File Coverage

blib/lib/Image/ExifTool/WritePDF.pl

Criterion	Covered	Total	%
statement	276	391	70.5
branch	169	306	55.2
condition	55	101	54.4
subroutine	7	9	77.7
pod	0	7	0.0
total	507	814	62.2

#------------------------------------------------------------------------------
# File:         WritePDF.pl
#
# Description:  Write PDF meta information
#
# Revisions:    12/08/2007 - P. Harvey Created
#
# References:   1) http://partners.adobe.com/public/developer/pdf/index_reference.html
#
# Notes:        The special "PDF-update" group can be deleted to revert exiftool updates
#------------------------------------------------------------------------------
package Image::ExifTool::PDF;

use strict;
use vars qw($lastFetched);

sub WriteObject($$);
sub EncodeString($);
sub CryptObject($);

# comments to mark beginning and end of ExifTool incremental update
my $beginComment = '%BeginExifToolUpdate';
my $endComment   = '%EndExifToolUpdate ';

my $keyExt;     # crypt key extension
my $pdfVer;     # version of PDF file we are currently writing

# internal tags used in dictionary objects
my %myDictTags = (
    _tags => 1, _stream => 1, _decrypted => 1, _needCrypt => 1,
    _filtered => 1, _entry_size => 1, _table => 1,
);

# map for directories that we can add
my %pdfMap = (
    XMP => 'PDF',
);

#------------------------------------------------------------------------------
# Validate raw PDF values for writing (string date integer real boolean name)
# Inputs: 0) ExifTool object ref, 1) tagInfo hash ref, 2) raw value ref
# Returns: error string or undef (and possibly changes value) on success
sub CheckPDF($$$)
{
    my ($et, $tagInfo, $valPtr) = @_;
    my $format = $$tagInfo{Writable} || $tagInfo->{Table}->{WRITABLE};
    if (not $format) {
        return 'No writable format';
    } elsif ($format eq 'string') {
        # (encode later because list-type string tags need to be encoded as a unit)
    } elsif ($format eq 'date') {
        # be flexible about this for now
        return 'Bad date format' unless $$valPtr =~ /^\d{4}/;
    } elsif ($format eq 'integer') {
        return 'Not an integer' unless Image::ExifTool::IsInt($$valPtr);
    } elsif ($format eq 'real') {
        return 'Not a real number' unless $$valPtr =~ /^[+-]?(?=\d|\.\d)\d*(\.\d*)?$/;
    } elsif ($format eq 'boolean') {
        $$valPtr = ($$valPtr and $$valPtr !~ /^f/i) ? 'true' : 'false';
    } elsif ($format eq 'name') {
        return 'Invalid PDF name' if $$valPtr =~ /\0/;
    } else {
        return "Invalid PDF format '${format}'";
    }
    return undef;   # value is OK
}

#------------------------------------------------------------------------------
# Format value for writing to PDF file
# Inputs: 0) ExifTool ref, 1) value, 2) format string (string,date,integer,real,boolean,name)
# Returns: formatted value or undef on error
# Notes: Called at write time, so $pdfVer may be checked
sub WritePDFValue($$$)
{
    my ($et, $val, $format) = @_;
    if (not $format) {
        return undef;
    } elsif ($format eq 'string') {
        # encode as UCS2 if it contains any special characters
        $val = "\xfe\xff" . $et->Encode($val,'UCS2','MM') if $val =~ /[\x80-\xff]/;
        EncodeString(\$val);
    } elsif ($format eq 'date') {
        # convert date to "D:YYYYmmddHHMMSS+-HH'MM'" format
        $val =~ s/([-+]\d{2}):(\d{2})/${1}'${2}'/;  # change timezone delimiters if necessary
        $val =~ tr/ ://d;                       # remove spaces and colons
        $val =  "D:$val";                       # add leading "D:"
        EncodeString(\$val);
    } elsif ($format =~ /^(integer|real|boolean)$/) {
        # no reformatting necessary
    } elsif ($format eq 'name') {
        return undef if $val =~ /\0/;
        if ($pdfVer >= 1.2) {
            $val =~ s/([\t\n\f\r ()<>[\]{}\/%#])/sprintf('#%.2x',ord $1)/sge;
        } else {
            return undef if $val =~ /[\t\n\f\r ()<>[\]{}\/%]/;
        }
        $val = "/$val"; # add leading '/'
    } else {
        return undef;
    }
    return $val;
}

#------------------------------------------------------------------------------
# Encode PDF string
# Inputs: 0) reference to PDF string
# Returns: (updates string with encoded data)
sub EncodeString($)
{
    my $strPt = shift;
    if (ref $$strPt eq 'ARRAY') {
        my $str;
        foreach $str (@{$$strPt}) {
            EncodeString(\$str);
        }
        return;
    }
    Crypt($strPt, $keyExt, 1);  # encrypt if necessary
    # encode as hex if we have any control characters (except tab)
    if ($$strPt=~/[\x00-\x08\x0a-\x1f\x7f\xff]/) {
        # encode as hex
        my $str='';
        my $len = length $$strPt;
        my $i = 0;
        for (;;) {
            my $n = $len - $i or last;
            $n = 40 if $n > 40; # break into reasonable-length lines
            $str .= $/ if $i;
            $str .= unpack('H*', substr($$strPt, $i, $n));
            $i += $n;
        }
        $$strPt = "<$str>";
    } else {
        $$strPt =~ s/([()\\])/\\$1/g;   # must escape round brackets and backslashes
        $$strPt = "($$strPt)";
    }
}

#------------------------------------------------------------------------------
# Encrypt an object
# Inputs: 0) PDF object (encrypts in place)
# Notes: Encrypts according to "_needCrypt" dictionary entry,
#        then deletes "_needCrypt" when done
sub CryptObject($)
{
    my $obj = $_[0];
    if (not ref $obj) {
        # only literal strings and hex strings are encrypted
        if ($obj =~ /^[(<]/) {
            undef $lastFetched; # (reset this just in case)
            my $val = ReadPDFValue($obj);
            EncodeString(\$val);
            $_[0] = $val;
        }
    } elsif (ref $obj eq 'HASH') {
        my $tag;
        my $needCrypt = $$obj{_needCrypt};
        foreach $tag (keys %$obj) {
            next if $myDictTags{$tag};
            # re-encrypt necessary objects only (others are still encrypted)
            # (this is really annoying, but is necessary because objects stored
            # in encrypted streams are decrypted when extracting, but strings stored
            # as direct objects are decrypted later since they must be decoded
            # before being decrypted)
            if ($needCrypt) {
                next unless defined $$needCrypt{$tag} ? $$needCrypt{$tag} : $$needCrypt{'*'};
            }
            CryptObject($$obj{$tag});
        }
        delete $$obj{_needCrypt};   # avoid re-re-crypting
    } elsif (ref $obj eq 'ARRAY') {
        my $val;
        foreach $val (@$obj) {
            CryptObject($val);
        }
    }
}

#------------------------------------------------------------------------------
# Get free entries from xref stream dictionary that we wrote previously
# Inputs: 0) xref dictionary reference
# Returns: free entry hash (keys are object numbers, values are xref entry list refs)
sub GetFreeEntries($)
{
    my $dict = shift;
    my %xrefFree;
    # from the start we have only written xref stream entries in 'CNn' format,
    # so we can simplify things for now and only support this type of entry
    my $w = $$dict{W};
    if (ref $w eq 'ARRAY' and "@$w" eq '1 4 2') {
        my $size = $$dict{_entry_size}; # this will be 7 for 'CNn'
        my $index = $$dict{Index};
        my $len = length $$dict{_stream};
        # scan the table for free objects
        my $num = scalar(@$index) / 2;
        my $pos = 0;
        my ($i, $j);
        for ($i=0; $i<$num; ++$i) {
            my $start = $$index[$i*2];
            my $count = $$index[$i*2+1];
            for ($j=0; $j<$count; ++$j) {
                last if $pos + $size > $len;
                my @t = unpack("x$pos CNn", $$dict{_stream});
                # add entry if object was free
                $xrefFree{$start+$j} = [ $t[1], $t[2], 'f' ] if $t[0] == 0;
                $pos += $size;  # step to next entry
            }
        }
    }
    return \%xrefFree;
}

#------------------------------------------------------------------------------
# Write PDF object
# Inputs: 0) output file or scalar ref, 1) PDF object
# Returns: true on success
# Notes: inserts white space before object, but none afterward
sub WriteObject($$)
{
    my ($outfile, $obj) = @_;
    if (ref $obj eq 'SCALAR') {
        Write($outfile, ' ', $$obj) or return 0;
    } elsif (ref $obj eq 'ARRAY') {
        # write array
        Write($outfile, @$obj > 10 ? $/ : ' ', '[') or return 0;
        my $item;
        foreach $item (@$obj) {
            WriteObject($outfile, $item) or return 0;
        }
        Write($outfile, ' ]') or return 0;
    } elsif (ref $obj eq 'HASH') {
        # write dictionary
        my $tag;
        Write($outfile, $/, '<<') or return 0;
        # prepare object as required if it has a stream
        if ($$obj{_stream}) {
            # encrypt stream if necessary (must be done before determining Length)
            CryptStream($obj, $keyExt) if $$obj{_decrypted};
            # write "Length" entry in dictionary
            $$obj{Length} = length $$obj{_stream};
            push @{$$obj{_tags}}, 'Length';
            # delete Filter-related entries since we don't yet write filtered streams
            delete $$obj{Filter};
            delete $$obj{DecodeParms};
            delete $$obj{DL};
        }
        # don't write my internal entries
        my %wrote = %myDictTags;
        # write tags in original order, adding new ones later alphabetically
        foreach $tag (@{$$obj{_tags}}, sort keys %$obj) {
            # ignore already-written or missing entries
            next if $wrote{$tag} or not defined $$obj{$tag};
            Write($outfile, $/, "/$tag") or return 0;
            WriteObject($outfile, $$obj{$tag}) or return 0;
            $wrote{$tag} = 1;
        }
        Write($outfile, $/, '>>') or return 0;
        if ($$obj{_stream}) {
            # write object stream
            # (a single 0x0d may not follow 'stream', so use 0x0d+0x0a here to be sure)
            Write($outfile, $/, "stream\x0d\x0a") or return 0;
            Write($outfile, $$obj{_stream}, $/, 'endstream') or return 0;
        }
    } else {
        # write string, number, name or object reference
        Write($outfile, ' ', $obj);
    }
    return 1;
}

#------------------------------------------------------------------------------
# Write PDF File
# Inputs: 0) ExifTool object reference, 1) dirInfo reference
# Returns: 1 on success, 0 if not valid PDF file, -1 on write error
# Notes: dictionary structure:  Main --+--> Info
#                                      +--> Root --> Metadata
sub WritePDF($$)
{
    my ($et, $dirInfo) = @_;
    my $raf = $$dirInfo{RAF};
    my $outfile = $$dirInfo{OutFile};
    my ($buff, %capture, %newXRef, %newObj, $objRef);
    my ($out, $id, $gen, $obj);

    # make sure this is a PDF file
    my $pos = $raf->Tell();
    $raf->Read($buff, 1024) >= 8 or return 0;
    $buff =~ /^(\s*)%PDF-(\d+\.\d+)/ or return 0;
    $$et{PDFBase} = length $1;
    $raf->Seek($pos, 0);

    # create a new ExifTool object and use it to read PDF and XMP information
    my $newTool = new Image::ExifTool;
    $newTool->Options(List => 1);
    $newTool->Options(Password => $et->Options('Password'));
    $newTool->Options(NoPDFList => $et->Options('NoPDFList'));
    $$newTool{PDF_CAPTURE} = \%capture;
    my $info = $newTool->ImageInfo($raf, 'XMP', 'PDF:*', 'Error', 'Warning');
    # not a valid PDF file unless we got a version number
    # (note: can't just check $$info{PDFVersion} due to possibility of XMP-pdf:PDFVersion)
    my $vers = $newTool->GetInfo('PDF:PDFVersion');
    # take highest version number if multiple versions in an incremental save
    ($pdfVer) = sort { $b <=> $a } values %$vers;
    $pdfVer or $et->Error('Missing PDF:PDFVersion'), return 0;
    # check version number
    if ($pdfVer > 1.7) {
        $et->Warn("The PDF $pdfVer specification is not freely available", 1);
        # (so writing by ExifTool is based on trial and error)
    }
    # fail if we had any serious errors while extracting information
    if ($capture{Error} or $$info{Error}) {
        $et->Error($capture{Error} || $$info{Error});
        return 1;
    }
    # make sure we have everything we need to rewrite this file
    foreach $obj (qw(Main Root xref)) {
        next if $capture{$obj};
        # any warning we received may give a clue about why this object is missing
        $et->Error($$info{Warning}) if $$info{Warning};
        $et->Error("Can't find $obj object");
        return 1;
    }
    $et->InitWriteDirs(\%pdfMap, 'XMP');

    # copy file up to start of previous exiftool update or end of file
    # (comment, startxref & EOF with 11-digit offsets and 2-byte newlines is 63 bytes)
    $raf->Seek(-64,2) and $raf->Read($buff,64) and $raf->Seek(0,0) or return -1;
    my $rtn = 1;
    my $prevUpdate;
    # (now $endComment is before "startxref", but pre-7.41 we wrote it after the EOF)
    if ($buff =~ /$endComment(\d+)\s+(startxref\s+\d+\s+%%EOF\s+)?$/s) {
        $prevUpdate = $1;
        # rewrite the file up to the original EOF
        Image::ExifTool::CopyBlock($raf, $outfile, $prevUpdate + $$et{PDFBase}) or $rtn = -1;
        # verify that we are now at the start of an ExifTool update
        unless ($raf->Read($buff, length $beginComment) and $buff eq $beginComment) {
            $et->Error('Previous ExifTool update is corrupted');
            return $rtn;
        }
        $raf->Seek($prevUpdate+$$et{PDFBase}, 0) or $rtn = -1;
        if ($$et{DEL_GROUP}{'PDF-update'}) {
            $et->VPrint(0, "  Reverted previous ExifTool updates\n");
            ++$$et{CHANGED};
            return $rtn;
        }
    } elsif ($$et{DEL_GROUP}{'PDF-update'}) {
        $et->Error('File contains no previous ExifTool update');
        return $rtn;
    } else {
        # rewrite the whole file
        while ($raf->Read($buff, 65536)) {
            Write($outfile, $buff) or $rtn = -1;
        }
    }
    $out = $et->Options('TextOut') if $et->Options('Verbose');
#
# create our new PDF objects to write
#
    my $xref = $capture{xref};
    my $mainDict = $capture{Main};
    my $metaRef = $capture{Root}->{Metadata};
    my $nextObject;

    # start by finding reference for info object in case it was deleted
    # in a previous edit so we can re-use it here if adding PDF Info
    my $prevInfoRef;
    if ($prevUpdate) {
        unless ($capture{Prev}) {
            $et->Error("Can't locate trailer dictionary prior to last edit");
            return $rtn;
        }
        $prevInfoRef = $capture{Prev}->{Info};
        # start from previous size so the xref table doesn't continue
        # to grow if we repeatedly add and delete the Metadata object
        $nextObject = $capture{Prev}->{Size};
        # don't re-use Meta reference if object was added in a previous update
        undef $metaRef if $metaRef and $$metaRef=~/^(\d+)/ and $1 >= $nextObject;
    } else {
        $prevInfoRef = $$mainDict{Info};
        $nextObject = $$mainDict{Size};
    }

    # delete entire PDF group if specified
    my $infoChanged = 0;
    if ($$et{DEL_GROUP}{PDF} and $capture{Info}) {
        delete $capture{Info};
        $info = { XMP => $$info{XMP} }; # remove extracted PDF tags
        print $out "  Deleting PDF Info dictionary\n" if $out;
        ++$infoChanged;
    }

    # create new Info dictionary if necessary
    $capture{Info} = { _tags => [ ] } unless $capture{Info};
    my $infoDict = $capture{Info};

    # must pre-determine Info reference to be used in encryption
    my $infoRef = $prevInfoRef || \ "$nextObject 0 R";
    $keyExt = $$infoRef;

    # must encrypt all values in dictionary if they came from an encrypted stream
    CryptObject($infoDict) if $$infoDict{_needCrypt};

    # must set line separator before calling WritePDFValue()
    local $/ = $capture{newline};

    # rewrite PDF Info tags
    my $newTags = $et->GetNewTagInfoHash(\%Image::ExifTool::PDF::Info);
    my $tagID;
    foreach $tagID (sort keys %$newTags) {
        my $tagInfo = $$newTags{$tagID};
        my $nvHash = $et->GetNewValueHash($tagInfo);
        my (@vals, $deleted);
        my $tag = $$tagInfo{Name};
        my $val = $$info{$tag};
        my $tagKey = $tag;
        unless (defined $val) {
            # must check for tag key with copy number
            ($tagKey) = grep /^$tag/, keys %$info;
            $val = $$info{$tagKey} if $tagKey;
        }
        if (defined $val) {
            my @oldVals;
            if (ref $val eq 'ARRAY') {
                @oldVals = @$val;
                $val = shift @oldVals;
            }
            for (;;) {
                if ($et->IsOverwriting($nvHash, $val) > 0) {
                    $deleted = 1;
                    $et->VerboseValue("- PDF:$tag", $val);
                    ++$infoChanged;
                } else {
                    push @vals, $val;
                }
                last unless @oldVals;
                $val = shift @oldVals;
            }
            # don't write this out if we deleted all values
            delete $$infoDict{$tagID} unless @vals;
        } elsif ($$nvHash{EditOnly}) {
            next;
        }
        # decide whether we want to write this tag
        # (native PDF information is always preferred, so don't check IsCreating)
        next unless $deleted or $$tagInfo{List} or not exists $$infoDict{$tagID};

        # add new values to existing ones
        my @newVals = $et->GetNewValue($nvHash);
        if (@newVals) {
            push @vals, @newVals;
            ++$infoChanged;
            if ($out) {
                foreach $val (@newVals) {
                    $et->VerboseValue("+ PDF:$tag", $val);
                }
            }
        }
        unless (@vals) {
            # remove this entry from the Info dictionary if no values remain
            delete $$infoDict{$tagID};
            next;
        }
        # format value(s) for writing to PDF file
        my $writable = $$tagInfo{Writable} || $Image::ExifTool::PDF::Info{WRITABLE};
        if (not $$tagInfo{List}) {
            $val = WritePDFValue($et, shift(@vals), $writable);
        } elsif ($$tagInfo{List} eq 'array') {
            foreach $val (@vals) {
                $val = WritePDFValue($et, $val, $writable);
                defined $val or undef(@vals), last;
            }
            $val = @vals ? \@vals : undef;
        } else {
            $val = WritePDFValue($et, join($et->Options('ListSep'), @vals), $writable);
        }
        if (defined $val) {
            $$infoDict{$tagID} = $val;
            ++$infoChanged;
        } else {
            $et->Warn("Error converting $$tagInfo{Name} value");
        }
    }
    if ($infoChanged) {
        $$et{CHANGED} += $infoChanged;
    } elsif ($prevUpdate) {
        # must still write Info dictionary if it was previously updated
        my $oldPos = LocateObject($xref, $$infoRef);
        $infoChanged = 1 if $oldPos and $oldPos > $prevUpdate;
    }

    # create new Info dictionary if necessary
    if ($infoChanged) {
        # increment object count if we used a new object here
        if (scalar(keys %{$capture{Info}}) > 1) {
            $newObj{$$infoRef} = $capture{Info};# save to write later
            $$mainDict{Info} = $infoRef;        # add reference to trailer dictionary
            ++$nextObject unless $prevInfoRef;
        } else {
            # remove Info from Main (trailer) dictionary
            delete $$mainDict{Info};
            # write free entry in xref table if Info existed prior to all edits
            $newObj{$$infoRef} = '' if $prevInfoRef;
        }
    }

    # rewrite XMP
    my %xmpInfo = (
        DataPt => $$info{XMP},
        Parent => 'PDF',
    );
    my $xmpTable = Image::ExifTool::GetTagTable('Image::ExifTool::XMP::Main');
    my $oldChanged = $$et{CHANGED};
    my $newXMP = $et->WriteDirectory(\%xmpInfo, $xmpTable);
    $newXMP = $$info{XMP} ? ${$$info{XMP}} : '' unless defined $newXMP;

    # WriteDirectory() will increment CHANGED erroneously if non-existent
    # XMP is deleted as a block -- so check for this
    unless ($newXMP or $$info{XMP}) {
        $$et{CHANGED} = $oldChanged;
        $et->VPrint(0, "  (XMP not changed -- still empty)\n");
    }
    my ($metaChanged, $rootChanged);

    if ($$et{CHANGED} != $oldChanged and defined $newXMP) {
        $metaChanged = 1;
    } elsif ($prevUpdate and $capture{Root}->{Metadata}) {
        # must still write Metadata dictionary if it was previously updated
        my $oldPos = LocateObject($xref, ${$capture{Root}->{Metadata}});
        $metaChanged = 1 if $oldPos and $oldPos > $prevUpdate;
    }
    if ($metaChanged) {
        if ($newXMP) {
            unless ($metaRef) {
                # allocate new PDF object
                $metaRef = \ "$nextObject 0 R";
                ++$nextObject;
                $capture{Root}->{Metadata} = $metaRef;
                $rootChanged = 1;   # set flag to replace Root dictionary
            }
            # create the new metadata dictionary to write later
            $newObj{$$metaRef} = {
                Type       => '/Metadata',
                Subtype    => '/XML',
              # Length     => length $newXMP, (set by WriteObject)
                _tags      => [ qw(Type Subtype) ],
                _stream    => $newXMP,
                _decrypted => 1, # (this will be ignored if EncryptMetadata is false)
            };
        } elsif ($capture{Root}->{Metadata}) {
            # free existing metadata object
            $newObj{${$capture{Root}->{Metadata}}} = '';
            delete $capture{Root}->{Metadata};
            $rootChanged = 1;   # set flag to replace Root dictionary
        }
    }
    # add new Root dictionary if necessary
    my $rootRef = $$mainDict{Root};
    unless ($rootRef) {
        $et->Error("Can't find Root dictionary");
        return $rtn;
    }
    if (not $rootChanged and $prevUpdate) {
        # must still write Root dictionary if it was previously updated
        my $oldPos = LocateObject($xref, $$rootRef);
        $rootChanged = 1 if $oldPos and $oldPos > $prevUpdate;
    }
    $newObj{$$rootRef} = $capture{Root} if $rootChanged;
#
# write incremental update if anything was changed
#
    if ($$et{CHANGED}) {
        # remember position of original EOF
        my $oldEOF = Tell($outfile) - $$et{PDFBase};
        Write($outfile, $beginComment) or $rtn = -1;

        # write new objects
        foreach $objRef (sort keys %newObj) {
            $objRef =~ /^(\d+) (\d+)/ or $rtn = -1, last;
            ($id, $gen) = ($1, $2);
            if (not $newObj{$objRef}) {
                ++$gen if $gen < 65535;
                # write free entry in xref table
                $newXRef{$id} = [ 0, $gen, 'f' ];
                next;
            }
            # create new entry for xref table
            $newXRef{$id} = [ Tell($outfile) - $$et{PDFBase} + length($/), $gen, 'n' ];
            $keyExt = "$id $gen obj";  # (must set for stream encryption)
            Write($outfile, $/, $keyExt) or $rtn = -1;
            WriteObject($outfile, $newObj{$objRef}) or $rtn = -1;
            Write($outfile, $/, 'endobj') or $rtn = -1;
        }

        # Prev points to old xref table
        $$mainDict{Prev} = $capture{startxref} unless $prevUpdate;

        # add xref entry for head of free-object list
        $newXRef{0} = [ 0, 65535, 'f' ];

        # must insert free xref entries from previous exiftool update if applicable
        if ($prevUpdate) {
            my $mainFree;
            # extract free entries from our previous Main xref stream
            if ($$mainDict{Type} and $$mainDict{Type} eq '/XRef') {
                $mainFree = GetFreeEntries($xref->{dicts}->[0]);
            } else {
                # free entries from Main xref table already captured for us
                $mainFree = $capture{mainFree};
            }
            foreach $id (sort { $a <=> $b } keys %$mainFree) {
                $newXRef{$id} = $$mainFree{$id} unless $newXRef{$id};
            }
        }

        # connect linked list of free object in our xref table
        my $prevFree = 0;
        foreach $id (sort { $b <=> $a } keys %newXRef) { # (reverse sort)
            next unless $newXRef{$id}->[2] eq 'f';  # skip if not free
            # no need to add free entry for objects added by us
            # in previous edits then freed again
            if ($id >= $nextObject) {
                delete $newXRef{$id};   # Note: deleting newXRef entry!
                next;
            }
            $newXRef{$id}->[0] = $prevFree;
            $prevFree = $id;
        }

        # prepare our main dictionary for writing
        $$mainDict{Size} = $nextObject;    # update number of objects
        # must change the ID if it exists
        if (ref $$mainDict{ID} eq 'ARRAY' and @{$$mainDict{ID}} > 1) {
            # increment first byte since this is an easy change to make
            $id = $mainDict->{ID}->[1];
            if ($id =~ /^<([0-9a-f]{2})/i) {
                my $byte = unpack('H2',chr((hex($1) + 1) & 0xff));
                substr($id, 1, 2) = $byte;
            } elsif ($id =~ /^\((.)/s and $1 ne '\\' and $1 ne ')' and $1 ne '(') {
                my $ch = chr((ord($1) + 1) & 0xff);
                # avoid generating characters that could cause problems
                $ch = 'a' if $ch =~ /[()\\\x00-\x08\x0a-\x1f\x7f\xff]/;
                substr($id, 1, 1) = $ch;
            }
            $mainDict->{ID}->[1] = $id;
        }

        # remember position of xref table in file (we will write this next)
        my $startxref = Tell($outfile) - $$et{PDFBase} + length($/);

        # must write xref as a stream in xref-stream-only files
        if ($$mainDict{Type} and $$mainDict{Type} eq '/XRef') {

            # create entry for the xref stream object itself
            $newXRef{$nextObject++} = [ Tell($outfile) - $$et{PDFBase} + length($/), 0, 'n' ];
            $$mainDict{Size} = $nextObject;
            # create xref stream and Index entry
            $$mainDict{W} = [ 1, 4, 2 ];    # int8u, int32u, int16u ('CNn')
            $$mainDict{Index} = [ ];
            $$mainDict{_stream} = '';
            my @ids = sort { $a <=> $b } keys %newXRef;
            while (@ids) {
                my $startID = $ids[0];
                for (;;) {
                    $id = shift @ids;
                    my ($pos, $gen, $type) = @{$newXRef{$id}};
                    if ($pos > 0xffffffff) {
                        $et->Error('Huge files not yet supported');
                        last;
                    }
                    $$mainDict{_stream} .= pack('CNn', $type eq 'f' ? 0 : 1, $pos, $gen);
                    last if not @ids or $ids[0] != $id + 1;
                }
                # add Index entries for this section of the xref stream
                push @{$$mainDict{Index}}, $startID, $id - $startID + 1;
            }
            # write the xref stream object
            $keyExt = "$id 0 obj";  # (set anyway, but xref stream should NOT be encrypted)
            Write($outfile, $/, $keyExt) or $rtn = -1;
            WriteObject($outfile, $mainDict) or $rtn = -1;
            Write($outfile, $/, 'endobj') or $rtn = -1;

        } else {

            # write new xref table
            Write($outfile, $/, 'xref', $/) or $rtn = -1;
            # lines must be exactly 20 bytes, so pad newline if necessary
            my $endl = (length($/) == 1 ? ' ' : '') . $/;
            my @ids = sort { $a <=> $b } keys %newXRef;
            while (@ids) {
                my $startID = $ids[0];
                $buff = '';
                for (;;) {
                    $id = shift @ids;
                    $buff .= sprintf("%.10d %.5d %s%s", @{$newXRef{$id}}, $endl);
                    last if not @ids or $ids[0] != $id + 1;
                }
                # write this (contiguous-numbered object) section of the xref table
                Write($outfile, $startID, ' ', $id - $startID + 1, $/, $buff) or $rtn = -1;
            }

            # write main (trailer) dictionary
            Write($outfile, 'trailer') or $rtn = -1;
            WriteObject($outfile, $mainDict) or $rtn = -1;
        }
        # write trailing comment (marker to allow edits to be reverted)
        Write($outfile, $/, $endComment, $oldEOF, $/) or $rtn = -1;

        # write pointer to main xref table and EOF marker
        Write($outfile, 'startxref', $/, $startxref, $/, '%%EOF', $/) or $rtn = -1;

    } elsif ($prevUpdate) {

        # nothing new changed, so copy over previous incremental update
        $raf->Seek($prevUpdate+$$et{PDFBase}, 0) or $rtn = -1;
        while ($raf->Read($buff, 65536)) {
            Write($outfile, $buff) or $rtn = -1;
        }
    }
    if ($rtn > 0 and $$et{CHANGED} and ($$et{DEL_GROUP}{PDF} or $$et{DEL_GROUP}{XMP})) {
        $et->Warn('ExifTool PDF edits are reversible. Deleted tags may be recovered!', 1);
    }
    undef $newTool;
    undef %capture;
    return $rtn;
}


1; # end

__END__