fix(core/json): stably_encode fails to encode cjson.null values

apisix/core/json.lua

@@ -33,14 +33,54 @@ local cached_tab = {}
 
 cjson.encode_escape_forward_slash(false)
 cjson.decode_array_with_array_mt(true)
+
+
+local dkjson = require("dkjson")
+local dkjson_null = dkjson.null
+
+
+local function convert_cjson_null(data, seen)
+    if data == cjson_null then
+        return dkjson_null
+    end
+
+    if type(data) ~= "table" then
+        return data
+    end
+
+    seen = seen or {}
+    if seen[data] then
+        return data
+    end
+    seen[data] = true
+
+    local t = {}
+    for k, v in pairs(data) do
+        t[convert_cjson_null(k, seen)] = convert_cjson_null(v, seen)
+    end
+
+    return t
+end
+
+
+local function stably_encode(data)
+    if data == cjson_null then
+        data = dkjson_null
+    elseif type(data) == "table" then
+        data = convert_cjson_null(data)
+    end
+    return dkjson.encode(data)
+end
+
+
 local _M = {
     version = 0.1,
     array_mt = cjson.array_mt,
     null = cjson_null,
     -- This method produces the same encoded string when the input is not changed.
     -- Different calls with cjson.encode will produce different string because
     -- it doesn't maintain the object key order.
-    stably_encode = require("dkjson").encode
+    stably_encode = stably_encode
 }
 
 

t/core/json.t

@@ -193,3 +193,59 @@ b.d: 1
 e: text
 a or default: default
 top-level null: nil
+
+
+
+=== TEST 9: stably_encode with cjson.null
+--- config
+    location /t {
+        content_by_lua_block {
+            local core = require("apisix.core")
+            local data = {a = 1, b = core.json.null}
+            ngx.say(core.json.stably_encode(data))
+        }
+    }
+--- response_body
+{"a":1,"b":null}
+
+
+
+=== TEST 10: stably_encode with nested cjson.null
+--- config
+    location /t {
+        content_by_lua_block {
+            local core = require("apisix.core")
+            local data = {outer = {inner = core.json.null, val = "test"}}
+            ngx.say(core.json.stably_encode(data))
+        }
+    }
+--- response_body
+{"outer":{"inner":null,"val":"test"}}
+
+
+
+=== TEST 11: stably_encode stability with cjson.null
+--- config
+    location /t {
+        content_by_lua_block {
+            local core = require("apisix.core")
+            local data1 = {z = 1, a = core.json.null}
+            local data2 = {a = core.json.null, z = 1}
+            ngx.say(core.json.stably_encode(data1) == core.json.stably_encode(data2))
+        }
+    }
+--- response_body
+true
+
+
+
+=== TEST 12: stably_encode top-level cjson.null
+--- config
+    location /t {
+        content_by_lua_block {
+            local core = require("apisix.core")
+            ngx.say(core.json.stably_encode(core.json.null))
+        }
+    }
+--- response_body
+null