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unzip-6.0/proginfo/extrafld.txt  view on Meta::CPAN

         -Info-ZIP Unix Extra Field (type 1):
          ==================================

          The following is the layout of the old Info-ZIP extra block for
          Unix.  It has been replaced by the extended-timestamp extra block
          (0x5455) and the Unix type 2 extra block (0x7855).
          (Last Revision 19970118)

          Local-header version:

          Value         Size        Description
          -----         ----        -----------
  (Unix1) 0x5855        Short       tag for this extra block type ("UX")
          TSize         Short       total data size for this block
          AcTime        Long        time of last access (UTC/GMT)
          ModTime       Long        time of last modification (UTC/GMT)
          UID           Short       Unix user ID (optional)
          GID           Short       Unix group ID (optional)

          Central-header version:

          Value         Size        Description
          -----         ----        -----------
  (Unix1) 0x5855        Short       tag for this extra block type ("UX")
          TSize         Short       total data size for this block
          AcTime        Long        time of last access (GMT/UTC)
          ModTime       Long        time of last modification (GMT/UTC)

          The file access and modification times are in standard Unix signed-
          long format, indicating the number of seconds since 1 January 1970
          00:00:00.  The times are relative to Coordinated Universal Time
          (UTC), also sometimes referred to as Greenwich Mean Time (GMT).  To
          convert to local time, the software must know the local timezone
          offset from UTC/GMT.  The modification time may be used by non-Unix
          systems to support inter-timezone freshening and updating of zip
          archives.

          The local-header extra block may optionally contain UID and GID
          info for the file.  The local-header TSize value is the only
          indication of this.  Note that Unix UIDs and GIDs are usually
          specific to a particular machine, and they generally require root
          access to restore.

          This extra field type is obsolete, but it has been in use since
          mid-1994.  Therefore future archiving software should continue to
          support it.  Some guidelines:

              An archive member should either contain the old "Unix1"
              extra field block or the new extra field types "time" and/or
              "Unix2".

              If both the old "Unix1" block type and one or both of the new
              block types "time" and "Unix2" are found, the "Unix1" block
              should be considered invalid and ignored.

              Unarchiving software should recognize both old and new extra
              field block types, but the info from new types overrides the
              old "Unix1" field.

              Archiving software should recognize "Unix1" extra fields for
              timestamp comparison but never create it for updated, freshened
              or new archive members.  When copying existing members to a new
              archive, any "Unix1" extra field blocks should be converted to
              the new "time" and/or "Unix2" types.


         -Info-ZIP UNIX Extra Field (type 2):
          ==================================

          The following is the layout of the new Info-ZIP extra block for
          Unix.  (Last Revision 19960922)

          Local-header version:

          Value         Size        Description
          -----         ----        -----------
  (Unix2) 0x7855        Short       tag for this extra block type ("Ux")
          TSize         Short       total data size for this block (4)
          UID           Short       Unix user ID
          GID           Short       Unix group ID

          Central-header version:

          Value         Size        Description
          -----         ----        -----------
  (Unix2) 0x7855        Short       tag for this extra block type ("Ux")
          TSize         Short       total data size for this block (0)

          The data size of the central-header version is zero; it is used
          solely as a flag that UID/GID info is present in the local-header
          extra field.  If additional fields are ever added to the local
          version, the central version may be extended to indicate this.

          Note that Unix UIDs and GIDs are usually specific to a particular
          machine, and they generally require root access to restore.


         -Info-ZIP New Unix Extra Field:
          ====================================

          Currently stores Unix UIDs/GIDs up to 32 bits.
          (Last Revision 20080509)

          Value         Size        Description
          -----         ----        -----------
  (UnixN) 0x7875        Short       tag for this extra block type ("ux")
          TSize         Short       total data size for this block
          Version       1 byte      version of this extra field, currently 1
          UIDSize       1 byte      Size of UID field
          UID           Variable    UID for this entry
          GIDSize       1 byte      Size of GID field
          GID           Variable    GID for this entry

          Currently Version is set to the number 1.  If there is a need
          to change this field, the version will be incremented.  Changes
          may not be backward compatible so this extra field should not be
          used if the version is not recognized.

          UIDSize is the size of the UID field in bytes.  This size should
          match the size of the UID field on the target OS.