https client libevent

你可以使用libevent来实现一个基于HTTPS的客户端。libevent是一个开源的事件驱动库，支持多种网络协议和I/O模型。下面是一个简单的示例代码，演示如何使用libevent创建一个HTTPS客户端：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <event2/event.h>
#include <event2/bufferevent_ssl.h>
#include <openssl/ssl.h>

void read_cb(struct bufferevent* bev, void* arg) {
    char buf[1024];
    int n;
    while ((n = bufferevent_read(bev, buf, sizeof(buf) - 1)) > 0) {
        buf[n] = '\0';
        printf("Received: %s\n", buf);
    }
}

void event_cb(struct bufferevent* bev, short events, void* arg) {
    if (events & BEV_EVENT_CONNECTED) {
        printf("Connected to server.\n");

        const char* request = "GET / HTTP/1.1\r\n"
                              "Host: www.example.com\r\n"
                              "Connection: close\r\n\r\n";
        bufferevent_write(bev, request, strlen(request));
    } else if (events & BEV_EVENT_ERROR) {
        printf("Error: %s\n", strerror(errno));
    } else if (events & BEV_EVENT_EOF) {
        printf("Connection closed.\n");
    }

    bufferevent_free(bev);
}

int main() {
    struct event_base* base;
    struct bufferevent* bev;
    SSL_CTX* ssl_ctx;

    SSL_library_init();
    SSL_load_error_strings();
    ssl_ctx = SSL_CTX_new(SSLv23_client_method());

    base = event_base_new();
    bev = bufferevent_socket_new(base, -1, BEV_OPT_CLOSE_ON_FREE);
    bufferevent_setcb(bev, read_cb, NULL, event_cb, NULL);
    bufferevent_enable(bev, EV_READ | EV_WRITE);

    bufferevent_openssl_set_allow_dirty_shutdown(bev, 1);
    bufferevent_openssl_set_ssl(bev, ssl_ctx, SSL_new(ssl_ctx), BUFFEREVENT_SSL_CONNECTING, BEV_OPT_CLOSE_ON_FREE);

    struct sockaddr_in sin;
    memset(&sin, 0, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = htonl(0x7f000001);  // 127.0.0.1
    sin.sin_port = htons(443);  // HTTPS default port

    if (bufferevent_socket_connect(bev, (struct sockaddr*)&sin, sizeof(sin)) < 0) {
        printf("Error starting connection.\n");
        return 1;
    }

    event_base_dispatch(base);

    SSL_CTX_free(ssl_ctx);
    event_base_free(base);

    return 0;
}

这段代码使用libevent创建了一个基于SSL的客户端，并发送了一个简单的HTTP GET请求。你可以根据你的需求进行修改和扩展。注意，你需要在编译时链接libevent和OpenSSL库。