fix: add fallback injection logic

This change handles the edge case exposed in our tests where the agent
may fail to inject the cache naming function at enable because it looked
for drupal and symfony classes before composer autoload had time to load
them. In the normal flow, this would only be a temporary problem since
nr_drupal_enable should be re-run every request, and subsequent requests
should have these resources available. Our test setup, however, shows
that if in the process of handling one request, another request is
generated and the agent doesn't re-trigger RINIT processing, the
function name from the first request will bleed through to the second
request and result in an incorrect name.
To fix, extract logic responsible for injecting the cache naming
function to its own function and call both at enable and within the
PageCache::get function instrumentation, provided the injection function
(newrelic_name_cached) is not detected when we look for it. This should
strike the best balance between performance and correctness.

agent/fw_drupal8.c

@@ -312,6 +312,58 @@
 }
 NR_PHP_WRAPPER_END
 
+static nr_status_t nr_inject_drupal_cache_naming() {
+  int retval = FAILURE;
+  zend_class_entry* drupal_ce = NULL;
+  zend_class_entry* symfony_ce = NULL;
+
+  drupal_ce = nr_php_find_class("Drupal\\Core\\Routing\\RouteMatch");
+  if (NULL == drupal_ce) {
+    nrl_warning(NRL_FRAMEWORK, "Missing Drupal RouteMatch Class");
+    return NR_FAILURE;
+  }
+
+  symfony_ce = nr_php_find_class("Symfony\\Component\\HttpFoundation\\Request");
+  if (NULL == symfony_ce) {
+    nrl_warning(NRL_FRAMEWORK, "Missing Symfony Request Class");
+    return NR_FAILURE;
+  }
+
+  // clang-format off
+  retval = zend_eval_string(
+    "namespace newrelic\\Drupal8;"
+
+    "use Symfony\\Component\\HttpFoundation\\Request;"
+    "use Drupal\\Core\\Routing\\RouteMatch;"
+
+    "if (!function_exists('newrelic\\Drupal8\\newrelic_name_cached')) {"
+    " function newrelic_name_cached(Request $request) {"
+    "   try {"
+    "     $routeCollection = \\Drupal::service('router.route_provider')->getRouteCollectionForRequest($request);"
+    "     $routeMatch = RouteMatch::createFromRequest($request);"
+    "     $route = $routeCollection->get($routeMatch->getRouteName());"
+    "     $defaults = $route->getDefaults();"
+    "     if (isset($defaults['_controller'])) {"
+    "       $controller = str_replace('::', '->', $defaults['_controller']);"
+    "       $controller = ltrim($controller, '\\\\');"
+    "       return $controller;"
+    "     }"
+    "   } catch (Throwable $e) {}"
+    " }"
+    "}",
+    NULL, "newrelic/Drupal8");
+  // clang-format on
+
+  if (SUCCESS != retval) {
+    nrl_warning(NRL_FRAMEWORK,
+                "%s: error injecting newrelic page cache naming code",
+                __func__);
+    return NR_FAILURE;
+  }
+
+  return NR_SUCCESS;
+}
+
 /*
  * txn naming scheme:
  * In this case, `nr_txn_set_path` is called after `NR_PHP_WRAPPER_CALL` with
@@ -324,9 +376,6 @@
   char* name = NULL;
   zval** retval_ptr = NR_GET_RETURN_VALUE_PTR;
   zval* request = NULL;
-
-  zend_function* nrfn = NULL;
-
   zval* controller = NULL;
 
   (void)wraprec;
@@ -351,14 +400,30 @@
   }
 
   if (!NRINI(drupal_page_cache_naming)) {
+    nrl_verbosedebug(NRL_FRAMEWORK,
+                     "Skipping PageCache naming due to INI setting");
     goto end;
   }
 
-  nrfn = nr_php_find_function("newrelic_name_cached");
-  if (NULL == nrfn) {
-    nrl_warning(NRL_FRAMEWORK,
-                "Failed to retrieve NR cached page naming function");
-    goto end;
+  if (NULL == nr_php_find_function("newrelic_name_cached")) {
+    nrl_debug(NRL_FRAMEWORK,
+              "Failed to retrieve NR cached page naming function, attempting "
+              "to re-inject");
+
+    // Re-attempt injection of the naming function in case we were too early in
+    // enable
+    if (NR_FAILURE == nr_inject_drupal_cache_naming()) {
+      nrl_warning(NRL_FRAMEWORK,
+                  "%s: Failed to re-inject drupal cache naming function",
+                  __FUNCTION__);
+      goto end;
+    }
+
+    if (NULL == nr_php_find_function("newrelic_name_cached")) {
+      nrl_warning(NRL_FRAMEWORK,
+                  "Failed to retrieve NR cached page naming function");
+      goto end;
+    }
   }
 
   controller
@@ -376,8 +441,10 @@
    * Symfony\Component\HttpFoundation\Response if there is a cache hit and false
    * otherwise.
    */
   if (retval_ptr && nr_php_is_zval_valid_object(*retval_ptr)) {
     if (NULL == name) {
+      nrl_debug(NRL_FRAMEWORK,
+                "Unable to find cached name, defaulting to 'page_cache'");
       name = nr_strdup("page_cache");
     }
     nr_txn_set_path("Drupal8", NRPRG(txn), name, NR_PATH_TYPE_ACTION,
@@ -797,62 +864,8 @@
 }
 
 void nr_drupal8_enable(TSRMLS_D) {
-  int retval;
-  zend_class_entry* drupal_ce = NULL;
-  zend_class_entry* symfony_ce = NULL;
-  bool inject = true;
-
   if (NRINI(drupal_page_cache_naming)) {
-    drupal_ce = nr_php_find_class("Drupal\\Core\\Routing\\RouteMatch");
-
-    if (NULL == drupal_ce) {
-      inject = false;
-      nrl_warning(NRL_FRAMEWORK, "Missing Drupal RouteMatch Class");
-    } else {
-      symfony_ce
-          = nr_php_find_class("Symfony\\Component\\HttpFoundation\\Request");
-      if (NULL == symfony_ce) {
-        inject = false;
-        nrl_warning(NRL_FRAMEWORK, "Missing Symfony Request Class");
-      }
-    }
-
-    if (inject) {
-      // clang-format off
-      retval = zend_eval_string(
-        "namespace newrelic\\Drupal8;"
-
-        "use Symfony\\Component\\HttpFoundation\\Request;"
-        "use Drupal\\Core\\Routing\\RouteMatch;"
-
-        "if (!function_exists('newrelic\\Drupal8\\newrelic_name_cached')) {"
-        " function newrelic_name_cached(Request $request) {"
-        "   try {"
-        "     $routeCollection = \\Drupal::service('router.route_provider')->getRouteCollectionForRequest($request);"
-        "     $routeMatch = RouteMatch::createFromRequest($request);"
-        "     $route = $routeCollection->get($routeMatch->getRouteName());"
-        "     $defaults = $route->getDefaults();"
-        "     if (isset($defaults['_controller'])) {"
-        "       $controller = str_replace('::', '->', $defaults['_controller']);"
-        "       $controller = ltrim($controller, '\\\\');"
-        "       return $controller;"
-        "     }"
-        "   } catch (Throwable $e) {}"
-        " }"
-        "}",
-        NULL, "newrelic/Drupal8");
-      // clang-format on
-
-      if (SUCCESS != retval) {
-        nrl_warning(NRL_FRAMEWORK,
-                    "%s: error injecting newrelic page cache naming code",
-                    __func__);
-      }
-    } else {
-      nrl_warning(
-          NRL_FRAMEWORK,
-          "Skipped injecting page_cache naming function: Missing Classes");
-    }
+    nr_inject_drupal_cache_naming();
   }
 
   /*