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% Copyright (C) 2002 Artifex Software, Inc. All rights reserved.
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% This software is provided AS-IS with no warranty, either express or
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% This software is distributed under license and may not be copied,
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% modified or distributed except as expressly authorized under the terms
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% of the license contained in the file LICENSE in this distribution.
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% For more information about licensing, please refer to
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% http://www.ghostscript.com/licensing/. For information on
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% commercial licensing, go to http://www.artifex.com/licensing/ or
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% contact Artifex Software, Inc., 101 Lucas Valley Road #110,
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% San Rafael, CA 94903, U.S.A., +1(415)492-9861.
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% $Id: pdf_rbld.ps 8472 2008-01-01 14:28:30Z alexcher $
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% pdf_rbld.ps - Rebuilding of broken PDF files (xref errors)
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% This module contains routines that are used if we detect an error
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% while reading the xref tables. These routines will scan the file and
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% build an xref table by finding the objects. We also need to find the
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% appropriate trailer dictionary. Note: One procedure is also used
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% even if we do not need to rebuild a PDF file.
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% This module cannot rebuild a PDF file which has had errors created inside
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% of objects or binary data streams. It often succeeds with files that
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% have had its end of lines converted between unix and dos versions.
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% if true --> we have an object with duplicate object and generation numbers.
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/dup_obj_gen_num false def
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% Note: This procedure is also used by non-rebuild code.
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% Store a line in the xref array (Actually Objects and Generations arrays)
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% <obj num> (strm num> <obj loc> <gen num> <rebuild>
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% setxrefentry <obj num> strm num> <obj loc> <gen num>
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dup 65535 or 65535 ne {
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( **** Warning: Generation number out of 0..65535 range, assuming 0.\n)
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% We store generation numbers as value + 1
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% We reserve 0 to indicate an free xref entry
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1 add % increment generation number
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% To save space, generations numbers are stored in a lstring unless we
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% find a generation number greater than 255. If so then transfer to
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Generations ltype /stringtype eq { % Convert Generations to an larray.
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larray Generations llength lgrowto dup % Create new larray
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0 1 2 index llength 1 sub { % Copy from old lstring to new larray
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Generations 1 index lget lput dup
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/Generations exch store % Save new Generations larray
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% Verify that the new values are for a new object. If the current
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% entry is null then we have a new entry.
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Objects 4 index lget null eq {
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ObjectStream 4 index 4 index cvx lput % Save ObjectStream object number
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Objects 4 index 3 index cvx lput % Save object location
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Generations 4 index 2 index lput % Save geenration number
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% Verify that the new entry has at least as high a generaton number
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% We accept equal entry number because we have found PDF files in
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% which there are multiple objects with the same object and entry
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% numbers. The normal xref logic only accepts the first such
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% entry that it finds. However the 'rebuild PDF' logic can find
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% both such entries. The correct one is usually the last one.
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Generations 4 index lget 1 index le {
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ObjectStream 4 index 4 index cvx lput % Save ObjectStream object number
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Objects 4 index 3 index cvx lput % Save object location
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Generations 4 index 2 index lput % Save geenration number
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% Set error flag if we have equal object and generation numbers
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Generations 4 index lget 1 index eq { /dup_obj_gen_num true def } if
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} 8 -1 roll { ifelse } { pop if } ifelse % Run 'else' only when rebuilding.
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% Print the contents of the xref array. This actually consists of three
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% arrays (Objects, Generations, and ObjectStream). All three are larrays.
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% larrays are a special Ghostscript object which can be arrays with more
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/print_xref % - print_xref -
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{ 0 1 Objects llength 1 sub % stack: 0 1 <number of objects - 1>
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{ dup =only % print object number
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dup Generations exch lget 1 sub =only % print Generation number
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dup ObjectStream exch lget ==only % print ObjectStream object number
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Objects exch lget === % print object location
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% Get token from string and check its type
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% <string> <type> typed_token <false> % no token or not match
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% <string> <type> typed_token <obj> <last> <true> % matching token type
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% Where last is the string remainder
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token_nofail % get token
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dup type % stack: type last token type
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4 -1 roll eq { % stack: last token bool
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exch true % desired object found - set exit status
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pop pop false % not type - clear stack, set exit status
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pop false % no token - pop type, set exit status
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} ifelse % check if we got token
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% Allocate space for post_eof_count to be bound into procedures below.
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/post_eof_count 0 def
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% We want the location of the trailer dictionary at the start of file.
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% First we will find the xref. Then we will skip over the xref entries
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/search_start_trailer % - search_start_trailer <trailer loc>
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{ % Read the first 300 bytes and check for xref
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PDFfile 0 setfileposition
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PDFfile bytesavailable post_eof_count sub % location of end of data
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300 .min % block size to read
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dup string 0 1 4 -1 roll 1 sub
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{ 2 copy PDFfile read pop put pop } for
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exch pop exch pop length 4 add PDFfile exch setfileposition
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PDFfile token pop % get starting entry - or 'trailer'
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(trailer) ne { % if we do not already have 'trailer'
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PDFfile token pop % get number of entries
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PDFfile token pop pop % this moves us into the middle of the first entry
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25 string exch % define working string for readline
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{ PDFfile 1 index readline pop pop
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} repeat % skip entries
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pop % pop working string
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PDFfile token pop pop % get 'trailer'
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PDFfile fileposition % get file position
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pop search_end_trailer % no xref, should not happen, search end of file
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% We want the location of the trailer dictionary at the end of file.
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% We will read the last block of data and search for the final occurance
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% of the word 'trailer'
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/search_end_trailer % - search_end_trailer <trailer loc>
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{ % Position to read block of data from the end of the file. Note: We ignore
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% anything past the last %%EOF since this is not PDF data.
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PDFfile 0 setfileposition
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PDFfile bytesavailable post_eof_count sub % location of end of data
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dup 65535 .min % block size to read
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% stack: <file end pos> <block size>
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% move file position to the start of the block
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2 copy sub PDFfile exch setfileposition
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dup string 0 1 4 -1 roll 1 sub { 2 copy PDFfile read pop put pop } for
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% search for last occurance of 'trailer'
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(trailer) { search not { exit } if pop } loop
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% determine where the trailer is in the file
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% trailer loc = end loc - remaing string length
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% We want to find the trailer dictionary. There is a trailer dictionary
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% for each xref object list. We only want the trailer dictionary associated
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% with the first xref object list. In theory this can be anywhere in the
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% file. However since we are trying to repair a broken file, we cannot simply
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% follow the xref links. So we are falling back to a simple strategy. We
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% find the specified location of the first xref list. If its location is in
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% the first half of the file then we search for the first trailer dictionary
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% at the start of the file. Otherwise we search for the last trailer at the
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/search_trailer % - search_trailer -
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{ % Find the 'startxref' and associated position at the end of the file.
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% Position to read block of data from the end of the file. Note: We
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% actually end at the end of the last %%EOF since this is the end of the
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% useful PDF data. (Some files contain trailing garbage.)
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PDFfile 0 setfileposition
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PDFfile bytesavailable % size of file
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post_eof_count sub dup % location of end of last %%EOF
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dup 4096 .min % block size to read
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% stack: <useful file size> <useful file size file> <block size>
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% move file position to the start of the block
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2 copy sub PDFfile exch setfileposition
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dup string 0 1 4 -1 roll 1 sub { 2 copy PDFfile read pop put pop } for
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% search for last occurance of 'startxref'
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false % Assume that startxref not present
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search not { exit } if % Exit loop when no more startxref's
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pop 3 -1 roll pop true 3 1 roll % Idicate that we have found starxref
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exch % Exch last string and 'found' flag
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% determine where the startxref is in the file
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% 'startxref' loc = end loc - remaing string length - 9 bytes
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% move the file to this position and read startxref and position
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PDFfile exch setfileposition PDFfile token
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pop pop PDFfile token pop
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% startxref not found. We will search the end of the file for trailer.
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% compare xref position to 1/2 the length of the file and search for trailer
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exch 2 div lt { search_start_trailer } { search_end_trailer } ifelse
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PDFfile exch setfileposition % set to the specified trailer location
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/dictlevelcount 0 def
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PDFfile traileropdict .pdfrun % read trailer info
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% This routine will determine if there is stuff after the %%EOF. There is
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% supposed to be only a line termination. However many real life files
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% contain some garbage. This routine checks how much. We then ignore this
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% stuff when we are scanning for objects.
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/determine_post_eof_count % - determine_post_eof_count <count>
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{ % Position to read block of data from the end of the file.
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PDFfilelen % size of file
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dup 4096 .min % block size to read
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% stack: <file size> <file size> <block size>
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% move file position to the start of the block
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2 copy sub PDFfile exch setfileposition
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dup string 0 1 4 -1 roll 1 sub { 2 copy PDFfile read pop put pop } for
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% search for last occurance of '%%EOF'
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(%%EOF) { search not { exit } if pop } loop
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% how much is left = remaining string length
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length exch pop % pop /%%EOF
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% This routine will scan a file searaching for object locations to build
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% an alternate version of the data in the xref tables.
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% Its purpose is to provide a basis for an xref fixing facility.
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/search_objects % - search_objects -
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{ % Initialize the Objects, Generations, etc. larrays
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% reset duplicate object and generation numbers error flag
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/dup_obj_gen_num false def
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% Determine how many bytes are in the file after the final %%EOF
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/post_eof_count determine_post_eof_count def
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% Start at the beginning of the file
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PDFfile 0 setfileposition
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% Create a working string (and also store its length on stack). We are
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% using a maximum size string size the logic below wants a recovered object
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% to fit into our working string.
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{ % Now loop through the entire file lloking for objects
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PDFfile fileposition % save current file position
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% When we get near the end of the file, we use a smaller interval of
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% our working string to prevent reading past the end. (See comments on
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% EOF testing below.)
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PDFfile bytesavailable post_eof_count sub 10 sub dup 4 index lt {
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2 index 0 3 -1 roll getinterval % near EOF, use interval of string
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} { pop 1 index % not near end, use full working string
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% Read a line from file. If the line does not fit into our working string,
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% or any other error, then we will discard it.
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PDFfile exch { readline } .internalstopped
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{ pop pop false } if % indicate no string if we stopped
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{ % stack: <length> <working_str> <loc> <string>
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% Now that we have line, get obj num, ref num, and 'obj'. Verify that each
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% of these is correct type.
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/integertype typed_token { % get obj number
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/integertype typed_token { % get ref number
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/nametype typed_token { % get 'obj' text
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pop % pop remaining string
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/obj eq { % verify name is 'obj'
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% make sure we have room in the arrays. We work in increments
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% of 20 each time we increase the size.
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1 index 20 add 20 idiv 20 mul
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% save xref parameters into ObjectStream, Objects and Generations
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1 index 0 % rearrange parms for setxrefentry
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4 index PDFoffset sub 3 index
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//true setxrefentry % save parameters
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pop pop pop pop % clear parameters
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} if % check if name is 'obj'
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} if % check if we got 'obj" string
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pop % remove ref number
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} if % check if we got ref number
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pop % remove obj number
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} if % check if we got object number
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} if % check if got a string from readline
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pop % remove location
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% Check if we are approaching the end of the file. We do not want to
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% read past the end of the file since that closes it. We actually stop
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% 10-20 bytes early since there cannot be an object that close to the end.
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% (There is a Trailer dictionary, etc. at the end of the file.)
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PDFfile bytesavailable post_eof_count sub 20 lt { exit } if
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} loop % loop through the entire file
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pop pop % remove working string and its length
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% Output warning if we have two objects with the same object and generation
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( **** Warning: There are objects with matching object and generation\n)
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( **** numbers. The accuracy of the resulting image is unknown.\n)
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% Print warning message because we found a problem while reading the xref
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{ ( **** Warning: An error occurred while reading an XREF table.\n)
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( **** The file has been damaged. This may have been caused\n)
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( **** by a problem while converting or transfering the file.\n)
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( **** Ghostscript will attempt to recover the data.\n)
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% Attempt to recover the XRef data. This is called if we have a failure
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% while reading the normal XRef tables. This routine usually works
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% only for pre PDF1.5 versions of PDF files.
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/recover_xref_data % - recover_xref_data -
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{ print_xref_warning % Print warning message
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count pdfemptycount sub { pop } repeat % remove anything left by readxref
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search_objects % Search for objects
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lib/pdf_rbld.ps
