#
# $Id: Escape.pm 1514 2004-11-28 17:55:28Z dsully $
#

package URI::Escape;
use strict;

=head1 NAME

URI::Escape - Escape and unescape unsafe characters

=head1 SYNOPSIS

 use URI::Escape;
 $safe = uri_escape("10% is enough\n");
 $verysafe = uri_escape("foo", "\0-\377");
 $str  = uri_unescape($safe);

=head1 DESCRIPTION

This module provides functions to escape and unescape URI strings as
defined by RFC 2396 (and updated by RFC 2732).
A URI consists of a restricted set of characters,
denoted as C<uric> in RFC 2396.  The restricted set of characters
consists of digits, letters, and a few graphic symbols chosen from
those common to most of the character encodings and input facilities
available to Internet users:

  "A" .. "Z", "a" .. "z", "0" .. "9",
  ";", "/", "?", ":", "@", "&", "=", "+", "$", ",", "[", "]",   # reserved
  "-", "_", ".", "!", "~", "*", "'", "(", ")"

In addition, any byte (octet) can be represented in a URI by an escape
sequence: a triplet consisting of the character "%" followed by two
hexadecimal digits.  A byte can also be represented directly by a
character, using the US-ASCII character for that octet (iff the
character is part of C<uric>).

Some of the C<uric> characters are I<reserved> for use as delimiters
or as part of certain URI components.  These must be escaped if they are
to be treated as ordinary data.  Read RFC 2396 for further details.

The functions provided (and exported by default) from this module are:

=over 4

=item uri_escape( $string )

=item uri_escape( $string, $unsafe )

Replaces each unsafe character in the $string with the corresponding
escape sequence and returns the result.  The $string argument should
be a string of bytes.  The uri_escape() function will croak if given a
characters with code above 255.  Use uri_escape_utf8() if you know you
have such chars or/and want chars in the 128 .. 255 range treated as
UTF-8.

The uri_escape() function takes an optional second argument that
overrides the set of characters that are to be escaped.  The set is
specified as a string that can be used in a regular expression
character class (between [ ]).  E.g.:

  "\x00-\x1f\x7f-\xff"          # all control and hi-bit characters
  "a-z"                         # all lower case characters
  "^A-Za-z"                     # everything not a letter

The default set of characters to be escaped is all those which are
I<not> part of the C<uric> character class shown above as well as the
reserved characters.  I.e. the default is:

  "^A-Za-z0-9\-_.!~*'()"

=item uri_escape_utf8( $string )

=item uri_escape_utf8( $string, $unsafe )

Works like uri_escape(), but will encode chars as UTF-8 before
escaping them.  This makes this function able do deal with characters
with code above 255 in $string.  Note that chars in the 128 .. 255
range will be escaped differently by this function compared to what
uri_escape() would.  For chars in the 0 .. 127 range there is no
difference.

The call:

    $uri = uri_escape_utf8($string);

will be the same as:

    use Encode qw(encode);
    $uri = uri_escape(encode("UTF-8", $string));

but will even work for perl-5.6 for chars in the 128 .. 255 range.

Note: Javascript has a function called escape() that produce the
sequence "%uXXXX" for chars in the 256 .. 65535 range.  This function
has really nothing to do with URI escaping but some folks got confused
since it "does the right thing" in the 0 .. 255 range.  Because of
this you sometimes see "URIs" with these kind of escapes.  The
JavaScript encodeURI() function is similar to uri_escape_utf8().

=item uri_unescape($string,...)

Returns a string with each %XX sequence replaced with the actual byte
(octet).

This does the same as:

   $string =~ s/%([0-9A-Fa-f]{2})/chr(hex($1))/eg;

but does not modify the string in-place as this RE would.  Using the
uri_unescape() function instead of the RE might make the code look
cleaner and is a few characters less to type.

In a simple benchmark test I did,
calling the function (instead of the inline RE above) if a few chars
were unescaped was something like 40% slower, and something like 700% slower if none were.  If
you are going to unescape a lot of times it might be a good idea to
inline the RE.

If the uri_unescape() function is passed multiple strings, then each
one is returned unescaped.

=back

The module can also export the C<%escapes> hash, which contains the
mapping from all 256 bytes to the corresponding escape codes.  Lookup
in this hash is faster than evaluating C<sprintf("%%%02X", ord($byte))>
each time.

=head1 SEE ALSO

L<URI>


=head1 COPYRIGHT

Copyright 1995-2004 Gisle Aas.

This program is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=cut

use vars qw(@ISA @EXPORT @EXPORT_OK $VERSION);
use vars qw(%escapes);

require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(uri_escape uri_unescape);
@EXPORT_OK = qw(%escapes uri_escape_utf8);
$VERSION = sprintf("%d.%02d", q$Revision: 1.2 $ =~ /(\d+)\.(\d+)/);

use Carp ();

# Build a char->hex map
for (0..255) {
    $escapes{chr($_)} = sprintf("%%%02X", $_);
}

my %subst;  # compiled patternes

sub uri_escape
{
    my($text, $patn) = @_;
    return undef unless defined $text;
    if (defined $patn){
	unless (exists  $subst{$patn}) {
	    # Because we can't compile the regex we fake it with a cached sub
	    (my $tmp = $patn) =~ s,/,\\/,g;
	    eval "\$subst{\$patn} = sub {\$_[0] =~ s/([$tmp])/\$escapes{\$1} || _fail_hi(\$1)/ge; }";
	    Carp::croak("uri_escape: $@") if $@;
	}
	&{$subst{$patn}}($text);
    } else {
	# Default unsafe characters.  RFC 2732 ^(uric - reserved)
	$text =~ s/([^A-Za-z0-9\-_.!~*'()])/$escapes{$1} || _fail_hi($1)/ge;
    }
    $text;
}

sub _fail_hi {
    my $chr = shift;
    Carp::croak(sprintf "Can't escape \\x{%04X}, try uri_escape_utf8() instead", ord($chr));
}

sub uri_escape_utf8
{
    my $text = shift;
    if ($] < 5.008) {
	$text =~ s/([^\0-\x7F])/do {my $o = ord($1); sprintf("%c%c", 0xc0 | ($o >> 6), 0x80 | ($o & 0x3f)) }/ge;
    }
    else {
	utf8::encode($text);
    }

    return uri_escape($text, @_);
}

sub uri_unescape
{
    # Note from RFC1630:  "Sequences which start with a percent sign
    # but are not followed by two hexadecimal characters are reserved
    # for future extension"
    my $str = shift;
    if (@_ && wantarray) {
	# not executed for the common case of a single argument
	my @str = ($str, @_);  # need to copy
	foreach (@str) {
	    s/%([0-9A-Fa-f]{2})/chr(hex($1))/eg;
	}
	return @str;
    }
    $str =~ s/%([0-9A-Fa-f]{2})/chr(hex($1))/eg if defined $str;
    $str;
}

1;
