fix(declarative-config): empty hash for default config

ensure the default (empty) config returns the appropriate hash that
identifies the empty configuration: 00000000000000000000000000000000

kong/db/declarative/init.lua

@@ -660,6 +660,11 @@ end
 declarative.unique_field_key = unique_field_key
 
 
+local function config_is_empty(entities)
+  -- empty configuration has no entries other than workspaces
+  return entities["workspaces"] and tablex.size(entities) == 1
+end
+
 
 -- entities format:
 --   {
@@ -687,7 +692,7 @@ function declarative.load_into_cache(entities, meta, hash)
 
   assert(type(fallback_workspace) == "string")
 
-  if not hash or hash == "" then
+  if not hash or hash == "" or config_is_empty(entities) then
     hash = DECLARATIVE_EMPTY_CONFIG_HASH
   end
 

spec/02-integration/02-cmd/02-start_stop_spec.lua

@@ -474,7 +474,7 @@ describe("kong start/stop #" .. strategy, function()
         end, 10)
       end)
 
-      it("configuration hash is set correctly", function()
+      it("hash is set correctly for a non-empty configuration", function()
         local yaml_file = helpers.make_yaml_file [[
           _format_version: "1.1"
           services:
@@ -531,6 +531,52 @@ describe("kong start/stop #" .. strategy, function()
         assert.equals(32, #json_body.configuration_hash)
         assert.not_equal(constants.DECLARATIVE_EMPTY_CONFIG_HASH, json_body.configuration_hash)
       end)
+
+      it("hash is set correctly for an empty configuration", function()
+
+        local admin_client, json_body
+
+        finally(function()
+          helpers.stop_kong(helpers.test_conf.prefix)
+          if admin_client then
+            admin_client:close()
+          end
+        end)
+
+        -- not specifying declarative_config this time
+        assert(helpers.start_kong({
+          database = "off",
+          nginx_conf = "spec/fixtures/custom_nginx.template",
+        }))
+
+        helpers.wait_until(function()
+          helpers.wait_until(function()
+            local pok
+            pok, admin_client = pcall(helpers.admin_client)
+            return pok
+          end, 10)
+
+          local res = assert(admin_client:send {
+            method = "GET",
+            path = "/status"
+          })
+          if res.status ~= 200 then
+            return false
+          end
+          local body = assert.res_status(200, res)
+          json_body = cjson.decode(body)
+
+          if admin_client then
+            admin_client:close()
+            admin_client = nil
+          end
+
+          return true
+        end, 10)
+
+        assert.is_string(json_body.configuration_hash)
+        assert.equals(constants.DECLARATIVE_EMPTY_CONFIG_HASH, json_body.configuration_hash)
+      end)
     end)
   end
 

spec/02-integration/04-admin_api/02-kong_routes_spec.lua

@@ -211,9 +211,7 @@ describe("Admin API - Kong routes with strategy #" .. strategy, function()
       assert.is_number(json.server.connections_waiting)
       assert.is_number(json.server.total_requests)
       if strategy == "off" then
-        assert.is_string(json.configuration_hash)
-        assert.equal(32, #json.configuration_hash)
-        assert.is_not_equal(empty_config_hash, json.configuration_hash)
+        assert.is_equal(empty_config_hash, json.configuration_hash) -- all 0 in DBLESS mode until configuration is applied
       else
         assert.is_nil(json.configuration_hash) -- not present in DB mode
       end