mdns-termux/bin/resolve

#!/data/data/com.termux/files/usr/bin/bash
# resolve: hostname -> IP
# Order:  mdns (zeroconf) -> mdns-resolve (stdlib) -> Tailscale DNS -> local cache
# Use in any command:
#   ping $(resolve lenovo)   /   curl "http://$(resolve hp62a)"
set -e
HOST="${1:-}"
[[ -z "$HOST" ]] && { echo "Usage: resolve <hostname>" >&2; exit 1; }

CACHE="$HOME/.ssh/resolve-cache"
TAILSCALE_DOMAIN="${TAILSCALE_DOMAIN:-tailb0bb74.ts.net}"
MDNS_TIMEOUT="${MDNS_TIMEOUT:-2}"

QUERY="${HOST%.local}"
QUERY="${QUERY%.${TAILSCALE_DOMAIN}}"

declare -A ALIASES=(
    [dell]="dell-latitude3400"
    [lenovo]="lenovo-ideapad"
)
[[ -n "${ALIASES[$QUERY]:-}" ]] && QUERY="${ALIASES[$QUERY]}"

IP=""

# 1. mdns (zeroconf-based, richer: retries + TTL cache)
if command -v mdns >/dev/null 2>&1; then
    IP=$(mdns resolve --timeout "$MDNS_TIMEOUT" "$QUERY" 2>/dev/null || true)
fi

# 2. stdlib fallback (no zeroconf needed)
if [[ -z "$IP" ]] && command -v mdns-resolve >/dev/null 2>&1; then
    IP=$(mdns-resolve "${QUERY}.local" "$MDNS_TIMEOUT" 2>/dev/null || true)
fi

# 3. Tailscale MagicDNS (off-LAN)
if [[ -z "$IP" ]]; then
    IP=$(python -c "import socket; print(socket.gethostbyname('${QUERY}.${TAILSCALE_DOMAIN}'))" 2>/dev/null || true)
fi

# 4. Legacy flat cache (last resort)
if [[ -z "$IP" && -f "$CACHE" ]]; then
    IP=$(grep "^${QUERY} " "$CACHE" 2>/dev/null | awk '{print $2}')
fi

if [[ -z "$IP" ]]; then
    echo "Error: could not resolve '${HOST}'" >&2
    exit 1
fi

mkdir -p "$(dirname "$CACHE")"
grep -v "^${QUERY} " "$CACHE" > "${CACHE}.tmp" 2>/dev/null || true
echo "${QUERY} ${IP}" >> "${CACHE}.tmp"
mv "${CACHE}.tmp" "$CACHE"

echo "$IP"