mirror of
https://github.com/livekit/livekit.git
synced 2026-07-02 11:22:04 +00:00
David Chen
290 lines
9.3 KiB
Bash
Executable File
290 lines
9.3 KiB
Bash
Executable File
#!/usr/bin/env bash
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#
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# Simulate packet loss on the SFU's media UDP port so FlexFEC recovery can be
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# observed end-to-end. Works on macOS (dnctl/dummynet + pfctl) and Linux (tc netem).
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#
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# Because publisher, SFU and subscriber all run on one machine, media flows over the
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# loopback interface. Loss is matched by the SFU UDP port (default 7882):
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# - "down" drops packets coming FROM the SFU port -> SFU -> subscriber path
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# (exercises subscriber-side / downlink FEC generation+recovery)
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# - "up" drops packets going TO the SFU port -> publisher -> SFU path
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# (exercises publisher-side / uplink FEC reception+recovery)
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# - "both" drops in both directions
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#
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# Usage:
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# sudo scripts/flexfec/netem.sh start [loss_percent] [up|down|both] [delay_ms] # uniform loss; default: 5 down 0
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# sudo scripts/flexfec/netem.sh burst [loss_percent] [burst_ms] [gap_ms] [up|down|both] [delay_ms] # bursty loss
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# sudo scripts/flexfec/netem.sh stop
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# sudo scripts/flexfec/netem.sh status
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#
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# delay_ms adds one-way latency (so RTT ~= 2*delay_ms on loopback). Models the
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# robot's access-network round trip; RTX recovery costs ~1 RTT of buffering.
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#
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# "burst" emulates handoff/fade-style correlated loss: it toggles the loss rate
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# between loss_percent (for burst_ms) and 0 (for gap_ms) on a duty cycle, holding
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# the delay constant. Average loss ~= loss_percent * burst_ms/(burst_ms+gap_ms).
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# Run it in its own terminal; Ctrl-C stops and restores the network.
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# This is where RTX (retransmit storms, each costing an RTT) and FlexFEC (fixed
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# inline overhead) diverge most.
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#
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# Env overrides:
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# SFU_UDP_PORT media port to shape (default 7882)
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# NETEM_IFACE (Linux only) interface to shape (default lo)
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set -euo pipefail
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PORT="${SFU_UDP_PORT:-7882}"
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ANCHOR="flexfec-loss"
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STATE_DIR="${TMPDIR:-/tmp}/flexfec-netem"
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PF_STATE="$STATE_DIR/pf.enabled"
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OS="$(uname -s)"
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require_root() {
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if [[ "$(id -u)" -ne 0 ]]; then
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echo "error: this command needs root; re-run with sudo" >&2
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exit 1
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fi
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}
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validate_dir() {
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case "$1" in
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up | down | both) ;;
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*)
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echo "error: direction must be up|down|both (got '$1')" >&2
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exit 1
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;;
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esac
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}
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# ----------------------------------------------------------------------------- macOS
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# Install the pf anchor + dummynet rules for the requested direction. Pipes are
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# (re)configured separately so loss can be toggled live for burst mode.
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macos_setup() {
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local dir="$1"
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mkdir -p "$STATE_DIR"
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# Remember whether pf was already enabled so `stop` can restore it.
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if [[ ! -f "$PF_STATE" ]]; then
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if pfctl -s info 2>/dev/null | grep -q 'Status: Enabled'; then
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echo enabled >"$PF_STATE"
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else
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echo disabled >"$PF_STATE"
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fi
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fi
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local rules=""
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case "$dir" in
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down | both) rules+="dummynet out proto udp from any port $PORT to any pipe 1"$'\n' ;;
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esac
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case "$dir" in
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up | both) rules+="dummynet out proto udp from any to any port $PORT pipe 2"$'\n' ;;
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esac
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# Re-load the system ruleset plus references to our named anchor (non-destructive:
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# existing /etc/pf.conf rules are preserved), then install our rules in the anchor.
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{
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cat /etc/pf.conf 2>/dev/null || true
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echo "dummynet-anchor \"$ANCHOR\""
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echo "anchor \"$ANCHOR\""
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} | pfctl -f - 2>/dev/null
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printf '%s' "$rules" | pfctl -a "$ANCHOR" -f - 2>/dev/null
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pfctl -e 2>/dev/null || true
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if pfctl -sa 2>/dev/null | grep -qi 'skip on lo'; then
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echo "warning: pf is configured to 'skip on lo'; loopback shaping may not apply" >&2
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fi
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}
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# macos_set_loss <loss_percent> <delay_ms>
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macos_set_loss() {
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local plr
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plr="$(awk "BEGIN { printf \"%.4f\", $1 / 100 }")"
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dnctl pipe 1 config plr "$plr" delay "$2" >/dev/null
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dnctl pipe 2 config plr "$plr" delay "$2" >/dev/null
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}
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macos_start() {
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local loss="$1" dir="$2" delay="$3"
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macos_setup "$dir"
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macos_set_loss "$loss" "$delay"
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echo "==> macOS dummynet loss enabled: ${loss}% loss, ${delay}ms delay (${dir}) on udp/${PORT}"
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}
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macos_burst() {
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local loss="$1" burst_ms="$2" gap_ms="$3" dir="$4" delay="$5"
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local burst_s gap_s avg
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burst_s="$(awk "BEGIN { printf \"%.3f\", $burst_ms / 1000 }")"
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gap_s="$(awk "BEGIN { printf \"%.3f\", $gap_ms / 1000 }")"
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avg="$(awk "BEGIN { printf \"%.1f\", $loss * $burst_ms / ($burst_ms + $gap_ms) }")"
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macos_setup "$dir"
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macos_set_loss 0 "$delay"
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trap 'echo; echo "==> stopping burst"; macos_stop; exit 0' INT TERM
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echo "==> macOS bursty loss: ${loss}% for ${burst_ms}ms every $((burst_ms + gap_ms))ms (~${avg}% avg), ${delay}ms delay (${dir}) on udp/${PORT}"
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echo " Ctrl-C to stop and restore the network."
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while true; do
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macos_set_loss "$loss" "$delay"
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printf '\r [burst ON %s%% loss] ' "$loss"
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sleep "$burst_s"
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macos_set_loss 0 "$delay"
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printf '\r [burst off 0%% loss] ' "$loss"
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sleep "$gap_s"
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done
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}
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macos_stop() {
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dnctl -q flush 2>/dev/null || true
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printf '' | pfctl -a "$ANCHOR" -f - 2>/dev/null || true
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pfctl -f /etc/pf.conf 2>/dev/null || true
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if [[ -f "$PF_STATE" && "$(cat "$PF_STATE")" == "disabled" ]]; then
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pfctl -d 2>/dev/null || true
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fi
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rm -f "$PF_STATE"
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echo "==> macOS dummynet loss disabled"
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}
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macos_status() {
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echo "== dummynet pipes =="
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dnctl list 2>/dev/null || true
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echo "== pf anchor '$ANCHOR' =="
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pfctl -a "$ANCHOR" -s rules 2>/dev/null || true
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echo "== pf status =="
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pfctl -s info 2>/dev/null | head -1 || true
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}
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# ----------------------------------------------------------------------------- Linux
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# linux_setup <dir> <delay_ms>: build prio qdisc + netem band (loss starts at 0)
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# and funnel matching UDP packets into it.
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linux_setup() {
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local dir="$1" delay="$2"
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local dev="${NETEM_IFACE:-lo}"
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local netem_args=(loss 0%)
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if [[ "$delay" -gt 0 ]]; then
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netem_args+=(delay "${delay}ms")
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fi
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tc qdisc del dev "$dev" root 2>/dev/null || true
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tc qdisc add dev "$dev" root handle 1: prio
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tc qdisc add dev "$dev" parent 1:3 handle 30: netem "${netem_args[@]}"
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if [[ "$dir" == "down" || "$dir" == "both" ]]; then
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tc filter add dev "$dev" parent 1:0 protocol ip prio 3 u32 \
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match ip protocol 17 0xff match ip sport "$PORT" 0xffff flowid 1:3
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fi
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if [[ "$dir" == "up" || "$dir" == "both" ]]; then
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tc filter add dev "$dev" parent 1:0 protocol ip prio 3 u32 \
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match ip protocol 17 0xff match ip dport "$PORT" 0xffff flowid 1:3
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fi
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}
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# linux_set_loss <loss_percent> <delay_ms>
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linux_set_loss() {
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local dev="${NETEM_IFACE:-lo}"
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if [[ "$2" -gt 0 ]]; then
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tc qdisc change dev "$dev" parent 1:3 handle 30: netem loss "${1}%" delay "${2}ms"
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else
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tc qdisc change dev "$dev" parent 1:3 handle 30: netem loss "${1}%"
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fi
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}
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linux_start() {
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local loss="$1" dir="$2" delay="$3"
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local dev="${NETEM_IFACE:-lo}"
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linux_setup "$dir" "$delay"
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linux_set_loss "$loss" "$delay"
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echo "==> Linux netem enabled: ${loss}% loss, ${delay}ms delay (${dir}) on udp/${PORT} dev ${dev}"
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}
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linux_burst() {
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local loss="$1" burst_ms="$2" gap_ms="$3" dir="$4" delay="$5"
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local dev="${NETEM_IFACE:-lo}"
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local burst_s gap_s avg
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burst_s="$(awk "BEGIN { printf \"%.3f\", $burst_ms / 1000 }")"
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gap_s="$(awk "BEGIN { printf \"%.3f\", $gap_ms / 1000 }")"
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avg="$(awk "BEGIN { printf \"%.1f\", $loss * $burst_ms / ($burst_ms + $gap_ms) }")"
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linux_setup "$dir" "$delay"
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trap 'echo; echo "==> stopping burst"; linux_stop; exit 0' INT TERM
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echo "==> Linux bursty loss: ${loss}% for ${burst_ms}ms every $((burst_ms + gap_ms))ms (~${avg}% avg), ${delay}ms delay (${dir}) on udp/${PORT} dev ${dev}"
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echo " Ctrl-C to stop and restore the network."
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while true; do
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linux_set_loss "$loss" "$delay"
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printf '\r [burst ON %s%% loss] ' "$loss"
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sleep "$burst_s"
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linux_set_loss 0 "$delay"
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printf '\r [burst off 0%% loss] ' "$loss"
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sleep "$gap_s"
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done
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}
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linux_stop() {
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local dev="${NETEM_IFACE:-lo}"
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tc qdisc del dev "$dev" root 2>/dev/null || true
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echo "==> Linux netem loss disabled (dev ${dev})"
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}
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linux_status() {
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local dev="${NETEM_IFACE:-lo}"
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echo "== qdisc (dev ${dev}) =="
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tc qdisc show dev "$dev" || true
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echo "== filters (dev ${dev}) =="
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tc filter show dev "$dev" || true
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}
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# ----------------------------------------------------------------------------- dispatch
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cmd="${1:-}"
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case "$cmd" in
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start)
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require_root
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loss="${2:-5}"
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dir="${3:-down}"
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delay="${4:-0}"
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validate_dir "$dir"
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case "$OS" in
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Darwin) macos_start "$loss" "$dir" "$delay" ;;
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Linux) linux_start "$loss" "$dir" "$delay" ;;
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*) echo "error: unsupported OS '$OS'" >&2; exit 1 ;;
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esac
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;;
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burst)
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require_root
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loss="${2:-40}"
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burst_ms="${3:-200}"
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gap_ms="${4:-2000}"
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dir="${5:-down}"
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delay="${6:-20}"
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validate_dir "$dir"
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case "$OS" in
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Darwin) macos_burst "$loss" "$burst_ms" "$gap_ms" "$dir" "$delay" ;;
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Linux) linux_burst "$loss" "$burst_ms" "$gap_ms" "$dir" "$delay" ;;
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*) echo "error: unsupported OS '$OS'" >&2; exit 1 ;;
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esac
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;;
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stop)
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require_root
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case "$OS" in
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Darwin) macos_stop ;;
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Linux) linux_stop ;;
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esac
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;;
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status)
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case "$OS" in
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Darwin) macos_status ;;
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Linux) linux_status ;;
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esac
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;;
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*)
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echo "usage: sudo $0 {start [loss%] [up|down|both] [delay_ms]" >&2
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echo " | burst [loss%] [burst_ms] [gap_ms] [up|down|both] [delay_ms]" >&2
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echo " | stop | status}" >&2
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exit 1
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;;
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esac
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