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net.resolvers.service: Honour record 'weight' when picking SRV targets
#NotHappyEyeballs
This commit is contained in:
Matthew Wild
parent
d1c2e34e61
commit
d26811f5e5
2 changed files with 309 additions and 13 deletions
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@ -2,23 +2,78 @@ local adns = require "net.adns";
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local basic = require "net.resolvers.basic";
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local inet_pton = require "util.net".pton;
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local idna_to_ascii = require "util.encodings".idna.to_ascii;
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local unpack = table.unpack or unpack; -- luacheck: ignore 113
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local methods = {};
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local resolver_mt = { __index = methods };
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local function new_target_selector(rrset)
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local rr_count = rrset and #rrset;
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if not rr_count or rr_count == 0 then
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rrset = nil;
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else
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table.sort(rrset, function (a, b) return a.srv.priority < b.srv.priority end);
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end
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local rrset_pos = 1;
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local priority_bucket, bucket_total_weight, bucket_len, bucket_used;
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return function ()
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if not rrset then return; end
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if not priority_bucket or bucket_used >= bucket_len then
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if rrset_pos > rr_count then return; end -- Used up all records
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-- Going to start on a new priority now. Gather up all the next
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-- records with the same priority and add them to priority_bucket
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priority_bucket, bucket_total_weight, bucket_len, bucket_used = {}, 0, 0, 0;
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local current_priority;
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repeat
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local curr_record = rrset[rrset_pos].srv;
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if not current_priority then
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current_priority = curr_record.priority;
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elseif current_priority ~= curr_record.priority then
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break;
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end
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table.insert(priority_bucket, curr_record);
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bucket_total_weight = bucket_total_weight + curr_record.weight;
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bucket_len = bucket_len + 1;
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rrset_pos = rrset_pos + 1;
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until rrset_pos > rr_count;
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end
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bucket_used = bucket_used + 1;
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local n, running_total = math.random(0, bucket_total_weight), 0;
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local target_record;
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for i = 1, bucket_len do
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local candidate = priority_bucket[i];
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if candidate then
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running_total = running_total + candidate.weight;
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if running_total >= n then
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target_record = candidate;
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bucket_total_weight = bucket_total_weight - candidate.weight;
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priority_bucket[i] = nil;
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break;
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end
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end
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end
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return target_record;
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end;
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end
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-- Find the next target to connect to, and
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-- pass it to cb()
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function methods:next(cb)
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if self.targets then
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if not self.resolver then
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if #self.targets == 0 then
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if self.resolver or self._get_next_target then
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if not self.resolver then -- Do we have a basic resolver currently?
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-- We don't, so fetch a new SRV target, create a new basic resolver for it
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local next_srv_target = self._get_next_target and self._get_next_target();
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if not next_srv_target then
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-- No more SRV targets left
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cb(nil);
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return;
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end
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local next_target = table.remove(self.targets, 1);
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self.resolver = basic.new(unpack(next_target, 1, 4));
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-- Create a new basic resolver for this SRV target
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self.resolver = basic.new(next_srv_target.target, next_srv_target.port, self.conn_type, self.extra);
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end
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-- Look up the next (basic) target from the current target's resolver
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self.resolver:next(function (...)
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if self.resolver then
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self.last_error = self.resolver.last_error;
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@ -31,6 +86,9 @@ function methods:next(cb)
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end
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end);
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return;
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elseif self.in_progress then
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cb(nil);
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return;
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end
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if not self.hostname then
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@ -39,9 +97,9 @@ function methods:next(cb)
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return;
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end
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local targets = {};
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self.in_progress = true;
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local function ready()
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self.targets = targets;
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self:next(cb);
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end
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@ -63,7 +121,7 @@ function methods:next(cb)
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if #answer == 0 then
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if self.extra and self.extra.default_port then
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table.insert(targets, { self.hostname, self.extra.default_port, self.conn_type, self.extra });
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self.resolver = basic.new(self.hostname, self.extra.default_port, self.conn_type, self.extra);
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else
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self.last_error = "zero SRV records found";
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end
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@ -77,10 +135,7 @@ function methods:next(cb)
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return;
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end
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table.sort(answer, function (a, b) return a.srv.priority < b.srv.priority end);
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for _, record in ipairs(answer) do
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table.insert(targets, { record.srv.target, record.srv.port, self.conn_type, self.extra });
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end
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self._get_next_target = new_target_selector(answer);
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else
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self.last_error = err;
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end
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241
spec/net_resolvers_service_spec.lua
Normal file
241
spec/net_resolvers_service_spec.lua
Normal file
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@ -0,0 +1,241 @@
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local set = require "util.set";
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insulate("net.resolvers.service", function ()
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local adns = {
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resolver = function ()
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return {
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lookup = function (_, cb, qname, qtype, qclass)
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if qname == "_xmpp-server._tcp.example.com"
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and (qtype or "SRV") == "SRV"
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and (qclass or "IN") == "IN" then
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cb({
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{ -- 60+35+60
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srv = { target = "xmpp0-a.example.com", port = 5228, priority = 0, weight = 60 };
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};
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{
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srv = { target = "xmpp0-b.example.com", port = 5216, priority = 0, weight = 35 };
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};
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{
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srv = { target = "xmpp0-c.example.com", port = 5200, priority = 0, weight = 0 };
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};
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{
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srv = { target = "xmpp0-d.example.com", port = 5256, priority = 0, weight = 120 };
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};
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{
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srv = { target = "xmpp1-a.example.com", port = 5273, priority = 1, weight = 30 };
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};
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{
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srv = { target = "xmpp1-b.example.com", port = 5274, priority = 1, weight = 30 };
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};
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{
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srv = { target = "xmpp2.example.com", port = 5275, priority = 2, weight = 0 };
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};
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});
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elseif qname == "_xmpp-server._tcp.single.example.com"
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and (qtype or "SRV") == "SRV"
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and (qclass or "IN") == "IN" then
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cb({
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{
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srv = { target = "xmpp0-a.example.com", port = 5269, priority = 0, weight = 0 };
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};
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});
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elseif qname == "_xmpp-server._tcp.half.example.com"
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and (qtype or "SRV") == "SRV"
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and (qclass or "IN") == "IN" then
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cb({
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{
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srv = { target = "xmpp0-a.example.com", port = 5269, priority = 0, weight = 0 };
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};
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{
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srv = { target = "xmpp0-b.example.com", port = 5270, priority = 0, weight = 1 };
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};
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});
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elseif qtype == "A" then
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local l = qname:match("%-(%a)%.example.com$") or "1";
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local d = ("%d"):format(l:byte())
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cb({
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{
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a = "127.0.0."..d;
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};
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});
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elseif qtype == "AAAA" then
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local l = qname:match("%-(%a)%.example.com$") or "1";
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local d = ("%04d"):format(l:byte())
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cb({
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{
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aaaa = "fdeb:9619:649e:c7d9::"..d;
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};
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});
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else
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cb(nil);
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end
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end;
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};
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end;
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};
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package.loaded["net.adns"] = mock(adns);
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local resolver = require "net.resolvers.service";
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math.randomseed(os.time());
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it("works for 99% of deployments", function ()
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-- Most deployments only have a single SRV record, let's make
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-- sure that works okay
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local expected_targets = set.new({
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-- xmpp0-a
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"tcp4 127.0.0.97 5269";
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"tcp6 fdeb:9619:649e:c7d9::0097 5269";
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});
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local received_targets = set.new({});
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local r = resolver.new("single.example.com", "xmpp-server");
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local done = false;
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local function handle_target(...)
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if ... == nil then
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done = true;
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-- No more targets
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return;
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end
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received_targets:add(table.concat({ ... }, " ", 1, 3));
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end
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r:next(handle_target);
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while not done do
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r:next(handle_target);
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end
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-- We should have received all expected targets, and no unexpected
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-- ones:
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assert.truthy(set.xor(received_targets, expected_targets):empty());
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end);
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it("supports A/AAAA fallback", function ()
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-- Many deployments don't have any SRV records, so we should
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-- fall back to A/AAAA records instead when that is the case
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local expected_targets = set.new({
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-- xmpp0-a
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"tcp4 127.0.0.97 5269";
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"tcp6 fdeb:9619:649e:c7d9::0097 5269";
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});
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local received_targets = set.new({});
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local r = resolver.new("xmpp0-a.example.com", "xmpp-server", "tcp", { default_port = 5269 });
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local done = false;
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local function handle_target(...)
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if ... == nil then
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done = true;
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-- No more targets
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return;
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end
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received_targets:add(table.concat({ ... }, " ", 1, 3));
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end
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r:next(handle_target);
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while not done do
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r:next(handle_target);
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end
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-- We should have received all expected targets, and no unexpected
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-- ones:
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assert.truthy(set.xor(received_targets, expected_targets):empty());
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end);
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it("works", function ()
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local expected_targets = set.new({
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-- xmpp0-a
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"tcp4 127.0.0.97 5228";
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"tcp6 fdeb:9619:649e:c7d9::0097 5228";
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"tcp4 127.0.0.97 5273";
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"tcp6 fdeb:9619:649e:c7d9::0097 5273";
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-- xmpp0-b
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"tcp4 127.0.0.98 5274";
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"tcp6 fdeb:9619:649e:c7d9::0098 5274";
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"tcp4 127.0.0.98 5216";
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"tcp6 fdeb:9619:649e:c7d9::0098 5216";
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-- xmpp0-c
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"tcp4 127.0.0.99 5200";
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"tcp6 fdeb:9619:649e:c7d9::0099 5200";
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-- xmpp0-d
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"tcp4 127.0.0.100 5256";
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"tcp6 fdeb:9619:649e:c7d9::0100 5256";
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-- xmpp2
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"tcp4 127.0.0.49 5275";
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"tcp6 fdeb:9619:649e:c7d9::0049 5275";
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});
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local received_targets = set.new({});
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local r = resolver.new("example.com", "xmpp-server");
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local done = false;
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local function handle_target(...)
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if ... == nil then
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done = true;
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-- No more targets
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return;
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end
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received_targets:add(table.concat({ ... }, " ", 1, 3));
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end
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r:next(handle_target);
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while not done do
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r:next(handle_target);
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end
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-- We should have received all expected targets, and no unexpected
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-- ones:
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assert.truthy(set.xor(received_targets, expected_targets):empty());
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end);
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it("balances across weights correctly #slow", function ()
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-- This mimics many repeated connections to 'example.com' (mock
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-- records defined above), and records the port number of the
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-- first target. Therefore it (should) only return priority
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-- 0 records, and the input data is constructed such that the
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-- last two digits of the port number represent the percentage
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-- of times that record should (on average) be picked first.
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-- To prevent random test failures, we test across a handful
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-- of fixed (randomly selected) seeds.
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for _, seed in ipairs({ 8401877, 3943829, 7830992 }) do
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math.randomseed(seed);
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local results = {};
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local function run()
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local run_results = {};
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local r = resolver.new("example.com", "xmpp-server");
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local function record_target(...)
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if ... == nil then
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-- No more targets
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return;
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end
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run_results = { ... };
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end
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r:next(record_target);
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return run_results[3];
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end
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for _ = 1, 1000 do
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local port = run();
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results[port] = (results[port] or 0) + 1;
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end
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local ports = {};
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for port in pairs(results) do
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table.insert(ports, port);
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end
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table.sort(ports);
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for _, port in ipairs(ports) do
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--print("PORT", port, tostring((results[port]/1000) * 100).."% hits (expected "..tostring(port-5200).."%)");
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local hit_pct = (results[port]/1000) * 100;
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local expected_pct = port - 5200;
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--print(hit_pct, expected_pct, math.abs(hit_pct - expected_pct));
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assert.is_true(math.abs(hit_pct - expected_pct) < 5);
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end
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--print("---");
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end
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end);
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end);
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