5 files changed, 92 insertions, 1 deletions

diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index abfb8f94b..135e2cfcd 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -1530,7 +1530,16 @@ minetest.parse_json(string[, nullvalue]) -> something
 ^ nullvalue: returned in place of the JSON null; defaults to nil
 ^ On success returns a table, a string, a number, a boolean or nullvalue
 ^ On failure outputs an error message and returns nil
-^ Example: parse_json("[10, {\"a\":false}]") -> {[1] = 10, [2] = {a = false}}
+^ Example: parse_json("[10, {\"a\":false}]") -> {10, {a = false}}
+minetest.write_json(data[, styled]) -> string
+^ Convert a Lua table into a JSON string
+^ styled: Outputs in a human-readable format if this is set, defaults to false
+^ Un-serializable things like functions and userdata are saved as null.
+^ Warning: JSON is more strict than the Lua table format.
+    1. You can only use strings and positive integers of at least one as keys.
+    2. You can not mix string and integer keys.
+    This is due to the fact that Javascript has two distinct array and object values.
+^ Example: write_json({10, {a = false}}) -> "[10, {\"a\": false}]"
 minetest.serialize(table) -> string
 ^ Convert a table containing tables, strings, numbers, booleans and nils
   into string form readable by minetest.deserialize
diff --git a/src/script/common/c_content.cpp b/src/script/common/c_content.cpp
index cf9f28d30..8eb57ba41 100644
--- a/src/script/common/c_content.cpp
+++ b/src/script/common/c_content.cpp
@@ -1081,3 +1081,52 @@ bool push_json_value(lua_State *L, const Json::Value &value, int nullindex)
 	else
 		return false;
 }
+
+// Converts Lua table --> JSON
+void get_json_value(lua_State *L, Json::Value &root, int index)
+{
+	int type = lua_type(L, index);
+	if (type == LUA_TBOOLEAN) {
+		root = (bool) lua_toboolean(L, index);
+	} else if (type == LUA_TNUMBER) {
+		root = lua_tonumber(L, index);
+	} else if (type == LUA_TSTRING) {
+		size_t len;
+		const char *str = lua_tolstring(L, index, &len);
+		root = std::string(str, len);
+	} else if (type == LUA_TTABLE) {
+		lua_pushnil(L);
+		while (lua_next(L, index)) {
+			// Key is at -2 and value is at -1
+			Json::Value value;
+			get_json_value(L, value, lua_gettop(L));
+
+			Json::ValueType roottype = root.type();
+			int keytype = lua_type(L, -1);
+			if (keytype == LUA_TNUMBER) {
+				lua_Number key = lua_tonumber(L, -1);
+				if (roottype != Json::nullValue && roottype != Json::arrayValue) {
+					throw LuaError(NULL, "Can't mix array and object values in JSON");
+				} else if (key < 1) {
+					throw LuaError(NULL, "Can't use zero-based or negative indexes in JSON");
+				} else if (floor(key) != key) {
+					throw LuaError(NULL, "Can't use indexes with a fractional part in JSON");
+				}
+				root[(Json::ArrayIndex) key - 1] = value;
+			} else if (keytype == LUA_TSTRING) {
+				if (roottype != Json::nullValue && roottype != Json::objectValue) {
+					throw LuaError(NULL, "Can't mix array and object values in JSON");
+				}
+				root[lua_tostring(L, -1)] = value;
+			} else {
+				throw LuaError(NULL, "Lua key to convert to JSON is not a string or number");
+			}
+		}
+	} else if (type == LUA_TNIL) {
+		root = Json::nullValue;
+	} else {
+		throw LuaError(NULL, "Can only store booleans, numbers, strings, objects, arrays, and null in JSON");
+	}
+	lua_pop(L, 1); // Pop value
+}
+
diff --git a/src/script/common/c_content.h b/src/script/common/c_content.h
index 27019e29e..3b85e5403 100644
--- a/src/script/common/c_content.h
+++ b/src/script/common/c_content.h
@@ -150,6 +150,9 @@ void               luaentity_get             (lua_State *L,u16 id);
 bool               push_json_value           (lua_State *L,
                                               const Json::Value &value,
                                               int nullindex);
+void               get_json_value            (lua_State *L,
+                                              Json::Value &root,
+                                              int index);
 
 extern struct EnumString es_TileAnimationType[];
 
diff --git a/src/script/lua_api/l_util.cpp b/src/script/lua_api/l_util.cpp
index fe10e4f57..9fa6fcb77 100644
--- a/src/script/lua_api/l_util.cpp
+++ b/src/script/lua_api/l_util.cpp
@@ -179,6 +179,32 @@ int ModApiUtil::l_parse_json(lua_State *L)
 	return 1;
 }
 
+// write_json(data[, styled]) -> string
+int ModApiUtil::l_write_json(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+
+	bool styled = false;
+	if (!lua_isnone(L, 2)) {
+		styled = lua_toboolean(L, 2);
+		lua_pop(L, 1);
+	}
+
+	Json::Value root;
+	get_json_value(L, root, 1);
+
+	std::string out;
+	if (styled) {
+		Json::StyledWriter writer;
+		out = writer.write(root);
+	} else {
+		Json::FastWriter writer;
+		out = writer.write(root);
+	}
+	lua_pushlstring(L, out.c_str(), out.size());
+	return 1;
+}
+
 // get_dig_params(groups, tool_capabilities[, time_from_last_punch])
 int ModApiUtil::l_get_dig_params(lua_State *L)
 {
@@ -249,6 +275,7 @@ void ModApiUtil::Initialize(lua_State *L, int top)
 	API_FCT(setting_save);
 
 	API_FCT(parse_json);
+	API_FCT(write_json);
 
 	API_FCT(get_dig_params);
 	API_FCT(get_hit_params);
diff --git a/src/script/lua_api/l_util.h b/src/script/lua_api/l_util.h
index d91c880cf..13357587a 100644
--- a/src/script/lua_api/l_util.h
+++ b/src/script/lua_api/l_util.h
@@ -64,6 +64,9 @@ private:
 	// parse_json(str[, nullvalue])
 	static int l_parse_json(lua_State *L);
 
+	// write_json(data[, styled])
+	static int l_write_json(lua_State *L);
+
 	// get_dig_params(groups, tool_capabilities[, time_from_last_punch])
 	static int l_get_dig_params(lua_State *L);