X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FHash%2FUtil.pm;h=3d65ee0b11604a3c5fa757242096a94bffd0c88c;hb=f1317c8d183c687b884dabebf7d01723441851a4;hp=0c8979d61b3c7f70fa2cb2de9950b9af5c0f6c96;hpb=a94e8023b124b822fcd2c4e28f8dc89b1f24e54a;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/lib/Hash/Util.pm b/lib/Hash/Util.pm
index 0c8979d..3d65ee0 100644
--- a/lib/Hash/Util.pm
+++ b/lib/Hash/Util.pm
@@ -7,9 +7,9 @@ use Carp;
 require Exporter;
 our @ISA        = qw(Exporter);
 our @EXPORT_OK  = qw(lock_keys unlock_keys lock_value unlock_value
-                     lock_hash unlock_hash
+                     lock_hash unlock_hash hash_seed
                     );
-our $VERSION    = 0.04;
+our $VERSION    = 0.05;
 
 =head1 NAME
 
@@ -19,7 +19,8 @@ Hash::Util - A selection of general-utility hash subroutines
 
   use Hash::Util qw(lock_keys   unlock_keys
                     lock_value  unlock_value
-                    lock_hash   unlock_hash);
+                    lock_hash   unlock_hash
+                    hash_seed);
 
   %hash = (foo => 42, bar => 23);
   lock_keys(%hash);
@@ -32,6 +33,8 @@ Hash::Util - A selection of general-utility hash subroutines
   lock_hash  (%hash);
   unlock_hash(%hash);
 
+  my $hashes_are_randomised = hash_seed() != 0;
+
 =head1 DESCRIPTION
 
 C<Hash::Util> contains special functions for manipulating hashes that
@@ -59,10 +62,11 @@ This is intended to largely replace the deprecated pseudo-hashes.
 
 Restricts the given %hash's set of keys to @keys.  If @keys is not
 given it restricts it to its current keyset.  No more keys can be
-added.  delete() and exists() will still work, but it does not effect
-the set of allowed keys. B<Note>: the current implementation does not
-allow you to bless() the resulting hash, so if you want to use
-lock_keys() for an object, you need to bless it prior to locking it.
+added. delete() and exists() will still work, but will not alter
+the set of allowed keys. B<Note>: the current implementation prevents
+the hash from being bless()ed while it is in a locked state. Any attempt
+to do so will raise an exception. Of course you can still bless()
+the hash before you call lock_keys() so this shouldn't be a problem.
 
   unlock_keys(%hash);
 
@@ -175,8 +179,37 @@ sub unlock_hash (\%) {
 }
 
 
+=item B<hash_seed>
+
+    my $hash_seed = hash_seed();
+
+hash_seed() returns the seed number used to randomise hash ordering.
+Zero means the "traditional" random hash ordering, non-zero means the
+new even more random hash ordering introduced in Perl 5.8.1.
+
+B<Note that the hash seed is sensitive information>: by knowing it one
+can craft a denial-of-service attack against Perl code, even remotely,
+see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
+B<Do not disclose the hash seed> to people who don't need to know it.
+See also L<perlrun/PERL_HASH_SEED_DEBUG>.
+
+=cut
+
+sub hash_seed () {
+    Internals::rehash_seed();
+}
+
 =back
 
+=head1 CAVEATS
+
+Note that the trapping of the restricted operations is not atomic:
+for example
+
+    eval { %hash = (illegal_key => 1) }
+
+leaves the C<%hash> empty rather than with its original contents.
+
 =head1 AUTHOR
 
 Michael G Schwern <schwern@pobox.com> on top of code by Nick
@@ -184,7 +217,8 @@ Ing-Simmons and Jeffrey Friedl.
 
 =head1 SEE ALSO
 
-L<Scalar::Util>, L<List::Util>, L<Hash::Util>
+L<Scalar::Util>, L<List::Util>, L<Hash::Util>,
+and L<perlsec/"Algorithmic Complexity Attacks">.
 
 =cut