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Additions to dns.lua from Patrik Karlsson. Adds an answer fetcher for
TXT and SRV records, and a function get answers from the additional section.
This commit is contained in:
david
204
nselib/dns.lua
204
nselib/dns.lua
@@ -280,7 +280,11 @@ answerFetcher[types.TXT] = function(dec, retAll)
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return false, "No Answers"
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else
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for _, v in ipairs(dec.answers) do
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if v.data then table.insert(answers, string.sub(v.data, 2)) end
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if v.TXT and v.TXT.text then
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for _, v in ipairs( v.TXT.text ) do
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table.insert(answers, v)
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end
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end
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end
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end
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if #answers == 0 then
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@@ -373,6 +377,30 @@ answerFetcher[types.MX] = function(dec, retAll)
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return true, answers
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end
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-- Answer fetcher for SRV records.
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-- @param dec Decoded DNS response.
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-- @param retAll If true, return all entries, not just the first.
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-- @return True if one or more answers of the required type were found - otherwise false.
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-- @return String first dns SRV record or Table of SRV records or String Error message.
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-- Note that the format of a returned SRV answer is "priority:weight:port:target" where zero
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-- or more IP addresses may be present.
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answerFetcher[types.SRV] = function(dec, retAll)
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local srv, ip, answers = {}, {}, {}
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for _, ans in ipairs(dec.answers) do
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if ans.dtype == types.SRV then
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if not retAll then
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return true, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target )
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end
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table.insert( answers, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target ) )
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end
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end
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if #answers == 0 then
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stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: SRV")
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return false, "No Answers"
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end
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return true, answers
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end
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---
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-- Answer fetcher for NS records.
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@@ -442,6 +470,141 @@ function findNiceAnswer(dtype, dec, retAll)
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end
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end
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---
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-- Table for additional fetching functions.
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-- Some servers return their answers in the additional section. The
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-- findNiceAdditional function with its relevant additionalFetcher functions
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-- addresses this. This unfortunately involved some code duplication (because
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-- of current design of the dns library) from the answerFetchers to the
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-- additionalFetchers.
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local additionalFetcher = {}
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---
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-- Additional fetcher for TXT records.
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-- @param dec Decoded DNS response.
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-- @param retAll If true, return all entries, not just the first.
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-- @return True if one or more answers of the required type were found - otherwise false.
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-- @return String first dns TXT record or Table of TXT records or String Error message.
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additionalFetcher[types.TXT] = function(dec, retAll)
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local answers = {}
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if not retAll and dec.add[1].data then
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return string.sub(dec.add[1].data, 2)
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elseif not retAll then
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stdnse.print_debug(1, "dns.aditionalFetcher found no records of the required type: TXT")
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return false, "No Answers"
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else
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for _, v in ipairs(dec.add) do
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if v.TXT and v.TXT.text then
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for _, v in ipairs( v.TXT.text ) do
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table.insert(answers, v)
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end
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end
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end
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end
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if #answers == 0 then
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stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: TXT")
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return false, "No Answers"
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end
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return true, answers
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end
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---
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-- Additional fetcher for A records
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-- @param dec Decoded DNS response.
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-- @param retAll If true, return all entries, not just the first.
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-- @return True if one or more answers of the required type were found - otherwise false.
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-- @return String first dns A record or Table of A records or String Error message.
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additionalFetcher[types.A] = function(dec, retAll)
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local answers = {}
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for _, ans in ipairs(dec.add) do
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if ans.dtype == types.A then
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if not retAll then
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return true, ans.ip
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end
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table.insert(answers, ans.ip)
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end
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end
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if not retAll or #answers == 0 then
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stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: A")
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return false, "No Answers"
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end
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return true, answers
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end
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-- Additional fetcher for SRV records.
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-- @param dec Decoded DNS response.
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-- @param retAll If true, return all entries, not just the first.
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-- @return True if one or more answers of the required type were found - otherwise false.
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-- @return String first dns SRV record or Table of SRV records or String Error message.
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-- Note that the format of a returned SRV answer is "priority:weight:port:target" where zero
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-- or more IP addresses may be present.
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additionalFetcher[types.SRV] = function(dec, retAll)
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local srv, ip, answers = {}, {}, {}
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for _, ans in ipairs(dec.add) do
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if ans.dtype == types.SRV then
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if not retAll then
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return true, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target )
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end
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table.insert( answers, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target ) )
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end
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end
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if #answers == 0 then
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stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: SRV")
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return false, "No Answers"
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end
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return true, answers
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end
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---
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-- Additional fetcher for AAAA records.
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-- @param dec Decoded DNS response.
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-- @param retAll If true, return all entries, not just the first.
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-- @return True if one or more answers of the required type were found - otherwise false.
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-- @return String first dns AAAA record or Table of AAAA records or String Error message.
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additionalFetcher[types.AAAA] = function(dec, retAll)
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local answers = {}
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for _, ans in ipairs(dec.add) do
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if ans.dtype == types.AAAA then
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if not retAll then
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return true, ans.ipv6
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end
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table.insert(answers, ans.ipv6)
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end
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end
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if not retAll or #answers == 0 then
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stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: AAAA")
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return false, "No Answers"
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end
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return true, answers
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end
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---
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-- Calls the answer fetcher for <code>dtype</code> or returns an error code in
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-- case of a "no such name" error.
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-- @param dtype DNS resource record type.
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-- @param dec Decoded DNS response.
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-- @param retAll If true, return all entries, not just the first.
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-- @return True if one or more answers of the required type were found - otherwise false.
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-- @return Answer according to the answer fetcher for <code>dtype</code> or an Error message.
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function findNiceAdditional(dtype, dec, retAll)
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if (#dec.add > 0) then
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if additionalFetcher[dtype] then
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return additionalFetcher[dtype](dec, retAll)
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else
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stdnse.print_debug(1, "dns.findNiceAdditional() does not have an additionalFetcher for dtype %s",
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(type(dtype) == 'string' and dtype) or type(dtype) or "nil")
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return false, "Unable to handle response"
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end
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elseif (dec.flags.RC3 and dec.flags.RC4) then
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return false, "No Such Name"
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else
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stdnse.print_debug(1, "dns.findNiceAdditional() found zero answers in a response, but got an unexpected flags.replycode")
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return false, "No Answers"
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end
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end
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---
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-- Encodes the question part of a DNS request.
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@@ -684,7 +847,27 @@ decoder[types.PTR] = decDomain
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-- @param entry RR in packet.
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-- @param data Complete encoded DNS packet.
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-- @param pos Position in packet after RR.
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decoder[types.TXT] = function () end
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decoder[types.TXT] =
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function (entry, data, pos)
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local len = entry.data:len()
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local np = pos - #entry.data
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local txt_len
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local txt
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if len > 0 then
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entry.TXT = {}
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entry.TXT.text = {}
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end
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while len > 0 do
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np, txt_len = bin.unpack("C", data, np)
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np, txt = bin.unpack("A" .. txt_len, data, np )
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len = len - txt_len - 1
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table.insert( entry.TXT.text, txt )
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end
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end
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---
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-- Decodes MX record, puts it in <code>entry.MX</code>.
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@@ -703,6 +886,23 @@ decoder[types.MX] =
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_, entry.MX.server = decStr(data, np)
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end
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---
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-- Decodes SRV record, puts it in <code>entry.SRV</code>.
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--
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-- <code>entry.SRV</code> has the fields <code>prio</code>,
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-- <code>weight</code>, <code>port</code> and
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-- <code>target</code>.
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-- @param entry RR in packet.
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-- @param data Complete encoded DNS packet.
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-- @param pos Position in packet after RR.
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decoder[types.SRV] =
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function(entry, data, pos)
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local np = pos - #entry.data
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local _
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entry.SRV = {}
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np, entry.SRV.prio, entry.SRV.weight, entry.SRV.port = bin.unpack(">S>S>S", data, np)
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np, entry.SRV.target = decStr(data, np)
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end
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---
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-- Decodes returned resource records (answer, authority, or additional part).
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