(fd, buf, sizeof(buf), 0,
(struct sockaddr*)&client_addr, &addr_len)) > 0) {
// 处理接收到的数据
printf("Received %zd bytes from %s:%d\n",
n, inet_ntoa(client_addr.sin_addr),
ntohs(client_addr.sin_port));
// 简单回显
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 服务器示例代码
#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 1500
struct 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;
// 查找或创建客户端记录
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) {
// 查找空闲槽位
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);
// 业务处理
printf("Received %zd bytes from %s:%d\n",
n, inet_ntoa(client_addr.sin_addr),
ntohs(client_addr.sin_port));
// 回显
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));
// 创建socket
server->sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (server->sockfd < 0) {
perror("socket");
free(server);
return NULL;
}
// 绑定地址
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;
}
// 设置非阻塞
evutil_make_socket_nonblocking(server->sockfd);
// 创建事件基
server->base = event_base_new();
if (!server->base) {
close(server->sockfd);
free(server);
return NULL;
}
// 创建事件
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 客户器示例代码
#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