ref: 435a0f18d5a5f372b4d5a30953e8d6bfd9cf6d17
dir: /sys/lib/ghostscript/pdf_rbld.ps/
% 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
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 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