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defects/nginx/unit/NginxHideHeadersDedupAlgorithmTest.java

@@ -0,0 +1,100 @@
+package unit;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * nginx-0002: ngx_http_upstream_hide_headers_hash dedup O(H²) vs O(H).
+ *
+ * slow: for each of H headers in user config, walk the already-accumulated
+ *       list with strcasecmp to detect duplicates — mirrors:
+ *         for (i=0; i < conf->hide_headers->nelts; i++) {
+ *             hk = hide_headers.elts;
+ *             for (j=0; j < hide_headers.nelts; j++) {
+ *                 if (ngx_strcasecmp(h[i].data, hk[j].key.data) == 0) goto exist;
+ *             }
+ *         }
+ *
+ * fast: accumulate into HashSet (case-insensitive by lowercasing),
+ *       O(H) total — mirrors using ngx_hash for O(1) per check.
+ *
+ * Assert: slowOps > fastOps * (H/2) for H=100 headers.
+ */
+public class NginxHideHeadersDedupAlgorithmTest {
+
+    static long slowOps;
+    static long fastOps;
+
+    // ---- slow: O(H²) dedup (defect) -----------------------------------------
+
+    static List<String> slowDedup(String[] headers) {
+        List<String> deduped = new ArrayList<>();
+        for (String h : headers) {
+            boolean found = false;
+            for (String existing : deduped) {    // O(D) inner scan
+                slowOps++;
+                if (existing.equalsIgnoreCase(h)) {
+                    found = true;
+                    break;
+                }
+            }
+            if (!found) {
+                deduped.add(h);
+            }
+        }
+        return deduped;
+    }
+
+    // ---- fast: O(H) dedup via HashSet (fix) ---------------------------------
+
+    static List<String> fastDedup(String[] headers) {
+        List<String> deduped = new ArrayList<>();
+        Set<String> seen = new HashSet<>();
+        for (String h : headers) {
+            fastOps++;             // O(1) set lookup
+            String lower = h.toLowerCase();
+            if (seen.add(lower)) {
+                deduped.add(h);
+            }
+        }
+        return deduped;
+    }
+
+    // ---- benchmark driver ---------------------------------------------------
+
+    public static void main(String[] args) {
+        final int H = 100; // hide_headers entries
+
+        // All unique, lowercase (no duplicates = maximum inner work)
+        String[] headers = new String[H];
+        for (int i = 0; i < H; i++) {
+            headers[i] = "X-Hide-Header-" + i;
+        }
+
+        slowOps = 0;
+        fastOps = 0;
+
+        List<String> slowResult = slowDedup(headers);
+        List<String> fastResult = fastDedup(headers);
+
+        if (slowResult.size() != fastResult.size()) {
+            System.err.printf("FAIL: slow=%d entries fast=%d entries (mismatch)%n",
+                    slowResult.size(), fastResult.size());
+            System.exit(1);
+        }
+
+        long ratio = slowOps / Math.max(fastOps, 1);
+        boolean pass = slowOps > fastOps * (H / 2 - 2);
+
+        System.out.printf("nginx-0002  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, H / 2 - 2);
+            System.exit(1);
+        }
+    }
+}