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-rw-r--r--net/resolvers/service.lua81
-rw-r--r--spec/net_resolvers_service_spec.lua241
2 files changed, 309 insertions, 13 deletions
diff --git a/net/resolvers/service.lua b/net/resolvers/service.lua
index 3810cac8..a7ce76a3 100644
--- a/net/resolvers/service.lua
+++ b/net/resolvers/service.lua
@@ -2,23 +2,78 @@ local adns = require "net.adns";
local basic = require "net.resolvers.basic";
local inet_pton = require "util.net".pton;
local idna_to_ascii = require "util.encodings".idna.to_ascii;
-local unpack = table.unpack or unpack; -- luacheck: ignore 113
local methods = {};
local resolver_mt = { __index = methods };
+local function new_target_selector(rrset)
+ local rr_count = rrset and #rrset;
+ if not rr_count or rr_count == 0 then
+ rrset = nil;
+ else
+ table.sort(rrset, function (a, b) return a.srv.priority < b.srv.priority end);
+ end
+ local rrset_pos = 1;
+ local priority_bucket, bucket_total_weight, bucket_len, bucket_used;
+ return function ()
+ if not rrset then return; end
+
+ if not priority_bucket or bucket_used >= bucket_len then
+ if rrset_pos > rr_count then return; end -- Used up all records
+
+ -- Going to start on a new priority now. Gather up all the next
+ -- records with the same priority and add them to priority_bucket
+ priority_bucket, bucket_total_weight, bucket_len, bucket_used = {}, 0, 0, 0;
+ local current_priority;
+ repeat
+ local curr_record = rrset[rrset_pos].srv;
+ if not current_priority then
+ current_priority = curr_record.priority;
+ elseif current_priority ~= curr_record.priority then
+ break;
+ end
+ table.insert(priority_bucket, curr_record);
+ bucket_total_weight = bucket_total_weight + curr_record.weight;
+ bucket_len = bucket_len + 1;
+ rrset_pos = rrset_pos + 1;
+ until rrset_pos > rr_count;
+ end
+
+ bucket_used = bucket_used + 1;
+ local n, running_total = math.random(0, bucket_total_weight), 0;
+ local target_record;
+ for i = 1, bucket_len do
+ local candidate = priority_bucket[i];
+ if candidate then
+ running_total = running_total + candidate.weight;
+ if running_total >= n then
+ target_record = candidate;
+ bucket_total_weight = bucket_total_weight - candidate.weight;
+ priority_bucket[i] = nil;
+ break;
+ end
+ end
+ end
+ return target_record;
+ end;
+end
+
-- Find the next target to connect to, and
-- pass it to cb()
function methods:next(cb)
- if self.targets then
- if not self.resolver then
- if #self.targets == 0 then
+ if self.resolver or self._get_next_target then
+ if not self.resolver then -- Do we have a basic resolver currently?
+ -- We don't, so fetch a new SRV target, create a new basic resolver for it
+ local next_srv_target = self._get_next_target and self._get_next_target();
+ if not next_srv_target then
+ -- No more SRV targets left
cb(nil);
return;
end
- local next_target = table.remove(self.targets, 1);
- self.resolver = basic.new(unpack(next_target, 1, 4));
+ -- Create a new basic resolver for this SRV target
+ self.resolver = basic.new(next_srv_target.target, next_srv_target.port, self.conn_type, self.extra);
end
+ -- Look up the next (basic) target from the current target's resolver
self.resolver:next(function (...)
if self.resolver then
self.last_error = self.resolver.last_error;
@@ -31,6 +86,9 @@ function methods:next(cb)
end
end);
return;
+ elseif self.in_progress then
+ cb(nil);
+ return;
end
if not self.hostname then
@@ -39,9 +97,9 @@ function methods:next(cb)
return;
end
- local targets = {};
+ self.in_progress = true;
+
local function ready()
- self.targets = targets;
self:next(cb);
end
@@ -63,7 +121,7 @@ function methods:next(cb)
if #answer == 0 then
if self.extra and self.extra.default_port then
- table.insert(targets, { self.hostname, self.extra.default_port, self.conn_type, self.extra });
+ self.resolver = basic.new(self.hostname, self.extra.default_port, self.conn_type, self.extra);
else
self.last_error = "zero SRV records found";
end
@@ -77,10 +135,7 @@ function methods:next(cb)
return;
end
- table.sort(answer, function (a, b) return a.srv.priority < b.srv.priority end);
- for _, record in ipairs(answer) do
- table.insert(targets, { record.srv.target, record.srv.port, self.conn_type, self.extra });
- end
+ self._get_next_target = new_target_selector(answer);
else
self.last_error = err;
end
diff --git a/spec/net_resolvers_service_spec.lua b/spec/net_resolvers_service_spec.lua
new file mode 100644
index 00000000..53ce4754
--- /dev/null
+++ b/spec/net_resolvers_service_spec.lua
@@ -0,0 +1,241 @@
+local set = require "util.set";
+
+insulate("net.resolvers.service", function ()
+ local adns = {
+ resolver = function ()
+ return {
+ lookup = function (_, cb, qname, qtype, qclass)
+ if qname == "_xmpp-server._tcp.example.com"
+ and (qtype or "SRV") == "SRV"
+ and (qclass or "IN") == "IN" then
+ cb({
+ { -- 60+35+60
+ srv = { target = "xmpp0-a.example.com", port = 5228, priority = 0, weight = 60 };
+ };
+ {
+ srv = { target = "xmpp0-b.example.com", port = 5216, priority = 0, weight = 35 };
+ };
+ {
+ srv = { target = "xmpp0-c.example.com", port = 5200, priority = 0, weight = 0 };
+ };
+ {
+ srv = { target = "xmpp0-d.example.com", port = 5256, priority = 0, weight = 120 };
+ };
+
+ {
+ srv = { target = "xmpp1-a.example.com", port = 5273, priority = 1, weight = 30 };
+ };
+ {
+ srv = { target = "xmpp1-b.example.com", port = 5274, priority = 1, weight = 30 };
+ };
+
+ {
+ srv = { target = "xmpp2.example.com", port = 5275, priority = 2, weight = 0 };
+ };
+ });
+ elseif qname == "_xmpp-server._tcp.single.example.com"
+ and (qtype or "SRV") == "SRV"
+ and (qclass or "IN") == "IN" then
+ cb({
+ {
+ srv = { target = "xmpp0-a.example.com", port = 5269, priority = 0, weight = 0 };
+ };
+ });
+ elseif qname == "_xmpp-server._tcp.half.example.com"
+ and (qtype or "SRV") == "SRV"
+ and (qclass or "IN") == "IN" then
+ cb({
+ {
+ srv = { target = "xmpp0-a.example.com", port = 5269, priority = 0, weight = 0 };
+ };
+ {
+ srv = { target = "xmpp0-b.example.com", port = 5270, priority = 0, weight = 1 };
+ };
+ });
+ elseif qtype == "A" then
+ local l = qname:match("%-(%a)%.example.com$") or "1";
+ local d = ("%d"):format(l:byte())
+ cb({
+ {
+ a = "127.0.0."..d;
+ };
+ });
+ elseif qtype == "AAAA" then
+ local l = qname:match("%-(%a)%.example.com$") or "1";
+ local d = ("%04d"):format(l:byte())
+ cb({
+ {
+ aaaa = "fdeb:9619:649e:c7d9::"..d;
+ };
+ });
+ else
+ cb(nil);
+ end
+ end;
+ };
+ end;
+ };
+ package.loaded["net.adns"] = mock(adns);
+ local resolver = require "net.resolvers.service";
+ math.randomseed(os.time());
+ it("works for 99% of deployments", function ()
+ -- Most deployments only have a single SRV record, let's make
+ -- sure that works okay
+
+ local expected_targets = set.new({
+ -- xmpp0-a
+ "tcp4 127.0.0.97 5269";
+ "tcp6 fdeb:9619:649e:c7d9::0097 5269";
+ });
+ local received_targets = set.new({});
+
+ local r = resolver.new("single.example.com", "xmpp-server");
+ local done = false;
+ local function handle_target(...)
+ if ... == nil then
+ done = true;
+ -- No more targets
+ return;
+ end
+ received_targets:add(table.concat({ ... }, " ", 1, 3));
+ end
+ r:next(handle_target);
+ while not done do
+ r:next(handle_target);
+ end
+
+ -- We should have received all expected targets, and no unexpected
+ -- ones:
+ assert.truthy(set.xor(received_targets, expected_targets):empty());
+ end);
+
+ it("supports A/AAAA fallback", function ()
+ -- Many deployments don't have any SRV records, so we should
+ -- fall back to A/AAAA records instead when that is the case
+
+ local expected_targets = set.new({
+ -- xmpp0-a
+ "tcp4 127.0.0.97 5269";
+ "tcp6 fdeb:9619:649e:c7d9::0097 5269";
+ });
+ local received_targets = set.new({});
+
+ local r = resolver.new("xmpp0-a.example.com", "xmpp-server", "tcp", { default_port = 5269 });
+ local done = false;
+ local function handle_target(...)
+ if ... == nil then
+ done = true;
+ -- No more targets
+ return;
+ end
+ received_targets:add(table.concat({ ... }, " ", 1, 3));
+ end
+ r:next(handle_target);
+ while not done do
+ r:next(handle_target);
+ end
+
+ -- We should have received all expected targets, and no unexpected
+ -- ones:
+ assert.truthy(set.xor(received_targets, expected_targets):empty());
+ end);
+
+
+ it("works", function ()
+ local expected_targets = set.new({
+ -- xmpp0-a
+ "tcp4 127.0.0.97 5228";
+ "tcp6 fdeb:9619:649e:c7d9::0097 5228";
+ "tcp4 127.0.0.97 5273";
+ "tcp6 fdeb:9619:649e:c7d9::0097 5273";
+
+ -- xmpp0-b
+ "tcp4 127.0.0.98 5274";
+ "tcp6 fdeb:9619:649e:c7d9::0098 5274";
+ "tcp4 127.0.0.98 5216";
+ "tcp6 fdeb:9619:649e:c7d9::0098 5216";
+
+ -- xmpp0-c
+ "tcp4 127.0.0.99 5200";
+ "tcp6 fdeb:9619:649e:c7d9::0099 5200";
+
+ -- xmpp0-d
+ "tcp4 127.0.0.100 5256";
+ "tcp6 fdeb:9619:649e:c7d9::0100 5256";
+
+ -- xmpp2
+ "tcp4 127.0.0.49 5275";
+ "tcp6 fdeb:9619:649e:c7d9::0049 5275";
+
+ });
+ local received_targets = set.new({});
+
+ local r = resolver.new("example.com", "xmpp-server");
+ local done = false;
+ local function handle_target(...)
+ if ... == nil then
+ done = true;
+ -- No more targets
+ return;
+ end
+ received_targets:add(table.concat({ ... }, " ", 1, 3));
+ end
+ r:next(handle_target);
+ while not done do
+ r:next(handle_target);
+ end
+
+ -- We should have received all expected targets, and no unexpected
+ -- ones:
+ assert.truthy(set.xor(received_targets, expected_targets):empty());
+ end);
+
+ it("balances across weights correctly #slow", function ()
+ -- This mimics many repeated connections to 'example.com' (mock
+ -- records defined above), and records the port number of the
+ -- first target. Therefore it (should) only return priority
+ -- 0 records, and the input data is constructed such that the
+ -- last two digits of the port number represent the percentage
+ -- of times that record should (on average) be picked first.
+
+ -- To prevent random test failures, we test across a handful
+ -- of fixed (randomly selected) seeds.
+ for _, seed in ipairs({ 8401877, 3943829, 7830992 }) do
+ math.randomseed(seed);
+
+ local results = {};
+ local function run()
+ local run_results = {};
+ local r = resolver.new("example.com", "xmpp-server");
+ local function record_target(...)
+ if ... == nil then
+ -- No more targets
+ return;
+ end
+ run_results = { ... };
+ end
+ r:next(record_target);
+ return run_results[3];
+ end
+
+ for _ = 1, 1000 do
+ local port = run();
+ results[port] = (results[port] or 0) + 1;
+ end
+
+ local ports = {};
+ for port in pairs(results) do
+ table.insert(ports, port);
+ end
+ table.sort(ports);
+ for _, port in ipairs(ports) do
+ --print("PORT", port, tostring((results[port]/1000) * 100).."% hits (expected "..tostring(port-5200).."%)");
+ local hit_pct = (results[port]/1000) * 100;
+ local expected_pct = port - 5200;
+ --print(hit_pct, expected_pct, math.abs(hit_pct - expected_pct));
+ assert.is_true(math.abs(hit_pct - expected_pct) < 5);
+ end
+ --print("---");
+ end
+ end);
+end);
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