基于mbedtls编写一个建立tls连接并且发送一段测试数据的例子。

以下是一个基于mbedtls的建立TLS连接并发送测试数据的示例代码。请注意，此示例代码仅供参考，实际使用时应根据具体需求进行修改和完善。

#include "mbedtls/net_sockets.h"
#include "mbedtls/ssl.h"
#include "mbedtls/error.h"

#include <stdio.h>
#include <string.h>

#define SERVER_NAME "www.example.com"
#define SERVER_PORT "443"
#define TEST_DATA "Hello, TLS!"

int main(void)
{
    int ret;
    mbedtls_net_context server_fd;
    mbedtls_ssl_context ssl;
    mbedtls_ssl_config conf;
    unsigned char buf[1024];
    size_t len;

    mbedtls_net_init(&server_fd);
    mbedtls_ssl_init(&ssl);
    mbedtls_ssl_config_init(&conf);

    // 1. 连接服务器
    ret = mbedtls_net_connect(&server_fd, SERVER_NAME, SERVER_PORT, MBEDTLS_NET_PROTO_TCP);
    if (ret != 0) {
        printf("Failed to connect to %s:%s, returned %d\n", SERVER_NAME, SERVER_PORT, ret);
        goto exit;
    }

    // 2. 初始化SSL/TLS配置
    ret = mbedtls_ssl_config_defaults(&conf, MBEDTLS_SSL_IS_CLIENT, MBEDTLS_SSL_TRANSPORT_STREAM, MBEDTLS_SSL_PRESET_DEFAULT);
    if (ret != 0) {
        printf("Failed to set SSL/TLS defaults, returned %d\n", ret);
        goto exit;
    }
    mbedtls_ssl_conf_authmode(&conf, MBEDTLS_SSL_VERIFY_NONE); // 禁用证书验证

    // 3. 配置SSL/TLS上下文并绑定socket
    ret = mbedtls_ssl_setup(&ssl, &conf);
    if (ret != 0) {
        printf("Failed to set up SSL/TLS context, returned %d\n", ret);
        goto exit;
    }
    mbedtls_ssl_set_bio(&ssl, &server_fd, mbedtls_net_send, mbedtls_net_recv, NULL);

    // 4. 建立TLS连接
    do {
        ret = mbedtls_ssl_handshake(&ssl);
    } while (ret == MBEDTLS_ERR_SSL_WANT_READ || ret == MBEDTLS_ERR_SSL_WANT_WRITE);
    if (ret != 0) {
        printf("Failed to perform TLS handshake, returned %d\n", ret);
        mbedtls_strerror(ret, (char *)buf, sizeof(buf));
        printf("Last error was: %s\n", buf);
        goto exit;
    }

    // 5. 发送测试数据
    len = strlen(TEST_DATA);
    ret = mbedtls_ssl_write(&ssl, (const unsigned char *)TEST_DATA, len);
    if (ret != len) {
        printf("Failed to send test data, returned %d\n", ret);
        goto exit;
    }

    // 6. 关闭TLS连接
    do {
        ret = mbedtls_ssl_close_notify(&ssl);
    } while (ret == MBEDTLS_ERR_SSL_WANT_WRITE);
    if (ret != 0) {
        printf("Failed to close TLS connection, returned %d\n", ret);
        goto exit;
    }

    printf("TLS connection closed successfully.\n");

exit:
    mbedtls_ssl_session_reset(&ssl);
    mbedtls_net_free(&server_fd);
    mbedtls_ssl_free(&ssl);
    mbedtls_ssl_config_free(&conf);

    return ret;
}