shell script to mirror locally a subset of packages from an external repository

apt-local-mirror.sh

#!/bin/sh -e

# - create a root directory (into /var/local or similar, eg: apt-repos/)
# - create a somerepo.conf file (will be sourced by this script)
#
#    # _URL+_DIR is the path to download the source Packages.gz
#    # "Filename:" in Packages is relative to _URL (eg: _URL/pool/...)
#    SRC_REPO_URL="http://some-url"
#    SRC_REPO_DIR="dists/sid/main/binary-amd64"
#
#    # names of the packages to watch/mirror separated by space
#    PACKAGES="package1 package2"
#
#    # a label to be used as output directory/namespace
#    OUT_REPO_DIR="somerepo-sid-amd64"

# - run the script like "script /var/local/my-repos/ /var/local/my-repos/somerepo.conf"

# ├── somerepo-sid-amd64
# │   ├── Packages
# │   ├── pool
# │   │   └── main
# │   │       └── p
# │   │           └── package1
# │   │               └── package1_bla_amd64.deb
# │   │           └── package2
# │   │               └── package2_bla_amd64.deb
# │   └── Release
# ├── somerepo.conf
# └── src
#     └── somerepo-sid-amd64
#         └── Packages.gz

# - add "deb [trust=yes] file:/var/local/somerepo-sid-amd64/ ./" to sources.list
#   # careful with [trust]
# - (optional) add and edit /etc/apt/apt.conf.d/99-apt-watch
#   APT::Update::Pre-Invoke { "/var/local/apt-repos/apt-local-mirror.sh /var/local/apt-repos /var/local/apt-repos/somerepo.conf" };
# - apt-get update

# to force an update just remove the generated Release

dl_src_repo_Packages() {
    wget -q -P "$ROOT/$1" -N "$SRC_REPO_URL/$SRC_REPO_DIR/Packages.gz"
}

pkg_to_file() {
    # TODO better way to escape special chars for awk's matches?
    F="$(echo "$1" | sed 's/\+/\\+/g')"
    zcat "$ROOT/$2/Packages.gz" | \
        awk 'BEGIN{}/^Package: '"$F"'$/,/Filename:/{FILE=$2;next}END{print FILE}'
}

dl_package() {
    wget -q -P "$(dirname "$1")" -N "$SRC_REPO_URL/$1"
}

main() {
    if [ ! -e "$2" ]; then
        echo "conf '$2' doesn't exist" >&2
        exit 1
    fi
    . "$2"

    SRC_REPO_NS="src/$OUT_REPO_DIR"

    ROOT="$(realpath -e "$1")"
    cd "$ROOT"
    dl_src_repo_Packages "$SRC_REPO_NS"

    [ -d "$OUT_REPO_DIR" ] || mkdir -p "$OUT_REPO_DIR"
    cd "$OUT_REPO_DIR"
    
    if [ ! -e ./Release ] \
           || [ "$ROOT/$SRC_REPO_NS/Packages.gz" -nt ./Release ] ;
    then
        for P in $PACKAGES; do
            PKG="$(pkg_to_file "$P" "$SRC_REPO_NS")"
            # if the file doesn't exists then is the first time or a new version
            if [ ! -e "$PKG" ]; then
                dl_package "$PKG"
            fi
        done
        apt-ftparchive packages . > Packages
        apt-ftparchive release . > Release
        #gpg --clearsign --output InRelease Release
        #echo "deb [trusted=yes] file:$PWD/ ./"
    fi
}

usage() {
    echo "command [root] [conf]" >&2
    exit 1
}

if [ $# -lt 2 ] ; then
    usage
fi

echo "apt-local-mirror: updating $2..." >&2

main "$1" "$2"