70 lines
1.9 KiB
Lua
70 lines
1.9 KiB
Lua
local resolver = require("resty.dns.resolver")
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local lrucache = require("resty.lrucache")
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local configuration = require("configuration")
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local util = require("util")
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local _M = {}
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local CACHE_SIZE = 10000
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local MAXIMUM_TTL_VALUE = 2147483647 -- maximum value according to https://tools.ietf.org/html/rfc2181
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local cache, err = lrucache.new(CACHE_SIZE)
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if not cache then
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return error("failed to create the cache: " .. (err or "unknown"))
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end
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local function a_records_and_max_ttl(answers)
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local addresses = {}
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local ttl = MAXIMUM_TTL_VALUE -- maximum value according to https://tools.ietf.org/html/rfc2181
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for _, ans in ipairs(answers) do
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if ans.address then
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table.insert(addresses, ans.address)
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if ttl > ans.ttl then
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ttl = ans.ttl
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end
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end
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end
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return addresses, ttl
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end
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function _M.resolve(host)
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local cached_addresses = cache:get(host)
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if cached_addresses then
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ngx.log(ngx.INFO, string.format("addresses %s for host %s was resolved from cache", table.concat(cached_addresses, ", "), host))
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return cached_addresses
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end
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local r, err = resolver:new{
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nameservers = util.deepcopy(configuration.nameservers),
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retrans = 5,
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timeout = 2000, -- 2 sec
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}
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if not r then
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ngx.log(ngx.ERR, "failed to instantiate the resolver: " .. tostring(err))
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return { host }
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end
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local answers, err, _tries = r:query(host, { qtype = r.TYPE_A }, {})
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if not answers then
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ngx.log(ngx.ERR, "failed to query the DNS server: " .. tostring(err))
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return { host }
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end
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if answers.errcode then
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ngx.log(ngx.ERR, string.format("server returned error code: %s: %s", answers.errcode, answers.errstr))
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return { host }
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end
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local addresses, ttl = a_records_and_max_ttl(answers)
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if #addresses == 0 then
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ngx.log(ngx.ERR, "no A record resolved")
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return { host }
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end
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cache:set(host, addresses, ttl)
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return addresses
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end
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return _M
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