File Coverage

blib/lib/File/KDBX/Util.pm

Criterion	Covered	Total	%
statement	360	488	73.7
branch	151	268	56.3
condition	87	152	57.2
subroutine	88	104	84.6
pod	45	45	100.0
total	731	1057	69.1

package File::KDBX::Util;
# ABSTRACT: Utility functions for working with KDBX files

use 5.010;
use warnings;
use strict;

use Crypt::PRNG qw(random_bytes random_string);
use Encode qw(decode encode);
use Exporter qw(import);
use File::KDBX::Error;
use List::Util 1.33 qw(any all);
use Module::Load;
use Ref::Util qw(is_arrayref is_coderef is_hashref is_ref is_refref is_scalarref);
use Scalar::Util qw(blessed looks_like_number readonly);
use Time::Piece 1.33;
use boolean;
use namespace::clean -except => 'import';

our $VERSION = '0.906'; # VERSION

our %EXPORT_TAGS = (
    assert      => [qw(DEBUG assert)],
    class       => [qw(extends has list_attributes)],
    clone       => [qw(clone clone_nomagic)],
    coercion    => [qw(to_bool to_number to_string to_time to_tristate to_uuid)],
    crypt       => [qw(pad_pkcs7)],
    debug       => [qw(DEBUG dumper)],
    fork        => [qw(can_fork)],
    function    => [qw(memoize recurse_limit)],
    empty       => [qw(empty nonempty)],
    erase       => [qw(erase erase_scoped)],
    gzip        => [qw(gzip gunzip)],
    int         => [qw(int64 pack_ql pack_Ql unpack_ql unpack_Ql)],
    io          => [qw(read_all)],
    load        => [qw(load_optional load_xs try_load_optional)],
    search      => [qw(query query_any search simple_expression_query)],
    text        => [qw(snakify trim)],
    uuid        => [qw(format_uuid generate_uuid is_uuid uuid UUID_NULL)],
    uri         => [qw(split_url uri_escape_utf8 uri_unescape_utf8)],
);

$EXPORT_TAGS{all} = [map { @$_ } values %EXPORT_TAGS];
our @EXPORT_OK = @{$EXPORT_TAGS{all}};

BEGIN {
    my $debug = $ENV{DEBUG};
    $debug = looks_like_number($debug) ? (0 + $debug) : ($debug ? 1 : 0);
    *DEBUG = $debug == 1 ? sub() { 1 } :
             $debug == 2 ? sub() { 2 } :
             $debug == 3 ? sub() { 3 } :
             $debug == 4 ? sub() { 4 } : sub() { 0 };
}

my %OPS = (
    'eq'        =>  2, # binary
    'ne'        =>  2,
    'lt'        =>  2,
    'gt'        =>  2,
    'le'        =>  2,
    'ge'        =>  2,
    '=='        =>  2,
    '!='        =>  2,
    '<'         =>  2,
    '>'         =>  2,
    '<='        =>  2,
    '>='        =>  2,
    '=~'        =>  2,
    '!~'        =>  2,
    '!'         =>  1, # unary
    '!!'        =>  1,
    '-not'      =>  1, # special
    '-false'    =>  1,
    '-true'     =>  1,
    '-defined'  =>  1,
    '-undef'    =>  1,
    '-empty'    =>  1,
    '-nonempty' =>  1,
    '-or'       => -1,
    '-and'      => -1,
);
my %OP_NEG = (
    'eq'    =>  'ne',
    'ne'    =>  'eq',
    'lt'    =>  'ge',
    'gt'    =>  'le',
    'le'    =>  'gt',
    'ge'    =>  'lt',
    '=='    =>  '!=',
    '!='    =>  '==',
    '<'     =>  '>=',
    '>'     =>  '<=',
    '<='    =>  '>',
    '>='    =>  '<',
    '=~'    =>  '!~',
    '!~'    =>  '=~',
);
my %ATTRIBUTES;


my $XS_LOADED;
sub load_xs {
    my $version = shift;

    goto IS_LOADED if defined $XS_LOADED;

    if ($ENV{PERL_ONLY} || (exists $ENV{PERL_FILE_KDBX_XS} && !$ENV{PERL_FILE_KDBX_XS})) {
        return $XS_LOADED = !1;
    }

    $XS_LOADED = !!eval { require File::KDBX::XS; 1 };

    IS_LOADED:
    {
        local $@;
        return $XS_LOADED if !$version;
        return !!eval { File::KDBX::XS->VERSION($version); 1 };
    }
}


sub assert(&) { ## no critic (ProhibitSubroutinePrototypes)
    return if !DEBUG;
    my $code = shift;
    return if $code->();

    (undef, my $file, my $line) = caller;
    $file =~ s!([^/\\]+)$!$1!;
    my $assertion = '';
    if (try_load_optional('B::Deparse')) {
        my $deparse = B::Deparse->new(qw{-P -x9});
        $assertion = $deparse->coderef2text($code);
        $assertion =~ s/^\{(?:\s*(?:package[^;]+|use[^;]+);)*\s*(.*?);\s*\}$/$1/s;
        $assertion =~ s/\s+/ /gs;
        $assertion = ": $assertion";
    }
    die "$0: $file:$line: Assertion failed$assertion\n";
}


sub can_fork {
    require Config;
    return 1 if $Config::Config{d_fork};
    return 0 if $^O ne 'MSWin32' && $^O ne 'NetWare';
    return 0 if !$Config::Config{useithreads};
    return 0 if $Config::Config{ccflags} !~ /-DPERL_IMPLICIT_SYS/;
    return 0 if $] < 5.008001;
    if ($] == 5.010000 && $Config::Config{ccname} eq 'gcc' && $Config::Config{gccversion}) {
        return 0 if $Config::Config{gccversion} !~ m/^(\d+)\.(\d+)/;
        my @parts = split(/[\.\s]+/, $Config::Config{gccversion});
        return 0 if $parts[0] > 4 || ($parts[0] == 4 && $parts[1] >= 8);
    }
    return 0 if $INC{'Devel/Cover.pm'};
    return 1;
}


sub clone {
    require Storable;
    goto &Storable::dclone;
}


sub clone_nomagic {
    my $thing = shift;
    if (is_arrayref($thing)) {
        my @arr = map { clone_nomagic($_) } @$thing;
        return \@arr;
    }
    elsif (is_hashref($thing)) {
        my %hash;
        $hash{$_} = clone_nomagic($thing->{$_}) for keys %$thing;
        return \%hash;
    }
    elsif (is_ref($thing)) {
        return clone($thing);
    }
    return $thing;
}


sub dumper {
    require Data::Dumper;
    # avoid "once" warnings
    local $Data::Dumper::Deepcopy = $Data::Dumper::Deepcopy = 1;
    local $Data::Dumper::Deparse = $Data::Dumper::Deparse = 1;
    local $Data::Dumper::Indent = 1;
    local $Data::Dumper::Quotekeys = 0;
    local $Data::Dumper::Sortkeys = 1;
    local $Data::Dumper::Terse = 1;
    local $Data::Dumper::Trailingcomma = 1;
    local $Data::Dumper::Useqq = 1;

    my @dumps;
    for my $struct (@_) {
        my $str = Data::Dumper::Dumper($struct);

        # boolean
        $str =~ s/bless\( do\{\\\(my \$o = ([01])\)\}, 'boolean' \)/boolean($1)/gs;
        # Time::Piece
        $str =~ s/bless\([^\)]+?(\d+)'?,\s+\d+,?\s+\], 'Time::Piece' \),/
            "scalar gmtime($1), # " . scalar gmtime($1)->datetime/ges;

        print STDERR $str if !defined wantarray;
        push @dumps, $str;
        return $str;
    }
    return join("\n", @dumps);
}


sub empty    {  _empty(@_) }
sub nonempty { !_empty(@_) }

sub _empty {
    return 1 if @_ == 0;
    local $_ = shift;
    return !defined $_
        || $_ eq ''
        || (is_arrayref($_)  && @$_ == 0)
        || (is_hashref($_)   && keys %$_ == 0)
        || (is_scalarref($_) && (!defined $$_ || $$_ eq ''))
        || (is_refref($_)    && _empty($$_));
}


BEGIN {
    if (load_xs) {
        *_CowREFCNT = \&File::KDBX::XS::CowREFCNT;
    }
    elsif (eval { require B::COW; 1 }) {
        *_CowREFCNT = \&B::COW::cowrefcnt;
    }
    else {
        *_CowREFCNT = sub { undef };
    }
}

sub erase {
    # Only bother zeroing out memory if we have the last SvPV COW reference, otherwise we'll end up just
    # creating a copy and erasing the copy.
    # TODO - Is this worth doing? Need some benchmarking.
    for (@_) {
        if (!is_ref($_)) {
            next if !defined $_ || readonly $_;
            my $cowrefcnt = _CowREFCNT($_);
            goto FREE_NONREF if defined $cowrefcnt && 1 < $cowrefcnt;
            # if (__PACKAGE__->can('erase_xs')) {
            #     erase_xs($_);
            # }
            # else {
                substr($_, 0, length($_), "\0" x length($_));
            # }
            FREE_NONREF: {
                no warnings 'uninitialized';
                undef $_;
            }
        }
        elsif (is_scalarref($_)) {
            next if !defined $$_ || readonly $$_;
            my $cowrefcnt = _CowREFCNT($$_);
            goto FREE_REF if defined $cowrefcnt && 1 < $cowrefcnt;
            # if (__PACKAGE__->can('erase_xs')) {
            #     erase_xs($$_);
            # }
            # else {
                substr($$_, 0, length($$_), "\0" x length($$_));
            # }
            FREE_REF: {
                no warnings 'uninitialized';
                undef $$_;
            }
        }
        elsif (is_arrayref($_)) {
            erase(@$_);
            @$_ = ();
        }
        elsif (is_hashref($_)) {
            erase(values %$_);
            %$_ = ();
        }
        else {
            throw 'Cannot erase this type of scalar', type => ref $_, what => $_;
        }
    }
}


sub erase_scoped {
    throw 'Programmer error: Cannot call erase_scoped in void context' if !defined wantarray;
    my @args;
    for (@_) {
        !is_ref($_) || is_arrayref($_) || is_hashref($_) || is_scalarref($_)
            or throw 'Cannot erase this type of scalar', type => ref $_, what => $_;
        push @args, is_ref($_) ? $_ : \$_;
    }
    require Scope::Guard;
    return Scope::Guard->new(sub { erase(@args) });
}


sub extends {
    my $parent  = shift;
    my $caller  = caller;
    load $parent;
    no strict 'refs'; ## no critic (ProhibitNoStrict)
    @{"${caller}::ISA"} = $parent;
}


sub has {
    my $name = shift;
    my %args = @_ % 2 == 1 ? (default => shift, @_) : @_;

    my ($package, $file, $line) = caller;

    my $d = $args{default};
    my $default = is_arrayref($d) ? sub { [@$d] } : is_hashref($d) ? sub { +{%$d} } : $d;
    my $coerce  = $args{coerce};
    my $is      = $args{is} || 'rw';

    my $store = $args{store};
    ($store, $name) = split(/\./, $name, 2) if $name =~ /\./;

    my @path = split(/\./, $args{path} || '');
    my $last = pop @path;
    my $path = $last ? join('', map { qq{->$_} } @path) . qq{->{'$last'}}
                     : $store ? qq{->$store\->{'$name'}} : qq{->{'$name'}};
    my $member = qq{\$_[0]$path};


    my $default_code = is_coderef $default ? q{scalar $default->($_[0])}
                        : defined $default ? q{$default}
                                           : q{undef};
    my $get = qq{$member //= $default_code;};

    my $set = '';
    if ($is eq 'rw') {
        $set = is_coderef $coerce ? qq{$member = scalar \$coerce->(\@_[1..\$#_]) if \$#_;}
                : defined $coerce ? qq{$member = do { local @_ = (\@_[1..\$#_]); $coerce } if \$#_;}
                                  : qq{$member = \$_[1] if \$#_;};
    }

    push @{$ATTRIBUTES{$package} //= []}, $name;
    $line -= 4;
    my $code = <
# line $line "$file"
sub ${package}::${name} {
    return $default_code if !Scalar::Util::blessed(\$_[0]);
    $set
    $get
}
END
    eval $code; ## no critic (ProhibitStringyEval)
}


sub format_uuid {
    local $_    = shift // "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
    my $delim   = shift // '';
    length($_) == 16 or throw 'Must provide a 16-bytes UUID', size => length($_), str => $_;
    return uc(join($delim, unpack('H8 H4 H4 H4 H12', $_)));
}


sub generate_uuid {
    my $set  = @_ % 2 == 1 ? shift : undef;
    my %args = @_;
    my $test = $set //= $args{test};
    $test   = sub { !$set->{$_} } if is_hashref($test);
    $test //= sub { 1 };
    my $printable = $args{printable} // $args{print};
    local $_ = '';
    do {
        $_ = $printable ? random_string(16) : random_bytes(16);
    } while (!$test->($_));
    return $_;
}


sub gunzip {
    load_optional('Compress::Raw::Zlib');
    local $_ = shift;
    my ($i, $status) = Compress::Raw::Zlib::Inflate->new(-WindowBits => 31);
    $status == Compress::Raw::Zlib::Z_OK()
        or throw 'Failed to initialize compression library', status => $status;
    $status = $i->inflate($_, my $out);
    $status == Compress::Raw::Zlib::Z_STREAM_END()
        or throw 'Failed to decompress data', status => $status;
    return $out;
}


sub gzip {
    load_optional('Compress::Raw::Zlib');
    local $_ = shift;
    my ($d, $status) = Compress::Raw::Zlib::Deflate->new(-WindowBits => 31, -AppendOutput => 1);
    $status == Compress::Raw::Zlib::Z_OK()
        or throw 'Failed to initialize compression library', status => $status;
    $status = $d->deflate($_, my $out);
    $status == Compress::Raw::Zlib::Z_OK()
        or throw 'Failed to compress data', status => $status;
    $status = $d->flush($out);
    $status == Compress::Raw::Zlib::Z_OK()
        or throw 'Failed to compress data', status => $status;
    return $out;
}


sub int64 {
    require Config;
    if ($Config::Config{ivsize} < 8) {
        require Math::BigInt;
        return Math::BigInt->new(@_);
    }
    return 0 + shift;
}


sub pack_Ql {
    my $num = shift;
    require Config;
    if ($Config::Config{ivsize} < 8) {
        if (blessed $num && $num->can('as_hex')) {
            require Math::BigInt;
            return "\xff\xff\xff\xff\xff\xff\xff\xff" if Math::BigInt->new('18446744073709551615') <= $num;
            return "\x00\x00\x00\x00\x00\x00\x00\x80" if $num <= Math::BigInt->new('-9223372036854775808');
            my $neg;
            if ($num < 0) {
                $neg = 1;
                $num = -$num;
            }
            my $hex = $num->as_hex;
            $hex =~ s/^0x/000000000000000/;
            my $bytes = reverse pack('H16', substr($hex, -16));
            $bytes .= "\0" x (8 - length $bytes) if length $bytes < 8;
            if ($neg) {
                # two's compliment
                $bytes = join('', map { chr(~ord($_) & 0xff) } split(//, $bytes));
                substr($bytes, 0, 1, chr(ord(substr($bytes, 0, 1)) + 1));
            }
            return $bytes;
        }
        else {
            my $pad = $num < 0 ? "\xff" : "\0";
            return pack('L<', $num) . ($pad x 4);
        };
    }
    return pack('Q<', $num);
}


sub pack_ql { goto &pack_Ql }


sub unpack_Ql {
    my $bytes = shift;
    require Config;
    if ($Config::Config{ivsize} < 8) {
        require Math::BigInt;
        return Math::BigInt->new('0x' . unpack('H*', scalar reverse $bytes));
    }
    return unpack('Q<', $bytes);
}


sub unpack_ql {
    my $bytes = shift;
    require Config;
    if ($Config::Config{ivsize} < 8) {
        require Math::BigInt;
        if (ord(substr($bytes, -1, 1)) & 128) {
            return Math::BigInt->new('-9223372036854775808') if $bytes eq "\x00\x00\x00\x00\x00\x00\x00\x80";
            # two's compliment
            substr($bytes, 0, 1, chr(ord(substr($bytes, 0, 1)) - 1));
            $bytes = join('', map { chr(~ord($_) & 0xff) } split(//, $bytes));
            return -Math::BigInt->new('0x' . unpack('H*', scalar reverse $bytes));
        }
        else {
            return Math::BigInt->new('0x' . unpack('H*', scalar reverse $bytes));
        }
    }
    return unpack('q<', $bytes);
}


sub is_uuid { defined $_[0] && !is_ref($_[0]) && length($_[0]) == 16 }


sub list_attributes {
    my $package = shift;
    return @{$ATTRIBUTES{$package} // []};
}


sub load_optional {
    for my $module (@_) {
        eval { load $module };
        if (my $err = $@) {
            throw "Missing dependency: Please install $module to use this feature.\n",
                module  => $module,
                error   => $err;
        }
    }
    return wantarray ? @_ : $_[0];
}


sub memoize {
    my $func = shift;
    my @args = @_;
    my %cache;
    return sub { $cache{join("\0", grep { defined } @_)} //= $func->(@args, @_) };
}


sub pad_pkcs7 {
    my $data = shift // throw 'Must provide a string to pad';
    my $size = shift or throw 'Must provide block size';

    0 <= $size && $size < 256
        or throw 'Cannot add PKCS7 padding to a large block size', size => $size;

    my $pad_len = $size - length($data) % $size;
    $data .= chr($pad_len) x $pad_len;
}


sub query { _query(undef, '-or', \@_) }


sub query_any {
    my $code = shift;

    if (is_coderef($code) || overload::Method($code, '&{}')) {
        return $code;
    }
    elsif (is_scalarref($code)) {
        return simple_expression_query($$code, @_);
    }
    else {
        return query($code, @_);
    }
}


sub read_all($$$;$) { ## no critic (ProhibitSubroutinePrototypes)
    my $result = @_ == 3 ? read($_[0], $_[1], $_[2])
                         : read($_[0], $_[1], $_[2], $_[3]);
    return if !defined $result;
    return if $result != $_[2];
    return $result;
}


sub recurse_limit {
    my $func        = shift;
    my $max_depth   = shift // 200;
    my $error       = shift // sub {};
    my $depth = 0;
    return sub { return $error->(@_) if $max_depth < ++$depth; $func->(@_) };
};


sub search {
    my $list    = shift;
    my $query   = query_any(@_);

    my @match;
    for my $item (@$list) {
        push @match, $item if $query->($item);
    }
    return \@match;
}


sub simple_expression_query {
    my $expr = shift;
    my $op   = @_ && ($OPS{$_[0] || ''} || 0) == 2 ? shift : '=~';

    my $neg_op = $OP_NEG{$op};
    my $is_re  = $op eq '=~' || $op eq '!~';

    require Text::ParseWords;
    my @terms = Text::ParseWords::shellwords($expr);

    my @query = qw(-and);

    for my $term (@terms) {
        my @subquery = qw(-or);

        my $neg = $term =~ s/^-//;
        my $condition = [($neg ? $neg_op : $op) => ($is_re ? qr/\Q$term\E/i : $term)];

        for my $field (@_) {
            push @subquery, $field => $condition;
        }

        push @query, \@subquery;
    }

    return query(\@query);
}


sub snakify {
    local $_ = shift;
    s/UserName/Username/g;
    s/([a-z])([A-Z0-9])/${1}_${2}/g;
    s/([A-Z0-9]+)([A-Z0-9])(?![A-Z0-9]|$)/${1}_${2}/g;
    return lc($_);
}


sub split_url {
    local $_ = shift;
    my ($scheme, $auth, $host, $port, $path, $query, $hash) =~ m!
        ^([^:/\?\#]+) ://
        (?:([^\@]+)\@)
        ([^:/\?\#]*)
        (?::(\d+))?
        ([^\?\#]*)
        (\?[^\#]*)?
        (\#(.*))?
    !x;

    $scheme = lc($scheme);

    $host ||= 'localhost';
    $host = lc($host);

    $path = "/$path" if $path !~ m!^/!;

    $port ||= $scheme eq 'http' ? 80 : $scheme eq 'https' ? 433 : undef;

    my ($username, $password) = split($auth, ':', 2);

    return ($scheme, $auth, $host, $port, $path, $query, $hash, $username, $password);
}


sub to_bool   { $_[0] // return; boolean($_[0]) }
sub to_number { $_[0] // return; 0+$_[0] }
sub to_string { $_[0] // return; "$_[0]" }
sub to_time   {
    $_[0] // return;
    return scalar gmtime($_[0]) if looks_like_number($_[0]);
    return scalar gmtime if $_[0] eq 'now';
    return Time::Piece->strptime($_[0], '%Y-%m-%d %H:%M:%S') if !blessed $_[0];
    return $_[0];
}
sub to_tristate { $_[0] // return; boolean($_[0]) }
sub to_uuid {
    my $str = to_string(@_) // return;
    return sprintf('%016s', $str) if length($str) < 16;
    return substr($str, 0, 16) if 16 < length($str);
    return $str;
}


sub trim($) { ## no critic (ProhibitSubroutinePrototypes)
    local $_ = shift // return;
    s/^\s*//;
    s/\s*$//;
    return $_;
}


sub try_load_optional {
    for my $module (@_) {
        eval { load $module };
        if (my $err = $@) {
            warn $err if 3 <= DEBUG;
            return;
        }
    }
    return @_;
}


my %ESC = map { chr($_) => sprintf('%%%02X', $_) } 0..255;
sub uri_escape_utf8 {
    local $_ = shift // return;
    $_ = encode('UTF-8', $_);
    # RFC 3986 section 2.3 unreserved characters
    s/([^A-Za-z0-9\-\._~])/$ESC{$1}/ge;
    return $_;
}


sub uri_unescape_utf8 {
    local $_ = shift // return;
    s/\%([A-Fa-f0-9]{2})/chr(hex($1))/;
    return decode('UTF-8', $_);
}


sub uuid {
    local $_ = shift // return "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
    s/-//g;
    /^[A-Fa-f0-9]{32}$/ or throw 'Must provide a formatted 128-bit UUID';
    return pack('H32', $_);

}


sub UUID_NULL() { "\0" x 16 }

### --------------------------------------------------------------------------

# Determine if an array looks like keypairs from a hash.
sub _looks_like_keypairs {
    my $arr = shift;
    return 0 if @$arr % 2 == 1;
    for (my $i = 0; $i < @$arr; $i += 2) {
        return 0 if is_ref($arr->[$i]);
    }
    return 1;
}

sub _is_operand_plain {
    local $_ = shift;
    return !(is_hashref($_) || is_arrayref($_));
}

sub _query {
    # dumper \@_;
    my $subject = shift;
    my $op      = shift // throw 'Must specify a query operator';
    my $operand = shift;

    return _query_simple($op, $subject) if defined $subject && !is_ref($op) && ($OPS{$subject} || 2) < 2;
    return _query_simple($subject, $op, $operand) if _is_operand_plain($operand);
    return _query_inverse(_query($subject, '-or', $operand)) if $op eq '-not' || $op eq '-false';
    return _query($subject, '-and', [%$operand]) if is_hashref($operand);

    my @queries;

    my @atoms = @$operand;
    while (@atoms) {
        if (_looks_like_keypairs(\@atoms)) {
            my ($atom, $operand) = splice @atoms, 0, 2;
            if (my $op_type = $OPS{$atom}) {
                if ($op_type == 1 && _is_operand_plain($operand)) { # unary
                    push @queries, _query_simple($operand, $atom);
                }
                else {
                    push @queries, _query($subject, $atom, $operand);
                }
            }
            elsif (!is_ref($atom)) {
                push @queries, _query($atom, 'eq', $operand);
            }
        }
        else {
            my $atom = shift @atoms;
            if ($OPS{$atom}) {     # apply new operator over the rest
                push @queries, _query($subject, $atom, \@atoms);
                last;
            }
            else {  # apply original operator over this one
                push @queries, _query($subject, $op, $atom);
            }
        }
    }

    if (@queries == 1) {
        return $queries[0];
    }
    elsif ($op eq '-and') {
        return _query_all(@queries);
    }
    elsif ($op eq '-or') {
        return _query_any(@queries);
    }
    throw 'Malformed query';
}

sub _query_simple {
    my $subject = shift;
    my $op      = shift // 'eq';
    my $operand = shift;

    # these special operators can also act as simple operators
    $op = '!!' if $op eq '-true';
    $op = '!'  if $op eq '-false';
    $op = '!'  if $op eq '-not';

    defined $subject or throw 'Subject is not set in query';
    $OPS{$op} >= 0   or throw 'Cannot use a non-simple operator in a simple query';
    if (empty($operand)) {
        if ($OPS{$op} < 2) {
            # no operand needed
        }
        # Allow field => undef and field => {'ne' => undef} to do the (arguably) right thing.
        elsif ($op eq 'eq' || $op eq '==') {
            $op = '-empty';
        }
        elsif ($op eq 'ne' || $op eq '!=') {
            $op = '-nonempty';
        }
        else {
            throw 'Operand is required';
        }
    }

    my $field = sub { blessed $_[0] && $_[0]->can($subject) ? $_[0]->$subject : $_[0]->{$subject} };

    my %map = (
        'eq'        => sub { local $_ = $field->(@_); defined && $_ eq $operand },
        'ne'        => sub { local $_ = $field->(@_); defined && $_ ne $operand },
        'lt'        => sub { local $_ = $field->(@_); defined && $_ lt $operand },
        'gt'        => sub { local $_ = $field->(@_); defined && $_ gt $operand },
        'le'        => sub { local $_ = $field->(@_); defined && $_ le $operand },
        'ge'        => sub { local $_ = $field->(@_); defined && $_ ge $operand },
        '=='        => sub { local $_ = $field->(@_); defined && $_ == $operand },
        '!='        => sub { local $_ = $field->(@_); defined && $_ != $operand },
        '<'         => sub { local $_ = $field->(@_); defined && $_ <  $operand },
        '>'         => sub { local $_ = $field->(@_); defined && $_ >  $operand },
        '<='        => sub { local $_ = $field->(@_); defined && $_ <= $operand },
        '>='        => sub { local $_ = $field->(@_); defined && $_ >= $operand },
        '=~'        => sub { local $_ = $field->(@_); defined && $_ =~ $operand },
        '!~'        => sub { local $_ = $field->(@_); defined && $_ !~ $operand },
        '!'         => sub { local $_ = $field->(@_); ! $_ },
        '!!'        => sub { local $_ = $field->(@_); !!$_ },
        '-defined'  => sub { local $_ = $field->(@_);  defined $_ },
        '-undef'    => sub { local $_ = $field->(@_); !defined $_ },
        '-nonempty' => sub { local $_ = $field->(@_); nonempty $_ },
        '-empty'    => sub { local $_ = $field->(@_); empty    $_ },
    );

    return $map{$op} // throw "Unexpected operator in query: $op",
        subject     => $subject,
        operator    => $op,
        operand     => $operand;
}

sub _query_inverse {
    my $query = shift;
    return sub { !$query->(@_) };
}

sub _query_all {
    my @queries = @_;
    return sub {
        my $val = shift;
        all { $_->($val) } @queries;
    };
}

sub _query_any {
    my @queries = @_;
    return sub {
        my $val = shift;
        any { $_->($val) } @queries;
    };
}

1;

__END__