winform上传文件，利用http，form-data格式上传

/// <summary>
/// 上传文件
/// </summary>
/// <param name="url">服务地址</param>
/// <param name="filePath">文件路径</param>
public static string DoPostFile(string url, string filePath)
{
string fileName = Path.GetFileName(filePath);

// 边界符
var boundary = "---------------" + DateTime.Now.Ticks.ToString("x");
var beginBoundary = Encoding.ASCII.GetBytes("--" + boundary + " ");
var fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);

// 最后的结束符
var endBoundary = Encoding.ASCII.GetBytes("--" + boundary + "-- ");

// 文件参数头
const string filePartHeader =
"Content-Disposition: form-data; name="{0}"; filename="{1}" " +
"Content-Type: application/octet-stream ";
var fileHeader = string.Format(filePartHeader, "file", fileName);
var fileHeaderBytes = Encoding.UTF8.GetBytes(fileHeader);

// 开始拼数据
var memStream = new MemoryStream();
memStream.Write(beginBoundary, 0, beginBoundary.Length);

// 文件数据
memStream.Write(fileHeaderBytes, 0, fileHeaderBytes.Length);
var buffer = new byte[1024];
int bytesRead; // =0
while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
{
memStream.Write(buffer, 0, bytesRead);
}
fileStream.Close();

// 写入字符串
var keyValue = "Content-Disposition: form-data; name="{0}" {1} ";
Dictionary<string, string> stringDict = new Dictionary<string, string>();
stringDict.Add("len", "500");
stringDict.Add("wid", "300");
foreach (string key in stringDict.Keys)
{
var keyValueBytes = Encoding.UTF8.GetBytes(string.Format(keyValue, key, stringDict[key]));
memStream.Write(beginBoundary, 0, beginBoundary.Length);
memStream.Write(keyValueBytes, 0, keyValueBytes.Length);
}

// 写入最后的结束边界符
memStream.Write(endBoundary, 0, endBoundary.Length);

//倒腾到tempBuffer
memStream.Position = 0;
var tempBuffer = new byte[memStream.Length];
memStream.Read(tempBuffer, 0, tempBuffer.Length);
memStream.Close();

// 创建webRequest并设置属性
HttpWebRequest webRequest = (HttpWebRequest)HttpWebRequest.Create(url);
//添加请求头
AddHttpHeader(webRequest);
webRequest.Method = "POST";
webRequest.Timeout = 100000;
webRequest.ContentType = "multipart/form-data; boundary=" + boundary;
webRequest.ContentLength = tempBuffer.Length;
webRequest.KeepAlive = false;
webRequest.ProtocolVersion = HttpVersion.Version10;

var requestStream = webRequest.GetRequestStream();
requestStream.Write(tempBuffer, 0, tempBuffer.Length);
requestStream.Close();

var httpWebResponse = (HttpWebResponse)webRequest.GetResponse();
string responseContent;
using (var httpStreamReader = new StreamReader(httpWebResponse.GetResponseStream(), Encoding.GetEncoding("utf-8")))
{
responseContent = httpStreamReader.ReadToEnd();
}

httpWebResponse.Close();
webRequest.Abort();
return responseContent;
}