练习：

将 epoll 服务器 客户端拿来用
客户端：写一个界面，里面有注册登录
服务器：处理注册和登录逻辑，注册的话将注册的账号密码写入数据库，登录的话查询数据库中是否存在账号，并验证密码是否正确
额外功能：客户端登录的时候，服务器向客户端发送一个验证码，只有验证码也正确的时候，才能登录成功·     

server.c 

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <sys/epoll.h>
#include <sqlite3.h>
#include <errno.h>
#include <time.h>#define MAX_EVENTS 100typedef struct sockaddr_in addr_in_t;
typedef struct sockaddr addr_t;enum Type {TYPE_REGIST,TYPE_LOGIN,TYPE_CHAT
};typedef struct Pack {enum Type type;char name[20];char pswd[20];char tarname[20];char text[1024];
} pack_t;sqlite3 *db;  // 数据库指针// 生成验证码
void generate_code(char *code, int length) {const char charset[] = "0123456789";srand(time(NULL));for (int i = 0; i < length; i++) {code[i] = charset[rand() % 10];}code[length] = '\0';
}// 设置文件描述符非阻塞模式
void set_nonblocking(int fd) {int flags = fcntl(fd, F_GETFL, 0);fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}// 处理客户端请求
void handle_client(int client) {pack_t pack = {0};int res = read(client, &pack, sizeof(pack));if (res <= 0) {printf("客户端断开连接\n");close(client);return;}char sql[256];char *errmsg = NULL;switch (pack.type) {case TYPE_REGIST:snprintf(sql, sizeof(sql), "INSERT INTO users (name, password) VALUES ('%s', '%s');", pack.name, pack.pswd);if (sqlite3_exec(db, sql, 0, 0, &errmsg) != SQLITE_OK) {printf("注册失败: %s\n", errmsg);strcpy(pack.text, "注册失败，该账号可能已存在！");sqlite3_free(errmsg);} else {strcpy(pack.text, "注册成功！");}write(client, &pack, sizeof(pack));break;case TYPE_LOGIN: {snprintf(sql, sizeof(sql), "SELECT password FROM users WHERE name = '%s';", pack.name);sqlite3_stmt *stmt;if (sqlite3_prepare_v2(db, sql, -1, &stmt, 0) == SQLITE_OK) {if (sqlite3_step(stmt) == SQLITE_ROW) {const char *db_pswd = (const char*)sqlite3_column_text(stmt, 0);if (strcmp(db_pswd, pack.pswd) == 0) {char code[6];generate_code(code, 5);snprintf(pack.text, sizeof(pack.text), "验证码：%s\n", code);write(client, &pack, sizeof(pack));// 等待客户端输入验证码read(client, &pack, sizeof(pack));if (strcmp(pack.text, code) == 0) {strcpy(pack.text, "登录成功！");} else {strcpy(pack.text, "验证码错误，登录失败！");}} else {strcpy(pack.text, "密码错误！");}} else {strcpy(pack.text, "账号不存在！");}sqlite3_finalize(stmt);}write(client, &pack, sizeof(pack));break;}case TYPE_CHAT:printf("收到消息: %s\n", pack.text);break;}
}int main(int argc, const char *argv[]) {if (argc != 2) {printf("请输入端口号\n");return 1;}int port = atoi(argv[1]);// 初始化数据库if (sqlite3_open("users.db", &db) != SQLITE_OK) {printf("无法打开数据库\n");return 1;}const char *create_table_sql = "CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY KEY, name TEXT UNIQUE, password TEXT);";char *errmsg = NULL;if (sqlite3_exec(db, create_table_sql, 0, 0, &errmsg) != SQLITE_OK) {printf("创建表失败: %s\n", errmsg);sqlite3_free(errmsg);return 1;}// 创建服务器 socketint server = socket(AF_INET, SOCK_STREAM, 0);addr_in_t addr = {0};addr.sin_family = AF_INET;addr.sin_port = htons(port);addr.sin_addr.s_addr = INADDR_ANY;bind(server, (addr_t*)&addr, sizeof(addr));listen(server, 10);// 设置非阻塞模式set_nonblocking(server);// 创建 epollint epoll_fd = epoll_create1(0);struct epoll_event ev, events[MAX_EVENTS];ev.events = EPOLLIN;ev.data.fd = server;epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server, &ev);printf("服务器启动，监听端口 %d...\n", port);while (1) {int n = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);for (int i = 0; i < n; i++) {if (events[i].data.fd == server) {// 处理新连接int client = accept(server, NULL, NULL);if (client < 0) {perror("accept");continue;}set_nonblocking(client);ev.events = EPOLLIN | EPOLLET;ev.data.fd = client;epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client, &ev);printf("新客户端连接: %d\n", client);} else {// 处理客户端请求handle_client(events[i].data.fd);}}}sqlite3_close(db);close(server);return 0;
}

client.c

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>typedef struct sockaddr_in addr_in_t;
typedef struct sockaddr addr_t;enum Type {TYPE_REGIST,TYPE_LOGIN,TYPE_CHAT
};typedef struct Pack {enum Type type;char name[20];char pswd[20];char tarname[20];char text[1024];
} pack_t;void handle_response(int client) {pack_t pack;int res = read(client, &pack, sizeof(pack));if (res > 0) {printf("服务器: %s\n", pack.text);}
}int main(int argc, const char *argv[]) {if (argc != 2) {printf("输入端口号\n");return 1;}int port = atoi(argv[1]);int client = socket(AF_INET, SOCK_STREAM, 0);addr_in_t addr = {0};addr.sin_family = AF_INET;addr.sin_port = htons(port);addr.sin_addr.s_addr = inet_addr("192.168.126.245");if (connect(client, (addr_t*)&addr, sizeof(addr)) == -1) {perror("连接失败");return 1;}printf("连接服务器成功！\n");while (1) {int ch;printf("1: 注册\n2: 登录\n3: 聊天\n0: 退出\n请选择: ");scanf("%d", &ch);while (getchar() != '\n');pack_t pack = {0};switch (ch) {case 1:printf("输入账号: ");scanf("%s", pack.name);while (getchar() != '\n');printf("输入密码: ");scanf("%s", pack.pswd);while (getchar() != '\n');pack.type = TYPE_REGIST;write(client, &pack, sizeof(pack));handle_response(client);break;case 2:printf("输入账号: ");scanf("%s", pack.name);while (getchar() != '\n');printf("输入密码: ");scanf("%s", pack.pswd);while (getchar() != '\n');pack.type = TYPE_LOGIN;write(client, &pack, sizeof(pack));handle_response(client); // 服务器发送验证码printf("输入验证码: ");scanf("%s", pack.text);while (getchar() != '\n');write(client, &pack, sizeof(pack));handle_response(client); // 登录成功 or 失败break;case 3:printf("输入聊天对象: ");scanf("%s", pack.tarname);while (getchar() != '\n');printf("输入消息: ");fgets(pack.text, sizeof(pack.text), stdin);pack.text[strcspn(pack.text, "\n")] = '\0'; // 去除换行符pack.type = TYPE_CHAT;write(client, &pack, sizeof(pack));handle_response(client);break;case 0:close(client);return 0;default:printf("无效选项\n");}}return 0;
}