flakenet

Wrap a net.Conn or net.PacketConn to simulate bandwidth limits, latency, jitter, and packet loss in Go tests. flakenet works at the connection level, so tests stay hermetic and run anywhere.

Iterates on cevatbarisyilmaz/lossy with two changes: queued delivery instead of a goroutine per packet, which bounds memory at high throughput, and FIFO ordering on streams, which fixes byte interleaving under high jitter.

Usage

lat := &policy.LatencyVar{}
lat.Set(100 * time.Millisecond)

conn := flakenet.NewPacketConn(udpConn, flakenet.PacketProfile{
    Latency: lat,
    Jitter:  policy.RandomJitter(20 * time.Millisecond),
    Loss:    policy.RandomLoss(0.01),
})

// Conditions can change while the connection is live.
lat.Set(500 * time.Millisecond)

Policies

Conditions are values, not constants. The Var types are safe for concurrent use and can be reset on an active connection, so a test can degrade a link mid-transfer without reconnecting.

• Bandwidth: throughput ceiling in bits/sec (StaticBandwidth, BandwidthVar)
• Latency: base propagation delay
• Jitter: delivery-time variance (RandomJitter is amplitude-based)
• Loss: packet drops (RandomLoss)
• Fault: trigger failures or closure on demand

Development

Tooling comes from the Nix flake. direnv allow (or nix develop) gets you a shell with the pinned Go toolchain, golangci-lint, and govulncheck.

make        # list targets
make init   # install the pre-commit hook
make ci     # fmt-check, lint, test, vuln