.net webclient上传文件

声明webclient对象，添加header。上传文件的content-type需指定multipart/form-data，multipart为多文件，boundary为分割符可以为任意字符串

WebClient webClient = new WebClient();
  webClient.Headers.Add("content-type", "multipart/form-data; boundary=" + boundary);
	webClient.Headers.Add("Accept", "*/*");
	webClient.Headers.Add("User-Agent", "PostmanRuntime/7.4.0");

添加上传数据，每个boundary前需要加上--，最后一个boundary前后都需要加入--。

try
{
   string ContentType = "Content-Disposition: form-data; name=\"FileName\"; filename=\"{0}\"\r\nContent-Type: application/xml\r\n\r\n";
   byte[] headByte = Encoding.UTF8.GetBytes("\r\n--" + boundary + "\r\n"); //头数据
   byte[] typeByte = Encoding.UTF8.GetBytes(string.Format(ContentType, fileName)); // ContentType 数据
   byte[] endBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n"); //尾数据
	
   FileStream fs = new FileStream(filePath, FileMode.Open,
                    FileAccess.Read, FileShare.Read);
   byte[] fileBytes = new byte[fs.Length]; // 文件的二进制数据
   fs.Read(fileBytes, 0, Convert.ToInt32(fs.Length));

   // 合成后的数组
   byte[] fieldData = new byte[fileBytes.Length + headByte.Length + endBytes.Length + typeByte.Length];
   headByte.CopyTo(fieldData, 0);
   typeByte.CopyTo(fieldData, headByte.Length);
   fileBytes.CopyTo(fieldData, headByte.Length + typeByte.Length);
   endBytes.CopyTo(fieldData, headByte.Length + fileBytes.Length + typeByte.Length);
   
 }

组装好的数据最终调用UploadData上传

responseBytes = webClient.UploadData(uploadUrl, fieldData);