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Backport empty array handling #2

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Backport empty array handling #2

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ef27691
Backport empty array handling
rzanol Sep 21, 2023
3c6fa1a
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rzanol Sep 21, 2023
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120 changes: 116 additions & 4 deletions lua_cjson.c
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Original file line number Diff line number Diff line change
Expand Up @@ -74,12 +74,19 @@
#define DEFAULT_DECODE_INVALID_NUMBERS 1
#define DEFAULT_ENCODE_KEEP_BUFFER 0
#define DEFAULT_ENCODE_NUMBER_PRECISION 14
#define DEFAULT_ENCODE_EMPTY_TABLE_AS_OBJECT 1
#define DEFAULT_DECODE_ARRAY_WITH_ARRAY_MT 0

#ifdef DISABLE_INVALID_NUMBERS
#undef DEFAULT_DECODE_INVALID_NUMBERS
#define DEFAULT_DECODE_INVALID_NUMBERS 0
#endif

// Unique key to index the empty array MT into the Lua registry
static char json_empty_array;
// Unique key to index an empty array into the Lua registry
static char json_array;

typedef enum {
T_OBJ_BEGIN,
T_OBJ_END,
Expand Down Expand Up @@ -130,9 +137,11 @@ typedef struct {
int encode_invalid_numbers; /* 2 => Encode as "null" */
int encode_number_precision;
int encode_keep_buffer;
int encode_empty_table_as_object;

int decode_invalid_numbers;
int decode_max_depth;
int decode_array_with_array_mt;
} json_config_t;

typedef struct {
Expand Down Expand Up @@ -306,6 +315,22 @@ static int json_cfg_encode_number_precision(lua_State *l)
return json_integer_option(l, 1, &cfg->encode_number_precision, 1, 14);
}

/* Configures how to treat an empty Lua table when encoding */
static int json_cfg_encode_empty_table_as_object(lua_State *l)
{
json_config_t *cfg = json_arg_init(l, 1);

return json_enum_option(l, 1, &cfg->encode_empty_table_as_object, NULL, 1);
}

/* Configures how to decode arrays */
static int json_cfg_decode_array_with_array_mt(lua_State *l)
{
json_config_t *cfg = json_arg_init(l, 1);

return json_enum_option(l, 1, &cfg->decode_array_with_array_mt, NULL, 1);
}

/* Configures JSON encoding buffer persistence */
static int json_cfg_encode_keep_buffer(lua_State *l)
{
Expand Down Expand Up @@ -396,6 +421,8 @@ static void json_create_config(lua_State *l)
cfg->decode_invalid_numbers = DEFAULT_DECODE_INVALID_NUMBERS;
cfg->encode_keep_buffer = DEFAULT_ENCODE_KEEP_BUFFER;
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;

#if DEFAULT_ENCODE_KEEP_BUFFER > 0
strbuf_init(&cfg->encode_buf, 0);
Expand Down Expand Up @@ -673,6 +700,8 @@ static void json_append_data(lua_State *l, json_config_t *cfg,
int current_depth, strbuf_t *json)
{
int len;
int as_array = 0;
int has_metatable;

switch (lua_type(l, -1)) {
case LUA_TSTRING:
Expand All @@ -690,20 +719,57 @@ static void json_append_data(lua_State *l, json_config_t *cfg,
case LUA_TTABLE:
current_depth++;
json_check_encode_depth(l, cfg, current_depth, json);

has_metatable = lua_getmetatable(l, -1);

if (has_metatable) {
// Check if the MT is the array MT
lua_pushlightuserdata(l, (void *)&json_array);
lua_rawget(l, LUA_REGISTRYINDEX);
as_array = lua_rawequal(l, -1, -2);
lua_pop(l, 2);
}

if (as_array) {
len = lua_rawlen(l, -1);
json_append_array(l, cfg, current_depth, json, len);
break;
}

len = lua_array_length(l, cfg, json);
if (len > 0)

if (len > 0 || (len == 0 && !cfg->encode_empty_table_as_object)) {
json_append_array(l, cfg, current_depth, json, len);
else
json_append_object(l, cfg, current_depth, json);
break;
}

if (has_metatable) {
// Check if the MT is the empty array
lua_getmetatable(l, -1);
lua_pushlightuserdata(l, (void *)&json_empty_array);
lua_rawget(l, LUA_REGISTRYINDEX);
as_array = lua_rawequal(l, -1, -2);
lua_pop(l, 2);

if (as_array) {
json_append_array(l, cfg, current_depth, json, 0);
break;
}
}

json_append_object(l, cfg, current_depth, json);
break;
case LUA_TNIL:
strbuf_append_mem(json, "null", 4);
break;
case LUA_TLIGHTUSERDATA:
if (lua_touserdata(l, -1) == NULL) {
strbuf_append_mem(json, "null", 4);
break;
} else if (lua_touserdata(l, -1) == (void *)&json_array) {
// encode `cjson.empty_array` as an empty array
json_append_array(l, cfg, current_depth, json, 0);
}
break;
default:
/* Remaining types (LUA_TFUNCTION, LUA_TUSERDATA, LUA_TTHREAD,
* and LUA_TLIGHTUSERDATA) cannot be serialised */
Expand Down Expand Up @@ -1206,6 +1272,13 @@ static void json_parse_array_context(lua_State *l, json_parse_t *json)

lua_newtable(l);

/* set array_mt on the table at the top of the stack */
if (json->cfg->decode_array_with_array_mt) {
lua_pushlightuserdata(l, (void *)&json_array);
lua_rawget(l, LUA_REGISTRYINDEX);
lua_setmetatable(l, -2);
}

json_next_token(json, &token);

/* Handle empty arrays */
Expand Down Expand Up @@ -1358,6 +1431,8 @@ static int lua_cjson_new(lua_State *l)
luaL_Reg reg[] = {
{ "encode", json_encode },
{ "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 },
{ "encode_sparse_array", json_cfg_encode_sparse_array },
{ "encode_max_depth", json_cfg_encode_max_depth },
{ "decode_max_depth", json_cfg_decode_max_depth },
Expand All @@ -1372,6 +1447,29 @@ static int lua_cjson_new(lua_State *l)
/* Initialise number conversions */
fpconv_init();

/* Test if array metatables are in registry */
lua_pushlightuserdata(l, (void *)&json_empty_array);
lua_rawget(l, LUA_REGISTRYINDEX);
if (lua_isnil(l, -1)) {
/* Create array metatables.
*
* If multiple calls to lua_cjson_new() are made,
* this prevents overriding the tables at the given
* registry's index with a new one.
*/
lua_pop(l, 1);

/* empty_array_mt */
lua_pushlightuserdata(l, (void *)&json_empty_array);
lua_newtable(l);
lua_rawset(l, LUA_REGISTRYINDEX);

/* array_mt */
lua_pushlightuserdata(l, (void *)&json_array);
lua_newtable(l);
lua_rawset(l, LUA_REGISTRYINDEX);
}

/* cjson module table */
lua_newtable(l);

Expand All @@ -1383,6 +1481,20 @@ static int lua_cjson_new(lua_State *l)
lua_pushlightuserdata(l, NULL);
lua_setfield(l, -2, "null");

/* Set cjson.empty_array_mt */
lua_pushlightuserdata(l, (void *)&json_empty_array);
lua_rawget(l, LUA_REGISTRYINDEX);
lua_setfield(l, -2, "empty_array_mt");

/* Set cjson.array_mt */
lua_pushlightuserdata(l, (void *)&json_array);
lua_rawget(l, LUA_REGISTRYINDEX);
lua_setfield(l, -2, "array_mt");

/* Set cjson.empty_array */
lua_pushlightuserdata(l, (void *)&json_array);
lua_setfield(l, -2, "empty_array");

/* Set module name / version fields */
lua_pushliteral(l, CJSON_MODNAME);
lua_setfield(l, -2, "_NAME");
Expand Down