nullclaw

Resource Limits

Problem

Rate limiting (actions/hour) prevents abuse, but without resource caps a runaway agent could:

• Exhaust available memory
• Spin CPU at 100%
• Fill disk with logs/output
• Fork-bomb via subprocesses

Enforcement Strategies

Memory Monitoring

nullclaw tracks heap usage and kills operations that exceed limits. Zig’s explicit allocator model makes this natural — wrap the allocator with a counting layer.

pub const LimitedAllocator = struct {
    inner: std.mem.Allocator,
    max_bytes: usize,
    used: std.atomic.Value(usize),

    pub fn alloc(self: *LimitedAllocator, len: usize, ...) ?[*]u8 {
        const current = self.used.fetchAdd(len, .monotonic);
        if (current + len > self.max_bytes) {
            self.used.fetchSub(len, .monotonic);
            return null; // OOM instead of crash
        }
        return self.inner.alloc(len, ...);
    }
};

CPU Timeout

Every tool execution has a configurable timeout. Shell commands use std.process.Child with a deadline — if the child doesn’t exit in time, it’s killed.

cgroups v2 (Linux)

When running as a systemd service, cgroups enforce hard limits:

[Service]
MemoryMax=512M
CPUQuota=100%
IOReadBandwidthMax=/dev/sda 10M
IOWriteBandwidthMax=/dev/sda 10M
TasksMax=100

Process Limits

Maximum concurrent subprocesses prevents fork-bomb scenarios. Each std.process.Child.init() checks the active count before spawning.

Configuration

{
  "security": {
    "resources": {
      "max_memory_mb": 512,
      "max_memory_per_command_mb": 128,
      "max_cpu_percent": 80,
      "max_cpu_time_seconds": 60,
      "max_subprocesses": 10,
      "max_log_size_mb": 100,
      "max_temp_storage_mb": 500
    }
  }
}

Implementation Priority

Phase	Feature	Effort	Impact
P0	Memory monitoring + OOM	Low	High
P1	CPU timeout per command	Low	High
P2	cgroups integration (Linux)	Medium	Very High
P3	Disk I/O limits	Medium	Medium

Hardware Compatibility

Even with full resource enforcement, nullclaw stays lightweight:

Hardware	RAM	Base	With Limits	Status
Raspberry Pi Zero	512 MB	~0.2%	~0.3%	Works
Orange Pi Zero	512 MB	~0.2%	~0.3%	Works
Rock64	1 GB	~0.1%	~0.15%	Works
Any $5 SBC	256 MB	~0.4%	~0.5%	Works