core-agent-linux/qrexec/qubes-rpc-multiplexer

#!/bin/sh

# write stderr to both calling party and local log; be very careful about
# closing file descriptors here - if either stdout or stderr will not be closed
# when service process does the same - service call will hang (waiting for EOF
# on stdout/stderr)
stderr_pipe=/tmp/qrexec-rpc-stderr.$$
mkfifo $stderr_pipe
# tee can't write to file descriptor, nor /proc/self/fd/2 (EXIO on open)
return_stderr_pipe=/tmp/qrexec-rpc-stderr-return.$$
mkfifo $return_stderr_pipe
{ cat <$return_stderr_pipe >&2 2>/dev/null; rm -f $return_stderr_pipe; } &
{ tee $return_stderr_pipe 2>/dev/null <$stderr_pipe |\
       logger -t "$1-$2" >/dev/null 2>&1; rm -f $stderr_pipe; } &
exec 2>$stderr_pipe

QUBES_RPC=/etc/qubes-rpc
LOCAL_QUBES_RPC=/usr/local/etc/qubes-rpc

if ! [ $# = 2 ] ; then
	echo "$0: bad argument count, usage: $0 SERVICE-NAME REMOTE-DOMAIN-NAME" >&2
	exit 1
fi
export QREXEC_REMOTE_DOMAIN="$2"
export QREXEC_SERVICE_FULL_NAME="$1"
SERVICE_WITHOUT_ARGUMENT="${1%%+*}"
if [ "${QREXEC_SERVICE_FULL_NAME}" != "${SERVICE_WITHOUT_ARGUMENT}" ]; then
    export QREXEC_SERVICE_ARGUMENT="${QREXEC_SERVICE_FULL_NAME#*+}"
fi

for CFG_FILE in $LOCAL_QUBES_RPC/"$1" $QUBES_RPC/"$1" \
        $LOCAL_QUBES_RPC/"${SERVICE_WITHOUT_ARGUMENT}" \
        $QUBES_RPC/"${SERVICE_WITHOUT_ARGUMENT}"; do
	if [ -s "$CFG_FILE" ]; then
        break
	fi
done

if [ -x "$CFG_FILE" ] ; then
    # shellcheck disable=SC2086
	exec "$CFG_FILE" ${QREXEC_SERVICE_ARGUMENT}
	echo "$0: failed to execute handler for" "$1" >&2
	exit 1
else
    # shellcheck disable=SC2086
	exec /bin/sh -- "$CFG_FILE" ${QREXEC_SERVICE_ARGUMENT}
	echo "$0: failed to execute handler for" "$1" >&2
	exit 1
fi