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, 0, Convert.ToInt32(fs.Length));
    fs.Close();

    RequestStream.Write(fileContentStrByte, 0, fileContentStrByte.Length);
    RequestStream.Write(filedata, 0, 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, 0, 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, 0, 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, 0, 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”。