修复 - System.Net.WebException:远程服务器返回错误:(500)语法错误，命令无法识别 [英] Fixing - System.Net.WebException: The remote server returned an error: (500) Syntax error, command unrecognized

问题描述

我创建了 FTP 代码来传输文件.此代码工作正常，但有时会导致错误 500.确切的错误是 -

I created FTP code to transfer files. This code works fine except that it sometimes causes an error 500. The exact error is -

Error: System.Reflection.TargetInvocationException: Exception has 
been thrown by the target of an invocation. 
---> System.Net.WebException: The remote server returned an error: 
(500) Syntax error, command unrecognized.
   at System.Net.FtpWebRequest.CheckError()
   at System.Net.FtpWebRequest.SyncRequestCallback(Object obj)
   at System.Net.CommandStream.Abort(Exception e)
   at System.Net.FtpWebRequest.FinishRequestStage(RequestStage stage)
   at System.Net.FtpWebRequest.GetRequestStream()
   at ST_772dn22cj49ndfddatee.csproj.ScriptMain.Main()
   --- End of inner exception stack trace --- 

我注意到在加载最大文件(即大约 290 KB)时会发生错误.所有其他文件都少于此，我对它们也不例外.我不知道为什么会这样.谁能告诉我为什么?

I noticed that the error occurs when the biggest file is loaded, ie about 290 KB. All other files are less than this and i get no exception for them. I don't know why this happens. Can someone tell me why ?

顺便说一句，如果您发现我的代码有一些改进空间或逻辑错误，请同时提及.我并不是真的在寻找代码审查，但它是受欢迎的.

As an aside, in case you notice some room for improvement in my code or logical error, then please mention that as well. I am not really looking for code reviews, but its welcome.

public void Main()
{

    Boolean conditions = true;

    if(conditions == true)
    {
    string fileLocation = "my windows directory";
    string fileName = "fileName.extension";

    string ftpFolder = @"/ftpFolder/";
    Boolean ftpMode = true; //passive or active. True = passive 
    string ftpPassword = "password";
    int ftpPort = 21;// the default
    string ftpServerName = "server name";
    string ftpUserName = "user name";

    //Create an object to communicate with the server.
    string ftpRequestString = "ftp://" + ftpServerName + ":" 
    + ftpPort + ftpFolder + fileName; 

    try{

    FtpWebRequest request = 
    (FtpWebRequest)WebRequest.Create(ftpRequestString);
    request.Method = WebRequestMethods.Ftp.UploadFile;

    request.Credentials = new NetworkCredential(ftpUserName, ftpPassword);

    //Set mode
    if(ftpMode == true){
        request.UsePassive = true;
    }

    //Copy the file to the request.

    string filePath = @fileLocation + "\" + fileName;
    StreamReader sourceStream = new StreamReader(filePath);
    byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());
    sourceStream.Close();
    request.ContentLength = fileContents.Length;

    Stream requestStream = request.GetRequestStream();
    requestStream.Write(fileContents, 0, fileContents.Length);
    requestStream.Close();

    FtpWebResponse response = (FtpWebResponse)request.GetResponse();

    response.Close();

    }
     catch (WebException ex)
     {
        MessageBox.Show(ex.Message);

     }//try-catch

    }

}//main

推荐答案

在阅读您的问题时，我怀疑这与将 KeepAlive 设置为 有关(或可以通过以下方式纠正)错误.看着 SO - 这个问题引用了同样的问题并指出它:https://stackoverflow.com/a/2071374/1803682

On reading your question I was suspicious this has to do with (or could be corrected by) setting the KeepAlive to false. Looking on SO - this question references the same problem and points to it as well: https://stackoverflow.com/a/2071374/1803682

尝试设置:

request.KeepAlive = false;

将 KeepAlive 设置为 false 您的连接将是 在每个请求结束时关闭.如果您要传输大量文件，这可能是一个问题 - 因为重新发送凭据等需要时间.好处是您以已知/初始状态重新创建连接，这应该可以解决您的问题(即使它不是根原因).

With KeepAlive set to false your connection will be closed at the end of each request. If you are transmitting a lot of files this could be an issue - as it takes time to resend credentials, etc. The upside is you recreate the connection in a known / initial state which should solve your problem (even if it is not the root cause).

要查看发生了什么，如果您可以在服务器上启用详细日志记录，您应该会在看到返回此错误之前看到发出的最后一条命令.这应该让您更好地了解发生了什么.发现这个帖子说了很多同样的话.

To see what is going on, if you can enable detailed logging on your server you should see the last command issued before seeing this error returned. This should give you a better idea of what is up. Found this thread saying much the same thing.

更新:

如果我阅读了我自己发布的链接的底部，我可能会回答得更好，重新发出的命令可能是登录过程的一部分(即 USER 用户名)，这是您可能遇到的问题:

If I had read to the bottom of the link I posted myself I could have answered even better, the command probably being reissued is some part of the login process (i.e. USER username) and this is your likely issue:

凭证可能不再有效的原因是WebRequest 使用在一定时间后到期的租约.如果您没有明确实例化租约并定义其超时，FtpWebRequest 似乎使用默认超时值.我相信发生的事情是，当租约到期时，FtpWebRequest 将然后尝试重新登录.

The reason the creadentials may no longer be valid is that the WebRequest uses a lease that expires after a certain amount of time. If you don't explicitly instantiate the lease and define its timeouts, the FtpWebRequest appears to use default timeout values. I believe what's happening is that when the lease expires the FtpWebRequest will then try to log on again.

看起来 这里 使用正确的搜索:

So looking here with the right search:

导致等待请求的默认超时不是无限的，因为 指定，但实际上10000 ms.这似乎是一个很大的差异.所以你也可以尝试设置:

yields that the default timeout waiting for requests is not infinite as specified but actually 10000 ms. Which seems a pretty big discrepancy. So you can also try setting:

request.Timeout = -1;

看看它是否能纠正你的错误.

And see if it corrects your error.

真的不认为这可能是您的问题，所以将其移至底部:

Really don't think this could be your issue so moving it to the bottom:

另外 - 检查您的 request.ReadWriteTimeout 是否适合您看到的较大文件的速度.默认值为 5分钟 这对于 290k 来说会很长，所以我希望这不是你的错误的根源.另外 - 如果这是问题，我预计会出现连接关闭错误.

Also - check that your request.ReadWriteTimeout is appropriate for the speed you see for the larger file. The default is 5 minutes which would be pretty long for 290k, so I expect this is not the source of your error. Also - I would expect a connection closed error if this was the problem.

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