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%    Copyright (C) 2002 artofcode LLC.  All rights reserved.

% 

% This software is provided AS-IS with no warranty, either express or

% implied.

% 

% This software is distributed under license and may not be copied,

% modified or distributed except as expressly authorized under the terms

% of the license contained in the file LICENSE in this distribution.

% 

% For more information about licensing, please refer to

% http://www.ghostscript.com/licensing/. For information on

% commercial licensing, go to http://www.artifex.com/licensing/ or

% contact Artifex Software, Inc., 101 Lucas Valley Road #110,

% San Rafael, CA  94903, U.S.A., +1(415)492-9861.

% $Id: pdf_rbld.ps,v 1.8 2005/02/07 06:38:02 dan Exp $

% pdf_rbld.ps - Rebuilding of broken PDF files (xref errors)

% This module contains routines that are used if we detect an error

% while reading the xref tables.  These routines will scan the file and

% build an xref table by finding the objects.  We also need to find the

% appropriate trailer dictionary.  Note:  One procedure is also used

% even if we do not need to rebuild a PDF file.

%

% This module cannot rebuild a PDF file which has had errors created inside

% of objects or binary data streams.  It often succeeds with files that

% have had its end of lines converted between unix and dos versions.

% if true --> we have an object with duplicate object and generation numbers.

/dup_obj_gen_num false def

% Note:  This routine is also used by non-rebuild code.

% Store a line in the xref array (Actually Objects and Generations arrays)

% <obj num> (strm num> <obj loc> <gen num>  setxrefentry <obj num> strm num>

% 						 	 <obj loc> <gen num>

/setxrefentry

{	% We store generation numbers as value + 1

	% We reserve 0 to indicate an free xref entry

  1 add			% increment generation number

	% To save space, generations numbers are stored in a lstring unless we

	% find a generation number greater than 255.  If so then transfer to 

	% an larray.

  dup 255 gt {

    Generations ltype /stringtype eq {	% Convert Generations to an larray.

      larray Generations llength lgrowto dup	% Create new larray

	Generations 1 index lget lput dup

      } for

      pop

      /Generations exch store		% Save new Generations larray

    } if

  } if

	% Verify that the new values are for a new object.  If the current

	% entry is null then we have a new entry.

  Objects 4 index lget null eq {

    ObjectStream 4 index 4 index cvx lput % Save ObjectStream object number

    Objects 4 index 3 index cvx lput	% Save object location

    Generations 4 index 2 index lput	% Save geenration number

  } {

	% Verify that the new entry has at least as high a generaton number

	% We accept equal entry number because we have found PDF files in

	% which there are multiple objects with the same object and entry

	% numbers.  The normal xref logic only accepts the first such

	% entry that it finds.  However the 'rebuild PDF' logic can find

	% both such entries.  The correct one is usually the last one.

    Generations 4 index lget 1 index le {

      ObjectStream 4 index 4 index cvx lput % Save ObjectStream object number

      Objects 4 index 3 index cvx lput	% Save object location

      Generations 4 index 2 index lput	% Save geenration number

    } if

	% Set error flag if we have equal object and generation numbers

    Generations 4 index lget 1 index eq { /dup_obj_gen_num true def } if

  } ifelse

} bind def

% Print the contents of the xref array.  This actually consists of two

% arrays (Objects and Generations).  Both are larrays.  larrays are a

% special Ghostscript object which can be arrays with more than 64k

% elements.

/print_xref				% - print_xref -

{ 0 1 Objects llength 1 sub		% stack: 0 1 <number of objects - 1>

  { dup =only				% print object number

    (  ) print

    dup Generations exch lget 1 sub =only % print Generation number

    (  ) print

    dup ObjectStream exch lget ==only	% print ObjectStream object number

    (  ) print

    Objects exch lget ===		% print object location

  } for

  flush

} bind def

% This is the same as the postscript token operator except that

% errors are ignored.

/token_nofail

{

  { token } .internalstopped

  { pop false } if

} bind odef

% Get token from string and check its type

%   <string> <type> typed_token <false>		% no token or not match

%   <string> <type> typed_token <obj> <last> <true>	% matching token type

% Where last is the string remainder

/typed_token

{ exch

  token_nofail			% get token

  {

    dup type			% stack:  type last token type

    4 -1 roll eq {		% stack:  last token bool

      exch true			% desired object found - set exit status

    } {

      pop pop false		% not type - clear stack, set exit status

    } ifelse

  } {

    pop false			% no token - pop type, set exit status

  } ifelse			% check if we got token

} bind def

% Allocate space for post_eof_count to be bound into procedures below.

/post_eof_count 0 def

% We want the location of the trailer dictionary at the start of file.

% First we will find the xref.  Then we will skip over the xref entries

% to the trailer.

/search_start_trailer		% - search_start_trailer <trailer loc>

{ % Read the first 300 bytes and check for xref

  PDFfile 0 setfileposition

  300 string 0 1 299 { 2 copy PDFfile read pop put pop } for

  (xref) search {

    % found 'xref'

    exch pop exch pop length 4 add PDFfile exch setfileposition

    PDFfile token pop		% get starting entry - or 'trailer'

    (trailer) ne {		% if we do not already have 'trailer'

      PDFfile token pop		% get number of entries

      PDFfile token pop pop	% this moves us into the middle of the first entry

      25 string exch		% define working string for readline

      { PDFfile 1 index readline pop pop

      } repeat			% skip entries

      pop			% pop working string

      PDFfile token pop pop	% get 'trailer'

      PDFfile fileposition	% get file position

    } if

  } {

    pop 0			% no xref - should not happen

  } ifelse

} bind def

% We want the location of the trailer dictionary at the end of file.

% We will read the last block of data and search for the final occurance

% of the word 'trailer'

/search_end_trailer		% - search_end_trailer <trailer loc>

{ % Position to read block of data from the end of the file.  Note:  We ignore

  % anything past the last %%EOF since this is not PDF data.

  PDFfile 0 setfileposition

  PDFfile bytesavailable post_eof_count sub	% location of end of data

  dup 4096 .min			% block size to read

				% stack: <file end pos> <block size>

  % move file position to the start of the block

  2 copy sub PDFfile exch setfileposition

  % read block of data

  dup string 0 1 4 -1 roll 1 sub { 2 copy PDFfile read pop put pop } for

  % search for last occurance of 'trailer'

  (trailer) { search not { exit } if pop } loop

  % determine where the trailer is in the file

  %   trailer loc = end loc - remaing string length

  length sub 

} bind def

% We want to find the trailer dictionary.  There is a trailer dictionary

% for each xref object list.  We only want the trailer dictionary associated

% with the first xref object list.  In theory this can be anywhere in the

% file.  However since we are trying to repair a broken file, we cannot simply

% follow the xref links.  So we are falling back to a simple strategy.  We

% find the specified location of the first xref list.  If its location is in

% the first half of the file then we search for the first trailer dictionary

% at the start of the file.  Otherwise we search for the last trailer at the

% end of the file.

/search_trailer			% - search_trailer -

{ % Find the 'startxref' and associated position at the end of the file.

  % Position to read block of data from the end of the file.  Note:  We

  % actually end at the end of the last %%EOF since this is the end of the

  % useful PDF data.  (Some files contain trailing garbage.)

  PDFfile 0 setfileposition

  PDFfile bytesavailable	% size of file

  post_eof_count sub dup	% location of end of last %%EOF

  dup 4096 .min			% block size to read

  % stack: <useful file size> <useful file size file> <block size>

  % move file position to the start of the block

  2 copy sub PDFfile exch setfileposition

  % read block of data

  dup string 0 1 4 -1 roll 1 sub { 2 copy PDFfile read pop put pop } for

  % search for last occurance of 'startxref'

  (startxref) { search not { exit } if pop } loop

  % determine where the trailer is in the file

  %   trailer loc = end loc - remaing string length

  length sub 9 sub

  % move the file to this position and read startxref and position

  PDFfile exch setfileposition

  PDFfile token pop pop PDFfile token pop

  % compare xref position to 1/2 the length of the file and search for trailer

  exch 2 div lt { search_start_trailer } { search_end_trailer } ifelse

  % get the trailer

  PDFfile exch setfileposition		% set to the specified trailer location

  PDFfile traileropdict .pdfrun		% read trailer info

  /Trailer exch def

} bind def

% This routine will determine if there is stuff after the %%EOF.  There is

% supposed to be only a line termination.  However many real life files

% contain some garbage.  This routine checks how much.  We then ignore this

% stuff when we are scanning for objects.

/determine_post_eof_count		% - determine_post_eof_count <count>

{ % Position to read block of data from the end of the file. 

  PDFfile 0 setfileposition

  PDFfile bytesavailable	% size of file

  dup 4096 .min			% block size to read

  % stack: <file size> <file size> <block size>

  % move file position to the start of the block

  2 copy sub PDFfile exch setfileposition

  % read block of data

  dup string 0 1 4 -1 roll 1 sub { 2 copy PDFfile read pop put pop } for

  % search for last occurance of '%%EOF'

  (%%EOF) { search not { exit } if pop } loop

  % how much is left = remaining string length

  length exch pop		% pop /%%EOF

} bind def

% This routine will scan a file searaching for object locations to build

% an alternate version of the data in the xref tables.

% Its purpose is to provide a basis for an xref fixing facility.

/search_objects				% - search_objects -

{ % Initialize the Objects, Generations, etc. larrays

  initPDFobjects

  % reset duplicate object and generation numbers error flag

  /dup_obj_gen_num false def

  % Determine how many bytes are in the file after the final %%EOF

  /post_eof_count determine_post_eof_count def

  % Start at the beginning of the file

  PDFfile 0 setfileposition

  % Create a working string (and also store its length on stack).  We are

  % using a maximum size string size the logic below wants a recovered object

  % to fit into our working string.

  65535 dup string

  { % Now loop through the entire file lloking for objects

    PDFfile fileposition		% save current file position

    % When we get near the end of the file, we use a smaller interval of

    % our working string to prevent reading past the end.  (See comments on

    % EOF testing below.)

    PDFfile bytesavailable post_eof_count sub 10 sub dup 4 index lt {

      2 index 0 3 -1 roll getinterval	% near EOF, use interval of string

    } { pop 1 index			% not near end, use full working string

    }ifelse

    % Read a line from file.  If the line does not fit into our working string,

    % or any other error, then we will discard it.

    PDFfile exch { readline } .internalstopped

    { pop pop false } if		% indicate no string if we stopped

    { % stack: <length> <working_str> <loc> <string>

      % Now that we have line, get obj num, ref num, and 'obj'.  Verify that each

      % of these is correct type.

      /integertype typed_token {	% get obj number

        /integertype typed_token {	% get ref number

          /nametype typed_token {	% get 'obj' text

	    pop				% pop remaining string

	    /obj eq {			% verify name is 'obj'

	      % make sure we have room in the arrays.  We work in increments

	      % of 20 each time we increase the size.

	      1 index 20 add 20 idiv 20 mul

	      growPDFobjects

	      % save xref parameters into ObjectStream, Objects and Generations

	      1 index 0 4 index 3 index	% rearrange parms for setxrefentry

	      setxrefentry		% save parameters

	      pop pop pop pop		% clear parameters

	    } if			% check if name is 'obj'

          } if				% check if we got 'obj" string

          pop				% remove ref number

        } if				% check if we got ref number

        pop				% remove obj number

      } if				% check if we got object number

    } if				% check if got a string from readline

    pop					% remove location

    % Check if we are approaching the end of the file.  We do not want to

    % read past the end of the file since that closes it.  We actually stop

    % 10-20 bytes early since there cannot be an object that close to the end.

    % (There is a Trailer dictionary, etc. at the end of the file.)

    PDFfile bytesavailable post_eof_count sub 20 lt { exit } if

  } loop				% loop through the entire file

  pop pop				% remove working string and its length

  % Output warning if we have two objects with the same object and generation

  % numbers.

  dup_obj_gen_num {

    (   **** Warning:  There are objects with matching object and generation\n)

    pdfformaterror

    (   **** numbers.  The accuracy of the resulting image is unknown.\n)

    pdfformaterror

  } if

} bind def

% Print warning message because we found a problem while reading the xref

% tables

/print_xref_warning

{ (   **** Warning:  An error occurred while reading an XREF table.\n)

  pdfformaterror

  (   **** The file has been damaged.  This may have been caused\n)

  pdfformaterror

  (   **** by a problem while converting or transfering the file.\n)

  pdfformaterror

  (   **** Ghostscript will attempt to recover the data.\n)

  pdfformaterror

} bind def

% Attempt to recover the XRef data.  This is called if we have a failure

% while reading the normal XRef tables.  This routine usually works

% only for pre PDF1.5 versions of PDF files.

/recover_xref_data		% - recover_xref_data -

{ print_xref_warning		% Print warning message

  count pdfemptycount sub { pop } repeat % remove anything left by readxref

  search_objects		% Search for objects

} bind def