make __len and __index behavior consistent for arrays

This allows encoding proxy arrays correctly (as in the included
test case), across all Lua versions.

lua_cjson.c

@@ -111,10 +111,6 @@
 #define json_lightudata_mask(ludata)    (ludata)
 #endif
 
-#if LUA_VERSION_NUM == 501
-#define lua_geti(L, t, i)	lua_rawgeti(L, (t), (i))
-#endif
-
 #if LUA_VERSION_NUM == 502
 #define lua_objlen(L,i)		lua_len(L, (i))
 #elif LUA_VERSION_NUM > 502
@@ -669,9 +665,9 @@ static int json_append_data(lua_State *l, json_config_t *cfg,
 /* json_append_array args:
  * - lua_State
  * - JSON strbuf
- * - Size of passwd Lua array (top of stack) */
+ * - Size of passed Lua array (top of stack) */
 static void json_append_array(lua_State *l, json_config_t *cfg, int current_depth,
-                              strbuf_t *json, int array_length)
+                              strbuf_t *json, int array_length, int raw)
 {
     int comma, i, json_pos, err;
 
@@ -683,7 +679,17 @@ static void json_append_array(lua_State *l, json_config_t *cfg, int current_dept
         if (comma++ > 0)
             strbuf_append_char(json, ',');
 
-        lua_geti(l, -1, i);
+        if (raw) {
+            lua_rawgeti(l, -1, i);
+        } else {
+#if LUA_VERSION_NUM == 501
+            lua_pushinteger(l, i);
+            lua_gettable(l, -2);
+#else
+            lua_geti(l, -1, i);
+#endif
+        }
+
         err = json_append_data(l, cfg, current_depth, json);
         if (err) {
             strbuf_set_length(json, json_pos);
@@ -798,6 +804,7 @@ static int json_append_data(lua_State *l, json_config_t *cfg,
     int len;
     int as_array = 0;
     int has_metatable;
+    int raw = 1;
 
     switch (lua_type(l, -1)) {
     case LUA_TSTRING:
@@ -823,22 +830,29 @@ static int json_append_data(lua_State *l, json_config_t *cfg,
             lua_rawget(l, LUA_REGISTRYINDEX);
             as_array = lua_rawequal(l, -1, -2);
             if (as_array) {
+                raw = 1;
                 lua_pop(l, 2);
+                len = lua_objlen(l, -1);
             } else {
-                lua_pop(l, 1);
-                as_array = (luaL_getmetafield(l, -1, "__len") != LUA_TNIL);
-                lua_pop(l, 1);
+                raw = 0;
+                lua_pop(l, 2);
+                if (luaL_getmetafield(l, -1, "__len")) {
+                    lua_pushvalue(l, -2);
+                    lua_call(l, 1, 1);
+                    len = lua_tonumber(l, -1);
+                    lua_pop(l, 1);
+                    as_array = 1;
+                }
             }
         }
 
         if (as_array) {
-            len = lua_objlen(l, -1);
-            json_append_array(l, cfg, current_depth, json, len);
+            json_append_array(l, cfg, current_depth, json, len, raw);
         } else {
             len = lua_array_length(l, cfg, json);
 
             if (len > 0 || (len == 0 && !cfg->encode_empty_table_as_object)) {
-                json_append_array(l, cfg, current_depth, json, len);
+                json_append_array(l, cfg, current_depth, json, len, raw);
             } else {
                 if (has_metatable) {
                     lua_getmetatable(l, -1);
@@ -848,7 +862,9 @@ static int json_append_data(lua_State *l, json_config_t *cfg,
                     as_array = lua_rawequal(l, -1, -2);
                     lua_pop(l, 2); /* pop pointer + metatable */
                     if (as_array) {
-                        json_append_array(l, cfg, current_depth, json, 0);
+                        len = lua_objlen(l, -1);
+                        raw = 1;
+                        json_append_array(l, cfg, current_depth, json, len, raw);
                         break;
                     }
                 }
@@ -863,7 +879,7 @@ static int json_append_data(lua_State *l, json_config_t *cfg,
         if (lua_touserdata(l, -1) == NULL) {
             strbuf_append_mem(json, "null", 4);
         } else if (lua_touserdata(l, -1) == json_lightudata_mask(&json_array)) {
-            json_append_array(l, cfg, current_depth, json, 0);
+            json_append_array(l, cfg, current_depth, json, 0, 1);
         }
         break;
     default:

tests/agentzh.t

@@ -332,3 +332,21 @@ Cannot serialise function: type not supported
 
 {"valid":"valid"}
 ["one","two","three"]
+
+
+
+=== TEST 23: array-like proxy object with __len and __index
+--- lua
+local cjson = require "cjson"
+local real_array = {"foo", "bar", "baz"}
+local proxy_array = {}
+setmetatable(proxy_array, {
+  __len = function() return 3 end,
+  __index = function(t, k)
+    return real_array[k]
+  end,
+})
+
+print(cjson.encode(proxy_array))
+--- out
+["foo","bar","baz"]