add NAPTR record support

Author: sergey-lukin

README.markdown

@@ -28,6 +28,7 @@ Table of Contents
     * [TYPE_TXT](#type_txt)
     * [TYPE_AAAA](#type_aaaa)
     * [TYPE_SRV](#type_srv)
+    * [TYPE_NAPTR](#type_naptr)
     * [TYPE_SPF](#type_spf)
     * [CLASS_IN](#class_in)
     * [SECTION_AN](#section_an)
@@ -373,6 +374,16 @@ See RFC 2782 for details.
 
 [Back to TOC](#table-of-contents)
 
+TYPE_NAPTR
+----------
+`syntax: typ = r.TYPE_NAPTR`
+
+The `NAPTR` resource record type, equal to the decimal number `35`.
+
+See RFC 2915 for details.
+
+[Back to TOC](#table-of-contents)
+
 TYPE_SPF
 ---------
 `syntax: typ = r.TYPE_SPF`

lib/resty/dns/resolver.lua

@@ -48,6 +48,7 @@ local TYPE_MX     = 15
 local TYPE_TXT    = 16
 local TYPE_AAAA   = 28
 local TYPE_SRV    = 33
+local TYPE_NAPTR  = 35
 local TYPE_SPF    = 99
 
 local CLASS_IN    = 1
@@ -67,6 +68,7 @@ local _M = {
     TYPE_TXT    = TYPE_TXT,
     TYPE_AAAA   = TYPE_AAAA,
     TYPE_SRV    = TYPE_SRV,
+    TYPE_NAPTR  = TYPE_NAPTR,
     TYPE_SPF    = TYPE_SPF,
     CLASS_IN    = CLASS_IN,
     SECTION_AN  = SECTION_AN,
@@ -210,6 +212,21 @@ local function _encode_name(s)
 end
 
 
+local function _decode_string(buf, pos)
+    local slen = byte(buf, pos)
+
+    if slen == 0 then
+        return "", pos + 1
+    end
+
+    if pos + 1 + slen >= #buf then
+        return nil, 'truncated'
+    end
+
+    return sub(buf, pos + 1, pos + slen), pos + slen + 1
+end
+
+
 local function _decode_name(buf, pos)
     local labels = {}
     local nptrs = 0
@@ -484,6 +501,50 @@ local function parse_section(answers, section, buf, start_pos, size,
 
             pos = p
 
+        elseif typ == TYPE_NAPTR then
+            if len < 7 then
+                return nil, "bad NAPTR record value length: " .. len
+            end
+
+            local order_hi = byte(buf, pos)
+            local order_lo = byte(buf, pos + 1)
+            ans.order = lshift(order_hi, 8) + order_lo
+
+            local preference_hi = byte(buf, pos + 2)
+            local preference_lo = byte(buf, pos + 3)
+            ans.preference = lshift(preference_hi, 8) + preference_lo
+
+            local flags_str, p = _decode_string(buf, pos + 4)
+            if not flags_str then
+                return nil, pos
+            end
+            ans.flags = flags_str
+
+            local services_str, p = _decode_string(buf, p)
+            if not services_str then
+                return nil, pos
+            end
+            ans.services = services_str
+
+            local regexp_str, p = _decode_string(buf, p)
+            if not regexp_str then
+                return nil, pos
+            end
+            ans.regexp = regexp_str
+
+            local replacements_str,p = _decode_name(buf, p)
+            if not replacements_str
+                then return nil, pos
+            end
+            ans.replacements = replacements_str
+
+            if p - pos ~= len then
+                return nil, format("bad NAPTR record length: %d ~= %d",
+                                   p - pos, len)
+            end
+
+            pos = p
+
         elseif typ == TYPE_NS then
 
             local name, p = _decode_name(buf, pos)