reverse DNS utitiies improvements

README.markdown

@@ -252,9 +252,9 @@ will yield `FF01::101` in the `new_addr` return value.
 
 expand_ipv6_addr
 ------------------
-`syntax: expandeded = resty.dns.resolver.expand_ipv6_addr(address)`
+`syntax: expanded = resty.dns.resolver.expand_ipv6_addr(address)`
 
-Expand the successive 16-bit zero groups in the textual format of the IPv6 address.
+Expands the successive 16-bit zero groups in the textual format of the IPv6 address.
 
 For example,
 

lib/resty/dns/resolver.lua

@@ -23,16 +23,22 @@ local log = ngx.log
 local DEBUG = ngx.DEBUG
 local randomseed = math.randomseed
 local ngx_time = ngx.time
+local unpack = unpack
 local setmetatable = setmetatable
 local type = type
 
+
 local ok, new_tab = pcall(require, "table.new")
 if not ok then
     new_tab = function (narr, nrec) return {} end
 end
 
+
 local DOT_CHAR = byte(".")
+local ZERO_CHAR = byte("0")
+local COLON_CHAR = byte(":")
 
+local IP6_ARPA = "ip6.arpa"
 
 local TYPE_A      = 1
 local TYPE_NS     = 2
@@ -74,6 +80,17 @@ local resolver_errstrs = {
 local mt = { __index = _M }
 
 
+local arpa_tmpl = new_tab(72, 0)
+
+for i = 1, #IP6_ARPA do
+    arpa_tmpl[64 + i] = byte(IP6_ARPA, i)
+end
+
+for i = 2, 64, 2 do
+    arpa_tmpl[i] = DOT_CHAR
+end
+
+
 function _M.new(class, opts)
     if not opts then
         return nil, "no options table specified"
@@ -803,66 +820,66 @@ end
 
 
 local function _expand_ipv6_addr(addr)
-    if find(addr, "::") then
-        local ncol = 0
+    if find(addr, "::", 1, true) then
+        local ncol, addrlen = 8, #addr
 
-        for i=1, #addr do
-            if sub(addr, i, i) == ":" then
-                ncol = ncol + 1
+        for i = 1, addrlen do
+            if byte(addr, i) == COLON_CHAR then
+                ncol = ncol - 1
             end
         end
 
-        if addr == "::" then
-            addr = "0::0"
-        elseif sub(addr, 1, 2) == "::" then
+        if byte(addr, 1) == COLON_CHAR then
             addr = "0" .. addr
         end
 
-        addr = re_sub(addr, "::", ":" .. rep("0:",8 - ncol), "jo")
+        if byte(addr, -1) == COLON_CHAR then
+            addr = addr .. "0"
+        end
+
+        addr = re_sub(addr, "::", ":" .. rep("0:", ncol), "jo")
     end
 
     return addr
 end
 
 
-function _M.expand_ipv6_addr = _expand_ipv6_addr
+_M.expand_ipv6_addr = _expand_ipv6_addr
 
 
 function _M.arpa_str(addr)
-    local arpa = ".in-addr.arpa"
-
-    if find(addr, ":") then
-        addr, arpa = _expand_ipv6_addr(addr), ".ip6.arpa"
-        local tmp, idx, hidx, addrlen = new_tab(32,0), 1, 1, #addr
-
-        for i = addrlen, 1, -1 do
-            local s = sub(addr, i, i)
-            if s == ":" then
+    if find(addr, ":", 1, true) then
+        addr = _expand_ipv6_addr(addr)
+        local idx, hidx, addrlen = 1, 1, #addr
+
+        for i = addrlen, 0, -1 do
+            local s = byte(addr, i)
+            if s == COLON_CHAR or not s then
                 for j = hidx, 4 do
-                    tmp[idx] = "0"
-                    idx = idx + 1
+                    arpa_tmpl[idx] = ZERO_CHAR
+                    idx = idx + 2
                 end
                 hidx = 1
             else
-                tmp[idx] = s
-                idx = idx + 1
+                arpa_tmpl[idx] = s
+                idx = idx + 2
                 hidx = hidx + 1
             end
         end
 
-        addr = concat(tmp, ".")
+        addr = char(unpack(arpa_tmpl))
     else
-        addr = re_sub(addr, [[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})]], 
-            "$4.$3.$2.$1", "ajo")
+        addr = re_sub(addr, [[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})]],
+                      "$4.$3.$2.$1.in-addr.arpa", "ajo")
     end
-    
-    return addr .. arpa
+
+    return addr
 end
 
 
 function _M.reverse_query(self, addr)
     return self.query(self, self.arpa_str(addr),
-        { qtype = self.TYPE_PTR })
+                      {qtype = self.TYPE_PTR})
 end