53  System Interface (i_net)

This tour explores linuxdoom’s networking interface (i_net), which handles UDP communication between game instances for multiplayer gameplay.

53.1 i_net.h

  • Declares:
    • I_InitNetwork: Initializes networking at startup
    • I_NetCmd: Handles network commands during runtime
// linuxdoom-1.10/i_net.h (lines 33–40)

53.2 i_net.c

53.2.1 Socket Setup

  • UDPsocket: Creates a new UDP network socket

    // lines 90–99

  • BindToLocalPort: Configures a socket to listen for incoming data

    // lines 105–120

53.2.2 Packet Transmission

  • PacketSend:

    • Copies netbuffer to local structure
    • Converts fields to network byte order
    • Sends via UDP
    // lines 127–155

  • PacketGet:

    • Receives packets
    • Returns doomcom->remotenode = -1 if none are available
    // doomstat.h lines 276–277

  • Validates packets:

    // lines 161–178

53.2.3 Initialization

  • I_InitNetwork:
    • Allocates doomcom
    • Checks -net argument
    • Sets up sockets and network addresses
// lines 187–218
// lines 243–252: fallback to single-player if -net not present
// lines 281–290: set function pointers
// lines 293–303: local player + host parsing
// lines 303–312: socket setup
// lines 327–332: final socket setup

53.2.4 Packet Handling & Dispatch

  • I_NetCmd:
    • Dispatches based on doomcom->command:
      • CMD_SEND: → netsend()
      • CMD_GET: → netget()
// d_net.c lines 568–572
// i_net.c lines 335–346
// d_net.c lines 185, 209

And that’s how linuxdoom’s i_net interface enables multiplayer networking via sockets and command dispatch.