java-topology/defects/libevent/unit/LibeventDispatchCallbackAlgorithmTest.java

package unit;

import java.util.*;

/**
 * Models libevent evhttp_dispatch_callback and evhttp_set_cb defects.
 *
 * libevent-0001: O(C) TAILQ scan per request → O(1) with HashMap.
 *                O(C²) setup dedup → O(C) with HashMap.
 *
 * CWE-407: http.c:3697 (dispatch), http.c:4290 (set_cb)
 */
public class LibeventDispatchCallbackAlgorithmTest {

    // =========================================================================
    // Slow — TAILQ_FOREACH analog (linked list)
    // =========================================================================

    static class SlowEvhttp {
        final List<String> callbacks = new ArrayList<>();
        long cmpOps = 0;

        /** evhttp_set_cb: O(C) dedup scan per registration → O(C²) total for C registrations */
        boolean setCb(String uri) {
            for (String cb : callbacks) {
                cmpOps++;
                if (cb.equals(uri)) return false; // duplicate
            }
            callbacks.add(uri);
            return true;
        }

        /** evhttp_dispatch_callback: O(C) per request */
        String dispatch(String uri) {
            for (String cb : callbacks) {
                cmpOps++;
                if (cb.equals(uri)) return cb;
            }
            return null;
        }

        long registerAll(List<String> uris) {
            cmpOps = 0;
            callbacks.clear();
            for (String u : uris) setCb(u);
            return cmpOps;
        }

        long dispatchAll(List<String> requests) {
            cmpOps = 0;
            for (String r : requests) dispatch(r);
            return cmpOps;
        }
    }

    // =========================================================================
    // Fast — HashMap
    // =========================================================================

    static class FastEvhttp {
        final Map<String, String> map = new HashMap<>();
        long cmpOps = 0;

        boolean setCb(String uri) {
            cmpOps++;
            return map.putIfAbsent(uri, uri) == null;
        }

        String dispatch(String uri) {
            cmpOps++;
            return map.get(uri);
        }

        long registerAll(List<String> uris) {
            cmpOps = 0;
            map.clear();
            for (String u : uris) setCb(u);
            return cmpOps;
        }

        long dispatchAll(List<String> requests) {
            cmpOps = 0;
            for (String r : requests) dispatch(r);
            return cmpOps;
        }
    }

    static List<String> makeRoutes(int n) {
        List<String> r = new ArrayList<>();
        for (int i = 0; i < n; i++) r.add("/api/v1/resource/" + i);
        return r;
    }

    public static void main(String[] args) {
        SlowEvhttp slow = new SlowEvhttp();
        FastEvhttp fast = new FastEvhttp();

        int passed = 0, total = 0;

        System.out.println("=== libevent-0001: evhttp_set_cb O(C²) setup ===");
        int[] sizes = {20, 50, 100, 200};
        for (int c : sizes) {
            List<String> routes = makeRoutes(c);
            long s = slow.registerAll(routes);
            long f = fast.registerAll(routes);
            double ratio = (double) s / Math.max(f, 1);
            total++;
            boolean ok = s > f && ratio >= 5.0;
            System.out.printf("C=%3d  setup slow=%7d fast=%4d ratio=%6.1fx  %s%n",
                c, s, f, ratio, ok ? "PASS" : "FAIL");
            if (ok) passed++;
        }

        System.out.println("=== libevent-0001: evhttp_dispatch_callback O(C) per request ===");
        for (int c : sizes) {
            List<String> routes = makeRoutes(c);
            slow.registerAll(routes);
            fast.registerAll(routes);
            // Requests target the last route (worst case — full scan)
            List<String> requests = new ArrayList<>();
            for (int i = 0; i < c; i++) requests.add("/api/v1/resource/" + (c - 1));

            long s = slow.dispatchAll(requests);
            long f = fast.dispatchAll(requests);
            double ratio = (double) s / Math.max(f, 1);
            total++;
            boolean ok = s > f && ratio >= 5.0;
            System.out.printf("C=%3d R=%3d  dispatch slow=%7d fast=%4d ratio=%6.1fx  %s%n",
                c, c, s, f, ratio, ok ? "PASS" : "FAIL");
            if (ok) passed++;
        }

        // Correctness: both dispatch same route
        List<String> routes100 = makeRoutes(100);
        slow.registerAll(routes100);
        fast.registerAll(routes100);
        String sr = slow.dispatch("/api/v1/resource/42");
        String fr = fast.dispatch("/api/v1/resource/42");
        total++;
        boolean correct = Objects.equals(sr, fr);
        System.out.printf("dispatch correctness: %s%n", correct ? "PASS" : "FAIL");
        if (correct) passed++;

        System.out.printf("%n%d/%d PASS%n", passed, total);
        if (passed < total) System.exit(1);
    }
}