用mbedtls 发送multipart/form-data post{ "did": "string", "productToken": "string", "state": 0 }

mbedtls是一个轻量级的加密库，主要提供了TLS/SSL协议实现和加密算法的实现。它并不直接提供发送HTTP请求的功能，但可以结合其他HTTP库（如libcurl）来发送HTTP请求。

对于multipart/form-data格式的POST请求，需要在请求头中指定Content-Type为multipart/form-data，并在请求体中按照格式组织数据。具体实现方法可以参考下面的示例代码：

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

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

#define HOSTNAME "example.com"
#define PORT "443"
#define REQUEST_BODY "--boundary\r\nContent-Disposition: form-data; name=\"did\"\r\n\r\nstring\r\n--boundary\r\nContent-Disposition: form-data; name=\"productToken\"\r\n\r\nstring\r\n--boundary\r\nContent-Disposition: form-data; name=\"state\"\r\n\r\n0\r\n--boundary--\r\n"

int main()
{
    int ret;
    mbedtls_net_context server_fd;
    mbedtls_ssl_context ssl;
    mbedtls_ssl_config conf;
    mbedtls_x509_crt cacert;

    mbedtls_net_init(&server_fd);
    mbedtls_ssl_init(&ssl);
    mbedtls_ssl_config_init(&conf);
    mbedtls_x509_crt_init(&cacert);

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

    ret = mbedtls_net_connect(&server_fd, HOSTNAME, PORT, MBEDTLS_NET_PROTO_TCP);
    if (ret != 0) {
        printf("failed to connect, ret=%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) {
        printf("failed to set ssl config defaults, ret=%d\n", ret);
        goto exit;
    }

    mbedtls_ssl_conf_authmode(&conf, MBEDTLS_SSL_VERIFY_REQUIRED);
    mbedtls_ssl_conf_ca_chain(&conf, &cacert, NULL);
    mbedtls_ssl_conf_rng(&conf, mbedtls_ctr_drbg_random, &ctr_drbg);

    ret = mbedtls_ssl_setup(&ssl, &conf);
    if (ret != 0) {
        printf("failed to setup ssl, ret=%d\n", ret);
        goto exit;
    }

    mbedtls_ssl_set_hostname(&ssl, HOSTNAME);

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

    while ((ret = mbedtls_ssl_handshake(&ssl)) != 0) {
        if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
            printf("failed to handshake with server, ret=%d\n", ret);
            goto exit;
        }
    }

    printf("handshake success!\n");

    // send POST request
    const char *request_fmt =
        "POST /api/v1/device/bind HTTP/1.1\r\n"
        "Host: %s:%s\r\n"
        "Content-Type: multipart/form-data; boundary=boundary\r\n"
        "Content-Length: %d\r\n\r\n%s";

    char request_buf[4096];
    int request_len = snprintf(request_buf, sizeof(request_buf), request_fmt, HOSTNAME, PORT, strlen(REQUEST_BODY), REQUEST_BODY);

    while ((ret = mbedtls_ssl_write(&ssl, (const unsigned char *)request_buf, request_len)) <= 0) {
        if (ret == MBEDTLS_ERR_SSL_WANT_READ || ret == MBEDTLS_ERR_SSL_WANT_WRITE) {
            continue;
        }
        printf("failed to write data to server, ret=%d\n", ret);
        goto exit;
    }

exit:
    mbedtls_x509_crt_free(&cacert);
    mbedtls_ssl_free(&ssl);
    mbedtls_ssl_config_free(&conf);
    mbedtls_net_free(&server_fd);

    return 0;
}

相关问题：
1. 如何使用mbedtls发送HTTP请求？
2. multipart/form-data格式的POST请求具体怎么组织数据？
3. 如何解析HTTP响应？