HTTP POST上传文件说明及注意事项

这一阵子因为项目需要要对接别家公司的restful接口，其中有一个接口是上传视频文件。接着上网找找资料。后来文件是上传成功了，但上服务器一看，文件没有后缀，我勒个去，这是什么个鬼。接着继续找资料，最终发现是因为在文件数据后面没加上“\r\n”引起的，特发此博文备忘。在此感谢【小伊同学】的《c#代码发送post请求，上传文件》https://www.cnblogs.com/yinq/p/6045995.html和【imEgo】的《HTTP POST上传文件格式说明》http://blog.sina.com.cn/s/blog_73b633110101jwxm.html。

 public static Response FileLoadRequest(string url, string filePath, string rename = "")
 {
     Response httpResponse = null;
     string fileName = FileHelper.GetFileName(filePath);
     string boundary = "ceshi";
     string Enter = "\r\n";

     HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
     request.Method = "POST";
     request.ContentType = "multipart/form-data;charset=utf8;boundary=" + boundary;  //boundary这个属性很重要
     //进行Session持久化
     request.CookieContainer = cookie;

     #region 将参数写入请求流中
     Stream RequestStream = request.GetRequestStream();
     string fileContentStr = "--" + boundary + Enter
             + "Content-Type:application/octet-stream" + Enter
             + "Content-Disposition: form-data; name=\"file\"; filename=\"" + fileName + "\"" + Enter + Enter;
     var fileContentStrByte = Encoding.UTF8.GetBytes(fileContentStr);

     FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);
     byte[] filedata = new byte[fs.Length];
     fs.Read(filedata, , Convert.ToInt32(fs.Length));
     fs.Close();

     RequestStream.Write(fileContentStrByte, , fileContentStrByte.Length);
     RequestStream.Write(filedata, , filedata.Length);

     //在文件数据末尾要加上“\r\n”
     string EndStr1 = Enter;
     var EndStr1Byte = Encoding.UTF8.GetBytes(EndStr1);
     RequestStream.Write(EndStr1Byte, , EndStr1Byte.Length);

     if (rename != "")
     {
         string fileNameStr = "--" + boundary + Enter
             + "Content-Disposition: form-data; name=\"file_name\"" + Enter + Enter
             + rename;
         var fileNameStrByte = Encoding.UTF8.GetBytes(fileNameStr);
         RequestStream.Write(fileNameStrByte, , fileNameStrByte.Length);
     }

     //在流末尾要加上--ceshi--的分隔符
     string EndStr = Enter + "--" + boundary + "--";
     var EndStrByte = Encoding.UTF8.GetBytes(EndStr);
     RequestStream.Write(EndStrByte, , EndStrByte.Length);
     #endregion

     string responseMessage = string.Empty;
     try
     {
         using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
         {

             StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
             responseMessage = sr.ReadToEnd();
             httpResponse = JsonConvert.DeserializeObject<Response>(responseMessage);
             response.Close();
         }
     }
     catch (WebException ex)
     {
         Program.log.Error(string.Format("System.Net.WebException:UrlGetRequest出错,URL='{0}':", request.RequestUri), ex);
     }
     catch (Exception ex)
     {
         Program.log.Error(string.Format("UrlGetRequest出错,URL='{0}':", request.RequestUri), ex);
     }

     return httpResponse;
 }

下面引用下RFC的Sample：

Content-Type: multipart/form-data, boundary=AaB03x

--AaB03x
Content-Disposition: form-data; name="field1"

Joe Blow
--AaB03x
Content-Disposition: form-data; name="pics"; filename="file1.txt"
Content-Type: text/plain

 ... contents of file1.txt ...
--AaB03x--

首先，在Content-Type中，boundary这个属性一定要加，但boundary属性值随意设置成什么都行，它不会出现在要上传的数据里，只是起到分隔的作用。上面是设置成“Aab03x”。重点来了：每个参数之前需要加上“--boundary”，注意前面有“--”。参数最后结尾要加“--boundary--”。文件数据后要跟上“\r\n”(我就是因为没加“\r\n，所以没有文件后缀”)。在上传文件的那一个参数的Content-Type：是根据上传文件的后缀进行设置的，详细对照表请参照：http://tool.oschina.net/commons/。如果不想根据文件后缀进行填充的话，可以直接用“application/octet-stream”。