fix(response-transformer) preserve empty arrays

When a response contains an empty array and it gets transformed, the empty array should remain an empty array (and not get transformed into an empty cjson object).

Fixes #1208.

kong/plugins/response-transformer/body_transformer.lua

@@ -1,4 +1,4 @@
-local cjson = require "cjson.safe"
+local cjson = require("cjson.safe").new()
 
 
 local insert = table.insert
@@ -10,6 +10,9 @@ local match = string.match
 local lower = string.lower
 
 
+cjson.decode_array_with_array_mt(true)
+
+
 local noop = function() end
 
 

spec/03-plugins/15-response-transformer/02-body_transformer_spec.lua

@@ -1,5 +1,6 @@
 local body_transformer = require "kong.plugins.response-transformer.body_transformer"
-local cjson = require "cjson"
+local cjson = require("cjson.safe").new()
+cjson.decode_array_with_array_mt(true)
 
 describe("Plugin: response-transformer", function()
   describe("transform_json_body()", function()
@@ -30,6 +31,13 @@ describe("Plugin: response-transformer", function()
         local body_json = cjson.decode(body)
         assert.same({p1 = "v1", p2 = "v1", p3 = "value:3", p4 = '"v1"'}, body_json)
       end)
+      it("preserves empty arrays", function()
+        local json = [[{"p2":"v1", "a":[]}]]
+        local body = body_transformer.transform_json_body(conf, json)
+        local body_json = cjson.decode(body)
+        assert.same({p1 = "v1", p2 = "v1", p3 = "value:3", p4 = '"v1"', a = {}}, body_json)
+        assert.equals('[]', cjson.encode(body_json.a))
+      end)
     end)
 
     describe("append", function()
@@ -65,6 +73,13 @@ describe("Plugin: response-transformer", function()
         local body_json = cjson.decode(body)
         assert.same({p1 = {"v1"}, p3 = {"v2",'"v1"'}}, body_json)
       end)
+      it("preserves empty arrays", function()
+        local json = [[{"p2":"v1", "a":[]}]]
+        local body = body_transformer.transform_json_body(conf, json)
+        local body_json = cjson.decode(body)
+        assert.same({ p2 = "v1", p1 = {"v1"}, p3 = {'"v1"'}, a = {} }, body_json)
+        assert.equals('[]', cjson.encode(body_json.a))
+      end)
     end)
 
     describe("remove", function()
@@ -87,6 +102,13 @@ describe("Plugin: response-transformer", function()
         local body = body_transformer.transform_json_body(conf, json)
         assert.equals("{}", body)
       end)
+      it("preserves empty arrays", function()
+        local json = [[{"p1" : "v1", "p2" : "v1", "a": []}]]
+        local body = body_transformer.transform_json_body(conf, json)
+        local body_json = cjson.decode(body)
+        assert.same({a = {}}, body_json)
+        assert.equals('[]', cjson.encode(body_json.a))
+      end)
     end)
 
     describe("replace", function()
@@ -122,6 +144,13 @@ describe("Plugin: response-transformer", function()
         local body_json = cjson.decode(body)
         assert.same({p2 = '"v2"'}, body_json)
       end)
+      it("preserves empty arrays", function()
+        local json = [[{"p1" : "v1", "p2" : "v1", "a": []}]]
+        local body = body_transformer.transform_json_body(conf, json)
+        local body_json = cjson.decode(body)
+        assert.same({p1 = "v2", p2 = '"v2"', a = {}}, body_json)
+        assert.equals('[]', cjson.encode(body_json.a))
+      end)
     end)
 
     describe("remove, replace, add, append", function()
@@ -145,6 +174,13 @@ describe("Plugin: response-transformer", function()
         local body_json = cjson.decode(body)
         assert.same({p2 = "v2", p3 = {"v1", "v2"}}, body_json)
       end)
+      it("preserves empty array", function()
+        local json = [[{"p1" : "v1", "p2" : "v1", "a" : []}]]
+        local body = body_transformer.transform_json_body(conf, json)
+        local body_json = cjson.decode(body)
+        assert.same({p2 = "v2", p3 = {"v1", "v2"}, a = {}}, body_json)
+        assert.equals('[]', cjson.encode(body_json.a))
+      end)
     end)
   end)