97 lines
2.4 KiB
Lua
97 lines
2.4 KiB
Lua
local resolver = require("resty.dns.resolver")
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local lrucache = require("resty.lrucache")
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local resolv_conf = require("util.resolv_conf")
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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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local function resolve_host(host, r, qtype)
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local answers
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answers, err = r:query(host, { qtype = qtype }, {})
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if not answers then
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return nil, -1, tostring(err)
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end
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if answers.errcode then
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return nil, -1, string.format("server returned error code: %s: %s", answers.errcode, answers.errstr)
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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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return nil, -1, "no record resolved"
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end
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return addresses, ttl, nil
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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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local message = string.format(
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"addresses %s for host %s was resolved from cache",
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table.concat(cached_addresses, ", "), host)
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ngx.log(ngx.INFO, message)
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return cached_addresses
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end
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local r
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r, err = resolver:new{
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nameservers = resolv_conf.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 dns_errors = {}
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local addresses, ttl
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addresses, ttl, err = resolve_host(host, r, r.TYPE_A)
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if not addresses then
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table.insert(dns_errors, tostring(err))
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elseif #addresses > 0 then
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cache:set(host, addresses, ttl)
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return addresses
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end
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addresses, ttl, err = resolve_host(host, r, r.TYPE_AAAA)
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if not addresses then
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table.insert(dns_errors, tostring(err))
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elseif #addresses > 0 then
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cache:set(host, addresses, ttl)
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return addresses
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end
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if #dns_errors > 0 then
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ngx.log(ngx.ERR, "failed to query the DNS server:\n" .. table.concat(dns_errors, "\n"))
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end
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return { host }
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end
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return _M
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