java-topology/defects/varnish/unit/VarnishBanCheckAlgorithmTest.java

package unit;

import java.util.ArrayList;
import java.util.List;

/**
 * varnish-0001: BAN_CheckObject O(B) ban list walk vs O(1) pre-filtered check.
 *
 * slow() models the defect: iterates the full ban list from head to object's
 *   creation ban, calling ban_evaluate on each non-completed ban.
 * fast() models the fix structural improvement: bans are indexed by field type;
 *   non-applicable bans are skipped in O(1) without calling evaluate.
 *
 * For benchmarking we model:
 *   slow: evaluateOps = B (all pending bans checked per object)
 *   fast: evaluateOps = 1 (only bans that share the object's field type checked)
 *
 * Assert: slowOps > fastOps * 5 for B=30 bans.
 */
public class VarnishBanCheckAlgorithmTest {

    static long slowOps;
    static long fastOps;

    // ---- simulated ban entry -----------------------------------------------

    enum BanField { URL, HEADER_HOST, HEADER_ACCEPT, REQ_ONLY }

    static class Ban {
        final BanField field;
        final String pattern;
        boolean completed;

        Ban(BanField field, String pattern) {
            this.field = field;
            this.pattern = pattern;
            this.completed = false;
        }
    }

    // ---- simulated cached object -------------------------------------------

    static class CachedObject {
        final String url;
        final int createdAtBanIndex; // object was created when ban list had this many entries
        CachedObject(String url, int createdAtBanIndex) {
            this.url = url;
            this.createdAtBanIndex = createdAtBanIndex;
        }
    }

    // ---- slow: O(B) walk, evaluate every non-completed ban (defect) --------

    static boolean slowBanCheck(List<Ban> banList, CachedObject obj) {
        // Walk from head (newest) to obj.createdAtBanIndex (exclusive)
        for (int i = 0; i < obj.createdAtBanIndex; i++) {
            Ban b = banList.get(i);
            if (b.completed) continue;
            slowOps++;                              // one evaluate call
            if (b.field == BanField.URL && obj.url.startsWith(b.pattern)) {
                return true; // object banned
            }
        }
        return false;
    }

    // ---- fast: O(1) indexed check (fix) ------------------------------------
    // Bans indexed by field; only URL bans relevant for URL-keyed objects

    static boolean fastBanCheck(List<Ban> urlBans, CachedObject obj) {
        for (Ban b : urlBans) {
            if (b.completed) continue;
            fastOps++;                              // only URL bans evaluated
            if (obj.url.startsWith(b.pattern)) return true;
        }
        return false;
    }

    // ---- benchmark driver --------------------------------------------------

    public static void main(String[] args) {
        final int B = 30;           // total pending bans
        final int URL_BANS = 3;     // only 3 are URL-field bans (the rest are HEADER/REQ)
        final int REQUESTS = 5_000;

        List<Ban> banList = new ArrayList<>();
        List<Ban> urlBanIndex = new ArrayList<>();

        // Mix: 3 URL bans, rest HEADER/REQ bans (non-matching)
        for (int i = 0; i < B; i++) {
            if (i < URL_BANS) {
                Ban b = new Ban(BanField.URL, "/static/v" + i + "/");
                banList.add(b);
                urlBanIndex.add(b);
            } else {
                banList.add(new Ban(BanField.HEADER_HOST, "example.com"));
            }
        }

        // Object created before any bans were added
        CachedObject obj = new CachedObject("/api/data", B);

        slowOps = 0;
        fastOps = 0;

        for (int r = 0; r < REQUESTS; r++) {
            slowBanCheck(banList, obj);
        }
        for (int r = 0; r < REQUESTS; r++) {
            fastBanCheck(urlBanIndex, obj);
        }

        // slow evaluates ALL B bans per object; fast evaluates only URL_BANS
        long ratio = slowOps / Math.max(fastOps, 1);
        boolean pass = slowOps > fastOps * (B / URL_BANS - 1);

        System.out.printf("varnish-0001  slow=%d  fast=%d  ratio=%dx  %s%n",
                slowOps, fastOps, ratio, pass ? "PASS" : "FAIL");

        if (!pass) {
            System.err.printf("FAIL: expected slowOps(%d) > fastOps(%d) * %d%n",
                    slowOps, fastOps, B / URL_BANS - 1);
            System.exit(1);
        }
    }
}