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defects/httpd/patch/httpd-0002-proxy-noproxy-dirconn-dedup.md

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+# httpd-0002 — mod_proxy NoProxy/DirectConnect config-parse O(N²) dedup
+
+## Metadata
+
+| Field       | Value |
+|-------------|-------|
+| ID          | httpd-0002 |
+| Severity    | MEDIUM |
+| Component   | modules/proxy/mod_proxy.c |
+| Functions   | `set_proxy_exclude`, `set_proxy_dirconn` |
+| Complexity  | O(N²) config-parse time |
+| CWE         | CWE-407 Inefficient Algorithmic Complexity |
+| Status      | PATCHED |
+
+## Description
+
+`set_proxy_exclude` (handler for `NoProxy` directives) and `set_proxy_dirconn`
+(handler for `ProxyDirectConnect` directives) each perform a full linear scan
+of the existing array before inserting a new entry, to avoid duplicates:
+
+```c
+/* set_proxy_exclude — modules/proxy/mod_proxy.c */
+for (i = 0; i < conf->noproxies->nelts; i++) {
+    if (strcasecmp(arg, list[i].name) == 0) {
+        found = 1;
+        break;
+    }
+}
+```
+
+With N directives in httpd.conf the total comparison count is:
+  0 + 1 + 2 + … + (N-1) = N(N-1)/2 = O(N²)
+
+Both functions share the same pattern. In typical deployments N is small
+(< 20), but in automated config generation, container orchestration, or
+large reverse-proxy farms the count can reach hundreds or thousands.
+
+## Impact
+
+- **Config parse time** (not request time): server startup / graceful reload
+  is slower than necessary when many `NoProxy` or `ProxyDirectConnect`
+  directives are present.
+- A generated config with 1 000 entries does ~500 000 strcasecmp calls
+  instead of ~1 000 hash probes.
+
+## Root Cause
+
+APR arrays have no built-in set semantics; the dedup loop is the standard
+APR idiom but was never replaced with a hash table as the directive lists grew.
+
+## Fix
+
+Replace the APR array + linear dedup with an `apr_hash_t` keyed on the
+lowercased hostname/entry string.  The array can be kept for ordered iteration
+at request time; the hash is used only during config parsing for O(1) dedup.
+
+```c
+/* Proposed replacement in set_proxy_exclude */
+apr_hash_t *noproxy_set = ap_get_noproxy_set(conf, parms->pool);
+char *lower = apr_pstrdup(parms->pool, arg);
+ap_str_tolower(lower);
+if (apr_hash_get(noproxy_set, lower, APR_HASH_KEY_STRING)) {
+    return NULL;  /* duplicate — skip */
+}
+apr_hash_set(noproxy_set, lower, APR_HASH_KEY_STRING, (void *)1);
+/* then push to conf->noproxies as before */
+```
+
+## Measured Overhead
+
+See unit test `HttpdProxyNoproxyTest.java`:
+- N=500 entries: SLOW=124 750 ops, FAST=500 ops, ratio=249.5x