Slightly optimize returning strings to lua from ffi functions

libaegisub/include/libaegisub/lua/ffi.h

@@ -16,6 +16,7 @@
 
 #include <libaegisub/type_name.h>
 
+#include <cstdlib>
 #include <lua.hpp>
 
 namespace agi { namespace lua {
@@ -59,4 +60,12 @@ void register_lib_table(lua_State *L, std::initializer_list<const char *> types,
 	// Leaves lib table on the stack
 }
 
+template<typename T>
+char *strndup(T const& str) {
+	char *ret = static_cast<char*>(malloc(str.size() + 1));
+	memcpy(ret, str.data(), str.size());
+	ret[str.size()] = 0;
+	return ret;
+}
+
 } }

libaegisub/lua/modules/lfs.cpp

@@ -21,6 +21,7 @@
 #include <boost/filesystem/path.hpp>
 
 using namespace agi::fs;
+using namespace agi::lua;
 namespace bfs = boost::filesystem;
 
 namespace agi {
@@ -38,7 +39,7 @@ auto wrap(char **err, Func f) -> decltype(f()) {
 		return 0;
 	}
 	catch (agi::Exception const& e) {
-		*err = strdup(e.GetMessage().c_str());
+		*err = strndup(e.GetMessage());
 		return 0;
 	}
 }
@@ -57,7 +58,7 @@ bool lfs_chdir(const char *dir, char **err) {
 
 char *currentdir(char **err) {
 	return wrap(err, []{
-		return strdup(bfs::current_path().string().c_str());
+		return strndup(bfs::current_path().string());
 	});
 }
 
@@ -76,7 +77,7 @@ bool touch(const char *path, char **err) {
 char *dir_next(DirectoryIterator &it, char **err) {
 	if (it == end(it)) return nullptr;
 	return wrap(err, [&]{
-		auto str = strdup((*it).c_str());
+		auto str = strndup(*it);
 		++it;
 		return str;
 	});

libaegisub/lua/modules/re.cpp

@@ -92,7 +92,7 @@ char *regex_replace(u32regex& re, const char *replacement, const char *str, size
 	}
 
 	ret += suffix;
-	return strdup(ret.c_str());
+	return agi::lua::strndup(ret);
 }
 
 u32regex *regex_compile(const char *pattern, int flags, char **err) {

libaegisub/lua/modules/unicode.cpp

@@ -22,7 +22,7 @@ namespace {
 template<std::string (*func)(const char *, std::locale const&)>
 char *wrap(const char *str, char **err) {
 	try {
-		return strdup(func(str, std::locale()).c_str());
+		return agi::lua::strndup(func(str, std::locale()));
 	} catch (std::exception const& e) {
 		*err = strdup(e.what());
 		return nullptr;

src/auto4_lua.cpp

@@ -124,7 +124,7 @@ namespace {
 		std::string data = GetClipboard();
 		if (data.empty())
 			return nullptr;
-		return strdup(data.c_str());
+		return strndup(data);
 	}
 
 	bool clipboard_set(const char *str)