Add decode option to ignore JSON null values

README.md

@@ -15,6 +15,7 @@ Table of Contents
     * [empty_array_mt](#empty_array_mt)
     * [encode_number_precision](#encode_number_precision)
     * [decode_array_with_array_mt](#decode_array_with_array_mt)
+    * [decode_json_null](#decode_json_null)
 
 Description
 ===========
@@ -193,3 +194,13 @@ cjson.encode(t) -- {"my_array":[]} properly re-encoded as an array
 ```
 
 [Back to TOC](#table-of-contents)
+
+decode_json_null
+-----------------------
+**syntax:** `cjson.decode_json_null(enabled)`
+
+**default:** true
+
+If disabled, JSON null values will be decoded to Lua `nil` (removed from table) instead of the default `cjson.null` lightuserdata value.
+
+[Back to TOC](#table-of-contents)

lua_cjson.c

@@ -81,6 +81,7 @@
 #define DEFAULT_ENCODE_NUMBER_PRECISION 14
 #define DEFAULT_ENCODE_EMPTY_TABLE_AS_OBJECT 1
 #define DEFAULT_DECODE_ARRAY_WITH_ARRAY_MT 0
+#define DEFAULT_DECODE_JSON_NULL 1
 
 #ifdef DISABLE_INVALID_NUMBERS
 #undef DEFAULT_DECODE_INVALID_NUMBERS
@@ -159,6 +160,7 @@ typedef struct {
     int decode_invalid_numbers;
     int decode_max_depth;
     int decode_array_with_array_mt;
+    int decode_json_null;
 } json_config_t;
 
 typedef struct {
@@ -350,6 +352,16 @@ static int json_cfg_decode_array_with_array_mt(lua_State *l)
     return 1;
 }
 
+/* Configures how to decode json null */
+static int json_cfg_decode_json_null(lua_State *l)
+{
+    json_config_t *cfg = json_arg_init(l, 1);
+
+    json_enum_option(l, 1, &cfg->decode_json_null, NULL, 1);
+
+    return 1;
+}
+
 /* Configures JSON encoding buffer persistence */
 static int json_cfg_encode_keep_buffer(lua_State *l)
 {
@@ -442,6 +454,7 @@ static void json_create_config(lua_State *l)
     cfg->encode_number_precision = DEFAULT_ENCODE_NUMBER_PRECISION;
     cfg->encode_empty_table_as_object = DEFAULT_ENCODE_EMPTY_TABLE_AS_OBJECT;
     cfg->decode_array_with_array_mt = DEFAULT_DECODE_ARRAY_WITH_ARRAY_MT;
+    cfg->decode_json_null = DEFAULT_DECODE_JSON_NULL;
 
 #if DEFAULT_ENCODE_KEEP_BUFFER > 0
     strbuf_init(&cfg->encode_buf, 0);
@@ -1341,7 +1354,10 @@ static void json_process_value(lua_State *l, json_parse_t *json,
     case T_NULL:
         /* In Lua, setting "t[k] = nil" will delete k from the table.
          * Hence a NULL pointer lightuserdata object is used instead */
-        lua_pushlightuserdata(l, NULL);
+        if (json->cfg->decode_json_null)
+            lua_pushlightuserdata(l, NULL);
+        else
+            lua_pushnil(l);
         break;;
     default:
         json_throw_parse_error(l, json, "value", token);
@@ -1450,6 +1466,7 @@ static int lua_cjson_new(lua_State *l)
         { "decode", json_decode },
         { "encode_empty_table_as_object", json_cfg_encode_empty_table_as_object },
         { "decode_array_with_array_mt", json_cfg_decode_array_with_array_mt },
+        { "decode_json_null", json_cfg_decode_json_null },
         { "encode_sparse_array", json_cfg_encode_sparse_array },
         { "encode_max_depth", json_cfg_encode_max_depth },
         { "decode_max_depth", json_cfg_decode_max_depth },

tests/agentzh.t

@@ -284,3 +284,19 @@ print(string.format("%16.0f", cjson.decode("9007199254740992")))
 9.007199254741e+15
 9007199254740992
 9007199254740992
+
+
+
+=== TEST 21: optional json null
+--- lua
+local cjson = require "cjson"
+local json = [[{"val1":"str","val2":null,"val3":{"val1":null,"val2":"str"}}]]
+print(cjson.encode(cjson.decode(json)))
+cjson.decode_json_null(false)
+print(cjson.encode(cjson.decode(json)))
+cjson.decode_json_null(true)
+print(cjson.encode(cjson.decode(json)))
+--- out
+{"val3":{"val2":"str","val1":null},"val1":"str","val2":null}
+{"val3":{"val2":"str"},"val1":"str"}
+{"val3":{"val2":"str","val1":null},"val1":"str","val2":null}