OCAP Recorder (Go)

About

A Go implementation of an ArmA 3 native extension that records gameplay to PostgreSQL, SQLite, or in-memory JSON. Captures unit positions, combat events, markers, and more for mission replay and analytics.

Architecture

Overview

ArmA 3 Game
    ↓ callExtension("ocap_recorder", [":COMMAND:", args])
RVExtensionArgs() [CGo boundary]
    ↓
Dispatcher.Dispatch(Event)
    ↓
    ├─ [Sync]     → Handler directly
    └─ [Buffered] → Channel → Goroutine → Handler
                                              ↓
                                   Parser (args → core types)
                                              ↓
                                   EntityCache (validate/enrich)
                                              ↓
                                   Storage Backend
                                     ├─ Memory → in-memory append → JSON export on save
                                     ├─ Postgres → Queue → DB writer (batch insert every 2s) → PostgreSQL
                                     └─ SQLite → Queue → DB writer (batch insert every 2s) → SQLite

Buffered handlers are gated on :STORAGE:INIT: — events queue in channels until the storage backend is ready.

DLL Entry Points

The extension exposes CGo-exported functions that ArmA 3 calls:

Function	Purpose
RVExtensionArgs()	Main entry point; receives command and arguments
RVExtension()	Legacy simple command handler
RVExtensionVersion()	Returns version string

Event Dispatcher

The dispatcher routes commands to handlers with optional buffering:

• Sync handlers: Execute immediately (entity creation)
• Buffered handlers: Queue events in channels for async processing (high-volume state updates)
• Metrics: OpenTelemetry integration for queue sizes, events processed/dropped

Project Structure

cmd/ocap_recorder/main.go    Entry point, initialization, lifecycle commands
pkg/a3interface/             CGo exports (RVExtension*)
internal/
├── dispatcher/              Event routing with async buffering
├── parser/                  Command parsing (args → core types)
├── worker/                  Handler registration and DB writer loop
├── queue/                   Thread-safe queues for batch writes
├── cache/                   Entity lookup caching (ObjectID → model)
├── model/                   Database models + converters
├── storage/                 Storage backends (memory, postgres, sqlite)
└── geo/                     Coordinate/geometry utilities

Design Principles

1. Low latency: Async buffered handlers don't block ArmA's game loop
2. High throughput: Batch writes every 2 seconds instead of per-event
3. Entity caching: Sync entity creation → cache → async state updates use cached FK
4. Pluggable storage: Memory (JSON export), PostgreSQL, or SQLite (in-memory with periodic disk dump)
5. Observability: OpenTelemetry metrics and structured logging (slog)

Building

Requires Docker with Linux containers.

Windows DLL

docker pull x1unix/go-mingw:1.24

docker run --rm -v ${PWD}:/go/work -w /go/work x1unix/go-mingw:1.24 \
  go build -buildvcs=false -o dist/ocap_recorder_x64.dll -buildmode=c-shared ./cmd/ocap_recorder

Linux .so

docker run --rm -v ${PWD}:/go/work -w /go/work golang:1.24-bullseye \
  go build -buildvcs=false -o dist/ocap_recorder_x64.so -buildmode=c-shared ./cmd/ocap_recorder

Uses Debian Bullseye (glibc 2.31) for broad compatibility with Linux game servers.

Configuration

Copy ocap_recorder.cfg.json.example to ocap_recorder.cfg.json alongside the DLL and edit as needed.

Supported Commands

All commands follow a :RESOURCE:ACTION: naming convention. New commands must use this pattern — resource noun first, then verb/qualifier (e.g., :SOLDIER:CREATE:, :EVENT:KILL:, :SYS:INIT:).

Entity Commands

Command	Buffer	Purpose
:SOLDIER:CREATE:	Sync	Register new unit
:SOLDIER:STATE:	10,000	Update unit position/state
:SOLDIER:DELETE:	500	Mark unit as removed (disconnect, respawn corpse)
:VEHICLE:CREATE:	Sync	Register new vehicle
:VEHICLE:STATE:	10,000	Update vehicle position/state
:VEHICLE:DELETE:	500	Mark vehicle as removed

Combat Commands

Command	Buffer	Purpose
:EVENT:PROJECTILE:	5,000	Projectile tracking (positions + hits)
:EVENT:KILL:	2,000	Kill event

General Commands

Command	Buffer	Purpose
:EVENT:GENERAL:	1,000	General gameplay event
:EVENT:CHAT:	1,000	Chat message
:EVENT:RADIO:	1,000	Radio transmission
:TELEMETRY:FRAME:	100	Server telemetry (FPS, entity counts, weather, player network stats)
:TIME:STATE:	100	Mission time/date tracking

Marker Commands

Command	Buffer	Purpose
:MARKER:CREATE:	Sync	Create map marker (needs immediate DB ID)
:MARKER:STATE:	1,000	Update marker position/appearance (pos, dir, alpha, text, color, size, type, brush, shape)
:MARKER:DELETE:	500	Delete marker

Placed Object Commands

Command	Buffer	Purpose
:PLACED:CREATE:	Sync	Register placed object (mine, explosive)
:PLACED:EVENT:	1,000	Placed object lifecycle event (detonated/deleted)

ACE3 Integration

Command	Buffer	Purpose
:ACE3:DEATH:	1,000	ACE3 death event
:ACE3:UNCONSCIOUS:	1,000	ACE3 unconscious event

Lifecycle Commands

Command	Purpose
:SYS:INIT:	Initialize extension, send :SYS:READY: callback
:STORAGE:INIT:	Initialize storage backend, ungate buffered handlers
:MISSION:START:	Start recording mission
:MISSION:SAVE:	End recording, flush data, upload if configured
:SYS:VERSION:	Get extension version