Create a Debian mirror from /var/cache/apt, /var/lib/apt and /var/lib/dpkg. Mirror directory can then be used as "file:///path/to/mirror"

make-debian-mirror.sh

#! /bin/bash

if test $# -ne 2; then
    echo "usage: $0 <chroot-dir> <mirror-dir>" >&2
    exit 2
fi

chroot_dir="$1"
mirror_dir="$2"

# collect path information
dpkg_dir="/var/lib/dpkg"
dpkg_available="${chroot_dir}/${dpkg_dir}/available"

declare -A dpkg_filenames
# pipeline doesn't work here, because of while subprocess
# awk '$1 == "Filename:" {print $2;}' "${dpkg_available}" | while read f; do
while read f; do
    base="${f##*/}"
    path="${f%/*}"
    dpkg_filenames["${base}"]="${path}"
done < <(awk '$1 == "Filename:" {print $2;}' "${dpkg_available}")

# create pool directories
apt_cache_dir="/var/cache/apt"
apt_archives="${apt_cache_dir}/archives"
cd "${chroot_dir}/${apt_archives}"
for f in *.deb; do
    # drop epoch prefix
    pkg="${f/?%3a}"
    path="${dpkg_filenames[${pkg}]}"
    mkdir -p "${mirror_dir}/${path}"
    cp "$f" "${mirror_dir}/${path}/${pkg}"
done

# create dists directories
apt_lib_dir="/var/lib/apt"
apt_lists_dir="${apt_lib_dir}/lists"
cd "${chroot_dir}/${apt_lists_dir}"
for f in *_dists_*; do
    # replace underscores with slashes
    : "${f//_/\/}"
    filename="${_##*/dists/}"
    base="${filename##*/}"
    path="${filename%/*}"
    mkdir -p "${mirror_dir}/dists/${path}"
    cp "$f" "${mirror_dir}/dists/${filename}"
done