ftp: Close passive port on failure

globus-url-copy hangs on proxied passive mode connections for which
the mover is killed. Although the proxy adapter is shut down and an
error is reported on the control channel, the fact that the server
socket for the passive mode is not closed and thus has an unaccepted
connection causes globus-url-copy to hang.

This patch closes the passive port on transfer failure. The mode state
is set to an invalid state to force the client to reset the data
channel using either PORT or PASV (or one of the variations).

I am not request backport further than 2.9 as I expect that we will
soon backport the entire door to get delayed passive and IPv6 functionality
in older releases.

Target: trunk
Request: 2.9
Require-notes: yes
Require-book: no
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: https://rb.dcache.org/r/7079/

modules/dcache-ftp/src/main/java/org/dcache/ftp/door/AbstractFtpDoorV1.java

@@ -292,14 +292,16 @@ public abstract class AbstractFtpDoorV1
      *
      * For ACTIVE transfers dCache establishes the data connection.
      *
+     * When INVALID, the client most reset the mode.
+     *
      * Depending on the values of _isProxyRequiredOnActive and
      * _isProxyRequiredOnPassive, the data connection with the client
      * will be established either to an adapter (proxy) at the FTP
      * door, or to the pool directly.
      */
     protected enum Mode
     {
-        PASSIVE, ACTIVE
+        PASSIVE, ACTIVE, INVALID
     }
 
 
@@ -1193,6 +1195,11 @@ protected synchronized void onFailure(Exception exception)
             if (_adapter != null) {
                 _adapter.close();
                 _adapter = null;
+
+                if (_mode == Mode.PASSIVE) {
+                    closePassiveModeServerSocket();
+                    AbstractFtpDoorV1.this._mode = Mode.INVALID;
+                }
             }
 
             if (isWrite()) {
@@ -3145,6 +3152,9 @@ private void retrieve(String file, long offset, long size,
         if (xferMode.equals("X") && mode == Mode.PASSIVE && _isProxyRequiredOnPassive) {
             throw new FTPCommandException(504, "Cannot use passive X mode");
         }
+        if (mode == Mode.INVALID) {
+            throw new FTPCommandException(425, "Issue PASV or PORT to reset data channel.");
+        }
         if (_checkSumFactory != null || _checkSum != null) {
             throw new FTPCommandException(503,"Expecting STOR ESTO PUT commands");
         }
@@ -3270,6 +3280,9 @@ private void store(String file, Mode mode, String xferMode,
         if (xferMode.equals("X") && mode == Mode.PASSIVE && _isProxyRequiredOnPassive) {
             throw new FTPCommandException(504, "Cannot use passive X mode");
         }
+        if (mode == Mode.INVALID) {
+            throw new FTPCommandException(425, "Issue PASV or PORT to reset data channel.");
+        }
 
         FtpTransfer transfer =
             new FtpTransfer(absolutePath(file),
@@ -3402,19 +3415,24 @@ public void ftp_mdtm(String arg)
     }
 
     private void openDataSocket()
-        throws IOException
+        throws IOException, FTPCommandException
     {
         /* Mode being PASSIVE means the client did a PASV.  Otherwise
          * we establish the data connection to the client.
          */
-        if (_mode == Mode.PASSIVE) {
+        switch (_mode) {
+        case PASSIVE:
             replyDelayedPassive(_delayedPassive, (InetSocketAddress) _passiveModeServerSocket.getLocalAddress());
             reply("150 Ready to accept ASCII mode data connection", false);
             _dataSocket = _passiveModeServerSocket.accept().socket();
-        } else {
+            break;
+        case ACTIVE:
             reply("150 Opening ASCII mode data connection", false);
             _dataSocket = new Socket();
             _dataSocket.connect(_clientDataAddress);
+            break;
+        default:
+            throw new FTPCommandException(425, "Issue PASV or PORT to reset data channel.");
         }
     }