extra.fld

zip压缩

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, 20010517

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

          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:

          0x0001        ZIP64 extended information extra field
          0x0007        AV Info
          0x0009        OS/2 extended attributes      (also Info-ZIP)
          0x000a        NTFS (Win9x/WinNT FileTimes)
          0x000c        OpenVMS                       (also Info-ZIP)
          0x000d        Unix
          0x000f        Patch Descriptor
          0x0014        PKCS#7 Store for X.509 Certificates
          0x0015        X.509 Certificate ID and Signature for
                        individual file
          0x0016        X.509 Certificate ID for Central Directory

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

          0x0065        IBM S/390 attributes - uncompressed
          0x0066        IBM S/390 attributes - compressed
          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 )
          0x4154        Tandem NSK
          0x4341        Acorn/SparkFS (David Pilling)
          0x4453        Windows NT security descriptor (binary ACL)
          0x4704        VM/CMS
          0x470f        MVS
          0x4854        Theos, old inofficial port
          0x4b46        FWKCS MD5 (see below)
          0x4c41        OS/2 access control list (text ACL)
          0x4d49        Info-ZIP OpenVMS (obsolete)
          0x4d63        Macintosh SmartZIP, by Macro Bambini
          0x4f4c        Xceed original location extra field
          0x5356        AOS/VS (binary ACL)
          0x5455        extended timestamp
          0x5855        Info-ZIP Unix (original; also OS/2, NT, etc.)
          0x554e        Xceed unicode extra field
          0x6542        BeOS (BeBox, PowerMac, etc.)
          0x6854        Theos
          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 (4)
          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 ("AL")
          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 ("AL")
          TSize         Short       total data size for this block (4)
          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 ("SD")
          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 ("SD")
          TSize         Short       total data size for this block (4)
          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 "NTFS" attributes
          "extra" block, introduced with the release of PKZIP 2.50 for
          Windows. (Last Revision 20001118)

          (Note: At this time the Mtime, Atime and Ctime values may
          be used on any WIN32 system.)
         [Info-ZIP note: In the current implementations, this field has
          a fixed total data size of 32 bytes and is only stored as local
          extra field.]

          Value         Size        Description
          -----         ----        -----------
  (NTFS)  0x000a        Short       Tag for this "extra" block type
          TSize         Short       Total Data Size for this block
          Reserved      Long        for future use
          Tag1          Short       NTFS attribute tag value #1
          Size1         Short       Size of attribute #1, in bytes
          (var.)        SubSize1    Attribute #1 data
          .
          .
          .
          TagN          Short       NTFS attribute tag value #N
          SizeN         Short       Size of attribute #N, in bytes
          (var.)        SubSize1    Attribute #N data

          For NTFS, values for Tag1 through TagN are as follows:
          (currently only one set of attributes is defined for NTFS)

          Tag        Size       Description
          -----      ----       -----------
          0x0001     2 bytes    Tag for attribute #1
          Size1      2 bytes    Size of attribute #1, in bytes (24)
          Mtime      8 bytes    64-bit NTFS file last modification time
          Atime      8 bytes    64-bit NTFS file last access time
          Ctime      8 bytes    64-bit NTFS file creation time

          The total length for this block is 28 bytes, resulting in a
          fixed size value of 32 for the TSize field of the NTFS block.

          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 OpenVMS Extra Field:
          ==========================

          The following is the layout of PKWARE's OpenVMS 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       OpenVMS attribute tag value #1
          Size1         Short       Size of attribute #1, in bytes
          (var.)        Size1       Attribute #1 data
          .
          .
          .
          TagN          Short       OpenVMS 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
             OpenVMS C.  Neither of these values will ever be zero.

          2. No word alignment or padding is performed.

          3. A well-behaved PKZIP/OpenVMS 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 ("JM")
          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-