c# 模拟表单提交，post form 上传文件、大数据内容

表单提交协议规定：

要先将 HTTP 要求的 Content-Type 设为 multipart/form-data，而且要设定一个 boundary 参数，

这个参数是由应用程序自行产生，它会用来识别每一份资料的边界 (boundary)，

用以产生多重信息部份 (message part)。

而 HTTP 服务器可以抓取 HTTP POST 的信息，

基本内容：

1. 每个信息部份都要用 --[BOUNDARY_NAME] 来包装，以分隔出信息的每个部份，而最后要再加上一个 --[BOUNDARY_NAME] 来表示结束。

2. 每个信息部份都要有一个 Content-Disposition: form-data; name=""，而 name 设定的就是 HTTP POST 的键值 (key)。

3. 声明区和值区中间要隔两个新行符号（\r\n）。

4. 中间可以夹入二进制资料，但二进制资料必须要格式化为二进制字符串。

5. 若要设定不同信息段的资料型别 (Content-Type)，则要在信息段内的声明区设定。

两个form内容模板

boundary = "----" + DateTime.Now.Ticks.ToString("x");//程序生成

1.文本内容

"\r\n--" + boundary +

"\r\nContent-Disposition: form-data; name=\"键\"; filename=\"文件名\"" +

"\r\nContent-Type: application/octet-stream" +

"\r\n\r\n";

2.文件内容

"\r\n--" + boundary +

"\r\nContent-Disposition: form-data; name=\"键\"" +

"\r\n\r\n内容";

代码
1.表示一个表单项的对象

/// <summary>
/// 表单数据项
/// </summary>
public class FormItemModel
{
  /// <summary>
  /// 表单键，request["key"]
  /// </summary>
  public string Key { set; get; }
  /// <summary>
  /// 表单值,上传文件时忽略，request["key"].value
  /// </summary>
  public string Value { set; get; }
  /// <summary>
  /// 是否是文件
  /// </summary>
  public bool IsFile
  {
    get
    {
      if (FileContent==null || FileContent.Length == 0)
        return false;

      if (FileContent != null && FileContent.Length > 0 && string.IsNullOrWhiteSpace(FileName))
        throw new Exception("上传文件时 FileName 属性值不能为空");
      return true;
    }
  }
  /// <summary>
  /// 上传的文件名
  /// </summary>
  public string FileName { set; get; }
  /// <summary>
  /// 上传的文件内容
  /// </summary>
  public Stream FileContent { set; get; }
}

2.提交表单主逻辑实现

/// <summary>
/// 使用Post方法获取字符串结果
/// </summary>
/// <param name="url"></param>
/// <param name="formItems">Post表单内容</param>
/// <param name="cookieContainer"></param>
/// <param name="timeOut">默认20秒</param>
/// <param name="encoding">响应内容的编码类型（默认utf-8）</param>
/// <returns></returns>
public static string PostForm(string url, List<FormItemModel> formItems, CookieContainer cookieContainer = null, string refererUrl = null, Encoding encoding = null,int timeOut = 20000)
{
  HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
  #region 初始化请求对象
  request.Method = "POST";
  request.Timeout = timeOut;
  request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
  request.KeepAlive = true;
  request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36";
  if (!string.IsNullOrEmpty(refererUrl))
    request.Referer = refererUrl;
  if (cookieContainer != null)
    request.CookieContainer = cookieContainer;
  #endregion

  string boundary = "----" + DateTime.Now.Ticks.ToString("x");//分隔符
  request.ContentType = string.Format("multipart/form-data; boundary={0}", boundary);
  //请求流
  var postStream = new MemoryStream();
  #region 处理Form表单请求内容
  //是否用Form上传文件
  var formUploadFile = formItems != null && formItems.Count > 0;
  if (formUploadFile)
  {
    //文件数据模板
    string fileFormdataTemplate =
      "\r\n--" + boundary +
      "\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"" +
      "\r\nContent-Type: application/octet-stream" +
      "\r\n\r\n";
    //文本数据模板
    string dataFormdataTemplate =
      "\r\n--" + boundary +
      "\r\nContent-Disposition: form-data; name=\"{0}\"" +
      "\r\n\r\n{1}";
    foreach (var item in formItems)
    {
      string formdata = null;
      if (item.IsFile)
      {
        //上传文件
        formdata = string.Format(
          fileFormdataTemplate,
          item.Key, //表单键
          item.FileName);
      }
      else
      {
        //上传文本
        formdata = string.Format(
          dataFormdataTemplate,
          item.Key,
          item.Value);
      }

      //统一处理
      byte[] formdataBytes = null;
      //第一行不需要换行
      if (postStream.Length == 0)
        formdataBytes = Encoding.UTF8.GetBytes(formdata.Substring(2, formdata.Length - 2));
      else
        formdataBytes = Encoding.UTF8.GetBytes(formdata);
      postStream.Write(formdataBytes, 0, formdataBytes.Length);

      //写入文件内容
      if (item.FileContent != null && item.FileContent.Length>0)
      {
        using (var stream = item.FileContent)
        {
          byte[] buffer = new byte[1024];
          int bytesRead = 0;
          while ((bytesRead = stream.Read(buffer, 0, buffer.Length)) != 0)
          {
            postStream.Write(buffer, 0, bytesRead);
          }
        }
      }
    }
    //结尾
    var footer = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");
    postStream.Write(footer, 0, footer.Length);

  }
  else
  {
    request.ContentType = "application/x-www-form-urlencoded";
  }
  #endregion

  request.ContentLength = postStream.Length;

  #region 输入二进制流
  if (postStream != null)
  {
    postStream.Position = 0;
    //直接写入流
    Stream requestStream = request.GetRequestStream();

    byte[] buffer = new byte[1024];
    int bytesRead = 0;
    while ((bytesRead = postStream.Read(buffer, 0, buffer.Length)) != 0)
    {
      requestStream.Write(buffer, 0, bytesRead);
    }

    debug
    //postStream.Seek(0, SeekOrigin.Begin);
    //StreamReader sr = new StreamReader(postStream);
    //var postStr = sr.ReadToEnd();
    postStream.Close();//关闭文件访问
  }
  #endregion

  HttpWebResponse response = (HttpWebResponse)request.GetResponse();
  if (cookieContainer != null)
  {
    response.Cookies = cookieContainer.GetCookies(response.ResponseUri);
  }

  using (Stream responseStream = response.GetResponseStream())
  {
    using (StreamReader myStreamReader = new StreamReader(responseStream, encoding ?? Encoding.UTF8))
    {
      string retString = myStreamReader.ReadToEnd();
      return retString;
    }
  }
}

3.调用模拟post表单

var url = "http://127.0.0.1/testformdata.aspx?aa=1&bb=2&ccc=3";
var log1=@"D:\temp\log1.txt";
var log2 = @"D:\temp\log2.txt";
var formDatas = new List<Grass.Net.FormItemModel>();
//添加文件
formDatas.Add(new Grass.Net.FormItemModel()
{
  Key="log1",
  Value="",
  FileName = "log1.txt",
  FileContent=File.OpenRead(log1)
});
formDatas.Add(new Grass.Net.FormItemModel()
{
  Key = "log2",
  Value = "",
  FileName = "log2.txt",
  FileContent = File.OpenRead(log2)
});
//添加文本
formDatas.Add(new Grass.Net.FormItemModel()
{
  Key = "id",
  Value = "id-test-id-test-id-test-id-test-id-test-"
});
formDatas.Add(new Grass.Net.FormItemModel()
{
  Key = "name",
  Value = "name-test-name-test-name-test-name-test-name-test-"
});
//提交表单
var result = PostForm(url, formDatas);