13  i_net: Networking Abstraction

The i_net module handles DOOM’s networking: sockets, packet I/O, and command dispatch.

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13.1 📄 File: i_net.h (lines 33–39)

Two networking functions: - I_InitNetwork: Initializes networking at startup
- I_NetCmd: Handles packet send/receive each frame

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13.2 🔧 Socket Setup and Packet Transmission

13.2.1 📄 File: i_net.c (lines 90–100)

Creates a UDP socket for player-to-player communication.

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13.2.2 📄 File: i_net.c (lines 113–119)

Binds the socket to all network interfaces (INADDR_ANY) at a specified port.

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13.2.3 📄 File: i_net.c (lines 132–139)

Converts values to network byte order before transmission (htonl, etc.).

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13.2.4 📄 File: i_net.c (lines 149–152)

Uses sendto() to transmit packets to other DOOM nodes.

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13.2.5 📄 File: i_net.c (lines 169–176)

Attempts to receive network packets using recvfrom().

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13.2.6 📄 File: i_net.c (lines 188–194)

Checks sender IP against known addresses; if none match, drops the packet.

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13.2.7 📄 File: i_net.c (lines 204–208)

Parses game state from received packets.

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13.3 🌐 Local Host Address Detection

13.3.1 📄 File: i_net.c (lines 229–231)

Uses gethostname() to get local machine’s name.

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13.3.2 📄 File: i_net.c (lines 233–237)

Resolves the hostname to an IP address with gethostbyname().

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13.4 🔄 I_InitNetwork and I_NetCmd

13.4.1 📄 File: i_net.c (lines 250–253)

Allocates doomcom to store shared network state.

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13.4.2 📄 File: i_net.c (lines 255–259)

-dup command-line argument sets ticdup for packet duplication.

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13.4.3 📄 File: i_net.c (lines 267–270)

-extratic enables backup tics in network packets.

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13.4.4 📄 File: i_net.c (lines 272–276)

Allows overriding the default network port.

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13.4.5 📄 File: i_net.c (lines 282–287)

If no multiplayer mode requested, configure single-player.

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13.4.6 📄 File: i_net.c (lines 293–296)

Enables networking by setting netgame = true and assigning packet handlers.

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13.4.7 📄 File: i_net.c (lines 298–300)

Initializes player number and number of nodes.

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13.4.8 📄 File: i_net.c (lines 302–304)

Parses command-line arguments for host addresses.

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13.4.9 📄 File: i_net.c (lines 305–309)

Parses IP address for target node.

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13.4.10 📄 File: i_net.c (lines 312–316)

Resolves each hostname to an IP address.

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13.4.11 📄 File: i_net.c (lines 327–331)

Creates separate sockets for sending and receiving.

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13.5 📡 I_NetCmd

13.5.1 📄 File: i_net.c (lines 345–347)

Unrecognized command triggers an error.

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And that’s DOOM’s networking layer — abstracting UDP communication to enable smooth multiplayer gameplay.