HTTP POST请求发送图片

ESP32中有HTTP相关的请求demo，但是demo中只是简单的HTTP header加上body。如果服务器对POST请求有要求，比如数据以key-value的形式传输，那么服务器会无法正常处理请求，从而返回错误码500。

发送POST请求

基于esp_http_client中的post请求demo进行修改，其中传输的图片通过cmake转化成二进制文件，具体可以参考esp-idf中的esp_http_client demo。

void http_send_img(){

    char *post = (char *)malloc(1024+(http_jpeg_end-http_jpeg_start-1));
    memset(post,0,1024+(http_jpeg_end-http_jpeg_start-1));
    esp_http_client_config_t config = {
        .url = "url",
        .event_handler = _http_event_handler,      
        .method = HTTP_METHOD_POST,
    };
    esp_http_client_handle_t client = esp_http_client_init(&config);

    esp_http_client_set_header(client, "Content-Type", "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW");
    memcpy(post,"------WebKitFormBoundary7MA4YWxkTrZu0gW\r\nContent-Disposition: form-data; name=\"file\"; filename=\"img.jpeg\"\r\nContent-Type: image/jpeg\r\n\r\n",135);
    memcpy(post+135,http_jpeg_start,(http_jpeg_end-http_jpeg_start-1));
    memcpy(post+135+(http_jpeg_end-http_jpeg_start-1),"\r\n------WebKitFormBoundary7MA4YWxkTrZu0gW--\r\n",45);
    esp_http_client_set_post_field(client, post, 180+(http_jpeg_end-http_jpeg_start-1));
    esp_err_t err = esp_http_client_perform(client);
    if (err == ESP_OK) {
        ESP_LOGI(TAG, "HTTP POST Status = %d, content_length = %d",
                esp_http_client_get_status_code(client),
                esp_http_client_get_content_length(client));
    } else {
        ESP_LOGE(TAG, "HTTP POST request failed: %s", esp_err_to_name(err));
    }
    esp_http_client_cleanup(client);
    
}