#!/bin/sh

set -eu


die()
{
    echo "$@" 1>&2
    exit 1
}


recv_hole()
{
    local n

    read n
    truncate --size "+$n" "$1"
}


recv_data()
{
    local n

    read n
    dd of="$1" conv=notrunc oflag=append bs=1 count="$n" status=noxfer 2>&1 |
    grep -Ev ' records (in|out)$' || true
}


output="$1"

touch "$output"
while read what
do
    case "$what" in
        DATA) recv_data "$output" ;;
        HOLE) recv_hole "$output" ;;
        *) die "Unknown instruction: $what" ;;
    esac
done