To continue (and finish) I implemented the functionality like this:

After the connection on a listening socket I have a connection object $c. With $c->get_request I have an HTTP::Request object $r.
HTTP::Response object is $ref = $self->response ($self is listening socket)

Then look for the requested wsdl document name:
$r->uri =~ /\/(\w+)\?wsdl$/i<br. Name of wsdl document is in $1.

Then set content-type of response to text/xml:
$ref->header('Content-Type' => 'text/xml')
Get wsdl document into a variable $content and encode in bytes.
Set content of response: $ref->content($content)

And send back to the client:
$c->send_response($ref)