for the RESTful ones, this is easy, i can just do content_length() on the LWP response.

content_length?! Take care, as it does not do what you might think: it just returns the value of the Content-Length header, which - of course - may be missing... or just plain wrong (as I've seen already too many wanna-be-smart web apps that have no idea about its meaning).

Is there an similar way to do this with SOAP::Lite?

Quite similar in fact, as SOAP::Lite uses the same LWP modules for HTTP transport.

The usual way to reach those HTTP::Response objects is to enable runtime tracing of transport events. Here's an example:

use strict;
use warnings;
use SOAP::Lite +trace => [
    transport => sub {
        my ($in) = @_;
        return if ref $in ne 'HTTP::Response';
        printf "Response length: %d bytes.\n", bytes::length( $in->con
+tent );
      }
];

my $sv = SOAP::Lite->new->service('.../foo.wsdl');
$sv->fooMethod( 'foo', 'bar' );
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