bugfix: fixed duplicated seeds.

ngx.time() + ngx.worker.pid() maybe get duplicated seeds. get from /dev/urandom first.

rootfs/etc/nginx/lua/lua_ingress.lua

@@ -2,25 +2,40 @@ local _M = {}
 
 local seeds = {}
 local original_randomseed = math.randomseed
-math.randomseed = function(seed)
-  local pid = ngx.worker.pid()
 
-  if seeds[pid] then
+local function get_seed_from_urandom()
+  local seed
+  local frandom = io.open("/dev/urandom", "rb")
+  if frandom then
+    local str = frandom:read(4)
+    frandom:close()
+    seed = 0
+    for i = 1, 4 do
+        seed = 256 * seed + str:byte(i)
+    end
+  end
+  return seed
+end
+
+math.randomseed = function()
+  local pid = ngx.worker.pid()
+  local seed = seeds[pid]
+  if seed then
     ngx.log(ngx.WARN,
       string.format("ignoring math.randomseed(%d) since PRNG is already seeded for worker %d", seed, pid))
     return
   end
 
+  seed = get_seed_from_urandom()
+  if not seed then
+    seed = ngx.now() * 1000 + pid
+  end
   original_randomseed(seed)
   seeds[pid] = seed
 end
 
-local function randomseed()
-  math.randomseed(ngx.time() + ngx.worker.pid())
-end
-
 function _M.init_worker()
-  randomseed()
+  math.randomseed()
 end
 
 return _M