packet_serializer.zig

pub const LoginPacket = struct {
    id: u32,
    x: u8,
    y: u8,
    z: u8,
};

pub const ByteBuf = struct {

    fn write(_: *ByteBuf, comptime T: type, value: T) void {
        std.debug.print("write({}, {})\n", .{T, value});
    }

    fn read(_: *ByteBuf, comptime T: type) T {
        std.debug.print("read({})\n", .{T});
        return 5;
    }

};

// comptime function to build a packet serializer by reading the fields of a struct
fn packet_serializer(comptime T: type) type {
    // return an anonymous struct
    return struct {

        // write a packet to a bytebuf
        fn write(byteBuf: *ByteBuf, packet: T) void {
            // compile-time type reflection
            switch (@typeInfo(T)) {
                .Struct => |*strct| {
                    // iterate over every field (at comptime)
                    inline for (strct.fields) |field| {
                        byteBuf.write(field.field_type, @field(packet, field.name));
                    }
                },
                else => unreachable, // T is not a struct, so we can't serialize it
            }
        }

        // read a packet from a bytebuf
        fn read(byteBuf: *ByteBuf) T {
            var packet: T = undefined;
            // compile-time type reflection
            switch (@typeInfo(T)) {
                .Struct => |*strct| {
                    // iterate over every field (at comptime)
                    inline for (strct.fields) |field| {
                        // write the read value to the packet
                        @field(packet, field.name) = byteBuf.read(field.field_type);
                    }
                },
                else => unreachable, // T is not a struct, so we can't serialize it
            }
            return packet;
        }
        
    };
}

test "packet serializer for LoginPacket" {
    const LoginPacketSerializer: type = comptime packet_serializer(LoginPacket);
    const byteBuf = ByteBuf{};
    LoginPacketSerializer.write(byteBuf, .{.id = 5, .x = 1, .y = 2, .z = 3});
    const packet = LoginPacketSerializer.read(byteBuf);
    try expect(packet.id == 5);
    try expect(packet.x == packet.y);
}