add support for ExternalName service type in dynamic mode

rootfs/etc/nginx/lua/test/util/dns_test.lua

@@ -0,0 +1,74 @@
+describe("resolve", function()
+  local dns = require("util.dns")
+  local dns_helper = require("test/dns_helper")
+
+  it("sets correct nameservers", function()
+    dns_helper.mock_new(function(self, options)
+      assert.are.same({ nameservers = { "1.2.3.4", "4.5.6.7" }, retrans = 5, timeout = 2000 }, options)
+      return nil, ""
+    end, { "1.2.3.4", "4.5.6.7" })
+    dns.resolve("example.com")
+  end)
+
+  it("returns host when an error happens", function()
+    local s_ngx_log = spy.on(ngx, "log")
+
+    dns_helper.mock_new(function(...) return nil, "an error" end)
+    assert.are.same({ "example.com" }, dns.resolve("example.com"))
+    assert.spy(s_ngx_log).was_called_with(ngx.ERR, "failed to instantiate the resolver: an error")
+
+    dns_helper.mock_dns_query(nil, "oops!")
+    assert.are.same({ "example.com" }, dns.resolve("example.com"))
+    assert.spy(s_ngx_log).was_called_with(ngx.ERR, "failed to query the DNS server: oops!")
+
+    dns_helper.mock_dns_query({ errcode = 1, errstr = "format error" })
+    assert.are.same({ "example.com" }, dns.resolve("example.com"))
+    assert.spy(s_ngx_log).was_called_with(ngx.ERR, "server returned error code: 1: format error")
+
+    dns_helper.mock_dns_query({})
+    assert.are.same({ "example.com" }, dns.resolve("example.com"))
+    assert.spy(s_ngx_log).was_called_with(ngx.ERR, "no A record resolved")
+
+    dns_helper.mock_dns_query({ { name = "example.com", cname = "sub.example.com", ttl = 60 } })
+    assert.are.same({ "example.com" }, dns.resolve("example.com"))
+    assert.spy(s_ngx_log).was_called_with(ngx.ERR, "no A record resolved")
+  end)
+
+  it("resolves all A records of given host, caches them with minimal ttl and returns from cache next time", function()
+    dns_helper.mock_dns_query({
+      {
+        name = "example.com",
+        address = "192.168.1.1",
+        ttl = 3600,
+      },
+      {
+        name = "example.com",
+        address = "1.2.3.4",
+        ttl = 60,
+      }
+    })
+
+    local lrucache = require("resty.lrucache")
+    local old_lrucache_new = lrucache.new
+    lrucache.new = function(...)
+      local cache = old_lrucache_new(...)
+
+      local old_set = cache.set
+      cache.set = function(self, key, value, ttl)
+        assert.equal("example.com", key)
+        assert.are.same({ "192.168.1.1", "1.2.3.4" }, value)
+        assert.equal(60, ttl)
+        return old_set(self, key, value, ttl)
+      end
+
+      return cache
+    end
+
+    assert.are.same({ "192.168.1.1", "1.2.3.4" }, dns.resolve("example.com"))
+
+    dns_helper.mock_new(function(...)
+      error("expected to short-circuit and return response from cache")
+    end)
+    assert.are.same({ "192.168.1.1", "1.2.3.4" }, dns.resolve("example.com"))
+  end)
+end)