ab-external.vcl

vcl 4.0;
import curl;
import cookie;
import std;

backend default {
    .host = "127.0.0.1";
    .port = "8000";
}


sub vcl_recv {

    cookie.parse(req.http.Cookie);

    # Set a UID so we don't rely on GA

    if (cookie.get("uid")) {
       set req.http.uid = cookie.get("uid");
    } else {
      set req.http.uid = std.random(1,1000000);
    }


    if (cookie.get("abgroup")) {
          std.log("User is already assigned");
          set req.http.abgroup = cookie.get("abgroup");

          if (req.http.abgroup !~ "A|B") {
              # if the user has an invalid value, just force A.
              std.log("Invalid group. Forcing value...");
              set req.http.abgroup = "A";
          }
    } else {
        # assign the user to A or B using external service
        curl.get("http://localhost:8080/uid=" + req.http.uid);
        set req.http.abgroup = curl.header("X-decision");
        curl.free();
        std.log("Callout decided user " +req.http.uid +" is in category " + req.http.abgroup);
    }
}

sub vcl_deliver {
    if (req.http.abgroup) {
        set resp.http.Set-Cookie = "abgroup=" + req.http.abgroup +
            ";uid=" + req.http.uid + "; Expires=" +
            cookie.format_rfc1123(now, 10m) + "; httpOnly";

        # mostly for debugging
        set resp.http.abgroup = req.http.abgroup;
        set resp.http.uid = req.http.uid;
    }
}