c# 模拟表单提交，post form 上传文件、数据内容

转自：https://www.cnblogs.com/DoNetCShap/p/10696277.html

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";

 /// <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 == )
                 return false;

             if (FileContent != null && FileContent.Length >  && 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; }
 }

 /// <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 = )
 {
     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 > ;
     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 == )
                 formdataBytes = Encoding.UTF8.GetBytes(formdata.Substring(, formdata.Length - ));
             else
                 formdataBytes = Encoding.UTF8.GetBytes(formdata);
             postStream.Write(formdataBytes, , formdataBytes.Length);

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

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

运行方式：

 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);

以下内容做了一些优化修改：

 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}";
         //头部
         var header = Encoding.UTF8.GetBytes("--" + boundary);
         postStream.Write(header, , header.Length);
         var index = ;
         foreach (var item in formItems)
         {
             index++;
             string formdata = null;
             if (item.IsFile)
             {
                 if (index == )
                 {
                     formdata = string.Format("\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\nContent-Type: application/octet-stream\r\n\r\n", item.Key, item.FileName);

                 }
                 else
                 {
                     //上传文件
                     formdata = string.Format(fileFormdataTemplate,item.Key,item.FileName);

                 }

             }
             else
             {
                 if (index==)
                 {
                     formdata = string.Format("\r\nContent-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}", item.Key, item.FileName);
                 }
                 else
                 {
                     //上传文本
                     formdata = string.Format(dataFormdataTemplate, item.Key, item.Value);
                 }

             }

             //统一处理
             byte[] formdataBytes = Encoding.UTF8.GetBytes(formdata);

             postStream.Write(formdataBytes, , formdataBytes.Length);

             //写入文件内容
             //if (item.FileContent != null && item.FileContent.Length > 0)
             if (item.IsFile)
             {

                 FileStream fs = new FileStream(item.FilePath, FileMode.Open, FileAccess.Read);//可以是其他重载方法
                 byte[] byData = new byte[fs.Length];
                 fs.Read(byData, , byData.Length);
                 fs.Close();
                 postStream.Write(byData, , byData.Length);
             }
         }
         //结尾
         var footer = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--");
         postStream.Write(footer, , footer.Length);

     }