refactor(dns): simplify the code of new dns utils

kong/dns/utils.lua

@@ -11,6 +11,7 @@ local type = type
 local ipairs = ipairs
 local tonumber = tonumber
 local math_random = math.random
+local table_new = require("table.new")
 local table_clear = require("table.clear")
 local table_insert = table.insert
 local table_remove = table.remove
@@ -32,12 +33,9 @@ local LOCALHOST = {
 local DEFAULT_HOSTS = { localhost = LOCALHOST, }
 
 
-local _M = {}
-
-
 -- checks the hostname type
 -- @return "ipv4", "ipv6", or "domain"
-function _M.hostname_type(name)
+local function hostname_type(name)
   local remainder, colons = name:gsub(":", "")
   if colons > 1 then
     return "ipv6"
@@ -55,8 +53,8 @@ end
 -- IPv6 addresses are always returned in square brackets
 -- @param name the string to check (this may contain a port number)
 -- @return `name/ip` + `port (or nil)` + `type ("ipv4", "ipv6" or "domain")`
-function _M.parse_hostname(name)
-  local t = _M.hostname_type(name)
+local function parse_hostname(name)
+  local t = hostname_type(name)
   if t == "ipv4" or t == "domain" then
     local ip, port = name:match("^([^:]+)%:*(%d*)$")
     return ip, tonumber(port), t
@@ -81,7 +79,7 @@ local function get_lines(path)
 end
 
 
-function _M.parse_hosts(path, enable_ipv6)
+local function parse_hosts(path, enable_ipv6)
   local lines, err = get_lines(path or DEFAULT_HOSTS_FILE)
   if not lines then
     log(NOTICE, "Invalid hosts file: ", err)
@@ -105,7 +103,7 @@ function _M.parse_hosts(path, enable_ipv6)
 
     -- Check if the line contains an IP address followed by hostnames
     if n >= 2 then
-      local ip, _, family = _M.parse_hostname(parts[1])
+      local ip, _, family = parse_hostname(parts[1])
 
       if family ~= "domain" then    -- ipv4/ipv6
         for i = 2, n do
@@ -132,7 +130,7 @@ end
 
 
 -- TODO: need to rewrite it instead of calling parseResolvConf from the old library
-function _M.parse_resolv_conf(path, enable_ipv6)
+local function parse_resolv_conf(path, enable_ipv6)
   local resolv, err = utils.parseResolvConf(path or DEFAULT_RESOLV_CONF)
   if not resolv then
     return nil, err
@@ -161,14 +159,16 @@ function _M.parse_resolv_conf(path, enable_ipv6)
 
   -- nameservers
   if resolv.nameserver then
+    local n = 0
     local nameservers = {}
 
     for _, address in ipairs(resolv.nameserver) do
       local ip, port, t = utils.parseHostname(address)
       if t == "ipv4" or
         (t == "ipv6" and not ip:find([[%]], nil, true) and enable_ipv6)
       then
-        table_insert(nameservers, port and { ip, port } or ip)
+        n = n + 1
+        nameservers[n] = port and { ip, port } or ip
       end
     end
 
@@ -179,7 +179,7 @@ function _M.parse_resolv_conf(path, enable_ipv6)
 end
 
 
-function _M.is_fqdn(name, ndots)
+local function is_fqdn(name, ndots)
   if name:sub(-1) == "." then
     return true
   end
@@ -191,33 +191,35 @@ end
 
 
 -- check if it matchs the SRV pattern: _<service>._<proto>.<name>
-function _M.is_srv(name)
+local function is_srv(name)
   return name:match("^_[^._]+%._[^._]+%.[^.]+") ~= nil
 end
 
 
 -- construct names from resolv options: search, ndots and domain
-function _M.search_names(name, resolv, hosts)
-  if not resolv.search or _M.is_fqdn(name, resolv.ndots) or
+local function search_names(name, resolv, hosts)
+  local resolv_search = resolv.search
+
+  if not resolv_search or is_fqdn(name, resolv.ndots) or
     (hosts and hosts[name])
   then
     return { name }
   end
 
-  local names = {}
+  local count = #resolv_search
+  local names = table_new(count + 1, 0)
 
-  for _, suffix in ipairs(resolv.search) do
-    table_insert(names, name .. "." .. suffix)
+  for i = 1, count do
+    names[i] = name .. "." .. resolv_search[i]
   end
-
-  table_insert(names, name) -- append the original name at last
+  names[count + 1] = name -- append the original name at last
 
   return names
 end
 
 
 -- add square brackets around IPv6 addresses if a non-strict check detects them
-function _M.ipv6_bracket(name)
+local function ipv6_bracket(name)
   if name:match("^[^[].*:") then  -- not start with '[' and contains ':'
     return "[" .. name .. "]"
   end
@@ -228,13 +230,14 @@ end
 
 -- util APIs to balance @answers
 
-function _M.get_next_round_robin_answer(answers)
+local function get_next_round_robin_answer(answers)
   answers.last = (answers.last or 0) % #answers + 1
 
   return answers[answers.last]
 end
 
 
+local get_next_weighted_round_robin_answer
 do
   -- based on the Nginx's SWRR algorithm and lua-resty-balancer
   local function swrr_next(answers)
@@ -296,7 +299,7 @@ do
   end
 
 
-  function _M.get_next_weighted_round_robin_answer(answers)
+  get_next_weighted_round_robin_answer = function(answers)
     local l = answers.lowest_prio_records or filter_lowest_priority_answers(answers)
 
     -- perform round robin selection on lowest priority answers @l
@@ -309,4 +312,15 @@ do
 end
 
 
-return _M
+return {
+  hostname_type = hostname_type,
+  parse_hostname = parse_hostname,
+  parse_hosts = parse_hosts,
+  parse_resolv_conf = parse_resolv_conf,
+  is_fqdn = is_fqdn,
+  is_srv = is_srv,
+  search_names = search_names,
+  ipv6_bracket = ipv6_bracket,
+  get_next_round_robin_answer = get_next_round_robin_answer,
+  get_next_weighted_round_robin_answer = get_next_weighted_round_robin_answer,
+}