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The following are the known types of zipfile extra fields as of this
writing.  Extra fields are documented in PKWARE's appnote.txt and are
intended to allow for backward- and forward-compatible extensions to
the zipfile format.  Multiple extra-field types may be chained together,
provided that the total length of all extra-field data is less than 64KB.
(In fact, PKWARE requires that the total length of the entire file header,
including timestamp, file attributes, filename, comment, extra field, etc.,
be no more than 64KB.)

Each extra-field type (or subblock) must contain a four-byte header con-
sisting of a two-byte header ID and a two-byte length (little-endian) for
the remaining data in the subblock.  If there are additional subblocks
within the extra field, the header for each one will appear immediately
following the data for the previous subblock (i.e., with no padding for
alignment).

All integer fields in the descriptions below are in little-endian (Intel)
format unless otherwise specified.  Note that "Short" means two bytes,
"Long" means four bytes, and "Long-Long" means eight bytes, regardless
of their native sizes.  Unless specifically noted, all integer fields should
be interpreted as unsigned (non-negative) numbers.

Christian Spieler, 19980918

                        -------------------------

          Header ID's of 0 thru 31 are reserved for use by PKWARE.
          The remaining ID's can be used by third party vendors for
          proprietary usage.

          The current Header ID mappings defined by PKWARE are:

          0x0007        AV Info
          0x0009        OS/2 extended attributes      (also Info-ZIP)
          0x000a        PKWARE Win95/WinNT FileTimes  [undocumented!]
          0x000c        PKWARE VAX/VMS                (also Info-ZIP)
          0x000d        PKWARE Unix
          0x000f        Patch Descriptor

          The Header ID mappings defined by Info-ZIP and third parties are:

          0x07c8        Info-ZIP Macintosh (old, J. Lee)
          0x2605        ZipIt Macintosh (first version)
          0x2705        ZipIt Macintosh v 1.3.5 and newer (w/o full filename)
          0x334d        Info-ZIP Macintosh (new, D. Haase's 'Mac3' field )
          0x4341        Acorn/SparkFS (David Pilling)
          0x4453        Windows NT security descriptor (binary ACL)
          0x4704        VM/CMS
          0x470f        MVS
          0x4b46        FWKCS MD5 (third party, see below)
          0x4c41        OS/2 access control list (text ACL)
          0x4d49        Info-ZIP VMS (VAX or Alpha)
          0x5356        AOS/VS (binary ACL)
          0x5455        extended timestamp
          0x5855        Info-ZIP Unix (original; also OS/2, NT, etc.)
          0x6542        BeOS (BeBox, PowerMac, etc.)
          0x756e        ASi Unix
          0x7855        Info-ZIP Unix (new)
          0xfb4a        SMS/QDOS

The following are detailed descriptions of the known extra-field block types:

         -OS/2 Extended Attributes Extra Field:
          ====================================

          The following is the layout of the OS/2 extended attributes "extra"
          block.  (Last Revision 19960922)

          Note: all fields stored in Intel low-byte/high-byte order.

          Local-header version:

          Value         Size            Description
          -----         ----            -----------
  (OS/2)  0x0009        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            uncompressed EA data size
          CType         Short           compression type
          EACRC         Long            CRC value for uncompressed EA data
          (var.)        variable        compressed EA data

          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (OS/2)  0x0009        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            size of uncompressed local EA data

          The value of CType is interpreted according to the "compression
          method" section above; i.e., 0 for stored, 8 for deflated, etc.

          The OS/2 extended attribute structure (FEA2LIST) is compressed and
          then stored in its entirety within this structure.  There will only
          ever be one block of data in the variable-length field.


         -OS/2 Access Control List Extra Field:
          ====================================

          The following is the layout of the OS/2 ACL extra block.
          (Last Revision 19960922)

          Local-header version:

          Value         Size            Description
          -----         ----            -----------
  (ACL)   0x4c41        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            uncompressed ACL data size
          CType         Short           compression type
          EACRC         Long            CRC value for uncompressed ACL data
          (var.)        variable        compressed ACL data

          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (ACL)   0x4c41        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            size of uncompressed local ACL data

          The value of CType is interpreted according to the "compression
          method" section above; i.e., 0 for stored, 8 for deflated, etc.

          The uncompressed ACL data consist of a text header of the form
          "ACL1:%hX,%hd\n", where the first field is the OS/2 ACCINFO acc_attr
          member and the second is acc_count, followed by acc_count strings
          of the form "%s,%hx\n", where the first field is acl_ugname (user
          group name) and the second acl_access.  This block type will be
          extended for other operating systems as needed.


         -Windows NT Security Descriptor Extra Field:
          ==========================================

          The following is the layout of the NT Security Descriptor (another
          type of ACL) extra block.  (Last Revision 19960922)

          Local-header version:

          Value         Size            Description
          -----         ----            -----------
  (SD)    0x4453        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            uncompressed SD data size
          Version       Byte            version of uncompressed SD data format
          CType         Short           compression type
          EACRC         Long            CRC value for uncompressed SD data
          (var.)        variable        compressed SD data

          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (SD)    0x4453        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            size of uncompressed local SD data

          The value of CType is interpreted according to the "compression
          method" section above; i.e., 0 for stored, 8 for deflated, etc.
          Version specifies how the compressed data are to be interpreted
          and allows for future expansion of this extra field type.  Currently
          only version 0 is defined.

          For version 0, the compressed data are to be interpreted as a single
          valid Windows NT SECURITY_DESCRIPTOR data structure, in self-relative
          format.


         -PKWARE Win95/WinNT Extra Field:
          ==============================

          The following description covers PKWARE's undocumented
          Windows 95 & Windows NT extra field, introduced with the
          release of PKZIP for Windows 2.50. (Last Revision 19980425)

          This field has a fixed data size of 32 bytes and is only stored
          as local extra field.

          Value         Size            Description
          -----         ----            -----------
 (WinNT)  0x000a        Short           Tag for this "extra" block type
          TSize         Short           Total Data Size for this block
          Unknwn1       Long            ???? (all 0 ?)
          Unknwn2       Long            ????
          ModTime       Long-Long       64-bit NTFS last-modified filetime
          AccTime       Long-Long       64-bit NTFS last-access filetime
          CreTime       Long-Long       64-bit NTFS creation filetime

          The NTFS filetimes are 64-bit unsigned integers, stored in Intel
          (least significant byte first) byte order. They determine the
          number of 1.0E-07 seconds (1/10th microseconds!) past WinNT "epoch",
          which is "01-Jan-1601 00:00:00 UTC".


         -PKWARE VAX/VMS Extra Field:
          ==========================

          The following is the layout of PKWARE's VAX/VMS attributes "extra"
          block.  (Last Revision 12/17/91)

          Note: all fields stored in Intel low-byte/high-byte order.

          Value         Size            Description
          -----         ----            -----------
  (VMS)   0x000c        Short           Tag for this "extra" block type
          TSize         Short           Total Data Size for this block
          CRC           Long            32-bit CRC for remainder of the block
          Tag1          Short           VMS attribute tag value #1
          Size1         Short           Size of attribute #1, in bytes
          (var.)        Size1           Attribute #1 data
          .
          .
          .
          TagN          Short           VMS attribute tage value #N
          SizeN         Short           Size of attribute #N, in bytes
          (var.)        SizeN           Attribute #N data

          Rules:

          1. There will be one or more of attributes present, which will
             each be preceded by the above TagX & SizeX values.  These
             values are identical to the ATR$C_XXXX and ATR$S_XXXX constants
             which are defined in ATR.H under VMS C.  Neither of these values
             will ever be zero.

          2. No word alignment or padding is performed.

          3. A well-behaved PKZIP/VMS program should never produce more than
             one sub-block with the same TagX value.  Also, there will never
             be more than one "extra" block of type 0x000c in a particular
             directory record.


         -Info-ZIP VMS Extra Field:
          ========================

          The following is the layout of Info-ZIP's VMS attributes extra
          block for VAX or Alpha AXP.  The local-header and central-header
          versions are identical.  (Last Revision 19960922)

          Value         Size            Description
          -----         ----            -----------
  (VMS2)  0x4d49        Short           tag for this extra block type
          TSize         Short           total data size for this block
          ID            Long            block ID
          Flags         Short           info bytes
          BSize         Short           uncompressed block size
          Reserved      Long            (reserved)
          (var.)        variable        compressed VMS file-attributes block

          The block ID is one of the following unterminated strings:

                "VFAB"          struct FAB
                "VALL"          struct XABALL
                "VFHC"          struct XABFHC
                "VDAT"          struct XABDAT
                "VRDT"          struct XABRDT
                "VPRO"          struct XABPRO
                "VKEY"          struct XABKEY
                "VMSV"          version (e.g., "V6.1"; truncated at hyphen)
                "VNAM"          reserved

          The lower three bits of Flags indicate the compression method.  The
          currently defined methods are:

                0       stored (not compressed)
                1       simple "RLE"
                2       deflated

          The "RLE" method simply replaces zero-valued bytes with zero-valued
          bits and non-zero-valued bytes with a "1" bit followed by the byte
          value.

          The variable-length compressed data contains only the data corre-
          sponding to the indicated structure or string.  Typically multiple
          VMS2 extra fields are present (each with a unique block type).


         -Info-ZIP Macintosh Extra Field:
          ==============================

          The following is the layout of the (old) Info-ZIP resource-fork extra
          block for Macintosh.  The local-header and central-header versions
          are identical.  (Last Revision 19960922)

          Value         Size            Description
          -----         ----            -----------
  (Mac)   0x07c8        Short           tag for this extra block type
          TSize         Short           total data size for this block
          "JLEE"        beLong          extra-field signature
          FInfo         16 bytes        Macintosh FInfo structure
          CrDat         beLong          HParamBlockRec fileParam.ioFlCrDat
          MdDat         beLong          HParamBlockRec fileParam.ioFlMdDat
          Flags         beLong          info bits
          DirID         beLong          HParamBlockRec fileParam.ioDirID
          VolName       28 bytes        volume name (optional)

          All fields but the first two are in native Macintosh format
          (big-endian Motorola order, not little-endian Intel).  The least
          significant bit of Flags is 1 if the file is a data fork, 0 other-
          wise.  In addition, if this extra field is present, the filename
          has an extra 'd' or 'r' appended to indicate data fork or resource
          fork.  The 28-byte VolName field may be omitted.


         -ZipIt Macintosh Extra Field (long):
          ==================================

          The following is the layout of the ZipIt extra block for Macintosh.
          The local-header and central-header versions are identical.
          (Last Revision 19970130)

          Value         Size            Description
          -----         ----            -----------
  (Mac2)  0x2605        Short           tag for this extra block type
          TSize         Short           total data size for this block
          "ZPIT"        beLong          extra-field signature
          FnLen         Byte            length of FileName
          FileName      variable        full Macintosh filename
          FileType      Byte[4]         four-byte Mac file type string
          Creator       Byte[4]         four-byte Mac creator string


         -ZipIt Macintosh Extra Field (short):
          ===================================

          The following is the layout of a shortened variant of the
          ZipIt extra block for Macintosh (without "full name" entry).
          This variant is used by ZipIt 1.3.5 and newer for entries that
          do not need a "full Mac filename" record.
          The local-header and central-header versions are identical.
          (Last Revision 19980903)

          Value         Size            Description
          -----         ----            -----------
  (Mac2b) 0x2705        Short           tag for this extra block type
          TSize         Short           total data size for this block
          "ZPIT"        beLong          extra-field signature
          FileType      Byte[4]         four-byte Mac file type string
          Creator       Byte[4]         four-byte Mac creator string


         -Info-ZIP Macintosh Extra Field (new):
          ====================================

          The following is the layout of the (new) Info-ZIP extra
          block for Macintosh, designed by Dirk Haase.
          All values are in little-endian.
          (Last Revision 19981005)

          Local-header version:

          Value         Size            Description
          -----         ----            -----------
  (Mac3)  0x334d        Short           tag for this extra block type ("M3")
          TSize         Short           total data size for this block
          BSize         Long            uncompressed finder attribute data size
          Flags         Short           info bits
          fdType        Byte[4]         Type of the File (4-byte string)
          fdCreator     Byte[4]         Creator of the File (4-byte string)
          (CType)       Short           compression type
          (CRC)         Long            CRC value for uncompressed MacOS data
          Attribs       variable        finder attribute data (see below)


          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (Mac3)  0x334d        Short           tag for this extra block type ("M3")
          TSize         Short           total data size for this block
          BSize         Long            uncompressed finder attribute data size
          Flags         Short           info bits
          fdType        Byte[4]         Type of the File (4-byte string)
          fdCreator     Byte[4]         Creator of the File (4-byte string)

          The third bit of Flags in both headers indicates whether
          the LOCAL extra field is uncompressed (and therefore whether CType
          and CRC are omitted):

          Bits of the Flags:
              bit 0           if set, file is a data fork; otherwise unset
              bit 1           if set, filename will be not changed
              bit 2           if set, Attribs is uncompressed (no CType, CRC)
              bit 3           if set, date and times are in 64 bit
                              if zero date and times are in 32 bit.
              bit 4           if set, timezone offsets fields for the native
                              Mac times are omitted (UTC support deactivated)
              bits 5-15       reserved;


          Attributes:

          Attribs is a Mac-specific block of data in little-endian format with
          the following structure (if compressed, uncompress it first):

          Value         Size            Description
          -----         ----            -----------
          fdFlags       Short           Finder Flags
          fdLocation.v  Short           Finder Icon Location
          fdLocation.h  Short           Finder Icon Location
          fdFldr        Short           Folder containing file

          FXInfo        16 bytes        Macintosh FXInfo structure
            FXInfo-Structure:
                fdIconID        Short
                fdUnused[3]     Short       unused but reserved 6 bytes
                fdScript        Byte        Script flag and number
                fdXFlags        Byte        More flag bits
                fdComment       Short       Comment ID
                fdPutAway       Long        Home Dir ID

          FVersNum      Byte            file version number
                                        may be not used by MacOS
          ACUser        Byte            directory access rights

          FlCrDat       ULong           date and time of creation
          FlMdDat       ULong           date and time of last modification
          FlBkDat       ULong           date and time of last backup
            These time numbers are original Mac FileTime values (local time!).
            Currently, date-time width is 32-bit, but future version may
            support be 64-bit times (see flags)

          CrGMTOffs     Long(signed!)   difference "local Creat. time - UTC"
          MdGMTOffs     Long(signed!)   difference "local Modif. time - UTC"
          BkGMTOffs     Long(signed!)   difference "local Backup time - UTC"
            These "local time - UTC" differences (stored in seconds) may be
            used to support timestamp adjustment after inter-timezone transfer.
            These fields are optional; bit 4 of the flags word controls their
            presence.

          Charset       Short           TextEncodingBase (Charset)
                                        valid for the following two fields

          FullPath      variable        Path of the current file.
                                        Zero terminated string (C-String)
                                        Currently coded in the native Charset.

          Comment       variable        Finder Comment of the current file.
                                        Zero terminated string (C-String)
                                        Currently coded in the native Charset.


         -Acorn SparkFS Extra Field:
          =========================

          The following is the layout of David Pilling's SparkFS extra block
          for Acorn RISC OS.  The local-header and central-header versions are
          identical.  (Last Revision 19960922)

          Value         Size            Description
          -----         ----            -----------
  (Acorn) 0x4341        Short           tag for this extra block type
          TSize         Short           total data size for this block
          "ARC0"        Long            extra-field signature
          LoadAddr      Long            load address or file type
          ExecAddr      Long            exec address
          Attr          Long            file permissions
          Zero          Long            reserved; always zero

          The following bits of Attr are associated with the given file
          permissions:

                bit 0           user-writable ('W')
                bit 1           user-readable ('R')
                bit 2           reserved
                bit 3           locked ('L')
                bit 4           publicly writable ('w')
                bit 5           publicly readable ('r')
                bit 6           reserved
                bit 7           reserved


         -VM/CMS Extra Field:
          ==================

          The following is the layout of the file-attributes extra block for
          VM/CMS.  The local-header and central-header versions are
          identical.  (Last Revision 19960922)

          Value         Size            Description
          -----         ----            -----------
 (VM/CMS) 0x4704        Short           tag for this extra block type
          TSize         Short           total data size for this block
          flData        variable        file attributes data

          flData is an uncompressed fldata_t struct.


         -MVS Extra Field:
          ===============

          The following is the layout of the file-attributes extra block for
          MVS.  The local-header and central-header versions are identical.
          (Last Revision 19960922)

          Value         Size            Description
          -----         ----            -----------
  (MVS)   0x470f        Short           tag for this extra block type
          TSize         Short           total data size for this block
          flData        variable        file attributes data

          flData is an uncompressed fldata_t struct.


         -PKWARE Unix Extra Field:
          ========================

          The following is the layout of PKWARE's Unix "extra" block.
          It was introduced with the release of PKZIP for Unix 2.50.
          Note: all fields are stored in Intel low-byte/high-byte order.
          (Last Revision 19980901)

          This field has a minimum data size of 12 bytes and is only stored
          as local extra field.

          Value         Size            Description
          -----         ----            -----------
 (Unix0)  0x000d        Short           Tag for this "extra" block type
          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
          GID           Short           Unix group ID
          (var)         variable        Variable length data field

          The variable length data field will contain file type
          specific data.  Currently the only values allowed are
          the original "linked to" file names for hard or symbolic links.

          The fixed part of this field has the same layout as Info-ZIP's
          abandoned "Unix1 timestamps & owner ID info" extra field;
          only the two tag bytes are different.


         -PATCH Descriptor Extra Field:
          ============================

          The following is the layout of the Patch Descriptor "extra"
          block.

          Note: all fields stored in Intel low-byte/high-byte order.

          Value         Size            Description
          -----         ----            -----------
  (Patch) 0x000f        Short           Tag for this "extra" block type
          TSize         Short           Size of the total "extra" block
          Version       Short           Version of the descriptor
          Flags         Long            Actions and reactions (see below)
          OldSize       Long            Size of the file about to be patched
          OldCRC        Long            32-bit CRC of the file about to be patched
          NewSize       Long            Size of the resulting file
          NewCRC        Long            32-bit CRC of the resulting file


          Actions and reactions

          Bits          Description
          ----          ----------------
          0             Use for autodetection
          1             Treat as selfpatch
          2-3           RESERVED
          4-5           Action (see below)
          6-7           RESERVED
          8-9           Reaction (see below) to absent file
          10-11         Reaction (see below) to newer file
          12-13         Reaction (see below) to unknown file
          14-15         RESERVED
          16-31         RESERVED

          Actions

          Action       Value
          ------       -----
          none         0
          add          1
          delete       2
          patch        3

          Reactions

          Reaction     Value
          --------     -----
          ask          0
          skip         1
          ignore       2
          fail         3


         -Extended Timestamp Extra Field:
          ==============================

          The following is the layout of the extended-timestamp extra block.
          (Last Revision 19970118)

          Local-header version:

          Value         Size            Description
          -----         ----            -----------
  (time)  0x5455        Short           tag for this extra block type
          TSize         Short           total data size for this block
          Flags         Byte            info bits
          (ModTime)     Long            time of last modification (UTC/GMT)
          (AcTime)      Long            time of last access (UTC/GMT)
          (CrTime)      Long            time of original creation (UTC/GMT)

          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (time)  0x5455        Short           tag for this extra block type
          TSize         Short           total data size for this block
          Flags         Byte            info bits (refers to local header!)
          (ModTime)     Long            time of last modification (UTC/GMT)

          The central-header extra field contains the modification time only,
          or no timestamp at all.  TSize is used to flag its presence or
          absence.  But note:

              If "Flags" indicates that Modtime is present in the local header
              field, it MUST be present in the central header field, too!
              This correspondence is required because the modification time
              value may be used to support trans-timezone freshening and
              updating operations with zip archives.

          The time values 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 lower three bits of Flags in both headers indicate which time-
          stamps are present in the LOCAL extra field:

                bit 0           if set, modification time is present
                bit 1           if set, access time is present
                bit 2           if set, creation time is present
                bits 3-7        reserved for additional timestamps; not set

          Those times that are present will appear in the order indicated, but
          any combination of times may be omitted.  (Creation time may be
          present without access time, for example.)  TSize should equal
          (1 + 4*(number of set bits in Flags)), as the block is currently
          defined.  Other timestamps may be added in the future.


         -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
          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
          GID           Short           Unix group ID

          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (Unix1) 0x5855        Short           tag for this extra block type
          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
          TSize         Short           total data size for this block
          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
          TSize         Short           total data size for this block

          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.


         -ASi Unix Extra Field:
          ====================

          The following is the layout of the ASi extra block for Unix.  The
          local-header and central-header versions are identical.
          (Last Revision 19960916)

          Value         Size            Description
          -----         ----            -----------
  (Unix3) 0x756e        Short           tag for this extra block type
          TSize         Short           total data size for this block
          CRC           Long            CRC-32 of the remaining data
          Mode          Short           file permissions
          SizDev        Long            symlink'd size OR major/minor dev num
          UID           Short           user ID
          GID           Short           group ID
          (var.)        variable        symbolic link filename

          Mode is the standard Unix st_mode field from struct stat, containing
          user/group/other permissions, setuid/setgid and symlink info, etc.

          If Mode indicates that this file is a symbolic link, SizDev is the
          size of the file to which the link points.  Otherwise, if the file
          is a device, SizDev contains the standard Unix st_rdev field from
          struct stat (includes the major and minor numbers of the device).
          SizDev is undefined in other cases.

          If Mode indicates that the file is a symbolic link, the final field
          will be the name of the file to which the link points.  The file-
          name length can be inferred from TSize.

          [Note that TSize may incorrectly refer to the data size not counting
           the CRC; i.e., it may be four bytes too small.]


         -BeOS Extra Field:
          ================

          The following is the layout of the file-attributes extra block for
          BeOS.  (Last Revision 19970531)

          Local-header version:

          Value         Size            Description
          -----         ----            -----------
  (BeOS)  0x6542        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            uncompressed file attribute data size
          Flags         Byte            info bits
          (CType)       Short           compression type
          (CRC)         Long            CRC value for uncompressed file attribs
          Attribs       variable        file attribute data

          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (BeOS)  0x6542        Short           tag for this extra block type
          TSize         Short           total data size for this block
          BSize         Long            size of uncompressed local EF block data
          Flags         Byte            info bits

          The least significant bit of Flags in both headers indicates whether
          the LOCAL extra field is uncompressed (and therefore whether CType
          and CRC are omitted):

                bit 0           if set, Attribs is uncompressed (no CType, CRC)
                bits 1-7        reserved; if set, assume error or unknown data

          Currently the only supported compression types are deflated (type 8)
          and stored (type 0); the latter is not used by Info-ZIP's Zip but is
          supported by UnZip.

          Attribs is a BeOS-specific block of data in big-endian format with
          the following structure (if compressed, uncompress it first):

              Value     Size            Description
              -----     ----            -----------
              Name      variable        attribute name (null-terminated string)
              Type      Long            attribute type (32-bit unsigned integer)
              Size      Long Long       data size for this sub-block (64 bits)
              Data      variable        attribute data

          The attribute structure is repeated for every attribute.  The Data
          field may contain anything--text, flags, bitmaps, etc.


         -SMS/QDOS Extra Field:
          ====================

          The following is the layout of the file-attributes extra block for
          SMS/QDOS.  The local-header and central-header versions are identical.
          (Last Revision 19960929)

          Value         Size            Description
          -----         ----            -----------
  (QDOS)  0xfb4a        Short           tag for this extra block type
          TSize         Short           total data size for this block
          LongID        Long            extra-field signature
          (ExtraID)     Long            additional signature/flag bytes
          QDirect       64 bytes        qdirect structure

          LongID may be "QZHD" or "QDOS".  In the latter case, ExtraID will
          be present.  Its first three bytes are "02\0"; the last byte is
          currently undefined.

          QDirect contains the file's uncompressed directory info (qdirect
          struct).  Its elements are in native (big-endian) format:

          d_length      beLong          file length
          d_access      byte            file access type
          d_type        byte            file type
          d_datalen     beLong          data length
          d_reserved    beLong          unused
          d_szname      beShort         size of filename
          d_name        36 bytes        filename
          d_update      beLong          time of last update
          d_refdate     beLong          file version number
          d_backup      beLong          time of last backup (archive date)


         -AOS/VS Extra Field:
          ==================

          The following is the layout of the extra block for Data General
          AOS/VS.  The local-header and central-header versions are identical.
          (Last Revision 19961125)

          Value         Size            Description
          -----         ----            -----------
  (AOSVS) 0x5356        Short           tag for this extra block type
          TSize         Short           total data size for this block
          "FCI\0"       Long            extra-field signature
          Version       Byte            version of AOS/VS extra block (10 = 1.0)
          Fstat         variable        fstat packet
          AclBuf        variable        raw ACL data ($MXACL bytes)

          Fstat contains the file's uncompressed fstat packet, which is one of
          the following:

                normal fstat packet             (P_FSTAT struct)
                DIR/CPD fstat packet            (P_FSTAT_DIR struct)
                unit (device) fstat packet      (P_FSTAT_UNIT struct)
                IPC file fstat packet           (P_FSTAT_IPC struct)

          AclBuf contains the raw ACL data; its length is $MXACL.


         -FWKCS MD5 Extra Field:
          =====================

          The following is the layout of the optional extra block used by the
          FWKCS utility.  There is no local-header version; the following
          applies only to the central header.  (Last Revision 19961207)

          Central-header version:

          Value         Size            Description
          -----         ----            -----------
  (MD5)   0x4b46        Short           tag for this extra block type
          TSize         Short           total data size for this block (19)
          "MD5"         3 bytes         extra-field signature
          MD5hash       16 bytes        128-bit MD5 hash of uncompressed data

          The MD5 hash in this extra block is used to automatically identify
          files independent of their filenames; it is an an enhanced contents-
          signature.

          FWKCS provides an option to strip this extra field, if
          present, from a zipfile central directory. In adding
          this extra field, FWKCS preserves Zipfile Authenticity
          Verification; if stripping this extra field, FWKCS
          preserves all versions of AV through PKZIP version 2.04g.

          ``The MD5 algorithm is being placed in the public domain for review
          and possible adoption as a standard.'' (Ron Rivest, MIT Laboratory
          for Computer Science and RSA Data Security, Inc., April 1992, RFC
          1321, 11.76-77).  FWKCS, and FWKCS Contents_Signature System, are
          trademarks of Frederick W. Kantor.