你好，

详情请参考：https://developers.weixin.qq.com/doc/offiaccount/Getting_Started/Global_Return_Code.html

使用HttpWebRequest 发送请求成功，代码如下

HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;

                CookieContainer cookieContainer = new CookieContainer();

                request.CookieContainer = cookieContainer;

                request.AllowAutoRedirect = true;

                request.Method = "POST";

                string boundary = DateTime.Now.Ticks.ToString("X");

                request.ContentType = "multipart/form-data;charset=utf-8;boundary=" + boundary;

                byte[] itemBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "\r\n");

                byte[] endBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");

                int pos = path.LastIndexOf("\\");

                string fileName = path.Substring(pos + 1);

                StringBuilder sbHeader = new StringBuilder(string.Format("Content-Disposition:form-data;name=\"" + formName + "\";filename=\"{0}\"\r\nContent-Type:application/octet-stream\r\n\r\n", fileName));

                byte[] postHeaderBytes = Encoding.UTF8.GetBytes(sbHeader.ToString());

                FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read);

                byte[] bArr = new byte[fs.Length];

                fs.Read(bArr, 0, bArr.Length);

                fs.Close();

                Stream postStream = request.GetRequestStream();

                postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);

                postStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);

                postStream.Write(bArr, 0, bArr.Length);

                byte[] bSplit = Encoding.UTF8.GetBytes("--" + boundary + "\r\n");

                postStream.Write(bSplit, 0, bSplit.Length);

                if (!string.IsNullOrEmpty(additionInfo))

                {

                    byte[] additionBytes = Encoding.UTF8.GetBytes("Content-Disposition: form-data; name=\"description\";\r\n\r\n");

                    postStream.Write(additionBytes, 0, additionBytes.Length);

                    byte[] additionContentBytes = Encoding.UTF8.GetBytes(additionInfo);

                    postStream.Write(additionContentBytes, 0, additionContentBytes.Length);

                    postStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);

                }

                postStream.Close();

                HttpWebResponse response = request.GetResponse() as HttpWebResponse;

                Stream instream = response.GetResponseStream();

                StreamReader sr = new StreamReader(instream, Encoding.UTF8);

                content = sr.ReadToEnd();

但是使用HttpClient就一直提示41005，代码如下

            using (var client = _clientFactory.CreateClient())

            {

                var file = new FileInfo(filePath);

    byte[] buffur = File.ReadAllBytes(filePath);

                using (var formData = new MultipartFormDataContent())

                {

                    ByteArrayContent fileContent = new ByteArrayContent(buffur);

    fileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data") { Name = formName, FileName = file.Name };

    formData.Add(fileContent);

                    var response = await client.PostAsync(url, formData);

                    if (response.IsSuccessStatusCode)

                    {

                        var result = await response.Content.ReadAsStringAsync();

                        return result;

                    }

                    else

                    {

                        throw new BadHttpResponseException(url, response.StatusCode);

                    }

                }

            }

对比了一下貌似区别在换行符上"\r\n",但是封装好的HttpClient又不知道如何添加相应的换行符。

不知道这个是不是根本原因。