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Distributed Systems Extensions for the Dunai FRP Library

This library provides a client/ server infrastructure by using Cloud Haskell for distributed FRP applications implemented with Dunai/ BearRiver.

Its features are demonstrated in an exemplary application called distributed-paddles. distributed-paddles needs SDL2(package libsdl2-dev in Ubuntu, SDL2-devel in rpm) and SDL2_gfx(package libsdl2-gfx-dev in Ubuntu, SDL2_gfx-devel in rpm) installed on the system.

Install them with your favorite package manager, e.g apt install libsdl2-dev; apt install libsdl2-gfx-dev.

To build/install the project with cabal --allow-newer needs to be used:

cabal build --allow-newer

cabal install --allow-newer

Installation and build process was tested with Cabal 3.2.0.0, GHC 8.2.2 and GHC 8.8.3.

Modules of the client/server architecture:

  • Network.Server exports functions necessary to create a server application. Servers generate state (which will be sent to clients) and are the central authority of an application in this project. They process commands received by clients.

  • Network.Client exports functions to create a client application. Clients display states and generate commands from user input, which will be sent to a server.

  • Network.Common contains types and functions used by both servers and clients

There is also support for several mechanisms to synchronise the state between running instances of an application:

  • Time Warp Synchronisation is supported for Servers, for a version of reactimate which uses time warp, see module FRP.BearRiver.Network.TimeWarp. A reactimate version for clients in this context is in module FRP.BearRiver.Network.Reactimate.

  • Dead Reckoning and Client Side Prediction is supported for Clients, see modules Data.MonadicStreamFunction.Prediction and FRP.BearRiver.Network.Prediction

Documentation of the project via Haddock is provided in directory doc. For example usage of the modules, see distributed-paddles and the unit tests.

distributed-paddles

distributed-paddles is an example application inspired by PONG™ (Atari Interactive, Inc., 1972).

Command line arguments are used to decide whether to host a session as a server or join a session as a client. In addition, command line arguments should be used to decide which consistency maintenance mechanisms to use.

Command line arguments for servers:

  • --host flag to initiate server startup
  • --ip IP on which IP to host the server (e.g localhost)
  • --p PORT port of server
  • --name NAME name of the session hosted
  • --d LENGTH length of the playable round in seconds
  • --t flag to turn on time warp synchronisation

To create a session called name on localhost, port 3000, maximum length of the game 30 seconds, using time warp, use:

cabal new-run distributed-paddles -- --host --ip 127.0.0.1 --p 3000 --name name --d 30 --t

When the server started correctly, it will print something like this: Server starts at: 127.0.0.1:3000:0 ... . 127.0.0.1:3000:0 is the address of the server which has to be used by clients to connect.

Command line arguments for clients:

  • --ip IP on which ip to start the server
  • --p PORT port of client
  • --nick NICK name of client
  • --name NAME name of session to join
  • --s ADDRESS address of the server, in this format: IP:PORT:0, see above
  • --csp turn on client side prediction (default is off)
  • --drmFirst turn on dead reckoning (default is off)

To join with a nickname A, receiving messages on port 3001, using client side prediction and dead reckoning:

cabal new-run distributed-paddles -- --ip 127.0.0.1 --p 3001 --name name --s 127.0.0.1:3000:0 --nick A --csp --drmFirst

Paddles can be moved up and down by pressing arrow keys.

Simple startup

To run a server with n hosts that join, run run_paddles n, e.g run_paddles 2.

Running with argument 0 only starts up a server.

When the server started successfully, press any key to start the clients.

To exit the session, press again any key.

Profiling

To automatically run a server with two hosts that join using profiling, run run_profiling. Running a profiled program called x always writes its output to x.prof/ x.hp. The workaround used here is to execute different copies of the executable. See comments in the file to get the script to work correctly.

Formatting

All Haskell source files are formatted via Brittany.

network-transport-tcp

The library uses a modified version of the package network-transport-tcp with an updated dependency to the network package to version 3.

distributed-process

A fork of distributed-process is used to get compatibility with GHC 8.8.