可以使用 FileZilla 或 WinSCP 连接到 FTP，但不能使用 FtpWebRequest 或 FluentFTP

编程问答 2022-05-31

问题描述

我试图在我的代码中通过 SSL 打开 FTP 连接。我可以使用 WinSCP 的 FileZilla 连接并列出目录。但是当使用 FtpWebClient 通过 .NET 代码列出目录时，我收到错误

(425) 无法打开数据连接

由于我可以在同一台计算机上使用 FileZilla 进行连接，因此我不确定如何解决此问题。

这是我的代码

public void FtpStuff()
{
   string url = "ftp://my.server.com";

   FtpWebRequest request = (FtpWebRequest)WebRequest.Create(url);
   request.Credentials = new NetworkCredential("myname","password");
   request.EnableSsl = true;
   request.Method = WebRequestMethods.Ftp.ListDirectory;
   FtpWebResponse response = (FtpWebResponse)request.GetResponse();
   StreamReader streamReader = new StreamReader(response.GetResponseStream());

   // This is the line that throws the exception
   string line = streamReader.ReadLine();
}

我也试过 FluentFTP。这是我的代码。我得到了例外

无法建立数据连接：不允许操作。

public void FtpStuff()
{
   FtpClient client = new FtpClient();
   client.Host = "my.server.com";
   client.Credentials = new NetworkCredential("myname","password");
   client.EncryptionMode = FtpEncryptionMode.Explicit;
   client.Connect();

   // This line gives me an exception.
   var files = client.GetListing();
}

这里是来自 FluentFTP 的日志信息。我更改了真实用户名和IP，但其余数据（包括端口）是真实数据。我的 FTP 服务提供商指定我必须在端口 21 上进行连接。在发出 EPSV 命令并在新端口上建立连接后，问题似乎发生在最后。

# Connect()
The thread 0x5514 has exited with code 0 (0x0).
The thread 0xc80 has exited with code 0 (0x0).
The thread 0x89d4 has exited with code 0 (0x0).
Status:   Connecting to 123.123.123.123:21
Response: 220 FTP Server Ready
Command:  AUTH TLS
Response: 234 AUTH TLS successful
Status:   FTPS Authentication Successful
Status:   Time to activate encryption: 0h 0m 0s.  Total Seconds: 0.1339995.
Command:  USER me@mysite.com
The thread 0x6ddc has exited with code 0 (0x0).
Response: 331 Password required for me@mysite.com
Status:   Testing connectivity using Socket.Poll()...
Command:  PASS ***
Response: 230-***************************************************************************
Response: NOTICE TO USERS
Response: This computer system is private property. It is for authorized use only.
Response: Users (authorized or unauthorized) have no explicit or implicit
Response: expectation of privacy.
Response: 
Response: Any or all uses of this system and all files on this system may be
Response: intercepted,monitored,recorded,copied,audited and inspected by
Response: using this system,the user consents to such interception,monitoring,Response: recording,copying,auditing,inspection,and disclosure at the
Response: discretion of such personnel or officials.  Unauthorized or improper use
Response: of this system may result in civil and criminal penalties and
Response: administrative or disciplinary action,as appropriate. By continuing to
Response: use this system you indicate your awareness of and consent to these terms
Response: and conditions of use. LOG OFF IMMEDIATELY if you do not agree to the
Response: conditions stated in this warning.
Response: ****************************************************************************
Response: 230 User me@mysite.com logged in
Command:  PBSZ 0
Response: 200 PBSZ 0 successful
Command:  PROT P
Response: 200 Protection set to Private
Command:  FEAT
Response: 211-Features:
Response: AUTH TLS
Response: CCC
Response: CLNT
Response: EPRT
Response: EPSV
Response: HOST
Response: MDTM
Response: MFF modify;UNIX.group;UNIX.mode;
Response: MFMT
Response: MLST modify*;perm*;size*;type*;unique*;UNIX.grouP*;UNIX.groupname*;UNIX.mode*;UNIX.owner*;UNIX.ownername*;
Response: PBSZ
Response: PROT
Response: REST STREAM
Response: SIZE
Response: SSCN
Response: TVFS
Response: 211 End
Status:   Text encoding: System.Text.ASCIIEncoding
Command:  SYST
Response: 215 UNIX Type: L8

# GetListing(null,Auto)

# GetWorkingDirectory()
Command:  PWD
Response: 257 "/" is the current directory
Command:  TYPE I
Response: 200 Type set to I

# OpenPassiveDataStream(Autopassive,"MLSD /",0)
Command:  EPSV
Response: 229 Entering Extended Passive Mode (|||50304|)
Status:   Connecting to 123.123.123.123:50304
Command:  MLSD /
Response: 150 opening BINARY mode data connection for MLSD
Status:   FTPS Authentication Successful
Status:   Time to activate encryption: 0h 0m 0s.  Total Seconds: 0.1210002.
+---------------------------------------+
-----------------------------------------
Status:   disposing FtpSocketStream...

# CloseDataStream()
Response: 425 Unable to build data connection: Operation not permitted
Status:   disposing FtpSocketStream...
Exception thrown: 'FluentFTP.FtpCommandException' in FluentFTP.dll

这是我的 FileZilla 日志。

Status: Resolving address of mysite.com
Status: Connecting to 123.123.123.123:21...
Status: Connection established,waiting for welcome message...
Response:   220 FTP Server Ready
Command:    AUTH TLS
Response:   234 AUTH TLS successful
Status: Initializing TLS...
Status: Verifying certificate...
Status: TLS connection established.
Command:    USER me@mysite.com
Response:   331 Password required for me@mysite.com
Command:    PASS ************
Response:   230-***************************************************************************
Response:                                NOTICE TO USERS
Response:    This computer system is private property. It is for authorized use only.
Response:    Users (authorized or unauthorized) have no explicit or implicit
Response:    expectation of privacy.
Response:    
Response:    Any or all uses of this system and all files on this system may be
Response:    intercepted,audited and inspected by
Response:    using this system,Response:    recording,and disclosure at the
Response:    discretion of such personnel or officials.  Unauthorized or improper use
Response:    of this system may result in civil and criminal penalties and
Response:    administrative or disciplinary action,as appropriate. By continuing to
Response:    use this system you indicate your awareness of and consent to these terms
Response:    and conditions of use. LOG OFF IMMEDIATELY if you do not agree to the
Response:    conditions stated in this warning.
Response:    ****************************************************************************
Response:   230 User me@mysite.com logged in
Command:    SYST
Response:   215 UNIX Type: L8
Command:    FEAT
Response:   211-Features:
Response:    AUTH TLS
Response:    CCC
Response:    CLNT
Response:    EPRT
Response:    EPSV
Response:    HOST
Response:    MDTM
Response:    MFF modify;UNIX.group;UNIX.mode;
Response:    MFMT
Response:    MLST modify*;perm*;size*;type*;unique*;UNIX.grouP*;UNIX.groupname*;UNIX.mode*;UNIX.owner*;UNIX.ownername*;
Response:    PBSZ
Response:    PROT
Response:    REST STREAM
Response:    SIZE
Response:    SSCN
Response:    TVFS
Response:   211 End
Status: Server does not support non-ASCII characters.
Command:    PBSZ 0
Response:   200 PBSZ 0 successful
Command:    PROT P
Response:   200 Protection set to Private
Status: Logged in
Status: Retrieving directory listing...
Command:    PWD
Response:   257 "/" is the current directory
Command:    TYPE I
Response:   200 Type set to I
Command:    PASV
Response:   227 Entering Passive Mode (123,123,197,68).
Command:    MLSD
Response:   150 opening BINARY mode data connection for MLSD
Response:   226 Transfer complete
Status: Directory listing of "/" successful

我也可以使用 WinSCP 进行连接。正如评论中所建议的，我确实检查了在打开数据连接时是否重用了 TLS/SSL 会话 ID。好像是的。

227 Entering Passive Mode (???)
MLSD
Connecting to ??? ...
Connection pending
Data connection opened
Trying reuse main TLS session ID
Session ID reused
150 opening data channel for directory listing of "/"

解决方法

.NET 框架不支持 TLS/SSL 会话重用。如果您的服务器需要它（它看起来是什么），则不能使用 FtpWebRequest 或 FluentFTP。两者都使用 TLS/SSL 的 .NET 实现。

您将不得不使用使用自己的 TLS/SSL 实现的 FTP 库。

您可以使用我的 WinSCP .NET assembly。 尽管与 FluentFTP 不同，它不是本机 .NET 库，但它依赖于外部二进制文件。但这就是让它起作用的原因。

一些参考：

c#c#fluentftpftpftpwebrequestssl