Allow download-frozen-images to work without `go`

Currently we use the `go` command to read GOARCH and use the value for
matching manifests.

This change allows:

1. Specifying the arch through `TARGETARCH`
2. Falling back to `dpkg` if `go` is not available
3. Falling back to `uname -m` if `dpkg` is not available
4. A default value (amd64) if none of these commands is available.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

Dockerfile

@@ -7,7 +7,9 @@ ARG GO_VERSION=1.13.15
 ARG DEBIAN_FRONTEND=noninteractive
 ARG VPNKIT_VERSION=0.4.0
 ARG DOCKER_BUILDTAGS="apparmor seccomp selinux"
-ARG GOLANG_IMAGE="golang:${GO_VERSION}-buster"
+
+ARG BASE_DEBIAN_DISTRO="buster"
+ARG GOLANG_IMAGE="golang:${GO_VERSION}-${BASE_DEBIAN_DISTRO}"
 
 FROM ${GOLANG_IMAGE} AS base
 RUN echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' > /etc/apt/apt.conf.d/keep-cache
@@ -79,12 +81,13 @@ RUN --mount=type=cache,target=/root/.cache/go-build \
         && git checkout -q "$GO_SWAGGER_COMMIT" \
         && go build -o /build/swagger github.com/go-swagger/go-swagger/cmd/swagger
 
-FROM base AS frozen-images
+FROM debian:${BASE_DEBIAN_DISTRO} AS frozen-images
 ARG DEBIAN_FRONTEND
 RUN --mount=type=cache,sharing=locked,id=moby-frozen-images-aptlib,target=/var/lib/apt \
     --mount=type=cache,sharing=locked,id=moby-frozen-images-aptcache,target=/var/cache/apt \
        apt-get update && apt-get install -y --no-install-recommends \
            ca-certificates \
+           curl \
            jq
 # Get useful and necessary Hub images so we can "docker load" locally instead of pulling
 COPY contrib/download-frozen-image-v2.sh /

contrib/download-frozen-image-v2.sh

@@ -8,7 +8,7 @@ set -eo pipefail
 # debian                           latest              f6fab3b798be3174f45aa1eb731f8182705555f89c9026d8c1ef230cbf8301dd   10 weeks ago        85.1 MB
 
 # check if essential commands are in our PATH
-for cmd in curl jq go; do
+for cmd in curl jq; do
 	if ! command -v $cmd &> /dev/null; then
 		echo >&2 "error: \"$cmd\" not found!"
 		exit 1
@@ -36,13 +36,11 @@ manifestJsonEntries=()
 doNotGenerateManifestJson=
 # repositories[busybox]='"latest": "...", "ubuntu-14.04": "..."'
 
-# bash v4 on Windows CI requires CRLF separator
+# bash v4 on Windows CI requires CRLF separator... and linux doesn't seem to care either way
 newlineIFS=$'\n'
-if [ "$(go env GOHOSTOS)" = 'windows' ]; then
+major=$(echo "${BASH_VERSION%%[^0.9]}" | cut -d. -f1)
-	major=$(echo "${BASH_VERSION%%[^0.9]}" | cut -d. -f1)
+if [ "$major" -ge 4 ]; then
-	if [ "$major" -ge 4 ]; then
+	newlineIFS=$'\r\n'
-		newlineIFS=$'\r\n'
-	fi
 fi
 
 registryBase='https://registry-1.docker.io'
@@ -201,6 +199,68 @@ handle_single_manifest_v2() {
 	manifestJsonEntries=("${manifestJsonEntries[@]}" "$manifestJsonEntry")
 }
 
+get_target_arch() {
+	if [ -n "${TARGETARCH:-}" ]; then
+		echo "${TARGETARCH}"
+		return 0
+	fi
+
+	if type go > /dev/null; then
+		go env GOARCH
+		return 0
+	fi
+
+	if type dpkg > /dev/null; then
+		debArch="$(dpkg --print-architecture)"
+		case "${debArch}" in
+			armel | armhf)
+				echo "arm"
+				return 0
+				;;
+			*64el)
+				echo "${debArch%el}le"
+				return 0
+				;;
+			*)
+				echo "${debArch}"
+				return 0
+				;;
+		esac
+	fi
+
+	if type uname > /dev/null; then
+		uArch="$(uname -m)"
+		case "${uArch}" in
+			x86_64)
+				echo amd64
+				return 0
+				;;
+			arm | armv[0-9]*)
+				echo arm
+				return 0
+				;;
+			aarch64)
+				echo arm64
+				return 0
+				;;
+			mips*)
+				echo >&2 "I see you are running on mips but I don't know how to determine endianness yet, so I cannot select a correct arch to fetch."
+				echo >&2 "Consider installing \"go\" on the system which I can use to determine the correct arch or specify it explictly by setting TARGETARCH"
+				exit 1
+				;;
+			*)
+				echo "${uArch}"
+				return 0
+				;;
+		esac
+
+	fi
+
+	# default value
+	echo >&2 "Unable to determine CPU arch, falling back to amd64. You can specify a target arch by setting TARGETARCH"
+	echo amd64
+}
+
 while [ $# -gt 0 ]; do
 	imageTag="$1"
 	shift
@@ -250,11 +310,12 @@ while [ $# -gt 0 ]; do
 					unset IFS
 
 					found=""
+					targetArch="$(get_target_arch)"
 					# parse first level multi-arch manifest
 					for i in "${!layers[@]}"; do
 						layerMeta="${layers[$i]}"
 						maniArch="$(echo "$layerMeta" | jq --raw-output '.platform.architecture')"
-						if [ "$maniArch" = "$(go env GOARCH)" ]; then
+						if [ "$maniArch" = "${targetArch}" ]; then
 							digest="$(echo "$layerMeta" | jq --raw-output '.digest')"
 							# get second level single manifest
 							submanifestJson="$(