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CS 378: Computer Game Technology

This project demonstrates a simple chat server and client using SDL_net for TCP networking, designed for the CS378 course at the University of Texas at Austin, taught by Don Fussell. The server handles multiple clients, allowing them to connect, send messages, and notify all active users when a new client joins or an existing client disconnects. The implementation includes error handling for initialization and socket management, along with a simple command structure for system interaction. Aimed at students learning game technology, it provides a foundational understanding of client-server architecture in gaming.

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CS 378: Computer Game Technology

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  1. CS 378: Computer Game Technology SDL_net Client-Server Example Spring 2012

  2. SDL_net TCP Chat Server if ( SDL_Init(0) < 0 ) { fprintf(stderr, "Couldn't initialize SDL: %s\n",SDL_GetError()); exit(1); } /* Initialize the network */ if ( SDLNet_Init() < 0 ) { fprintf(stderr, "Couldn't initialize net: %s\n”, SDLNet_GetError()); SDL_Quit(); exit(1); } /* Initialize the channels */ for ( i=0; i<CHAT_MAXPEOPLE; ++i ) { people[i].active = 0; people[i].sock = NULL; } /* Allocate the socket set */ socketset= SDLNet_AllocSocketSet(CHAT_MAXPEOPLE+1); if( socketset == NULL ) { fprintf(stderr, "Couldn'tcreatesocket set: %s\n”, SDLNet_GetError()); cleanup(2); } University of Texas at Austin CS 378 – Game Technology Don Fussell 2

  3. SDL_net TCP Chat Server /* Create the server socket */ SDLNet_ResolveHost(&serverIP, NULL, CHAT_PORT); printf("Server IP: %x, %d\n", serverIP.host, serverIP.port); servsock = SDLNet_TCP_Open(&serverIP); if ( servsock == NULL ) { fprintf(stderr, "Couldn't create server socket: %s\n”, SDLNet_GetError()); cleanup(2); } SDLNet_TCP_AddSocket(socketset, servsock); /* Loop, waiting for network events */ for ( ; ; ) { /* Wait for events */ SDLNet_CheckSockets(socketset, ~0); /* Check for new connections */ if ( SDLNet_SocketReady(servsock) ) { HandleServer(); } /* Check for events on existingclients */ for ( i=0; i<CHAT_MAXPEOPLE; ++i ) { if( SDLNet_SocketReady(people[i].sock) ) { HandleClient(i); } } } University of Texas at Austin CS 378 – Game Technology Don Fussell 3

  4. Handle New Connection void HandleServer(void) { TCPsocketnewsock; int which; unsigned char data; newsock = SDLNet_TCP_Accept(servsock); if ( newsock == NULL ) { return; } /* Look for unconnected person slot */ for ( which=0; which<CHAT_MAXPEOPLE; ++which ) if ( ! people[which].sock ) { break; } if ( which == CHAT_MAXPEOPLE ) { /* Look for inactive person slot */ for ( which=0; which<CHAT_MAXPEOPLE; ++which ) { if ( people[which].sock && ! people[which].active ) { /* Kick them out.. */ data = CHAT_BYE; SDLNet_TCP_Send(people[which].sock, &data, 1); SDLNet_TCP_DelSocket(socketset, people[which].sock); SDLNet_TCP_Close(people[which].sock); break; } } } University of Texas at Austin CS 378 – Game Technology Don Fussell 4

  5. Handle New Connection if ( which == CHAT_MAXPEOPLE ) { /* No more room... */ data = CHAT_BYE; SDLNet_TCP_Send(newsock, &data, 1); SDLNet_TCP_Close(newsock); } else { /* Addsocket as an inactive person */ people[which].sock = newsock; people[which].peer = *SDLNet_TCP_GetPeerAddress(newsock); SDLNet_TCP_AddSocket(socketset, people[which].sock); } } University of Texas at Austin CS 378 – Game Technology Don Fussell 5

  6. Chat void HandleClient(int which) { char data[512]; int i; /* Has the connectionbeenclosed? */ if ( SDLNet_TCP_Recv(people[which].sock, data, 512) <= 0 ) { /* Notify all activeclients */ if ( people[which].active ) { people[which].active = 0; data[0] = CHAT_DEL; data[CHAT_DEL_SLOT] = which; for ( i=0; i<CHAT_MAXPEOPLE; ++i ) if ( people[i].active ) SDLNet_TCP_Send(people[i].sock,data,CHAT_DEL_LEN); } SDLNet_TCP_DelSocket(socketset, people[which].sock); SDLNet_TCP_Close(people[which].sock); people[which].sock = NULL; University of Texas at Austin CS 378 – Game Technology Don Fussell 6

  7. Chat } else { switch (data[0]) { case CHAT_HELLO: { /* Yay! An active connection */ memcpy(&people[which].peer.port, &data[CHAT_HELLO_PORT], 2); memcpy(people[which].name, &data[CHAT_HELLO_NAME], 256); people[which].name[256] = 0; /* Notify all active clients */ for ( i=0; i<CHAT_MAXPEOPLE; ++i ) if ( people[i].active ) { SendNew(which, i); } /* Notify about all active clients */ people[which].active = 1; for ( i=0; i<CHAT_MAXPEOPLE; ++i ) if ( people[i].active ) { SendNew(i, which); } } break; default: { /* Unknownpacket type?? */; } break; } } } University of Texas at Austin CS 378 – Game Technology Don Fussell 7

  8. Chat /* Send a "new client" notification */ void SendNew(int about, int to) { char data[512]; int n; n = strlen((char *)people[about].name)+1; data[0] = CHAT_ADD; data[CHAT_ADD_SLOT] = about; memcpy(&data[CHAT_ADD_HOST], &people[about].peer.host, 4); memcpy(&data[CHAT_ADD_PORT], &people[about].peer.port, 2); data[CHAT_ADD_NLEN] = n; memcpy(&data[CHAT_ADD_NAME], people[about].name, n); SDLNet_TCP_Send(people[to].sock, data, CHAT_ADD_NAME+n); } University of Texas at Austin CS 378 – Game Technology Don Fussell 8

  9. SDL_net TCP Chat Client int main(intargc, char* argv[]) { /* Initialize SDL */ if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) { fprintf(stderr, "Couldn't initialize SDL: %s\n",SDL_GetError()); exit(1); } /* Initialize the network */ if( SDLNet_Init() < 0 ) { fprintf(stderr, "Couldn'tinitialize net: %s\n”, SDLNet_GetError()); SDL_Quit(); exit(1); } /* Allocate a vector of packets for client messages */ packets = SDLNet_AllocPacketV(4, CHAT_PACKETSIZE); if( packets == NULL ) { fprintf(stderr, "Couldn'tallocate packets: Outofmemory\n"); cleanup(2); } University of Texas at Austin CS 378 – Game Technology Don Fussell 9

  10. SDL_net TCP Chat Client /* Connect to remote host and create UDP endpoint */ server = argv[1]; termwin->AddText("Connecting to %s ... ", server); gui->Display(); SDLNet_ResolveHost(&serverIP, server, CHAT_PORT); if ( serverIP.host == INADDR_NONE ) { termwin->AddText("Couldn't resolve hostname\n"); } else { /* If wefail, it's okay, the GUI shows the problem */ tcpsock = SDLNet_TCP_Open(&serverIP); if ( tcpsock == NULL ) { termwin->AddText("Connect failed\n"); } else { termwin->AddText("Connected\n"); } } University of Texas at Austin CS 378 – Game Technology Don Fussell 10

  11. SDL_Net TCP Chat Client /* Try ports in the range {CHAT_PORT - CHAT_PORT+10} */ for ( i=0; (udpsock == NULL) && i<10; ++i ) udpsock = SDLNet_UDP_Open(CHAT_PORT+i); if ( udpsock == NULL ) { SDLNet_TCP_Close(tcpsock); tcpsock = NULL; termwin->AddText("Couldn'tcreate UDP endpoint\n"); } /* Allocate the socket set for polling the network */ socketset = SDLNet_AllocSocketSet(2); if ( socketset == NULL ) { fprintf(stderr, "Couldn'tcreatesocket set: %s\n", SDLNet_GetError()); cleanup(2); } SDLNet_TCP_AddSocket(socketset, tcpsock); SDLNet_UDP_AddSocket(socketset, udpsock); /* Run the GUI, handling network data */ SendHello(argv[2]); University of Texas at Austin CS 378 – Game Technology Don Fussell 11

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