PERL Miscellaneous - Re: Problem with IO::Socket [... on Mac OS X]

Author

Re: Problem with IO::Socket [... on Mac OS X]

Martin Kissner

2005-02-16, 9:00 pm

A. Sinan Unur wrote :
> Martin Kissner <news@chaos-net.de> wrote in
> news:slrnd178eu.1hq.news@maki.homeunix.net:

>
> You will need to give some more information regarding the system on which
> you are testing this in a clear and concise way.

Of course.
I should have done in the first place.

% uname -msr
Darwin 7.8.0 Power Macintosh
# which is Mac OS X

% perl -v
This is perl, v5.8.1-RC3 built for darwin-thread-multi-2level
(with 1 registered patch, see perl -V for more detail)

> Now, you can check if perl is able to do the mapping from service names
> to port addresses on your system by running this script (from Perl docs):

Thank you for the script.

% ./test_services.pl smtp
port for smtp is 25, aliases are

% ./test_services.pl http
port for http is 80, aliases are www www-http

works optimally and makes it still more surprising that the script doesn't

--
perl -e 'print 7.74.117.115.116.11.32.13.97.110.111.116.104.101.114.11
..32.13.112.101.114.108.11.32.13.104.97.99.107.101.114.10.7'

Anno Siegel

2005-02-17, 9:01 am

Martin Kissner <news@chaos-net.de> wrote in comp.lang.perl.misc:
> A. Sinan Unur wrote :

>
> Of course.
> I should have done in the first place.
>
> % uname -msr
> Darwin 7.8.0 Power Macintosh
> # which is Mac OS X

Something is fishy on Darwin. I also see it hang when the service is
given by name and reply as expected when given by port number. However,
just *calling* getservbyname() before opening the socket makes it work
with a name too.

use IO::Socket;

my $server = shift;

if ( my ( $port) = $server =~ /:(.*)/ ) {
# just call it
getservbyname( $port, 'tcp') or die "getservbyname( $port)";
}

print "Trying $server\n";
my $fh = IO::Socket::INET->new( $server) or die $!;
my $line = <$fh>;
print $line;

__END__

This gives the expected reply from "mail.hotmail.com:smtp". Comment out
the call to getservbyname() and it doesn't.

I'm not sure how Darwin deals with getservbyname(). It may use some
netinfo devilry instead of /etc/services. The man page is ominously
missing.

Anno

Martin Kissner

2005-02-17, 4:03 pm

Anno Siegel wrote :

> Something is fishy on Darwin.

I guess it is.
I will try this on FreeBSD as soon as possible.

> I also see it hang when the service is
> given by name and reply as expected when given by port number. However,
> just *calling* getservbyname() before opening the socket makes it work
> with a name too.
>
> use IO::Socket;
>
> my $server = shift;
>
> if ( my ( $port) = $server =~ /:(.*)/ ) {
> # just call it
> getservbyname( $port, 'tcp') or die "getservbyname( $port)";
> }
>
> print "Trying $server\n";
> my $fh = IO::Socket::INET->new( $server) or die $!;
> my $line = <$fh>;
> print $line;
>

Thank you for this code example. It works for me, too and examples like
this one expand my view since I am not so experienced in Perl
programming.

> This gives the expected reply from "mail.hotmail.com:smtp". Comment out
> the call to getservbyname() and it doesn't.
>
> I'm not sure how Darwin deals with getservbyname(). It may use some
> netinfo devilry instead of /etc/services. The man page is ominously
> missing.

Te documentation to Darwin sometimes is a drag. It has become better
with Panther, but it's still not goos enough.
However, Darwin does use /etc/services.
I tried by simply changing the name of a service in /etc/services.

--
perl -e 'print 7.74.117.115.116.11.32.13.97.110.111.116.104.101.114.11
..32.13.112.101.114.108.11.32.13.104.97.99.107.101.114.10.7'

Martin Kissner

2005-02-20, 3:56 pm

Anno Siegel wrote :

> Something is fishy on Darwin. I also see it hang when the service is
> given by name and reply as expected when given by port number. However,
> just *calling* getservbyname() before opening the socket makes it work
> with a name too.

After I had proved that servicenames can be resolved by Perl on Mac OS X
with the function 'getservbyname()' I was interested if I could find out
how IO::Socket::INET gets the servicenames and how this might be
different from 'getservbyname()'.
As far as I can see IO::Socket::INET uses 'getservbyname()'.
In Version 1.26 of IO::Socket::INET the conversion is done in line 58/59
of 'INET.pm'.

After all I tried the script once again without making any changes and
to my very great surprise it ran flawlessly with servicenames and with
portnumbers.
If Anno had not seen it hang when servicenames were given, I'd probably
doubted my mental health ;-).

I report this not because I expect that someone could explain this
but to give some final feedback to everybody who had to helped.

Best regards
Martin

--
perl -e 'print 7.74.117.115.116.11.32.13.97.110.111.116.104.101.114.11
..32.13.112.101.114.108.11.32.13.104.97.99.107.101.114.10.7'

Anno Siegel

2005-02-21, 8:57 am

Martin Kissner <news@chaos-net.de> wrote in comp.lang.perl.misc:
> Anno Siegel wrote :
>

[...]
[color=darkred]
> After all I tried the script once again without making any changes and
> to my very great surprise it ran flawlessly with servicenames and with
> portnumbers.
> If Anno had not seen it hang when servicenames were given, I'd probably
> doubted my mental health ;-).

I've seen that too. It wasn't reproducible, so I dismissed it for
the time being.

Anno

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