.net HttpWebRequest 模拟form提交

private static Stream GetPostStream(string filePath, NameValueCollection formData, string boundary)
        {
            Stream postDataStream = new System.IO.MemoryStream();

            //adding form data
            string formDataHeaderTemplate = Environment.NewLine + "--" + boundary + Environment.NewLine +
            "Content-Disposition: form-data; name=\"{0}\";" + Environment.NewLine + Environment.NewLine + "{1}";

            foreach (string key in formData.Keys)
            {
                byte[] formItemBytes = System.Text.Encoding.UTF8.GetBytes(string.Format(formDataHeaderTemplate,
                key, formData[key]));
                postDataStream.Write(formItemBytes, 0, formItemBytes.Length);
            }

            //adding file data
            FileInfo fileInfo = new FileInfo(filePath);

            string fileHeaderTemplate = Environment.NewLine + "--" + boundary + Environment.NewLine +
            "Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"" +
            Environment.NewLine + "Content-Type: image/jpeg" + Environment.NewLine + Environment.NewLine;

            byte[] fileHeaderBytes = System.Text.Encoding.UTF8.GetBytes(string.Format(fileHeaderTemplate,
            "UploadCSVFile", fileInfo.FullName));

            postDataStream.Write(fileHeaderBytes, 0, fileHeaderBytes.Length);

            FileStream fileStream = fileInfo.OpenRead();

            byte[] buffer = new byte[1024];

            int bytesRead = 0;

            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
            {
                postDataStream.Write(buffer, 0, bytesRead);
            }

            fileStream.Close();

            byte[] endBoundaryBytes = System.Text.Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");
            postDataStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);

            return postDataStream;
        }