如何基于标准mbed tls开发实现一个支持cipher suite name：TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256的mbed tls抽象层的设计？并给出示例代码

以下是基于mbed TLS的示例代码，实现了支持TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256的cipher suite name：

#include "mbedtls/config.h"
#include "mbedtls/ssl.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/error.h"
#include "mbedtls/net.h"

int main(void)
{
    mbedtls_entropy_context entropy;
    mbedtls_ctr_drbg_context ctr_drbg;
    mbedtls_ssl_context ssl;
    mbedtls_ssl_config conf;
    mbedtls_x509_crt cacert;
    mbedtls_x509_crt clicert;
    mbedtls_pk_context pkey;

    const char *pers = "mbedtls_ssl_client";

    mbedtls_entropy_init(&entropy);
    mbedtls_ctr_drbg_init(&ctr_drbg);
    mbedtls_ssl_init(&ssl);
    mbedtls_ssl_config_init(&conf);
    mbedtls_x509_crt_init(&cacert);
    mbedtls_x509_crt_init(&clicert);
    mbedtls_pk_init(&pkey);

    int ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy, (const unsigned char *)pers, strlen(pers));
    if (ret != 0) {
        mbedtls_printf("mbedtls_ctr_drbg_seed returned %d\n", ret);
        goto exit;
    }

    ret = mbedtls_x509_crt_parse_file(&cacert, "ca.crt");
    if (ret != 0) {
        mbedtls_printf("mbedtls_x509_crt_parse_file returned %d\n", ret);
        goto exit;
    }

    ret = mbedtls_x509_crt_parse_file(&clicert, "client.crt");
    if (ret != 0) {
        mbedtls_printf("mbedtls_x509_crt_parse_file returned %d\n", ret);
        goto exit;
    }

    ret = mbedtls_pk_parse_keyfile(&pkey, "client.key", NULL);
    if (ret != 0) {
        mbedtls_printf("mbedtls_pk_parse_keyfile returned %d\n", ret);
        goto exit;
    }

    ret = mbedtls_ssl_config_defaults(&conf, MBEDTLS_SSL_IS_CLIENT, MBEDTLS_SSL_TRANSPORT_STREAM, MBEDTLS_SSL_PRESET_DEFAULT);
    if (ret != 0) {
        mbedtls_printf("mbedtls_ssl_config_defaults returned %d\n", ret);
        goto exit;
    }

    mbedtls_ssl_conf_cipher_suites(&conf, MBEDTLS_TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, NULL);

    mbedtls_ssl_conf_ca_chain(&conf, &cacert, NULL);
    mbedtls_ssl_conf_own_cert(&conf, &clicert, &pkey);

    mbedtls_ssl_conf_rng(&conf, mbedtls_ctr_drbg_random, &ctr_drbg);

    ret = mbedtls_ssl_setup(&ssl, &conf);
    if (ret != 0) {
        mbedtls_printf("mbedtls_ssl_setup returned %d\n", ret);
        goto exit;
    }

    mbedtls_net_context server_fd;
    mbedtls_net_init(&server_fd);

    ret = mbedtls_net_connect(&server_fd, "localhost", "4433", MBEDTLS_NET_PROTO_TCP);
    if (ret != 0) {
        mbedtls_printf("mbedtls_net_connect returned %d\n", ret);
        goto exit;
    }

    mbedtls_ssl_set_bio(&ssl, &server_fd, mbedtls_net_send, mbedtls_net_recv, NULL);

    ret = mbedtls_ssl_handshake(&ssl);
    if (ret != 0) {
        mbedtls_printf("mbedtls_ssl_handshake returned %d\n", ret);
        goto exit;
    }

    mbedtls_ssl_close_notify(&ssl);

exit:
    mbedtls_x509_crt_free(&cacert);
    mbedtls_x509_crt_free(&clicert);
    mbedtls_pk_free(&pkey);
    mbedtls_ssl_free(&ssl);
    mbedtls_ssl_config_free(&conf);
    mbedtls_ctr_drbg_free(&ctr_drbg);
    mbedtls_entropy_free(&entropy);
    mbedtls_net_free(&server_fd);

    return ret;
}

在这个示例代码中，我们使用了`mbedtls_ssl_conf_cipher_suites`函数来指定了使用TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256这个cipher suite name。同时，我们还需要使用相应的证书和密钥来进行TLS连接。在示例代码中，我们假设ca.crt、client.crt和client.key文件都已经准备好了，可以通过`mbedtls_x509_crt_parse_file`和`mbedtls_pk_parse_keyfile`函数来解析这些文件。

值得注意的是，在实际使用过程中，我们需要根据具体的需求和场景来选择合适的cipher suite name，并且需要保证相应的证书和密钥的安全性。此外，我们还需要注意使用mbed TLS时的安全最佳实践，例如启用合适的加密套件、密钥长度和证书验证等。