//上传图片 isPermanentImage=true表示永久素材  filePath为http地址，如果本地文件的自行读取
   //isPermanentImage 表示是否是永久素材

    private async Task<string> UploadImageAsync(string accessToken, string filePath, bool isPermanentImage)
    {
        var http = new HttpClient();//net core中改为通过IHttpClientFactory.CreateClient()实现
        string url;
        if (isPermanentImage){
           //封装图片
            url = $"https://api.weixin.qq.com/cgi-bin/material/add_material?access_token={accessToken}&type=image";
        }
        else{
            //文章内容中的图片
            url = $"https://api.weixin.qq.com/cgi-bin/media/uploadimg?access_token={accessToken}&type=image";
        }
        string boundary = "Upload----" + DateTime.Now.Ticks.ToString("x");
        string fileName = System.IO.Path.GetFileName(filePath);
        var fileData = await http.GetByteArrayAsync(filePath);
        using var ms = new MemoryStream();

        // 1. 写入 boundary
        byte[] boundaryBytes = Encoding.UTF8.GetBytes($"--{boundary}\r\n");
        ms.Write(boundaryBytes, 0, boundaryBytes.Length);

        // 2. 写入媒体文件描述头
        string header =$"Content-Disposition: form-data; name=\"media\"; filename=\"{fileName}\"\r\n" +
        $"Content-Type: {GetMime(fileName)}\r\n\r\n";

        byte[] headerBytes = Encoding.UTF8.GetBytes(header);
        ms.Write(headerBytes, 0, headerBytes.Length);

        // 3. 写入文件内容
        ms.Write(fileData, 0, fileData.Length);

        // 4. 写入结束 boundary
        byte[] endBytes = Encoding.UTF8.GetBytes($"\r\n--{boundary}--\r\n");
        ms.Write(endBytes, 0, endBytes.Length);

        ms.Position = 0;

        // 发送请求
        using HttpClient client = new HttpClient();
        HttpContent content = new StreamContent(ms);
        content.Headers.ContentType = MediaTypeHeaderValue.Parse($"multipart/form-data; boundary={boundary}");

        var response = await client.PostAsync(url, content);
        string json = await response.Content.ReadAsStringAsync();
        Console.WriteLine(json);
        if (isPermanentImage)
        {
            return Newtonsoft.Json.Linq.JObject.Parse(json)["media_id"]?.ToString();
        }
        else
        {
            return Newtonsoft.Json.Linq.JObject.Parse(json)["url"]?.ToString();
        }

    }