diskimage-builder/elements/ubuntu/root.d/10-cache-ubuntu-tarball

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

set -e

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

shopt -s extglob

IMG_PATH=~/.cache/image-create
DIB_CLOUD_IMAGES=${DIB_CLOUD_IMAGES:-http://cloud-images.ubuntu.com/}
DIB_RELEASE=${DIB_RELEASE:-quantal}
BASE_IMAGE_FILE=${BASE_IMAGE_FILE:-$DIB_RELEASE-server-cloudimg-$ARCH-root.tar.gz}
SHA256SUMS=${SHA256SUMS:-https://${DIB_CLOUD_IMAGES##http?(s)://}/$DIB_RELEASE/current/SHA256SUMS}

cache_url()
{
    local url=$1
    local dest=$2
    local tmp=$(mktemp $(dirname $dest)/.download.XXXXXXXX)
    rcode=$(curl -o $tmp -z $dest -w '%{http_code}' $url)
    if [ "$rcode"  == "200" ] ; then
        echo "Server copy has changed. Using server version of $url"
        mv $tmp $dest
    elif [ "$rcode" == "304" ] ; then
        echo "Server copy has not changed. Using locally cached $url"
        rm -f $tmp
    else
        echo "Server returned an unexpected response code. [$rcode]"
        rm -f $tmp
        return 1
    fi
}

mkdir -p $IMG_PATH
echo "Fetching Base Image"
cache_url $SHA256SUMS $IMG_PATH/SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH
cache_url $DIB_CLOUD_IMAGES/$DIB_RELEASE/current/$BASE_IMAGE_FILE $IMG_PATH/$BASE_IMAGE_FILE
pushd $IMG_PATH
grep "$BASE_IMAGE_FILE" SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH | sha256sum --check -
popd
# Extract the base image
sudo tar -C $TARGET_ROOT -xzf $IMG_PATH/$BASE_IMAGE_FILE
sudo rmdir $TARGET_ROOT/lost+found