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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 8472 2008-01-01 14:28:30Z alexcher $
-% 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> <rebuild>
-% setxrefentry <obj num> strm num> <obj loc> <gen num>
-/setxrefentry
-{
- 5 1 roll
- dup 65535 or 65535 ne {
- ( **** Warning: Generation number out of 0..65535 range, assuming 0.\n)
- pdfformaterror
- pop 0
- } if
- % 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
- } 8 -1 roll { ifelse } { pop if } ifelse % Run 'else' only when rebuilding.
-} 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
- /dictlevelcount 0 def
- 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
- //true 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