| Description: |
CGIpack is a module I wrote in this response.
I came up with this solution. The encoder takes a list of data, together
with a list with the desired number of bits to be saved. The bits are
divided into chunks of 6 bits, that are encoded with the alphanumeric
characters *and* % and - (64 characters in total). The resulting string
is short, contains as little bits as possible and/or desired by the user.
See POD for further info.
Update:Version 0.02 has working 32 bit values
now. Still pondering 64 bits.
Update2:Thanx to ChOas, I now know that perl 5.6
has another implementation of pack, *and* that 64 bits can
be used only if you have a 64bit machine and 64 bit support
is compiled in. I've chosen to comment that line in decode,
you can uncomment it if your environment is right, otherwise
there is a risk of a fatal error. Please let me know if
you succesfully use 64 bits.
Wishlist:
- Apply tye's quad for 57 bit integers
- Add wrapper, to accomodate: characters, strings,
signed integers.
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package CGIpack;
use strict;
=head1 NAME
CGIpack - Transforms parameters into a packed list of URL-compatible c
+haracters
and vice versa.
=head1 SYNOPSIS
use CGIpack;
# Transform a list of numbers and back.
#Results in:
@data=(15,13,2**23,0,2**31);
@bitsizes = (4,14,24,1,55 );
$encoded=encode({ bitsizes=>[@bitsizes], data=>[@data]});
$decoded=join ', ', decode( {str=>$encoded, bitsizes=>[@bitsizes]} );
## only converted 32 bits instead of 55
#Data: 15, 13, 8388608, 0, 2147483648
#Encoded: V30000W000004000
#Decoded array: 15, 13, 8388608, 0, 2147483648
=head1 DESCRIPTION
CGIpack is a module I wrote in response to a question. Question went
+like:
"I want my users to save a URL containing a CGI with parameters. To a
+void
problems with email-readers, the list should be as short as possible,
+and
to avoid users messing around with the values I would like to see them
+
encoded in a certain way."
I came up with this solution. The encoder takes a list of data, toget
+her
with a list with the desired number of bits to be saved. The bits are
+
divided into chunks of 6 bits, that are encoded with the alphanumeric
characters *and* % and - (64 characters in total). The resulting strin
+g
is short, contains as little bits as possible and/or desired by the us
+er.
=over 4
=item encode( $hashref )
Takes a hashref, which should contain a member 'data', referring to a
+list,
and a member 'bitsizes', referring to a list containing the number of
desired bits for every value in the list.
=item decode( $hashref )
Takes a hashref, which should contain a member 'str', containing a str
+ing
of characters produced by encode (preferably, you may wanna roll your
+own
;-) and a member 'bitsizes', referring to a list containing the number
+ of
desired bits for every value encoded in the string.
=back
=head1 CAVEAT
If you want to encode characters, you will have to convert them manual
+ly
using unpack/pack 'c'. I just may add a wrapper for that in the futur
+e,
though.
It does work on 32 bit integers, but not yet on 64 bit. I'm a little p
+uzzled
why not, it may have something to do with the fact I'm working on a 32
+-bit
pentium right now. Will try at home with my PPC.
=head1 AUTHOR
Jeroen Elassaiss-Schaap
=head1 LICENSE
Perl/ artisitic license
=head1 STATUS
Alpha
=cut
use Exporter;
use vars qw( @EXPORT @ISA @VERSION);
@VERSION = 0.021;
@ISA = qw( Exporter );
@EXPORT = qw( &encode &decode);
sub encode{
my $hash = shift;
my @data = @{$hash->{'data'}};
my @bitsizes = @{$hash->{'bitsizes'}};
my ($str, $bitstr);
for my $bits (@bitsizes) {
$bitstr .= unpack("b$bits", pack('VV', shift( @data ) ));
}
$bitstr .= '0' x ( length($bitstr) % 6 );
for my $item (0..( length($bitstr) / 6 - 1 )){
my $val=pack('b6', substr($bitstr, $item*6, 6) );
for ($val) {
tr [\100\077\000-\010\011-\043\044-\075]
[\045\055\060-\071\101-\132\141-\172];
$str.=$_;
}
}
$str;
}
sub decode{
my $hash = shift;
my $str = $hash->{'str'};
my @bitsizes= @{$hash->{'bitsizes'}};
my ($bitstr, $val);
my @data;
for (split //, $str){
tr [\045\055\060-\071\101-\132\141-\172]
[\100\077\000-\010\011-\043\044-\075];
$bitstr .= unpack("b6",$_);
}
my $pointer = 0;
for my $bits (@bitsizes) {
my $val;
for ($bits) {
$val = unpack('c',pack("b$_",substr( $bitstr, $pointer, $_
+ ))), last
if $bits < 9;
$val = unpack('v',pack("b$_",substr( $bitstr, $pointer, $_
+ ))), last
if $bits < 17;
$val = unpack('V',pack("b32",substr( $bitstr, $pointer, $_
+ ))), last
if $bits < 33;
if (! eval('{$val = unpack("Q",pack("b$_",substr( '.
'$bitstr, $pointer, $_ )));1;}') ) {
warn "only converted 32 bits instead of $_\n";
$val = unpack('V',pack("b$_",
substr( $bitstr, $pointer, $_ )));
}
}
push( @data, $val);
$pointer += $bits;
}
@data;
}
1;
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