Merge pull request #853 from Onran0/io-streams-enhance

I/O Stream's enhance

src/logic/scripting/io_descriptors.cpp

@@ -66,6 +66,33 @@ void io_descriptors::flush(int id) {
     }
 }
 
+int io_descriptors::available(int id) {
+    if (!is_readable(id))
+        return 0;
+
+    auto* stream = descriptors[id]->in.get();
+
+    auto current_pos = stream->tellg();
+
+    if (current_pos == -1) {
+        return 0;
+    }
+
+    stream->seekg(0, std::ios::end);
+
+    auto end_pos = stream->tellg();
+
+    stream->seekg(current_pos,  std::ios::beg);
+
+    auto remaining = end_pos - current_pos;
+
+    if (remaining > std::numeric_limits<int>::max()) {
+        return std::numeric_limits<int>::max();
+    }
+
+    return static_cast<int>(remaining);
+}
+
 bool io_descriptors::has_descriptor(int id) {
     return id >= 0 && id < static_cast<int>(::descriptors.size()) &&
            ::descriptors[id].has_value();

src/logic/scripting/io_descriptors.hpp

@@ -13,6 +13,7 @@ namespace scripting::io_descriptors {
     std::ostream& require_output(int id);
 
     void flush(int id);
+    int available(int id);
 
     bool has_descriptor(int id);
 

src/logic/scripting/lua/libs/libfile.cpp

@@ -400,6 +400,20 @@ static int l_flush_descriptor(lua::State* L) {
     return 0;
 }
 
+static int l_available_descriptor(lua::State* L) {
+    int descriptor = lua::tointeger(L, 1);
+
+    if (!io_descriptors::has_descriptor(descriptor)) {
+        throw std::runtime_error("unknown descriptor");
+    }
+
+    if (!io_descriptors::is_readable(descriptor)) {
+        throw std::runtime_error("descriptor is not readable");
+    }
+
+    return lua::pushinteger(L, io_descriptors::available(descriptor));
+}
+
 static int l_close_descriptor(lua::State* L) {
     int descriptor = lua::tointeger(L, 1);
 
@@ -447,6 +461,7 @@ const luaL_Reg filelib[] = {
     {"__seek_descriptor", lua::wrap<l_seek_descriptor>},
     {"__tell_descriptor", lua::wrap<l_tell_descriptor>},
     {"__flush_descriptor", lua::wrap<l_flush_descriptor>},
+    {"__available_descriptor", lua::wrap<l_available_descriptor>},
     {"__close_descriptor", lua::wrap<l_close_descriptor>},
     {"__close_all_descriptors", lua::wrap<l_close_all_descriptors>},
     {nullptr, nullptr}