perf(request-debugging): improve performance (#11722)

Improve the performance of the request debugging feature.

- reduce the number of calls of ngx.ctx
- cache some functions at the module level
- delete debug request headers only when debug headers exist.
- reduce the number of calls of req_dyn_hook.runhooks().

KAG-2738

kong/dynamic_hook/init.lua

@@ -74,17 +74,28 @@ function _M.hook(group_name, hook_name, handler)
 end
 
 
-function _M.run_hooks(group_name, hook_name, ...)
-  if not always_enabled_groups[group_name] then
-    local dynamic_hook = ngx.ctx.dynamic_hook
-    if not dynamic_hook then
-      return
-    end
-
-    local enabled_groups = dynamic_hook.enabled_groups
-    if not enabled_groups[group_name] then
-      return
-    end
+function _M.is_group_enabled(group_name)
+  if always_enabled_groups[group_name] then
+    return true
+  end
+
+  local dynamic_hook = ngx.ctx.dynamic_hook
+  if not dynamic_hook then
+    return false
+  end
+
+  local enabled_groups = dynamic_hook.enabled_groups
+  if not enabled_groups[group_name] then
+    return false
+  end
+
+  return true
+end
+
+
+function _M.run_hooks(ctx, group_name, hook_name, ...)
+  if not _M.is_group_enabled(group_name) then
+    return
   end
 
   local hooks = non_function_hooks[group_name]

kong/dynamic_hook/wrap_function_gen.lua

@@ -3,6 +3,7 @@ local ngx_get_phase = ngx.get_phase
 local TEMPLATE = [[
   return function(always_enabled_groups, group_name, original_func, handlers)
     -- we cannot access upvalue here as this function is generated
+    local ngx = ngx
     local ngx_get_phase = ngx.get_phase
 
     return function(%s)