Issue #9065: no longer use "root" as the default for the

uname and gname field.

If tarfile creates a new archive and adds a file with a
uid/gid that doesn't have a corresponding name on the
system (e.g. because the user/group account was deleted) it
uses the empty string in the uname/gname field now instead
of "root". Using "root" as the default was a bad idea
because on extraction the uname/gname fields are supposed
to override the uid/gid fields. So, all archive members
with nameless uids/gids belonged to the root user after
extraction.

Lib/tarfile.py

@@ -945,8 +945,8 @@ class TarInfo(object):
         self.chksum = 0         # header checksum
         self.type = REGTYPE     # member type
         self.linkname = ""      # link name
-        self.uname = "root"     # user name
-        self.gname = "root"     # group name
+        self.uname = ""         # user name
+        self.gname = ""         # group name
         self.devmajor = 0       # device major number
         self.devminor = 0       # device minor number
 
@@ -1124,8 +1124,8 @@ class TarInfo(object):
             info.get("type", REGTYPE),
             stn(info.get("linkname", ""), 100, encoding, errors),
             info.get("magic", POSIX_MAGIC),
-            stn(info.get("uname", "root"), 32, encoding, errors),
-            stn(info.get("gname", "root"), 32, encoding, errors),
+            stn(info.get("uname", ""), 32, encoding, errors),
+            stn(info.get("gname", ""), 32, encoding, errors),
             itn(info.get("devmajor", 0), 8, format),
             itn(info.get("devminor", 0), 8, format),
             stn(info.get("prefix", ""), 155, encoding, errors)

Misc/NEWS

@@ -88,6 +88,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #9065: tarfile no longer uses "root" as the default for the uname and
+  gname field.
+
 - Issue #8980: Fixed a failure in distutils.command check that was shadowed
   by an environment that does not have docutils. Patch by Arfrever.