Fix retaring process for twine.

Also check the failing function works

tools/retar.py

@@ -1,60 +1,64 b''
 """
 Un-targz and retargz a targz file to ensure reproducible build. 
 
 usage: 
 
     $ export SOURCE_DATE_EPOCH=$(date +%s)
     ...
     $ python retar.py <tarfile.gz>
 
 The process of creating an sdist can be non-reproducible:
   - directory created during the process get a mtime of the creation date; 
   - gziping files embed the timestamp of fo zip creation. 
 
 This will untar-retar; ensuring that all mtime > SOURCE_DATE_EPOCH will be set
 equal to SOURCE_DATE_EPOCH.
 
 """
 
 import tarfile
 import sys
 import os
 import gzip
 import io
 
 if len(sys.argv) > 2:
     raise ValueError("Too many arguments")
 
 
 timestamp = int(os.environ["SOURCE_DATE_EPOCH"])
 
 old_buf = io.BytesIO()
 with open(sys.argv[1], "rb") as f:
     old_buf.write(f.read())
 old_buf.seek(0)
 old = tarfile.open(fileobj=old_buf, mode="r:gz")
 
 buf = io.BytesIO()
 new = tarfile.open(fileobj=buf, mode="w", format=tarfile.GNU_FORMAT)
 for i, m in enumerate(old):
     data = None
     # mutation does not work, copy
     if m.name.endswith('.DS_Store'):
         continue
     m2 = tarfile.TarInfo(m.name)
     m2.mtime = min(timestamp, m.mtime)
     m2.size = m.size
     m2.type = m.type
     m2.linkname = m.linkname
     if m.isdir():
+        new.addfile(m2)
+    else:
         data = old.extractfile(m)
         new.addfile(m2, data)
-    else:
-        new.addfile(m2)
 new.close()
 old.close()
 
 buf.seek(0)
 with open(sys.argv[1], "wb") as f:
     with gzip.GzipFile('', "wb", fileobj=f, mtime=timestamp) as gzf:
         gzf.write(buf.read())
+
+# checks the archive is valid.
+archive = tarfile.open(sys.argv[1])
+names = archive.getnames()