Apache Commons FTP Passive模式，如何设置远程监听端口（数据流）

Question

我尝试使用 apache-commons-net-3.7.2（隐式 TLS，使用客户端证书 + 登录名/密码的双因素身份验证）连接 FTP 服务器。

我可以验证自己，进入被动模式，但是客户端没有成功连接到服务器以通过数据套接字获取数据。

我可以在同一台计算机上使用 WinSCP（相同的设置）连接自己。我已激活 WinSCP 日志以查看协议详细信息，并使用相同的选项调整了我的源代码。我可以使用ProtocolCommandListener 验证我的协议是否正常。我知道被动模式是必需的，因为 WinSCP 会发出 PASV 命令。

我可以看到 WinSCP 连接到端口 62564 上的数据套接字（我已将 FTP IP 地址替换为 XXX）

2021-01-06 10:25:35.575 227 Entering Passive Mode (192,168,4,122,244,100).
2021-01-06 10:25:35.575 Server sent passive reply with unroutable address 192.168.4.122, using host address instead.
2021-01-06 10:25:35.575 MLSD
2021-01-06 10:25:35.575 Connexion à 83.XXX.XXX.XXX:62564...
2021-01-06 10:25:35.604 150 Transferring directory

我还可以看到服务器为PASV 命令发送的回复不包括要连接的端口。

public class TestApi {
    
    public static void _parseExtendedPassiveModeReply(String reply)
        {
            reply = reply.substring(reply.indexOf('(') + 1,
                    reply.indexOf(')')).trim();
    
            char delim1, delim2, delim3, delim4;
            delim1 = reply.charAt(0);
            delim2 = reply.charAt(1);
            delim3 = reply.charAt(2);
            delim4 = reply.charAt(reply.length()-1);
    
            if (!(delim1 == delim2) || !(delim2 == delim3)
                    || !(delim3 == delim4)) {
                System.out.println("Could not parse extended passive host information.\nServer Reply: " + reply);
            }
    
            int port;
            try
            {
                port = Integer.parseInt(reply.substring(3, reply.length()-1));
            }
            catch (NumberFormatException e)
            {
                System.out.println("Could not parse extended passive host information.\nServer Reply: " + reply);
            }
        }   
    
    public static void main(String[] args) throws SocketException, IOException, GeneralSecurityException {

        String hostname = args[0];
        int port = Integer.parseInt(args[1]);
        String login = args[2];
        String pwd = args[3];

        FTPSClient client = new FTPSClient("TLS",true);
        
        File clientCertStore = new File("myJCEKS keystore");        
        KeyManager keyManager = KeyManagerUtils.createClientKeyManager("JCEKS",clientCertStore,"","myalias","");        
        client.setKeyManager(keyManager);
        
        client.connect(hostname, port);
        int reply = client.getReplyCode();

        if (!FTPReply.isPositiveCompletion(reply)) {
            client.disconnect();
            System.err.println("FTP server refused connection.");
            System.exit(1);
        } else {
            if (client.login(login, pwd)) {
                
                client.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.err), true));
                client.sendCommand("OPTS","UTF8 ON");
                client.sendCommand("PBSZ","0");
                client.sendCommand("PROT","P");
                
                int retour = client.pasv();
                System.out.println(retour);
                _parseExtendedPassiveModeReply(client.getReplyString());                
                
                System.out.println(client.printWorkingDirectory());
                reply = client.getReplyCode();
                System.out.println(reply);
                
                System.out.println(client.listHelp());
                
                //it freezes here, after sending MLDS command 
                //same thing using regular api for listing files (WinSCP use MLSD while regular api uses LIST)      
                client.sendCommand("MLSD");

                //and so on

                System.out.println("LOGOUT");
                client.logout();
            } else {
                System.out.println("echec login");
            }
        }

    }
}

我想 API 不知道必须在哪个端口发送数据请求，并且使用了一个不合适的默认值。不知道WinSCP是如何成功计算62564端口号的。

OPTS UTF8 ON
200 Command OPTS succeed
PBSZ 0
200 PBSZ=0
PROT P
200 PRIVATE data channel protection level set
PASV
227 Entering Passive Mode (192,168,4,122,245,74).
227
PWD
Could not parse extended passive host information.
Server Reply: 192,168,4,122,245,74
Could not parse extended passive host information.
Server Reply: 192,168,4,122,245,74
257 "/" is current directory
/
257
HELP
214-The following commands are implemented
    ABOR  ACCT  ALLO* APPE  CDUP  CWD   DELE  FEAT+ HELP
    HOST+ LANG+ LIST  MDTM+ MLST+ MKD   MODE  NLST  NOOP
    OPTS+ PASS  PASV  PORT  PWD   QUIT  REIN  REST  RETR
    RMD   RNFR  RNTO  SITE  SIZE  SMNT  STAT  STOR  STOU
    STRU* SYST  TYPE  USER  XCUP  XCRC  XCWD  XMD5  XMKD
    XPWD  XRMD  XSIGN XSHA1 XSHA256 XSHA512 XQUOTA
214 Help complete
214-The following commands are implemented
    ABOR  ACCT  ALLO* APPE  CDUP  CWD   DELE  FEAT+ HELP
    HOST+ LANG+ LIST  MDTM+ MLST+ MKD   MODE  NLST  NOOP
    OPTS+ PASS  PASV  PORT  PWD   QUIT  REIN  REST  RETR
    RMD   RNFR  RNTO  SITE  SIZE  SMNT  STAT  STOR  STOU
    STRU* SYST  TYPE  USER  XCUP  XCRC  XCWD  XMD5  XMKD
    XPWD  XRMD  XSIGN XSHA1 XSHA256 XSHA512 XQUOTA
214 Help complete

MLSD

在 API 文档、源代码、FTP RFC 中搜索数小时后，我不知道该怎么做。

Answer 1

你的假设是错误的。您没有设置端口。服务器会告诉你要连接到哪个端口。

对于 WinSCP：

2021-01-06 10:25:35.575 227 进入被动模式 (192,168,4,122,244,100)。
...
2021-01-06 10:25:35.575 连接 à 83.XXX.XXX.XXX:62564...

其中 62564 = (244 100

见RFC 959, section 4.1.2. Transfer parameter commands, Page 28。

---

PASV 响应的解析失败，因为您使用了错误的代码。 _parseExtendedPassiveModeReply 用于 EPSV。对于PASV，请使用_parsePassiveModeReply。在那里您还将看到上述公式的实现：

int oct1 = Integer.parseInt(m.group(2));
int oct2 = Integer.parseInt(m.group(3));
__passivePort = (oct1 << 8) | oct2;