update.sh

#!/bin/bash
set -Eeuo pipefail

cd "$(dirname "$BASH_SOURCE")"

versions=( "$@" )
if [ ${#versions[@]} -eq 0 ]; then
	versions=( */ )
fi
versions=( "${versions[@]%/}" )

hostArch="$(dpkg --print-architecture)"
arch="$(cat arch 2>/dev/null || true)"
: ${arch:=$hostArch}

toVerify=()
for v in "${versions[@]}"; do
	thisTarBase="ubuntu-$v-core-cloudimg-$arch"
	thisTar="$thisTarBase-root.tar.gz"
	baseUrl="https://partner-images.canonical.com/core/$v"
	if \
		wget -q --spider "$baseUrl/current" \
		&& wget -q --spider "$baseUrl/current/$thisTar" \
	; then
		baseUrl+='/current'
	else
		# appears to be missing a "current" symlink (or $arch doesn't exist in /current/)
		# let's enumerate all the directories and try to find one that's satisfactory
		toAttempt=( $(wget -qO- "$baseUrl/" | awk -F '</?a[^>]*>' '$2 ~ /^[0-9.]+\/$/ { gsub(/\/$/, "", $2); print $2 }' | sort -rn) )
		current=
		for attempt in "${toAttempt[@]}"; do
			if wget -q --spider "$baseUrl/$attempt/$thisTar"; then
				current="$attempt"
				break
			fi
		done
		if [ -z "$current" ]; then
			echo >&2 "warning: cannot find 'current' for $v"
			echo >&2 "  (checked all dirs under $baseUrl/)"
			continue
		fi
		baseUrl+="/$current"
		echo "SERIAL=$current" > "$v/build-info.txt" # this will be overwritten momentarily if this directory has one
	fi

	(
		cd "$v"
		wget -qN "$baseUrl/"{{MD5,SHA{1,256}}SUMS{,.gpg},"$thisTarBase.manifest",'unpacked/build-info.txt'} || true
		wget -N "$baseUrl/$thisTar"
	)

	cat > "$v/Dockerfile" <<EOF
FROM scratch
ADD $thisTar /
EOF

	cat >> "$v/Dockerfile" <<'EOF'

# a few minor docker-specific tweaks
# see https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap
RUN set -xe \
	\
# https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L40-L48
	&& echo '#!/bin/sh' > /usr/sbin/policy-rc.d \
	&& echo 'exit 101' >> /usr/sbin/policy-rc.d \
	&& chmod +x /usr/sbin/policy-rc.d \
	\
# https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L54-L56
	&& dpkg-divert --local --rename --add /sbin/initctl \
	&& cp -a /usr/sbin/policy-rc.d /sbin/initctl \
	&& sed -i 's/^exit.*/exit 0/' /sbin/initctl \
	\
# https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L71-L78
	&& echo 'force-unsafe-io' > /etc/dpkg/dpkg.cfg.d/docker-apt-speedup \
	\
# https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L85-L105
	&& echo 'DPkg::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' > /etc/apt/apt.conf.d/docker-clean \
	&& echo 'APT::Update::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' >> /etc/apt/apt.conf.d/docker-clean \
	&& echo 'Dir::Cache::pkgcache ""; Dir::Cache::srcpkgcache "";' >> /etc/apt/apt.conf.d/docker-clean \
	\
# https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L109-L115
	&& echo 'Acquire::Languages "none";' > /etc/apt/apt.conf.d/docker-no-languages \
	\
# https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L118-L130
	&& echo 'Acquire::GzipIndexes "true"; Acquire::CompressionTypes::Order:: "gz";' > /etc/apt/apt.conf.d/docker-gzip-indexes \
	\
# https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L134-L151
	&& echo 'Apt::AutoRemove::SuggestsImportant "false";' > /etc/apt/apt.conf.d/docker-autoremove-suggests

# delete all the apt list files since they're big and get stale quickly
RUN rm -rf /var/lib/apt/lists/*
# this forces "apt-get update" in dependent images, which is also good

# enable the universe
RUN sed -i 's/^#\s*\(deb.*universe\)$/\1/g' /etc/apt/sources.list

# make systemd-detect-virt return "docker"
# See: https://github.com/systemd/systemd/blob/aa0c34279ee40bce2f9681b496922dedbadfca19/src/basic/virt.c#L434
RUN mkdir -p /run/systemd && echo 'docker' > /run/systemd/container

# overwrite this with 'CMD []' in a dependent Dockerfile
CMD ["/bin/bash"]
EOF

	toVerify+=( "$v" )
done

( set -x; ./verify.sh "${toVerify[@]}" )

if [ "$arch" = "$hostArch" ]; then
	repo="$(cat repo 2>/dev/null || true)"
	if [ -z "$repo" ]; then
		user="$(docker info | awk -F ': ' '$1 == "Username" { print $2; exit }')"
		repo="${user:+$user/}ubuntu-core"
	fi
	latest="$(< latest)"
	for v in "${versions[@]}"; do
		if [ ! -f "$v/Dockerfile" ]; then
			echo >&2 "warning: $v/Dockerfile does not exist; skipping $v"
			continue
		fi
		( set -x; docker build -t "$repo:$v" "$v" )
		serial="$(awk -F '=' '$1 == "SERIAL" { print $2; exit }' "$v/build-info.txt")"
		if [ "$serial" ]; then
			( set -x; docker tag "$repo:$v" "$repo:$v-$serial" )
		fi
		if [ -s "$v/alias" ]; then
			for a in $(< "$v/alias"); do
				( set -x; docker tag "$repo:$v" "$repo:$a" )
			done
		fi
		if [ "$v" = "$latest" ]; then
			( set -x; docker tag "$repo:$v" "$repo:latest" )
		fi
	done
fi