Add depth/index to decode depth error message

Include depth and character index when throwing decode nesting errors.

Pre-emptively add a test decoding a massively nested JSON array. Lua
stack overflow faults are unlikely to occur on simple data structures.
Valgrind can highlight stack allocation bugs with complicated JSON even
if the test succeeds.

2 files changed, 8 insertions, 4 deletions

diff --git a/lua_cjson.c b/lua_cjson.c
index 4a2ce0f..b64ed62 100644
--- a/lua_cjson.c
+++ b/lua_cjson.c
@@ -1034,7 +1034,7 @@ static void json_next_number_token(json_parse_t *json, json_token_t *token)
  */
 static void json_next_token(json_parse_t *json, json_token_t *token)
 {
-    json_token_type_t *ch2token = json->cfg->ch2token;
+    const json_token_type_t *ch2token = json->cfg->ch2token;
     int ch;
 
     /* Eat whitespace. */
@@ -1149,7 +1149,8 @@ static void json_decode_descend(lua_State *l, json_parse_t *json, int slots)
     }
 
     strbuf_free(json->tmp);
-    luaL_error(l, "Too many nested data structures");
+    luaL_error(l, "Found too many nested data structures (%d) at character %d",
+        json->current_depth, json->ptr - json->data);
 }
 
 static void json_parse_object_context(lua_State *l, json_parse_t *json)
diff --git a/tests/test.lua b/tests/test.lua
index 4c00453..8bb5b95 100755
--- a/tests/test.lua
+++ b/tests/test.lua
@@ -162,15 +162,18 @@ local cjson_tests = {
       true, { {{{{{ "nested" }}}}} } },
     { "Decode array over nested limit [throw error]",
       json.decode, { '[[[[[[ "nested" ]]]]]]' },
-      false, { "Too many nested data structures" } },
+      false, { "Found too many nested data structures (6) at character 6" } },
     { "Decode object at nested limit",
       json.decode, { '{"a":{"b":{"c":{"d":{"e":"nested"}}}}}' },
       true, { {a={b={c={d={e="nested"}}}}} } },
     { "Decode object over nested limit [throw error]",
       json.decode, { '{"a":{"b":{"c":{"d":{"e":{"f":"nested"}}}}}}' },
-      false, { "Too many nested data structures" } },
+      false, { "Found too many nested data structures (6) at character 26" } },
     { "Set decode_max_depth(1000)",
       json.decode_max_depth, { 1000 }, true, { 1000 } },
+    { "Decode deeply nested array [throw error]",
+      json.decode, { string.rep("[", 1100) .. '1100' .. string.rep("]", 1100)},
+      false, { "Found too many nested data structures (1001) at character 1001" } },
 
     -- Test encoding nested tables
     { "Set encode_max_depth(5)",