Introduce std::string_view into wider use (#14368)

src/script/common/c_content.cpp

@@ -1664,7 +1664,7 @@ Pointabilities read_pointabilities(lua_State *L, int index)
 			std::string name = luaL_checkstring(L, -2);
 
 			// handle groups
-			if(std::string_view(name).substr(0,6)=="group:") {
+			if (str_starts_with(name, "group:")) {
 				pointabilities.node_groups[name.substr(6)] = read_pointability_type(L, -1);
 			} else {
 				pointabilities.nodes[name] = read_pointability_type(L, -1);
@@ -1685,7 +1685,7 @@ Pointabilities read_pointabilities(lua_State *L, int index)
 			std::string name = luaL_checkstring(L, -2);
 
 			// handle groups
-			if(std::string_view(name).substr(0,6)=="group:") {
+			if (str_starts_with(name, "group:")) {
 				pointabilities.object_groups[name.substr(6)] = read_pointability_type(L, -1);
 			} else {
 				pointabilities.objects[name] = read_pointability_type(L, -1);

src/script/common/helper.cpp

@@ -25,6 +25,7 @@ extern "C" {
 #include <cmath>
 #include <irr_v2d.h>
 #include <irr_v3d.h>
+#include <string_view>
 #include "c_converter.h"
 #include "c_types.h"
 
@@ -78,11 +79,16 @@ v3f LuaHelper::readParam(lua_State *L, int index)
 }
 
 template <>
-std::string LuaHelper::readParam(lua_State *L, int index)
+std::string_view LuaHelper::readParam(lua_State *L, int index)
 {
 	size_t length;
-	std::string result;
 	const char *str = luaL_checklstring(L, index, &length);
-	result.assign(str, length);
-	return result;
+	return std::string_view(str, length);
+}
+
+template <>
+std::string LuaHelper::readParam(lua_State *L, int index)
+{
+	auto sv = readParam<std::string_view>(L, index);
+	return std::string(sv); // a copy
 }

src/script/common/helper.h

@@ -19,6 +19,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #pragma once
 
+#include <string_view>
+
 extern "C" {
 #include <lua.h>
 }
@@ -27,23 +29,22 @@ class LuaHelper
 {
 protected:
 	/**
-	 * Read a value using a template type T from Lua State L and index
-	 *
+	 * Read a value using a template type T from Lua state L at index
 	 *
 	 * @tparam T type to read from Lua
 	 * @param L Lua state
-	 * @param index Lua Index to read
+	 * @param index Lua index to read
 	 * @return read value from Lua
 	 */
 	template <typename T>
 	static T readParam(lua_State *L, int index);
 
 	/**
-	 * Read a value using a template type T from Lua State L and index
+	 * Read a value using a template type T from Lua state L at index
 	 *
 	 * @tparam T type to read from Lua
 	 * @param L Lua state
-	 * @param index Lua Index to read
+	 * @param index Lua index to read
 	 * @param default_value default value to apply if nil
 	 * @return read value from Lua or default value if nil
 	 */
@@ -53,3 +54,18 @@ protected:
 		return lua_isnoneornil(L, index) ? default_value : readParam<T>(L, index);
 	}
 };
+
+// (only declared for documentation purposes:)
+
+/**
+ * Read a string from Lua state L at index without copying it.
+ *
+ * Note that the returned string view is only valid as long as the value is on
+ * the stack and has not been modified. Be careful.
+ *
+ * @param L Lua state
+ * @param index Lua index to read
+ * @return string view
+ */
+template <>
+std::string_view LuaHelper::readParam(lua_State *L, int index);

src/script/lua_api/l_item.cpp

@@ -163,6 +163,9 @@ int LuaItemStack::l_get_metadata(lua_State *L)
 	NO_MAP_LOCK_REQUIRED;
 	LuaItemStack *o = checkObject<LuaItemStack>(L, 1);
 	ItemStack &item = o->m_stack;
+
+	log_deprecated(L, "ItemStack:get_metadata is deprecated", 1, true);
+
 	const std::string &value = item.metadata.getString("");
 	lua_pushlstring(L, value.c_str(), value.size());
 	return 1;
@@ -176,6 +179,8 @@ int LuaItemStack::l_set_metadata(lua_State *L)
 	LuaItemStack *o = checkObject<LuaItemStack>(L, 1);
 	ItemStack &item = o->m_stack;
 
+	log_deprecated(L, "ItemStack:set_metadata is deprecated", 1, true);
+
 	size_t len = 0;
 	const char *ptr = luaL_checklstring(L, 2, &len);
 	item.metadata.setString("", std::string(ptr, len));

src/script/lua_api/l_metadata.cpp

@@ -115,9 +115,7 @@ int MetaDataRef::l_set_string(lua_State *L)
 
 	MetaDataRef *ref = checkAnyMetadata(L, 1);
 	std::string name = luaL_checkstring(L, 2);
-	size_t len = 0;
-	const char *s = lua_tolstring(L, 3, &len);
-	std::string str(s, len);
+	auto str = readParam<std::string_view>(L, 3);
 
 	IMetadata *meta = ref->getmeta(!str.empty());
 	if (meta != NULL && meta->setString(name, str))
@@ -300,9 +298,8 @@ bool MetaDataRef::handleFromTable(lua_State *L, int table, IMetadata *meta)
 		while (lua_next(L, fieldstable) != 0) {
 			// key at index -2 and value at index -1
 			std::string name = readParam<std::string>(L, -2);
-			size_t cl;
-			const char *cs = lua_tolstring(L, -1, &cl);
-			meta->setString(name, std::string(cs, cl));
+			auto value = readParam<std::string_view>(L, -1);
+			meta->setString(name, value);
 			lua_pop(L, 1); // Remove value, keep key for next iteration
 		}
 		lua_pop(L, 1);

src/script/lua_api/l_util.cpp

@@ -318,8 +318,7 @@ int ModApiUtil::l_compress(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
 
-	size_t size;
-	const char *data = luaL_checklstring(L, 1, &size);
+	auto data = readParam<std::string_view>(L, 1);
 
 	LuaCompressMethod method = get_compress_method(L, 2);
 
@@ -330,13 +329,13 @@ int ModApiUtil::l_compress(lua_State *L)
 		if (!lua_isnoneornil(L, 3))
 			level = readParam<int>(L, 3);
 
-		compressZlib(reinterpret_cast<const u8 *>(data), size, os, level);
+		compressZlib(data, os, level);
 	} else if (method == LUA_COMPRESS_METHOD_ZSTD) {
 		int level = ZSTD_CLEVEL_DEFAULT;
 		if (!lua_isnoneornil(L, 3))
 			level = readParam<int>(L, 3);
 
-		compressZstd(reinterpret_cast<const u8 *>(data), size, os, level);
+		compressZstd(data, os, level);
 	}
 
 	std::string out = os.str();
@@ -350,12 +349,12 @@ int ModApiUtil::l_decompress(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
 
-	size_t size;
-	const char *data = luaL_checklstring(L, 1, &size);
+	auto data = readParam<std::string_view>(L, 1);
 
 	LuaCompressMethod method = get_compress_method(L, 2);
 
-	std::istringstream is(std::string(data, size), std::ios_base::binary);
+	// FIXME: zero copy possible in c++26 or with custom rdbuf
+	std::istringstream is(std::string(data), std::ios_base::binary);
 	std::ostringstream os(std::ios_base::binary);
 
 	if (method == LUA_COMPRESS_METHOD_DEFLATE) {
@@ -375,10 +374,9 @@ int ModApiUtil::l_encode_base64(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
 
-	size_t size;
-	const char *data = luaL_checklstring(L, 1, &size);
+	auto data = readParam<std::string_view>(L, 1);
 
-	std::string out = base64_encode((const unsigned char *)(data), size);
+	std::string out = base64_encode(data);
 
 	lua_pushlstring(L, out.data(), out.size());
 	return 1;
@@ -389,9 +387,7 @@ int ModApiUtil::l_decode_base64(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
 
-	size_t size;
-	const char *d = luaL_checklstring(L, 1, &size);
-	const std::string data = std::string(d, size);
+	auto data = readParam<std::string_view>(L, 1);
 
 	if (!base64_is_valid(data)) {
 		lua_pushnil(L);
@@ -487,12 +483,11 @@ int ModApiUtil::l_safe_file_write(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
 	const char *path = luaL_checkstring(L, 1);
-	size_t size;
-	const char *content = luaL_checklstring(L, 2, &size);
+	auto content = readParam<std::string_view>(L, 2);
 
 	CHECK_SECURE_PATH(L, path, true);
 
-	bool ret = fs::safeWriteToFile(path, std::string(content, size));
+	bool ret = fs::safeWriteToFile(path, content);
 	lua_pushboolean(L, ret);
 
 	return 1;
@@ -549,18 +544,16 @@ int ModApiUtil::l_get_version(lua_State *L)
 int ModApiUtil::l_sha1(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
-	size_t size;
-	const char *data = luaL_checklstring(L, 1, &size);
+
+	auto data = readParam<std::string_view>(L, 1);
 	bool hex = !lua_isboolean(L, 2) || !readParam<bool>(L, 2);
 
 	// Compute actual checksum of data
 	std::string data_sha1;
 	{
 		SHA1 ctx;
-		ctx.addBytes(data, size);
-		unsigned char *data_tmpdigest = ctx.getDigest();
-		data_sha1.assign((char*) data_tmpdigest, 20);
-		free(data_tmpdigest);
+		ctx.addBytes(data);
+		data_sha1 = ctx.getDigest();
 	}
 
 	if (hex) {
@@ -654,8 +647,8 @@ int ModApiUtil::l_urlencode(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
 
-	const char *value = luaL_checkstring(L, 1);
-	lua_pushstring(L, urlencode(value).c_str());
+	auto s = readParam<std::string_view>(L, 1);
+	lua_pushstring(L, urlencode(s).c_str());
 	return 1;
 }