ftp: add place-holder file size work-around for Globus directory listing

Motivation:

For files being currently uploaded we don't yet know the file's size.
As a result, the namespace declines to provide the file's size in the
FileAttributes object.

When making a directory listing with the MLSC command, Globus requires
files have a defined size.  It treats any lack of a SIZE fact as an
error.

Modification:

This patch adds a work-around where incomplete files (those still being
uploaded) have zero length, as a place-holder value.

Result:

Globus transfer service can now list directories that contain incomplete
files, those that are still being uploaded.

Target: master
Request: 7.0
Request: 6.2
Request: 6.1
Request: 6.0
Request: 5.2
Requires-notes: yes
Requires-book: no
Patch: https://rb.dcache.org/r/12768/
Acked-by: Tigran Mkrtchyan

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

@@ -395,7 +395,18 @@ private enum WorkAround
          * close our end of the TCP connection once any pending transfers have
          * completed.
          */
-        NO_REPLY_ON_QUIT
+        NO_REPLY_ON_QUIT,
+
+        /**
+         * Some clients (e.g., Globus) require that files returned during
+         * directory listing have a definite size.  When dCache is accepting a
+         * new file, the namespace does not know the final file's size so no
+         * file size is returned to the door.  Normally, dCache simply omits the
+         * file size information when building the response; however, this
+         * work-around results in such incomplete files being reported as having
+         * zero length.
+         */
+        USE_PLACEHOLDER_SIZE_FOR_INCOMPLETE_FILES,
     }
 
 
@@ -3185,6 +3196,21 @@ public void doClientinfo(String description)
         case "globus-url-copy":
             _activeWorkarounds.add(WorkAround.NO_REPLY_ON_QUIT);
             break;
+
+        // Globus (Online) agent for:
+        //     Providing web-portal with directory listing,
+        //     Deleting contents.
+        // Observed commands: MLST, MLSC, DELE, RMD
+        case "globusonline-dirlist":
+            _activeWorkarounds.add(WorkAround.USE_PLACEHOLDER_SIZE_FOR_INCOMPLETE_FILES);
+            break;
+
+        // Globus (Online) agent that seems to do a recursive directory listing
+        // in preparation of data transfer.
+        // Observed commands: MLSC, MLST
+        case "gshtest":
+            _activeWorkarounds.add(WorkAround.USE_PLACEHOLDER_SIZE_FOR_INCOMPLETE_FILES);
+            break;
         }
         reply("250 OK");
     }
@@ -4853,17 +4879,30 @@ public Set<FileAttribute> getRequiredAttributes()
                     break;
                 }
             }
+
+            if (_activeWorkarounds.contains(WorkAround.USE_PLACEHOLDER_SIZE_FOR_INCOMPLETE_FILES)
+                    && _currentFacts.contains(Fact.SIZE)) {
+                attributes.add(SIMPLE_TYPE);
+            }
+
             return attributes;
         }
 
         @Override
         public void print(FsPath dir, FileAttributes dirAttr, DirectoryEntry entry)
         {
+            FileAttributes attr = entry.getFileAttributes();
+
+            if (_activeWorkarounds.contains(WorkAround.USE_PLACEHOLDER_SIZE_FOR_INCOMPLETE_FILES)
+                    && attr.isDefined(TYPE) && attr.getFileType() == FileType.REGULAR
+                    && attr.isUndefined(SIZE)) {
+                attr.setSize(0L);
+            }
+
             FsPath path = (dir == null) ? FsPath.ROOT : dir.child(entry.getName());
 
             if (!_currentFacts.isEmpty()) {
                 AccessType access;
-                FileAttributes attr = entry.getFileAttributes();
 
                 for (Fact fact: _currentFacts) {
                     switch (fact) {