通过openssl库实现https通信，代码样例

在使用 OpenSSL 库实现 HTTPS 连接时，通常涉及客户端发起 HTTPS 请求的场景。以下是一个简单的 C++ 示例，使用 OpenSSL 来发送 GET 请求到一个服务器：

#include <openssl/ssl.h>
#include <openssl/err.h>
#include <string>
#include <iostream>

int main(int argc, char* argv[]) {
    if (argc != 2) {
        std::cerr << "Usage: ./openssl_http_client URL" << std::endl;
        return 1;
    }

    const char* server_url = argv[1];
    SSL_library_init();
    SSL_load_error_strings();

    // 创建套接字和 SSL 对象
    int socket_fd = ::socket(AF_INET, SOCK_STREAM, 0);
    SSL_CTX *ctx = SSL_CTX_new(TLS_client_method());

    // 设置服务器地址
    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(443); // HTTPS默认端口
    inet_pton(AF_INET, server_url, &addr.sin_addr);

    // 打开连接并进行SSL握手
    connect(socket_fd, (struct sockaddr*)&addr, sizeof(addr));
    SSL *ssl = SSL_new(ctx);
    SSL_set_fd(ssl, socket_fd);
    SSL_connect(ssl);

    // 发送请求
    BIO *bio_ssl = BIO_new_socket(socket_fd, BIO_NOCLOSE);
    SSL_set_bio(ssl, bio_ssl, bio_ssl);
    BIO_set_write_buffer_size(bio_ssl, 8192); // 调整缓冲大小
    BIO_write(bio_ssl, "GET / HTTP/1.1\r\nHost: ", strlen("GET / HTTP/1.1\r\nHost: "));
    BIO_write(bio_ssl, server_url, strlen(server_url));
    BIO_write(bio_ssl, "\r\n", 2);

    // 接收响应
    char response[4096];
    int bytes_received = -1;
    while ((bytes_received = SSL_read(ssl, response, sizeof(response))) > 0) {
        std::cout.write(response, bytes_received);
    }
    if (bytes_received < 0) {
        ERR_print_errors_fp(stderr);
    }

    // 关闭连接
    SSL_shutdown(ssl);
    BIO_free_all(bio_ssl);
    SSL_free(ssl);
    SSL_CTX_free(ctx);
    close(socket_fd);

    return 0;
}