Software Design14.1Networked games: ooga to noogaz Different games make writing general server difficult¾ Turn based games…¾ Multiplayer asynchronous games like Boggle…¾ Noah’s Ark, Samegame, …z Nooga story at Duke¾ Each summer for the past N summers …• Do we have a general, usable architecture?¾ What should we do next?z What are key issues in developing networked games¾ Don’t worry about robustness or generalitySoftware Design14.2multi-platform, multi-os client/serverz Suppose we send data between clients and servers…z Architectural issues impact client/server code¾ Little-endian/Big-endian issues• 0xabcd is a 32-bit value, which is MSB? How is this stored?¾ How big is an int? 32-bits, 64 bits, …z Towards raising the level of discussion¾ Worrying about integer byte order is not fun ¾ Let’s worry about sending objects back-and-forth, not bytes¾ How do we send and receive objects?Software Design14.3Client/Server Communicationz The Java stream hierarchy is a rich source of options¾ Object streams, Data streams, Buffered Readers, …¾ Often these convert between bytes and characters• What’s the story with Unicode? (e.g. compared to ASCII)• FileStream, BufferedReader, …, z We can read and write objects over sockets¾ Advantages compared to lower-level protocols?¾ Disadvantages?z Issues in understanding and implementing¾ Where do objects “live”, are classes different?¾ Subclass/Superclass issues¾ What about connection issues (where, how, knowledge)Software Design14.4Clients and Servers: server sidez Server socket exists on some machine, listens to a “port”¾ A port isn’t a physical concept, it’s an OS concept¾ The OS manages ports, some services listen at predetermined ports, e.g., mail at port 25• User programs use ports above 1024z Server gets a connection and handles the request, but what about other connection requests?¾ Can’t be too busy processing request, or will miss other attempts at connections¾ Spin off handler as a separate program/process z Server blocks on accepting connections, new jdk1.4 API for java.nio.channels might improve things¾ Why is blocking not ideal?Software Design14.5Networked Gamesz What will go over the network?¾ Board?¾ Move?¾ Other?z Where is the controller?¾ Server?¾ Client?¾ Combination?z How does the server work for many games?¾ Rules important?Software Design14.6Simple Client/Server codez The example shows how a client communicates commands to server¾ Deciding how to process a command is simple, but not robust/OO in the current modelz How are client and server similar? Different?¾ Both know about all commands?¾ How do they know this?Software Design14.7Architectural considerationsz What can we do to generalize things, move away from chain of if/else code¾ Create commands corresponding to protocol¾ Execute command obtained by mapz What’s in the map? Some commands require state, e.g., more data from server or client¾ Can have a map of string to object, but how to get information into the object?¾ Can map string to object factory, have a per-command factory¾ Factory knows how to create each
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