Update "download-frozen-image-v2.sh" such that redirects are optional

If the registry responds directly with blob contents, use them,
otherwise follow the redirect without Authorization headers (which
likely aren't valid for the server being redirected to).

This preserves the basic structure of the previous output with up to one
additional progress bar per-layer (for the redirect request and then the
following blob request).

Signed-off-by: Tianon Gravi <admwiggin@gmail.com>

contrib/download-frozen-image-v2.sh

@@ -44,16 +44,41 @@ if [ "$(go env GOHOSTOS)" = 'windows' ]; then
 	fi
 fi
 
-fetch_blob() {
-	url=$1
-	token=$2
-	dest=$3
-	echo "Attempting to download blob $url"
-	target=$(curl -sS -v -H "Authorization: Bearer $token" "$url" 2>&1 | grep "Location:" | sed 's/< Location: \(.*\)\r/\1/')
-	# curl blob (exclude auth token)
-	curl -fsS --progress "${target}" -o "$dest"
-}
+registryBase='https://registry-1.docker.io'
+authBase='https://auth.docker.io'
+authService='registry.docker.io'
 
+# https://github.com/moby/moby/issues/33700
+fetch_blob() {
+	local token="$1"; shift
+	local image="$1"; shift
+	local digest="$1"; shift
+	local targetFile="$1"; shift
+	local curlArgs=( "$@" )
+
+	local curlHeaders="$(
+		curl -S "${curlArgs[@]}" \
+			-H "Authorization: Bearer $token" \
+			"$registryBase/v2/$image/blobs/$digest" \
+			-o "$targetFile" \
+			-D-
+	)"
+	curlHeaders="$(echo "$curlHeaders" | tr -d '\r')"
+	if [ "$(echo "$curlHeaders" | awk 'NR == 1 { print $2; exit }')" != '200' ]; then
+		rm -f "$targetFile"
+
+		local blobRedirect="$(echo "$curlHeaders" | awk -F ': ' 'tolower($1) == "location" { print $2; exit }')"
+		if [ -z "$blobRedirect" ]; then
+			echo >&2 "error: failed fetching '$image' blob '$digest'"
+			echo "$curlHeaders" | head -1 >&2
+			return 1
+		fi
+
+		curl -fSL "${curlArgs[@]}" \
+			"$blobRedirect" \
+			-o "$targetFile"
+	fi
+}
 
 while [ $# -gt 0 ]; do
 	imageTag="$1"
@@ -70,14 +95,14 @@ while [ $# -gt 0 ]; do
 
 	imageFile="${image//\//_}" # "/" can't be in filenames :)
 
-	token="$(curl -fsSL "https://auth.docker.io/token?service=registry.docker.io&scope=repository:$image:pull" | jq --raw-output '.token')"
+	token="$(curl -fsSL "$authBase/token?service=$authService&scope=repository:$image:pull" | jq --raw-output '.token')"
 
 	manifestJson="$(
 		curl -fsSL \
 			-H "Authorization: Bearer $token" \
 			-H 'Accept: application/vnd.docker.distribution.manifest.v2+json' \
 			-H 'Accept: application/vnd.docker.distribution.manifest.v1+json' \
-			"https://registry-1.docker.io/v2/$image/manifests/$digest"
+			"$registryBase/v2/$image/manifests/$digest"
 	)"
 	if [ "${manifestJson:0:1}" != '{' ]; then
 		echo >&2 "error: /v2/$image/manifests/$digest returned something unexpected:"
@@ -98,7 +123,7 @@ while [ $# -gt 0 ]; do
 					imageId="${configDigest#*:}" # strip off "sha256:"
 
 					configFile="$imageId.json"
-					fetch_blob "https://registry-1.docker.io/v2/$image/blobs/$configDigest" $token "$dir/$configFile"
+					fetch_blob "$token" "$image" "$configDigest" "$dir/$configFile" -s
 
 					layersFs="$(echo "$manifestJson" | jq --raw-output --compact-output '.layers[]')"
 					IFS="$newlineIFS"
@@ -165,8 +190,8 @@ while [ $# -gt 0 ]; do
 									echo "skipping existing ${layerId:0:12}"
 									continue
 								fi
-								token="$(curl -fsSL "https://auth.docker.io/token?service=registry.docker.io&scope=repository:$image:pull" | jq --raw-output '.token')"
-								fetch_blob "https://registry-1.docker.io/v2/$image/blobs/$layerDigest" $token "$dir/$layerTar"
+								token="$(curl -fsSL "$authBase/token?service=$authService&scope=repository:$image:pull" | jq --raw-output '.token')"
+								fetch_blob "$token" "$image" "$layerDigest" "$dir/$layerTar" --progress
 								;;
 
 							*)
@@ -235,9 +260,8 @@ while [ $# -gt 0 ]; do
 					echo "skipping existing ${layerId:0:12}"
 					continue
 				fi
-				token="$(curl -fsSL "https://auth.docker.io/token?service=registry.docker.io&scope=repository:$image:pull" | jq --raw-output '.token')"
-				# find redirect using token:
-				fetch_blob "https://registry-1.docker.io/v2/$image/blobs/$imageLayer" $token "$dir/$layerId/layer.tar"
+				token="$(curl -fsSL "$authBase/token?service=$authService&scope=repository:$image:pull" | jq --raw-output '.token')"
+				fetch_blob "$token" "$image" "$imageLayer" "$dir/$layerId/layer.tar" --progress
 			done
 			;;