Redirect to the www hostname in Varnish

redirect.vcl

vcl 4.0;

import std;

sub vcl_recv {
    if (!req.http.X-Forwarded-Proto) {
        if(std.port(server.ip) == 443) {
            set req.http.X-Forwarded-Proto = "https";
        } else {
            set req.http.X-Forwarded-Proto = "http";        
        }
    }
    if (req.http.Host !~ "^www\.") {
        return (synth(301, req.http.X-Forwarded-Proto + "://www." + req.http.Host + req.url));
    }
}

sub vcl_synth {
    if (resp.status == 301 || resp.status == 302) {
        set resp.http.Location = resp.reason;
        set resp.reason = "Moved";
        return (deliver);
    }
}