vcod

Call of Duty multiplayer, rebuilt from scratch in Rust. A client and a dedicated server that read your copy's game files and speak each game's original wire protocol, against vcod's own server or the retail ones. Nobody ever wrote those protocols down, so I dug them out of the binaries.

Game	Patch	Protocol	Client	Server	Bots	Details
Call of Duty	1.1, 1.5	1, 6	Plays	Hosts	Yes	cod1.md
United Offensive	1.51	22	Plays, tanks and jeeps included	Hosts, tanks and jeeps included	Yes	uo.md
Call of Duty 2	1.3	118	Plays	Hosts	Yes	cod2.md
Call of Duty 4	1.7	6	Plays on stock 1.7 servers (not CoD4x)	Hosts	Yes	cod4.md

Each game's page says what works, what's still missing against retail, and what vcod adds. docs/features.md covers what they share.

All four games at 21:9 on the current build. Click the collage for the screenshots at full size.

Read this first: it plays, and it still has opinions

You can play it. Start a server, join it, pick a team, shoot bots or friends, plant the bomb, drive a tank in United Offensive, call in an airstrike in CoD 4. Most evenings it feels like Call of Duty. Now and then it finds a bug the original never had, and occasionally one it had and I copied on purpose.

• Retail is the referee. Movement, shots, grenades, collision, snapshots and the handshake are replayed against captures from the real servers of all four games, down to the float rounding of each build. When vcod and retail disagree, retail wins and the bytes go into a research doc.
• It still has bugs. Please report them.
• It's a hobby. I work on it while poking at old engines is fun. No roadmap, no "1.0", no promises.
• It needs your copy of the game. No assets ship here, and none will.
• Hosting is for friends, for now. There's no anti-cheat, rcon knows a few dozen commands, and the bots are the only players it has been tested against at length. A LAN or a few friends is fine. Your public server's regulars deserve better.
• Linux is the only platform I run. Windows and macOS builds exist and nobody has told me whether they work. Godspeed.

What every game gets

• The client opens on the game's own main menu and server browser, joins retail servers and vcod's, downloads missing files, and plays: movement and prediction, the weapons, the HUD, scoreboard, chat, votes and the server's script menus.
• The server runs Activision's own gametype scripts on vcod's own .gsc VM, so the stock modes play by the stock rules. Retail clients can join it.
• Bots (--bots N --bots-shoot) join through the menus, find their way around the map, play the objectives and fight back. They're bad at it. So am I. rcon's addbot and removebot manage them on a running server (docs/bots.md).
• Widescreen and ultrawide see more at the sides (Hor+) instead of losing picture at the top and bottom: by default on CoD 1, UO and CoD 2, with vc_windowAspect 1 on CoD 4.
• Extras retail never had on CoD 1 and UO, all off by default: soft sun shadows, SSAO, bloom, HDR, sun shafts, soft particles and a film grade. --rtx-on turns them all on for one run. Despite the name, no rays were harmed.

How to play

1. Own the game: CoD 1.1 or 1.5, United Offensive 1.51, CoD 2 1.3 or CoD 4 1.7.

2. Get vcod. Grab the archive for your OS from the nightly release (or build it) and put vcod and vcod-server in the game's directory. Each binary tells the games apart by the install. Elsewhere, point COD_DIR or --game-dir at it.

3. Play against bots:

   Game	Server
   CoD 1	vcod-server mp_carentan --bots 6 --bots-shoot --gametype tdm
   UO	vcod-server mp_cassino --mod-dir uo --bots 6 --bots-shoot --gametype tdm
   CoD 2	vcod-server mp_toujane --bots 6 --bots-shoot --gametype tdm
   CoD 4	vcod-server mp_crash --bots 6 --bots-shoot --gametype war

   Then vcod --connect 127.0.0.1:28960 (add --mod-dir uo for UO). Pick a team, pick a weapon, go get shot.

4. Play with friends or online. Run plain vcod and use Start New Server, or join from the browser. PunkBuster servers refuse vcod.

Controls are each game's stock ones. Every key, flag, console command and recipe is in docs/usage.md; the first steps per game are in docs/getting-started.md.

Reporting bugs

Use the bug report form. It asks for what I need to reproduce it, and the first thing is the version line. Every build names itself (vcod 0.1.0-7924565c linux-amd64) in the window title, the main menu, the console (version), the F3 overlay, vcod --version and the first line of the log. Press F3 before a screenshot, so I can see where you were standing.

Known gaps

The ones you'll hit first, in every game. Each game's page lists the rest.

• No listen server. Start New Server always runs a separate vcod-server.
• No PunkBuster, no anti-cheat.
• Audio follows the engine on paper but has had little checking by ear.
• CoD 4: most public servers run CoD4x, which no stock 1.7 client can play on. vcod refuses them and hides them in the browser.

And one that looks like a fix and is one. Asphalt footsteps are silent in CoD 1 retail because the engine asks for asphalt and the sound table spells it asphault. vcod uses the table's spelling, so you can hear asphalt. Twenty-three years late, Infinity Ward, you're welcome.

Building from source

Rust 1.90 or newer. The client needs a GPU with BC (DXT) texture compression, and wgpu picks the backend (WGPU_BACKEND=vulkan|gl|dx12|metal narrows it). The server needs no GPU.

cargo build --release
COD_DIR=/path/to/CallOfDuty cargo test

That gives target/release/vcod and target/release/vcod-server. Without COD_DIR the tests that need game data return early and pass, so a green run without the game proves nothing about the parsers. CI runs that way, because it can't ship the game either. A build outside a git checkout reads its sha from VCOD_GIT_SHA, or calls itself unknown.

How I know it's right (when it is)

The retail dedicated servers are the oracle. When vcod and retail disagree, retail wins and the disagreement goes into a research doc.

• A headless probe client (vcod --net-probe) joins a server and records what it sees, with a few dozen scripted modes: shoot someone, throw a grenade, plant the bomb, drive a tank into another tank.
• Retail's recordings are committed as fixtures. A/B tests replay the same inputs on vcod's server and diff the result snapshot by snapshot.
• Small .gsc probes run on retail and on vcod's VM, and the suite compares their output.

That catches a lot. Anything about how it looks or sounds still needs a human squinting at a screen, which is where you come in.

Documentation

• docs/features.md: the supported games, what they share, and a page per game on what works and what doesn't.
• docs/getting-started.md: a quick start per game, common recipes (LAN, public server, bots, demos), troubleshooting.
• docs/usage.md: command lines, server options, controls, the console, the menus.
• docs/bots.md: running bots, the rcon commands, the minimum player count, team balance and slots.
• docs/protocol-1.1.md: the 1.1 wire protocol, both directions, with every divergence from RTCW/Q3 at the end.
• docs/research/: about eighty documents on file formats, movement, combat, vehicles, sound, scripts, bots and the rest. Every claim names the binary address it rests on and says whether it was verified or inferred. I'd call this the most useful part of the repo.
• AGENTS.md: the contributor guide. Layout, measuring against retail, and the traps I already paid for.

The code is six crates. vcod-common holds CoD 1's formats, collision, movement and protocol and what every game shares, with no GPU or audio. vcod-cod2 and vcod-cod4 hold CoD 2's and CoD 4's formats, wire and movement. vcod is the client, vcod-server the server, and vcod-gsc the script VM, which depends on nothing else here.

Some numbers, for fun

As of the end of October 2026:

• about 630,000 lines of Rust, for four games that shipped in less,
• about 5,600 tests, and 91 of them replay a retail capture and refuse to pass until vcod agrees with it,
• close to a million words of protocol and research notes, four and a half Moby-Dicks with a worse plot, except the twist where grenade cooking turned out not to exist until United Offensive,
• one asphalt footstep restored, typo and all.

Why

Mostly to see whether it could be done. CoD 1 descends from id Tech 3, and the Quake III and RTCW sources are public, but CoD's wire protocol was never documented. Every field width, enum order and place Infinity Ward wandered off from RTCW had to come out of the binaries and be checked against the retail server. CoD 2 and CoD 4 went the same way later, on the same client and server. Also, watching a 2003 game come back to life in a window you built yourself is a lot of fun.

This is an AI-driven project

An AI coding agent wrote most of the code and docs here, under my direction. I decide what to build, review what comes back, run it against the real game and the retail servers, and do the pixel and by-ear checks the agent can't. The research docs label each fact verified or inferred so you can tell them apart. Treat the code as a working prototype, not a reference implementation.

Lineage and inspiration

• Quake III Arena and Return to Castle Wolfenstein by id Software, GPL. CoD1 descends from RTCW-MP, and its netcode, movement and animation code follow those sources closely. Where vcod ports a routine, the comment names the file it came from.
• ioquake3, for a cleaner reading of the same netcode.
• CoDExtended, a GPL server extension for CoD1 1.1 whose struct layouts were the starting point for the netfield tables.
• cod-asset-importer, a GPL Blender add-on. The xmodel triangle-strip decoder is ported from it.
• zk_libcod, an MIT CoD2 1.3 server library. tools/re reads its list of named 1.3 addresses to name functions in the retail server; some CoD2 docs use those names.

Consulted, not copied

These projects were read as references while working out CoD4. vcod contains no code from them. Where earlier CoD4 code had followed one of them too closely, I had it audited function by function and rewritten from the retail 1.7 binaries and captures, with the retail gates proving the behaviour held.

• kisakcod, GPLv3, a reconstruction of the CoD4 1.8 multiplayer executable. Used for function names and as a cross-check of behaviour. 1.7 is the target: the research docs cite 1.7 addresses, and a claim not yet confirmed on 1.7 says so.
• CoD4x Server, AGPLv3, for how CoD4x servers differ on the wire, so vcod can recognise and refuse them.
• COD4iOS-COD4NS, GPLv3, as a cross-check of the fastfile layout.

Libraries

• wgpu, winit and kira for graphics, windowing and audio.

Legal

vcod is not affiliated with or endorsed by Activision or Infinity Ward. Call of Duty is a trademark of Activision Publishing, Inc. This repository contains no game assets, game code or binaries; it reads the files of a copy you own. The reverse engineering was done to interoperate with the game's own files and servers. The research notes document file formats and the network protocol for that purpose: layouts and addresses recovered from the binaries, no copied code. The projects under "Consulted, not copied" were read as references, and no code from them is included. The screenshots show art owned by Activision.

Quake III Arena and Return to Castle Wolfenstein are trademarks of id Software. Their GPL sources, and the other ported code, are credited in NOTICE.

License

GPL-3.0-or-later; see LICENSE. The network code was written with the RTCW (GPLv3) and Quake 3 (GPLv2-or-later) sources as reference, so the project is GPL to stay compatible with them.