fix bug with lua sticky session implementation and refactor balancer

rootfs/etc/nginx/lua/util.lua

@@ -1,6 +1,34 @@
-local _M = {}
 local string_len = string.len
 local string_sub = string.sub
+local resty_str = require("resty.string")
+local resty_sha1 = require("resty.sha1")
+local resty_md5 = require("resty.md5")
+
+local _M = {}
+
+local function hash_digest(hash_factory, message)
+  local hash = hash_factory:new()
+  if not hash then
+    return nil, "failed to create object"
+  end
+  local ok = hash:update(message)
+  if not ok then
+    return nil, "failed to add data"
+  end
+  local binary_digest = hash:final()
+  if binary_digest == nil then
+    return nil, "failed to create digest"
+  end
+  return resty_str.to_hex(binary_digest), nil
+end
+
+function _M.sha1_digest(message)
+  return hash_digest(resty_sha1, message)
+end
+
+function _M.md5_digest(message)
+  return hash_digest(resty_md5, message)
+end
 
 -- given an Nginx variable i.e $request_uri
 -- it returns value of ngx.var[request_uri]