TCP port keeps changing with perl LWP in loop

Question

I'm analyzing a small LWP useragent in a loop with an HTTP analyzer and I noticed that every visit of the URL my port keeps changing.

While I have a small script also made in VB.Net httpwebrequest and that isn't changing my port number while visiting the URL 10 times.

Is it possible to keep a static ip:port while using perl?

Answer 1

For the HTTP client:

use LWP::Protocol::http qw( );

@LWP::Protocol::http::EXTRA_SOCK_OPTS = (
    LocalPort => $port,
);

If you also want to use a specific interface,

@LWP::Protocol::http::EXTRA_SOCK_OPTS = (
    LocalAddr => $ip,
    LocalPort => $port,
);

Of course, you run into problems if the port is already in use, which is likely if you just used it for another connection.

use LWP::Protocol::http qw( );
use LWP::UserAgent      qw( );

my $port = 12456;
@LWP::Protocol::http::EXTRA_SOCK_OPTS = (
    LocalPort => 12456,
);

my $ua = LWP::UserAgent->new();
print $ua->get('http://www.example.com/show_port')->content for 1..2;

Output:

>script.pl
12456
Can't connect to www.example.com:80 (10048)

LWP::Protocol::http::Socket: connect: 10048 at .../LWP/Protocol/http.pm line 51.

>perl -E"say $^E=10048"
Only one usage of each socket address (protocol/network address/port) is normally permitted

More likely, the port is not being reused, the connection is. You could also try reusing the connection by passing keep_alive => 1 to the LWP::UserAgent constructor.

use LWP::UserAgent qw( );

my $ua = LWP::UserAgent->new( keep_alive => 1 );
print $ua->get('http://www.example.com/show_port')->content for 1..2;

Output:

57842
57842