netchan-ipx demo

A reliable + unreliable multiplexed channel library (a subset of netchan) for IPX on 16-bit MS-DOS, plus a four-player, server-authoritative game (“thor”) with a Caves-of-Thor text-mode look.

The core is transport-agnostic. It builds on the host over UDP (for fast iteration and unit tests) with gcc, and on DOS over IPX with Open Watcom.

Layout

File	What it is
`netchan.c` / `netchan.h`	transport-agnostic core: handshake, channels, Go-Back-N reliability
`nc_addr.h`	opaque transport address (UDP 6 B, IPX 12 B)
`nc_udp.c`	host UDP transport
`nc_ipx.c` / `nc_ipx.h`	16-bit DOS IPX transport (INT 2Fh, polled ECBs, static pools)
`game.c` / `game.h`	portable server-authoritative game simulation
`game_net.c` / `game_net.h`	the game’s wire protocol and multi-peer server glue
`render.c`, `plat_*.c`, `plat.h`	text-mode rendering and platform layer (DOS + host)
`thor.c`	the game program (host-and-join)
`rng.c` / `rng.h`	tiny PRNG used for map and creature generation
`test_*.c`	host unit tests

Prerequisites

A C compiler (gcc) for the host build and tests.
Open Watcom for the DOS build, with the WATCOM environment variable set and $WATCOM/binl on PATH (provides wcc, wcl, wmake).
DOSBox to run the DOS binaries.
For networked play: an IPX-over-UDP relay that speaks the DOSBox tunnel protocol, e.g. ipxrelay.

Build

Host (development + tests):

make            # builds the host tools and the game (thor) over UDP
make check      # runs the host unit tests

DOS (Open Watcom):

wmake           # builds thor.exe, ipxtest.exe, ncdemo.exe (16-bit, large model)

The two build systems coexist in this directory: GNU make reads GNUmakefile (host), Open Watcom wmake reads makefile (DOS). Host objects are *.o, DOS objects are *.obj, so they never collide.

Run the unit tests (host)

./test_netchan   # handshake, reliable delivery under induced loss, unreliable
./test_gnet      # map streaming, state sync, input path, chat round-trip
./test_game      # prints ASCII frames of the simulation

Play it over IPX (DOSBox + relay)

Start the relay on the host, e.g. on UDP port 19900:
```
ipxrelay -F -p 19900 -a 127.0.0.1
```
Configure each DOSBox with IPX enabled, a fixed CPU cycle count, and an autoexec that connects to the relay and launches the game. A minimal dosbox.conf for the host player:
```
[cpu]
cycles=20000
[ipx]
ipx=true
[autoexec]
mount c /path/to/demo
c:
ipxnet connect 127.0.0.1 19900
thor.exe s
exit
```
For a joining player, use thor.exe (no s) instead of thor.exe s.

A fixed cycles value matters: cycles=max makes two co-running instances starve each other.
Run two (or more) DOSBox instances. Start the host first, then the joiners. Each joiner discovers the host with an IPX broadcast.

Controls

The game is a keyboard twin-stick shooter: one hand steers, the other aims.

Arrow keys — move in eight directions (hold to keep moving)
W A S D — fire north / west / south / east, independent of where you are moving (combine two keys for the diagonals)
Z or Space — fire in the direction you last moved (your facing)
Enter — open the chat line; type, then Enter to send (Esc cancels)
Q or Esc — quit

Test harness scripts

These automate the relay and a headless two-instance match; they only manage the processes they start.

scripts/relay.sh start|stop|restart|status   # manage the test relay
sh scripts/ipxtest.sh pair ipxtest.exe s     # reliability test over IPX (PASS/FAIL)
sh scripts/playtest.sh                        # run the game headless; dumps both screens

thor.exe accepts a dump argument that writes the current 40×25 screen to a text file once a second, which is how the headless harness and the article screenshot are captured.