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?

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

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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...

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This cross-posted from module-authors@perl.