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Local Doors — Native v86 Emulation

Native DOS Emulation via v86

ENiGMA½ includes a built-in x86/DOS emulator powered by v86 — a JavaScript x86 emulator that runs entirely within Node.js. The v86_door module boots a FreeDOS disk image and bridges COM1 directly to the user’s connection, with no external emulator installed on the server.

The emulator runs in a dedicated worker thread, so it does not block ENiGMA½’s event loop. Each active session gets its own isolated emulator instance.

How It Works

ENiGMA½ generates the appropriate drop file for the user (DORINFO, DOOR.SYS, etc.)
The drop file is written into a small in-memory FAT12 floppy image — no temp files on disk
v86 boots the op-supplied FreeDOS disk image from the hard drive (C:)
The drop file floppy is mounted as A: in FreeDOS
The door’s AUTOEXEC.BAT copies the drop file from A: and launches the game
COM1 serial I/O is bridged directly between v86 and the user’s connection
When the door exits and FreeDOS powers off, the session ends cleanly

Prerequisites

BIOS Files

v86 requires SeaBIOS and a VGA BIOS image. The ENiGMA½ installer (misc/install.sh) downloads these automatically to misc/v86_bios/. To download manually:

mkdir -p misc/v86_bios
curl -fL https://github.com/copy/v86/raw/master/bios/seabios.bin -o misc/v86_bios/seabios.bin
curl -fL https://github.com/copy/v86/raw/master/bios/vgabios.bin -o misc/v86_bios/vgabios.bin

Disk Image

You need a raw FreeDOS disk image (.img) with your door game pre-installed. Raw .img images are fully compatible between QEMU, DOSBox-X, and v86 — set up your image with QEMU or DOSBox-X, then point v86_door at it on the production server.

Configuration

Item	Required	Description
`name`		Door name. Used as a key for tracking concurrent sessions.
`image`		Path to the raw FreeDOS disk image (`.img`).
`dropFileType`		Drop file to generate and inject onto the `A:` floppy: `DORINFO`, `DOOR`, or `DOOR32`. Omit if the door needs no drop file.
`runBatch`		Multi-line batch script written to `A:\RUN.BAT` at runtime. Supports variable substitution. See One Image, Multiple Doors.
`nodeMax`		Max concurrent sessions. `0` = unlimited.
`tooManyArt`		Art spec to display when `nodeMax` is exceeded.
`memoryMb`		Guest RAM in MB. Default: `64`.
`biosPath`		Path to SeaBIOS image. Default: `misc/v86_bios/seabios.bin`.
`vgaBiosPath`		Path to VGA BIOS image. Default: `misc/v86_bios/vgabios.bin`.

Drop File Filenames on A:

`dropFileType`	Filename on `A:`
`DORINFO`	`DORINFOx.DEF` (x = node-based suffix per spec)
`DOOR`	`DOOR.SYS`
`DOOR32`	`door32.sys`

runBatch Variables

When runBatch is set, ENiGMA replaces the following variables before writing RUN.BAT:

Variable	Description	Example
`{dropFile}`	Drop file filename	`DORINFO1.DEF`
`{node}`	Node number	`1`
`{baud}`	Baud rate	`57600`

doorPimpWars: {
    desc: Playing PimpWars
    module: v86_door
    config: {
        name: PimpWars
        image: /path/to/images/freedos_doors.img
        dropFileType: DORINFO
        nodeMax: 1
        tooManyArt: DOORMANY
        runBatch:
            '''
            COPY A:\{dropFile} C:\DOORS\PW\
            C:\FOSSIL\X00.SYS
            CD C:\DOORS\PW
            PW.EXE {node}
            ECHO Returning to BBS, please wait... > COM1
            '''
    }
}

Image Preparation

Your disk image must contain:

A working FreeDOS installation
Your door game(s) installed (e.g. C:\DOORS\PIMPWARS\)
Optionally, a FOSSIL driver such as X00 — required by most classic DOS doors
An AUTOEXEC.BAT (or FDAUTO.BAT) that calls A:\RUN.BAT and powers off

AUTOEXEC.BAT Convention

Set up your image’s AUTOEXEC.BAT once. ENiGMA writes RUN.BAT to A: at runtime with the door-specific launch commands:

CALL A:\RUN.BAT
ECHO Shutting down, please wait... > COM1
FDAPM POWEROFF

CALL A:\RUN.BAT — executes the per-door launch script ENiGMA injects at runtime
ECHO ... > COM1 — sends a message to the user’s terminal while FreeDOS shuts down (can take a few seconds)
FDAPM POWEROFF — shuts FreeDOS down cleanly; placed after the CALL so it always fires even if the door crashes

One Image, Multiple Doors

Because RUN.BAT is generated at runtime, a single FreeDOS image can host multiple doors. Each door has its own menu entry pointing at the same image path with a different runBatch:

doorPimpWars: {
    module: v86_door
    config: {
        name: PimpWars
        image: /path/to/images/freedos_doors.img
        dropFileType: DORINFO
        nodeMax: 1
        runBatch:
            '''
            COPY A:\{dropFile} C:\DOORS\PW\
            C:\FOSSIL\X00.SYS
            CD C:\DOORS\PW
            PW.EXE {node}
            ECHO Returning to BBS, please wait... > COM1
            '''
    }
}

doorSmurfCombat: {
    module: v86_door
    config: {
        name: SmurfCombat
        image: /path/to/images/freedos_doors.img   // same image
        dropFileType: DOOR
        nodeMax: 1
        runBatch:
            '''
            COPY A:\{dropFile} C:\DOORS\SMURF\
            C:\FOSSIL\X00.SYS
            CD C:\DOORS\SMURF
            SMURF.EXE {node}
            ECHO Returning to BBS, please wait... > COM1
            '''
    }
}

Concurrent sessions on the same image file are safe — each worker loads the image into its own isolated memory buffer. nodeMax: 1 gates single-player doors, but even without it there is no shared state between sessions.

FOSSIL Driver

Most classic DOS doors use the FOSSIL serial interface for COM1 I/O. If your door fails to start or falls back to local mode, a FOSSIL driver is needed. X00 works well with v86.

Load it from runBatch (per-door, recommended) rather than FDCONFIG.SYS (global):

C:\FOSSIL\X00.SYS

Or in FDCONFIG.SYS if all doors on the image need it:

DEVICE=C:\FOSSIL\X00.SYS

Creating the Image with QEMU

# Create a 500MB raw image
qemu-img create -f raw freedos_mygame.img 500M

# Install FreeDOS (boot from CD)
qemu-system-i386 -hda freedos_mygame.img -cdrom FD14CD.iso -boot d

# Boot into FreeDOS to install your door
qemu-system-i386 -hda freedos_mygame.img

# Transfer files from host using QEMU's vfat driver — files appear on D:
qemu-system-i386 -hda freedos_mygame.img -hdb fat:/path/to/door/files

DOSBox-X is a graphical alternative for image setup on Windows, macOS, and Linux. See the DOSBox-X documentation for imgmount.

FreeDOS Boot Configuration for Fast Startup

For ~5 second boot times, configure FreeDOS to use Emergency Mode (no memory managers, no networking). In FDCONFIG.SYS:

MENUDEFAULT=5,0

Ensure the 5? config block loads your FOSSIL driver:

5?DEVICE=C:\FOSSIL\X00.SYS
5?SHELL=C:\FreeDOS\BIN\COMMAND.COM C:\FreeDOS\BIN /E:1024 /P=C:\FDAUTO.BAT