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+% Copyright (C) 2002 Artifex Software, Inc. 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 8022 2007-06-05 22:23:38Z giles $
+% 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 procedure 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
+ 0 1 2 index llength 1 sub { % Copy from old lstring to 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 three
+% arrays (Objects, Generations, and ObjectStream). All three 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
+
+% 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
+ PDFfile bytesavailable post_eof_count sub % location of end of data
+ 300 .min % block size to read
+ dup string 0 1 4 -1 roll 1 sub
+ { 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 search_end_trailer % no xref, should not happen, search end of file
+ } 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 65535 .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'
+ false % Assume that startxref not present
+ exch (startxref) {
+ search not { exit } if % Exit loop when no more startxref's
+ pop 3 -1 roll pop true 3 1 roll % Idicate that we have found starxref
+ } loop
+ exch % Exch last string and 'found' flag
+ {
+ % determine where the startxref is in the file
+ % 'startxref' loc = end loc - remaing string length - 9 bytes
+ 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
+ } {
+ % startxref not found. We will search the end of the file for trailer.
+ pop pop PDFfilelen
+ } ifelse
+ % 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.
+ PDFfilelen % 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 % rearrange parms for setxrefentry
+ 4 index PDFoffset sub 3 index
+ 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