refactor some lua code

rootfs/etc/nginx/lua/util/defer.lua

@@ -0,0 +1,57 @@
+local util = require("util")
+
+local timer_started = false
+local queue = {}
+local MAX_QUEUE_SIZE = 10000
+
+local _M = {}
+
+local function flush_queue(premature)
+  -- TODO Investigate if we should actually still flush the queue when we're
+  -- shutting down.
+  if premature then return end
+
+  local current_queue = queue
+  queue = {}
+  timer_started = false
+
+  for _,v in ipairs(current_queue) do
+    v.func(unpack(v.args))
+  end
+end
+
+-- `to_timer_phase` will enqueue a function that will be executed in a timer
+-- context, at a later point in time. The purpose is that some APIs (such as
+-- sockets) are not available during some nginx request phases (such as the
+-- logging phase), but are available for use in timers. There are no ordering
+-- guarantees for when a function will be executed.
+function _M.to_timer_phase(func, ...)
+  if ngx.get_phase() == "timer" then
+    func(...)
+    return true
+  end
+
+  if #queue >= MAX_QUEUE_SIZE then
+    ngx.log(ngx.ERR, "deferred timer queue full")
+    return nil, "deferred timer queue full"
+  end
+
+  table.insert(queue, { func = func, args = {...} })
+  if not timer_started then
+    local ok, err = ngx.timer.at(0, flush_queue)
+    if ok then
+      -- unfortunately this is to deal with tests - when running unit tests, we
+      -- dont actually run the timer, we call the function inline
+      if util.tablelength(queue) > 0 then
+        timer_started = true
+      end
+    else
+      local msg = "failed to create timer: " .. tostring(err)
+      ngx.log(ngx.ERR, msg)
+      return nil, msg
+    end
+  end
+  return true
+end
+
+return _M