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Source file : zip-headers.ads


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--    /../    |.|   |.____/     |.|__|.|  /....|  __\..\
--  _/../___  |.|   |.|    ===  |..__..| |. = .| | = ..|
-- /_______/  |_|  /__|        /__|  |_|  \__\_|  \__\_|

--  Zip.Headers
---------------
--
--  This package provides:
--
-- * Definiton of PKZIP information structures (cf appnote.txt),
-- * Reading a header from a data stream (Read_and_check),
-- * Copying a header from a buffer (Copy_and_check)
-- * Writing a header to a data stream (Write)

  -- Some quick explanations about the Zip file structure - GdM 2001, 2012
  --
  -- The zip archive containing N entries can be roughly seen as
  -- a data stream with the following structure:
  --
  -- 1) {local header, then compressed data} - that, N times
  -- 2) central directory, with a summary of each of the N entries
  -- 3) end-of-central-directory, with a summary of the central directory
  --
  -- Since N is not necessarily known before or during the phase 1,
  -- the central directory's size is also potentially unknown.
  -- Then obvious place for the central directory is *after* the data,
  -- it is why it appears on phase 2.
  --
  -- An advantage of that structure is that the .ZIP archive can be later
  -- appended to an .EXE, for self-extracting purposes, or to other
  -- kind of files.
  --
  -- So, the most general infos are at the end, and we crawl back
  -- for more precise infos:
  --
  --  1) end-of-central-directory
  --  2) central directory
  --  3) zipped data entries

-- Change log:
-- ==========
--
-- 22-Nov-2012: GdM: End-of-central-directory loaded in a single stream Read
--                      operation instead of up to ~1.4 million Read
--                      operations (for a non Zip file with 65535 times
--                      the letter 'P'). Execution flow simplified, without
--                      use of exceptions. Massive speedup there, on files
--                      that are either invalid Zip files, or Zip files with
--                      a large comment.
--
-- 30-Oct-2012: GdM: Removed all profiles using Zip_Streams' objects
--                      with accesses (cf 25-Oct's modifications)
-- 25-Oct-2012: GdM: Some procedures using Zip_Streams' objects also with
--                    pointer-free profiles (no more 'access' or access type)
-- 16-Nov-2009: GdM: Replaced Ada.Calendar.Time by Zip.Time in headers, due to
--                   perf. issues in some run-times' Ada.Calendar.Time_Of

with Interfaces;
with Zip_Streams;  use Zip_Streams;

package Zip.Headers is

  use Interfaces;

  ----------------------------------------------------------------------
  -- PKZIP data descriptor, put after streamed compressed data - PK78 --
  ----------------------------------------------------------------------

  type Data_descriptor is record
    -- PK78                           --  1.. 4
    crc_32             : Unsigned_32; --  5.. 8
    compressed_size,
    uncompressed_size  : Unsigned_32;
  end record;

  data_descriptor_length : constant:= 16;

  -- This header needs to be read in continuation of
  -- the compressed data -> access to a buffer
  procedure Copy_and_check(
    buffer        : in     Byte_Buffer;
    the_data_desc :    out Data_descriptor
  );

  procedure Read_and_check(
    stream        : in out Root_Zipstream_Type'Class;
    the_data_desc :    out Data_descriptor
  );

  bad_data_descriptor: exception;

  procedure Write(
    stream        : in out Root_Zipstream_Type'Class;
    the_data_desc : in     Data_descriptor
  );

  -----------------------------------------------------------------------
  -- PKZIP local file header, in front of every file in archive - PK34 --
  -----------------------------------------------------------------------

  --  Appnote: 4.4.4 general purpose bit flag: (2 bytes)
  --
  --  Bit 0:  If set, indicates that the file is encrypted.
  Encryption_Flag_Bit        : constant := 2 **  0;
  --  Bit 1:  If set, indicates an EOS marker is used.
  LZMA_EOS_Flag_Bit          : constant := 2 **  1;
  --  Bit 11: Language encoding flag (EFS). If this bit is set, the filename and
  --          comment fields for this file MUST be encoded using UTF-8.
  Language_Encoding_Flag_Bit : constant := 2 ** 11;

  type Local_File_Header is record
    -- PK34                                --  1.. 4
    needed_extract_version : Unsigned_16;  --  5.. 6
    bit_flag               : Unsigned_16;  --  Appnote: 4.4.4 general purpose bit flag
    zip_type               : Unsigned_16;
    file_timedate          : Time;
    dd                     : Data_descriptor;
    filename_length,
    extra_field_length     : Unsigned_16;
  end record;

  local_header_length: constant:= 30;

  procedure Read_and_check(
    stream : in out Root_Zipstream_Type'Class;
    header :    out Local_File_Header
  );

  bad_local_header: exception;

  procedure Write (
    stream : in out Root_Zipstream_Type'Class;
    header : in     Local_File_Header
  );

  -------------------------------------------------------
  -- PKZIP file header, as in central directory - PK12 --
  -------------------------------------------------------
  -- NB: a central header contains a local header in the middle

  type Central_File_Header is record
    -- PK12                                  --  1.. 4
    made_by_version     : Unsigned_16;       --  5.. 6
    short_info          : Local_File_Header; --  7..32
    comment_length      : Unsigned_16;       -- 33..34
    disk_number_start   : Unsigned_16;
    internal_attributes : Unsigned_16; -- internal properties of data
    external_attributes : Unsigned_32; -- 1st byte if MS-DOS: see below
    local_header_offset : Unsigned_32;
  end record;

  -- MS-DOS external attributes:
  --
  --   Bit 0     Read-Only
  --   Bit 1     Hidden
  --   Bit 2     System
  --   Bit 3     Volume Label
  --   Bit 4     Directory
  --   Bit 5     Archive

  central_header_length: constant:= 46;

  procedure Read_and_check(
    stream : in out Root_Zipstream_Type'Class;
    header :    out Central_File_Header
  );

  bad_central_header: exception;

  procedure Write(
    stream : in out Root_Zipstream_Type'Class;
    header : in     Central_File_Header
  );

  -------------------------------------------
  -- PKZIP end-of-central-directory - PK56 --
  -------------------------------------------

  type End_of_Central_Dir is record
    -- PK56                           --  1.. 4
    disknum            : Unsigned_16; --  5.. 6
    disknum_with_start : Unsigned_16;
    disk_total_entries : Unsigned_16;
    total_entries      : Unsigned_16;
    central_dir_size   : Unsigned_32;
    central_dir_offset : Unsigned_32;
    main_comment_length: Unsigned_16;
    -- The Zip archive may be appended to another file (for instance an
    -- executable for self-extracting purposes) of size N.
    -- Then, all offsets need to be shifted by N.
    -- N=0 if the Zip archive is on its own.
    -- The real offset of the end-of-central-dir
    -- will be N + central_dir_size + central_dir_offset.
    -- This way, we have an unique chance to determine N when reading the
    -- end-of-central-dir. N is stored in the field hereafter.
    offset_shifting    : Unsigned_32;
  end record;

  end_of_central_dir_length : constant:= 22;

  -- This header needs to be read in special
  -- ways (see Load) -> access to a buffer
  procedure Copy_and_check(
    buffer  : in     Byte_Buffer;
    the_end :    out End_of_Central_Dir
  );

  procedure Read_and_check(
    stream  : in out Root_Zipstream_Type'Class;
    the_end :    out End_of_Central_Dir
  );

  bad_end: exception;

  -- A bit more elaborated: from an open file (not a stream),
  -- find the End-of-Central-dir and load it; keep the file open.
  procedure Load(
    stream  : in out Root_Zipstream_Type'Class;
    the_end :    out End_of_Central_Dir
  );

  procedure Write(
    stream  : in out Root_Zipstream_Type'Class;
    the_end : in     End_of_Central_Dir
  );

end Zip.Headers;

Zip-Ada: Ada library for zip archive files (.zip). Ada programming.
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