diskimage-builder/elements/ubuntu-core/root.d/10-cache-ubuntu-image

#!/bin/bash
# These are useful, or at worst not harmful, for all images we build.

if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
    set -x
fi
set -eu
set -o pipefail

[ -n "$ARCH" ]
[ -n "$TARGET_ROOT" ]

shopt -s extglob

DIB_RELEASE=${DIB_RELEASE:-trusty}

declare -A release_numbers
release_numbers[precise]=12.04
release_numbers[trusty]=14.04
release_numbers[vivid]=15.04
release_numbers[wily]=15.10

numeric_release=${release_numbers[$DIB_RELEASE]}
DIB_CLOUD_IMAGES=${DIB_CLOUD_IMAGES:-http://cdimage.ubuntu.com/ubuntu-core/releases/$numeric_release/release}
BASE_IMAGE_FILE=${BASE_IMAGE_FILE:-ubuntu-core-$numeric_release-core-$ARCH.tar.gz}
SHA256SUMS=${SHA256SUMS:-$DIB_CLOUD_IMAGES/SHA256SUMS}
CACHED_FILE=$DIB_IMAGE_CACHE/$BASE_IMAGE_FILE
CACHED_FILE_LOCK=$DIB_IMAGE_CACHE/$BASE_IMAGE_FILE.lock
CACHED_SUMS=$DIB_IMAGE_CACHE/SHA256SUMS.ubuntu-core.$DIB_RELEASE.$ARCH

function get_ubuntu_tarball() {
    if [ -n "$DIB_OFFLINE" -a -f "$CACHED_FILE" ] ; then
        echo "Not checking freshness of cached $CACHED_FILE."
    else
        echo "Fetching Base Image"
        $TMP_HOOKS_PATH/bin/cache-url $SHA256SUMS $CACHED_SUMS
        $TMP_HOOKS_PATH/bin/cache-url \
            $DIB_CLOUD_IMAGES/$BASE_IMAGE_FILE $CACHED_FILE
        pushd $DIB_IMAGE_CACHE
        if ! grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check - ; then
            # It is likely that an upstream http(s) proxy has given us a skewed
            # result - either a cached SHA file or a cached image. Use cache-busting
            # to get (as long as caches are compliant...) fresh files.
            # Try the sha256sum first, just in case that is the stale one (avoiding
            # downloading the larger image), and then if the sums still fail retry
            # the image.
            $TMP_HOOKS_PATH/bin/cache-url -f $SHA256SUMS $CACHED_SUMS
            if ! grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check - ; then
                $TMP_HOOKS_PATH/bin/cache-url -f \
                    $DIB_CLOUD_IMAGES/$BASE_IMAGE_FILE $CACHED_FILE
                grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check -
            fi
        fi
        popd
    fi
    # Extract the base image (use --numeric-owner to avoid UID/GID mismatch between
    # image tarball and host OS e.g. when building Ubuntu image on an openSUSE host)
    sudo tar -C $TARGET_ROOT --numeric-owner -xzf $DIB_IMAGE_CACHE/$BASE_IMAGE_FILE
}

(
    echo "Getting $CACHED_FILE_LOCK: $(date)"
    # Wait up to 20 minutes for another process to download
    if ! flock -w 1200 9 ; then
        echo "Did not get $CACHED_FILE_LOCK: $(date)"
        exit 1
    fi
    get_ubuntu_tarball
) 9> $CACHED_FILE_LOCK