Perl - Test::Identity

Today I uploaded a new module to CPAN; Test::Identity. It's possibly the quickest module I've ever written, from when I decided to write it, to when it was actually uploaded:

(18:02) sub Test::Identity::identical { is refaddr $_[0], refaddr $_[1], $_[2] } <== I'm about to write such in a module, unless anyone can suggest me a module that already has it
...
(19:21) * GumbyPAN CPAN Upload: Test-Identity-0.01 by PEVANS

I won't spend a long time explaining why, I'll just quote the docs:

This module provides a single testing function, identical. It asserts that a given reference is as expected; that is, it either refers to the same object or is undef. It is similar to Test::More::is except that it uses refaddr, ensuring that it behaves correctly even if the references under test are objects that overload stringification or numification.

It also provides better diagnostics if the test fails:

$ perl -MTest::More=tests,1 -MTest::Identity -e'identical [], {}'
1..1
not ok 1
#   Failed test at -e line 1.
# Expected an anonymous HASH ref, got an anonymous ARRAY ref
# Looks like you failed 1 test of 1.

$ perl -MTest::More=tests,1 -MTest::Identity -e'identical [], []'
1..1
not ok 1
#   Failed test at -e line 1.
# Expected an anonymous ARRAY ref to the correct object
# Looks like you failed 1 test of 1.

Perl - IO::Socket::IP

IO::Socket::IP is a subclass of IO::Socket that provides a protocol-independent way to use IPv4 and IPv6 sockets. It provides an API compatible with the IPv4-only IO::Socket::INET, but does so in a way that ensures properly transparent IPv6 support.

The following example shows it has an identical API to the ::INET module:

use IO::Socket::IP;

my $sock = IO::Socket::IP->new(
   PeerHost => "www.google.com",
   PeerPort => "www",
) or die "Cannot construct socket - $@";

At this point, $sock is just another IO::Socket-derived filehandle, and supports all the usual methods and IO functionality. The only difference here is that, where IO::Socket::INET would have used a legacy gethostbyname call and made a PF_INET socket, IO::Socket::IP will use getaddrinfo (via Socket::GetAddrInfo), and will use either PF_INET or PF_INET6 as appropriate.

It's not yet a complete 100% API clone of ::INET though. While it supports all the methods, there are a few constructor arguments not yet supported, being Blocking and Timeout. The way that getaddrinfo returns a list of candidate addresses, to be tried in order, makes nonblocking support hard to do, and complicates the model for what timeout really means. For nonblocking connect support, better solutions already exist, such as IO::Async's Connector, which has always supported IPv6 via getaddrinfo. As for timeouts, eventually IO::Socket::IP should support it, but for now a local'ised $SIG{ALRM} and alarm call should suffice.

For almost all use cases, switching to using IO::Socket::IP should be a simple matter, because of the API similarities. Just adding an extra dependency (because ::IP isn't core), and substituting the package name in source should be enough.

Finally, in case you don't want to pull in an extra hard dependency, you might consider the following fragment I've used quite successfully:

   my $class = eval { require IO::Socket::IP
                         and "IO::Socket::IP" } ||
               do   { require IO::Socket::INET
                         and "IO::Socket::INET" };

   $socket = $class->new(
      PeerHost => $host,
      PeerPort => $port,
   ) or die "Cannot connect - $@\n";

There. Now you have no excuse for not being IPv6-ready.

Perl - IO::Async - version 0.30

Yesterday, I put the next version of IO::Async on CPAN; version 0.30. This was primarily an update to add some new features, though also a few minor bugfixes and documentation updates were included too. Here I want to focus on a few of these new features.

The first of these new features is nothing groundbreaking in itself, but feeds into the others. It's simply the addition of IO::Async::Socket, a notifier subclass to contain a socket that isn't necessarily a stream (primarily SOCK_DGRAM or SOCK_RAW sockets such as UDP, PF_PACKET or PF_NETLINK). This neatens up a few rough edges with trying to put such sockets directly in IO::Async::Handle objects.

The second main new feature is the creation of the IO::Async::Protocol class, and IO::Async::Protocol::Stream subclass. These derive directly from IO::Async::Notifier rather than IO::Async::Handle, and are intended to be abstract containers of code, and not perform any IO operations directly. Instead, they contain a Handle or Stream object as a child notifier. By exposing an API identical to IO::Async::Stream, the IO::Async::Protocol::Stream should be a drop-in replacement for any modules trying to implement a network protocol.

With the addition of IO::Async::SSL, not every stream-like connection can be represented by IO::Async::Stream, so separating the transport layer from the protocol layer is required. This wasn't possible by subclassing, whereas object containment makes it much simpler.

Net::Async::FTP, Net::Async::HTTP, and Net::Async::IRC have all been updated to use it, and most other use cases should be simple to change.

The final main change is that $loop->connect and IO::Async::Listener now support direct on_stream or on_socket continuations, which will be provided an instance of Stream or Socket directly, rather than requiring the invoked code to wrap one. This can then be easily configured as a IO::Async::Protocol's transport.

Having made this change, it leads the way to transparent SSL support across all protocols, and possibly other concerns like SOCKS proxies, by extending the arguments to $loop->connect or Listener. But that's for another post...

Finally, I should announce that I've now started a channel on irc.perl.org called #ioasync, as the official IRC home for IO::Async. Feel free to drop by if you have any issues, comments, questions,...

Perl - overload::substr

overload allows an object class to provide methods which Perl should use to implement certain operators, like numerical addition or string concatenation. One operator that overload doesn't allow to be provided, is substr.

overload::substr allows this to be overloaded. This allows objects that behave like a string, to specify to Perl how they will handle the substr operator.

$ cat example.pl 
#!/usr/bin/perl

use strict;
use feature qw( say );

package ExampleString;

use overload::substr;

sub new { return bless [ @_ ]; }

sub _substr
{
   my $self = shift;
   my ( $offs, $len, $replace ) = @_;

   return sprintf ">> %s between %d and %d <<", $self, $offs, $offs+$len;
}

package main;

my $str = ExampleString->new( "Hello, world" );

say substr( $str, 2, 5 );

$ perl example.pl
>> ExampleString=ARRAY(0x86dd9c8) between 2 and 7 <<

The module is still in its early days yet, but the basics appear to be working on all Perl versions back to 5.8. I also want to try extending it, so that split() and regexp matches with m// and substitutions with s/// also use the substr operation. The identity that

$1 == substr( $str, $-[1], $+[1] - $-[1] )

is sure to be useful here.

I need a good example to show it off with sometime. I have in mind a string-alike object with real positional cursors, which remember their contextual position even after edits in other parts of the string. But more on that later...

Module name suggestions: A proper IO::Socket for IPv4/IPv6 duallity

I currently don't have a good name for a module I'd like to write, because I think it is very much required right now.

We have IO::Socket::INET. It wraps PF_INET, thus making it IPv4 only.

We have IO::Socket::INET6. It wraps either PF_INET or PF_INET6, despite its name. It also uses Socket6, thus restricting it to only working on machines capable of supporting IPv6.

Thus any author wanting to write code to communicate to the internet (apparently that's some new fad everyone's talking about this week) is presented a moral dilema: Support IPv6 at the cost of not working on older v4-only machines, or support older machines but be incapable of using IPv6.

I originally partially solved this problem some years ago by the creation of Socket::GetAddrInfo, a module that presents the interface of RFC2553's getaddrinfo(3) and getnameinfo(3) functions. This however is not enough for actually connecting and using sockets.

I'd therefore like to propose a new IO::Socket subclass that uses these and only these functions, for converting between addresses and name/service pairs.

use IO::Socket::YourNameHere;

my $sock = IO::Socket::YourNameHere->new(
   PeerHost    => "www.google.com",
   PeerService => "www",
);

printf "Now connected to %s:%s\n", $sock->peerhost, $sock->peerservice;

...

Since it would use Socket::GetAddrInfo, it can transparently support IPv4 or IPv6. Since it would only use Socket::GetAddrInfo, it will work in a v4-only mode on machines incapable of supporting IPv6, and will not be restricted to only IPv4 or IPv6 if and when some new addressing family comes along to replace IPv6 one day; as v6 is now trying to do with v4.

In order to provide an easy transition period, I'd also support additional IO::Socket::INET options where they still make sense; e.g. accepting {Local/Peer}Port as a synonym for {Local/Peer}Service. The upshot here ought to be that you can simply

sed -i s/IO::Socket::INET/IO::Socket::YourNameHere/

and suddenly your code will JustWork on IPv6 in a good >90% of cases.

Can anyone suggest me a better module name for this?

---

Edit 2010/09/07: We seem to be settling on IO::Socket::IP for this currently.

---

Edit 2010/09/23: We did indeed settle on IO::Socket::IP; this is now up on CPAN, and will be the subject of a future posting...

---

This cross-posted from module-authors@perl.

Test to assert object identity

I've just copypasted the following test function into about the fifth different test script:

use Scalar::Util qw( refaddr );
sub identical
{
   my ( $got, $expected, $name ) = @_;

   my $got_addr = refaddr $got;
   my $exp_addr = refaddr $expected;

   ok( !defined $got_addr && !defined $exp_addr ||
          $got_addr == $exp_addr,
       $name ) or
      diag( "Expected $got and $expected to refer to the same object" );
}

Rather than continuing to copypaste it around some more, can anyone suggest a standard Test:: module that contains it? Failing that, if it's really honestly the case that nobody has yet felt it necessary to provide one, could someone suggest a suitable module to contain it?

This behaviour cannot be implemented using, say, is( $obj, $expected ) because that will attempt to compare numerical equality, which of course will fail for any object that overloads numberification or numeric comparison operators.

Perl - Config::XPath - new version 0.16

Config::XPath is a Perl module for accessing configuration files using XPath queries. It provides some wrapping around XML::XPath for convenience in using a single config file, and easily fetching string, list or map values from it. It plays nicely alongside, for example, Module::PluginFinder (about which I shall write more another day) for easily building powerful configuration-driven plugin-based programs.

use Config::XPath;
use Module::PluginFinder;

my $conf = Config::XPath->new( filename => 'foomangler.conf' );
my $finder = Module::PluginFinder->new(
                search_path => 'FooMangler::Plugin',
                typefunc    => 'TYPE',
             );

my %plugins;

foreach my $plugin_conf ( $conf->get_sub_list( '/plugin' ) ) {
   my $name = $plugin_conf->get_string( '@name' );
   my $type = $plugin_conf->get_string( '@type' );

   $plugins{$name} = $finder->construct( $type, $plugin_conf );
}

Given a config file that perhaps looks like

<foomangler>
  <plugin type="hello" name="hello_world">
    <message>Hello, world</message>
  </plugin>
</foomangler>

We can implement a plugin for this system quite simply, and have it be automatically discovered by the plugin system, instances created, and passed in its configuration from the config file:

package FooMangler::Plugin::Hello;
use constant TYPE => "hello";

sub new
{
   my $class = shift;
   my ( $config ) = @_;

   my $message = $config->get_string( 'message' );
   ...
}

As well as providing one-shot reading support, it also has a subclass Config::XPath::Reloadable which allows for convenient reloading of config files. It itself keeps track of which XML nodes it has already seen, based on some defined key attribute, so it can determine additions and deletions. It will invoke callback functions when items are added or deleted, or their underlying config may have changed.

use Config::XPath::Reloadable;

my $conf = Config::XPath::Reloadable->new( filename => 'foomangler.conf' );
my $finder = Module::PluginFinder->new( ... );

$SIG{HUP} = sub { $conf->reload };

my %manglers;

$conf->associate_nodeset( '/mangler', '@name',
   add => sub {
      my ( $name, $mangler_conf ) = @_;
      my $type = $mangler_conf->get_string( '@type' );

      $manglers{$name} = $finder->construct( $type, $mangler_conf );
   },

   keep => sub {
      my ( $name, $mangler_conf ) = @_;

      $manglers{$name}->reconfigure( $mangler_conf );
   },

   remove => sub {
      my ( $name ) = @_;

      delete $manglers{$name};
   },
);

Now, whenever a SIGHUP signal is received, the config file is re-read. The configurations for all the current manglers are updated, new ones added, and old ones deleted.

---

I've just uploaded a new release, 0.16. This release finally gets rid of the awkward Error-based exceptions, instead using plain-old Carp-based string exceptions. This removes a dependency on the old, deprecated, and unsupported Error distribution.

I've also manually set the configure_requires element to set the required version of Module::Build down to 0.2808, which is what Perl 5.10.0 shipped with, rather than let it pick its own version, where it sets it to 0.36. Hopefully this should lead to no awkward "please upgrade Module::Build" on clean-slate installs. If this comes out OK I might start applying that by default across all my dists (where appropriate). It does seem a little awkward, but then I can't really think of a neater way for it to detect that - hard for it to know, for example, about random methods or functionality invoked during the Build.PL file itself, or bugs/features implicitly relied upon. Something to think about for next time, I feel...