C# http系列之以form-data方式上传多个文件及键值对集合到远程服务器

<form id="form1" runat="server" action="usermanagehandler.ashx" method="post" enctype="multipart/form-data">
 <div>
  名称： <input type="text" name="uname" class="uname" /><br/>
  邮件： <input type="text" name="email" class="email" /><p/>
  附件1： <input type="file" name="file1" class="file" /><p/>
  附件2： <input type="file" name="file2" class="file" /><p/>
  附件3： <input type="file" name="file3" class="file" /><p/>
    <input type="submit" name="submit" value="提交" />
 </div>
</form>

httpfilecollection files = httpcontext.current.request.files;
 httppostedfile postedfile = files["fileupload"];
 postedfile.saveas(postedfile.filename);

/// <summary>
/// http请求(包含多分部数据,multipart/form-data)。
/// 将多个文件以及多个参数以多分部数据表单方式上传到指定url的服务器
/// </summary>
/// <param name="url">请求目标url</param>
/// <param name="filefullnames">待上传的文件列表(包含全路径的完全限定名)。如果某个文件不存在，则忽略不上传</param>
/// <param name="kvdatas">请求时表单键值对数据。</param>
/// <param name="method">请求的方法。请使用 webrequestmethods.http 的枚举值</param>
/// <param name="timeout">获取或设置 <see cref="m:system.net.httpwebrequest.getresponse" /> 和
///      <see cref="m:system.net.httpwebrequest.getrequeststream" /> 方法的超时值（以毫秒为单位）。
///      -1 表示永不超时
/// </param>
/// <returns></returns>
public httpresult uploadformbymultipart(string url, string[] filefullnames, namevaluecollection kvdatas = null, string method = webrequestmethods.http.post, int timeout = -1)
{
 #region 说明
 /* 阿里云文档：https://www.alibabacloud.com/help/zh/doc-detail/42976.htm
  c# 示例： https://github.com/aliyun/aliyun-oss-csharp-sdk/blob/master/samples/samples/postpolicysample.cs?spm=a2c63.p38356.879954.18.7f3f7c34w3br9u&file=postpolicysample.cs
     (c#示例中仅仅是把文件中的文本内容当做 formdata 中的项，与文件流是不一样的。本方法展示的是文件流，更通用)
  */

 /* 说明：multipart/form-data 方式提交文件
  *  (1) header 一定要有 content-type: multipart/form-data; boundary={boundary}。
  *  (2) header 和bod y之间由 \r\n--{boundary} 分割。
  *  (3) 表单域格式 ：content-disposition: form-data; name="{key}"\r\n\r\n
  *     {value}\r\n
  *     --{boundary}
  *  (4)表单域名称大小写敏感，如policy、key、file、ossaccesskeyid、ossaccesskeyid、content-disposition。
  *  (5)注意:表单域 file 必须为最后一个表单域。即必须放在最后写。
  */
 #endregion

 #region contenttype 说明
 /* 该contenttype的属性包含请求的媒体类型。分配给contenttype属性的值在请求发送content-typehttp标头时替换任何现有内容。
  
  要清除content-typehttp标头，请将contenttype属性设置为null。
  
  * 注意：此属性的值存储在webheadercollection中。如果设置了webheadercollection，则属性值将丢失。
  *  所以放置在headers 属性之后设置
  */
 #endregion

 #region method 说明
 /* 如果 contentlength 属性设置为-1以外的任何值，则必须将 method 属性设置为上载数据的协议属性。 */
 #endregion

 #region httpwebrequest.cookiecontainer 在 .net3.5 与 .net4.0 中的不同
 /* 请参考：https://www.crifan.com/baidu_emulate_login_for_dotnet_4_0_error_the_fisrt_two_args_should_be_string_type_0_1/ */
 #endregion

 httpresult httpresult = new httpresult();

 #region 校验

 if (filefullnames == null || filefullnames.length == 0)
 {
  httpresult.status = httpresult.status_fail;

  httpresult.refcode = (int)httpstatuscode2.user_file_not_exists;
  httpresult.reftext = httpstatuscode2.user_file_not_exists.getcustomattributedescription();

  return httpresult;
 }

 list<string> lstfiles = new list<string>();
 foreach (string filefullname in filefullnames)
 {
  if (file.exists(filefullname))
  {
   lstfiles.add(filefullname);
  }
 }

 if (lstfiles.count == 0)
 {
  httpresult.status = httpresult.status_fail;

  httpresult.refcode = (int)httpstatuscode2.user_file_not_exists;
  httpresult.reftext = httpstatuscode2.user_file_not_exists.getcustomattributedescription();

  return httpresult;
 }

 #endregion

 string boundary = createformdataboundary();          // 边界符
 byte[] beginboundarybytes = encoding.utf8.getbytes("--" + boundary + "\r\n");  // 边界符开始。【☆】右侧必须要有 \r\n 。
 byte[] endboundarybytes = encoding.utf8.getbytes("\r\n--" + boundary + "--\r\n"); // 边界符结束。【☆】两侧必须要有 --\r\n 。
 byte[] newlinebytes = encoding.utf8.getbytes("\r\n"); //换一行
 memorystream memorystream = new memorystream();

 httpwebrequest httpwebrequest = null;
 try
 {
  httpwebrequest = webrequest.create(url) as httpwebrequest; // 创建请求
  httpwebrequest.contenttype = string.format(httpcontenttype.multipart_form_data + "; boundary={0}", boundary);
  //httpwebrequest.referer = "http://bimface.com/user-console";
  httpwebrequest.method = method;
  httpwebrequest.keepalive = true;
  httpwebrequest.timeout = timeout;
  httpwebrequest.useragent = getuseragent();

  #region 步骤1：写入键值对
  if (kvdatas != null)
  {
   string formdatatemplate = "content-disposition: form-data; name=\"{0}\"\r\n\r\n" +
          "{1}\r\n";

   foreach (string key in kvdatas.keys)
   {
    string formitem = string.format(formdatatemplate, key.replace(stringutils.symbol.key_suffix, string.empty), kvdatas[key]);
    byte[] formitembytes = encoding.utf8.getbytes(formitem);

    memorystream.write(beginboundarybytes, 0, beginboundarybytes.length); // 1.1 写入formdata项的开始边界符
    memorystream.write(formitembytes, 0, formitembytes.length);   // 1.2 将键值对写入formdata项中
   }
  }
  #endregion

  #region 步骤2：写入文件(表单域 file 必须为最后一个表单域)

  const string filepartheadertemplate = "content-disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\n" +
            "content-type: application/octet-stream\r\n\r\n";

  int i = 0;
  foreach (var filefullname in lstfiles)
  {
   fileinfo fileinfo = new fileinfo(filefullname);
   string filename = fileinfo.name;

   string fileheaderitem = string.format(filepartheadertemplate, "file", filename);
   byte[] fileheaderitembytes = encoding.utf8.getbytes(fileheaderitem);

   if (i > 0)
   {
    // 第一笔及第一笔之后的数据项之间要增加一个换行 
    memorystream.write(newlinebytes, 0, newlinebytes.length);
   }
   memorystream.write(beginboundarybytes, 0, beginboundarybytes.length);  // 2.1 写入formdata项的开始边界符
   memorystream.write(fileheaderitembytes, 0, fileheaderitembytes.length); // 2.2 将文件头写入formdata项中

   int bytesread;
   byte[] buffer = new byte[1024];

   filestream filestream = new filestream(filefullname, filemode.open, fileaccess.read);
   while ((bytesread = filestream.read(buffer, 0, buffer.length)) != 0)
   {
    memorystream.write(buffer, 0, bytesread);        // 2.3 将文件流写入formdata项中
   }

   i++;
  }

  memorystream.write(endboundarybytes, 0, endboundarybytes.length);    // 2.4 写入formdata的结束边界符

  #endregion

  #region 步骤3：将表单域(内存流)写入 httpwebrequest 的请求流中，并发起请求
  httpwebrequest.contentlength = memorystream.length;

  stream requeststream = httpwebrequest.getrequeststream();

  memorystream.position = 0;
  byte[] tempbuffer = new byte[memorystream.length];
  memorystream.read(tempbuffer, 0, tempbuffer.length);
  memorystream.close();

  requeststream.write(tempbuffer, 0, tempbuffer.length);  // 将内存流中的字节写入 httpwebrequest 的请求流中
  requeststream.close();
  #endregion

  httpwebresponse httpwebresponse = httpwebrequest.getresponse() as httpwebresponse; // 获取响应
  if (httpwebresponse != null)
  {
   //getheaders(ref httpresult, httpwebresponse);
   getresponse(ref httpresult, httpwebresponse);
   httpwebresponse.close();
  }
 }
 catch (webexception webexception)
 {
  getwebexceptionresponse(ref httpresult, webexception);
 }
 catch (exception ex)
 {
  getexceptionresponse(ref httpresult, ex, method, httpcontenttype.multipart_form_data);
 }
 finally
 {
  if (httpwebrequest != null)
  {
   httpwebrequest.abort();
  }
 }

 return httpresult;
}

/// <summary>
/// http请求(包含多分部数据,multipart/form-data)。
/// 将文件以及多个参数以多分部数据表单方式上传到指定url的服务器
/// </summary>
/// <param name="url">请求目标url</param>
/// <param name="filefullname">待上传的文件(包含全路径的完全限定名)</param>
/// <param name="kvdatas">请求时表单键值对数据。</param>
/// <param name="method">请求的方法。请使用 webrequestmethods.http 的枚举值</param>
/// <param name="timeout">获取或设置 <see cref="m:system.net.httpwebrequest.getresponse" /> 和
///      <see cref="m:system.net.httpwebrequest.getrequeststream" /> 方法的超时值（以毫秒为单位）。
///      -1 表示永不超时
/// </param>
/// <returns></returns>
public httpresult uploadformbymultipart(string url, string filefullname, namevaluecollection kvdatas = null, string method = webrequestmethods.http.post, int timeout = -1)
{
 string[] filefullnames = { filefullname };

 return uploadformbymultipart(url, filefullnames, kvdatas, method, timeout);
}

/// <summary>
/// http请求(包含多分部数据,multipart/form-data)。
/// 将文件以多分部数据表单方式上传到指定url的服务器
/// </summary>
/// <param name="url">请求目标url</param>
/// <param name="filefullname">待上传的文件(包含全路径的完全限定名)</param>
/// <param name="kvdatas">请求时表单键值对数据。</param>
/// <param name="method">请求的方法。请使用 webrequestmethods.http 的枚举值</param>
/// <param name="timeout">获取或设置 <see cref="m:system.net.httpwebrequest.getresponse" /> 和
///      <see cref="m:system.net.httpwebrequest.getrequeststream" /> 方法的超时值（以毫秒为单位）。
///      -1 表示永不超时
/// </param>
/// <returns></returns>
public httpresult uploadformbymultipart(string url, string filefullname, dictionary<string, string> kvdatas = null, string method = webrequestmethods.http.post, int timeout = -1)
{
 var nvc = kvdatas.tonamevaluecollection();
 return uploadformbymultipart(url, filefullname, nvc, method, timeout);
}