#!/bin/bash
# brintos-agent — serve a control channel so a host-side agent can drive this
# machine. The host runs run-machine-agent.mjs --control-socket <path>, which
# publishes virtio-console port 1; the guest sees it as /dev/vport<dev>p1.
#
# Wire protocol: "<mark> <command>\n" in, "<output>\n<mark>\n" out.
# The mark travels as the FIRST WORD of the request, so a fresh mark per call
# can never collide with command output. It cannot be set by the request
# itself: eval runs inside $(...) — a subshell — so an assignment made there
# would never reach the printf.
#
# The port is SINGLE-OPEN: one fd, used for both directions.
PORT="${1:-/dev/vport1p1}"
[ -e "$PORT" ] || { echo "brintos-agent: no $PORT (host did not offer a control port)" >&2; exit 1; }
exec 4<>"$PORT"
while read -r __m __c <&4; do
  __o=$(eval "$__c" 2>&1)
  printf "%s\n%s\n" "$__o" "$__m" >&4
done