BuildSourceImage: expose "unpack" as subcommand

This may be a pattern we can do for some of the more useful functions.
But for now, folks can build, push, etc. and once they skopeo copy an
image to their host, they can

```bash
./BuildSourceImage unpack <src> <dest>
```

and it will be nicely exposed in the container build too

Also included, exporting the defaults into the bats test for easier
direct running. Perhaps we can move the srpm caching into bats too, so
the Makefile target isn't strictly required.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

BuildSourceImage.sh

@@ -28,6 +28,10 @@ _usage() {
     echo -e "       -D\t\tdebuging output. Can be set via DEBUG env variable"
     echo -e "       -h\t\tthis usage information"
     echo -e "       -v\t\tversion"
+    echo -e ""
+    echo -e "    Subcommands:"
+    echo -e "       unpack\tUnpack an OCI layout to a rootfs directory"
+    echo -e ""
 }
 
 # sanity checks on startup
@@ -44,6 +48,23 @@ _init() {
     done
 }
 
+# enable access to some of functions as subcommands!
+_subcommand() {
+    local command="${1}"
+    local ret
+
+    shift
+
+    case "${command}" in
+        unpack)
+            # (vb) i'd prefer this subcommand directly match the function name, but it isn't as pretty.
+            unpack_img "${@}"
+            ret=$?
+            exit "${ret}"
+            ;;
+    esac
+}
+
 # _is_sourced tests whether this script is being source, or executed directly
 _is_sourced() {
     # https://unix.stackexchange.com/a/215279
@@ -292,6 +313,20 @@ unpack_img() {
     local unpack_dir="${2}"
     local ret
 
+    while getopts ":h" opts; do
+        case "${opts}" in
+            *)
+                echo "$0 unpack <oci layout path> <unpack path>"
+                return 1
+                ;;
+        esac
+    done
+    shift $((OPTIND-1))
+
+    if [ -z "${image_dir}" ] || [ -z "${unpack_dir}" ] ; then
+        _error "[unpack_img] blank arguments provided"
+    fi
+
     if [ -d "${unpack_dir}" ] ; then
         _rm_rf "${unpack_dir}"
     fi
@@ -336,9 +371,10 @@ unpack_img_bash() {
         return ${ret}
     fi
 
-    # Since we're landing the reference as an OCI layout, this mediaType is fairly predictable
-    # TODO don't always assume +gzip
-    layer_dgsts="$(jq '.layers[] | select(.mediaType == "application/vnd.oci.image.layer.v1.tar+gzip") | .digest' "${image_dir}"/blobs/"${mnfst_dgst/:/\/}" | tr -d \")"
+    # TODO this will need to be refactored when we start seeing +zstd layers.
+    # Then it will be better to no just get a list of digests, but maybe to
+    # iterate on each descriptor independently?
+    layer_dgsts="$(jq '.layers | map(select(.mediaType == "application/vnd.oci.image.layer.v1.tar+gzip"),select(.mediaType == "application/vnd.oci.image.layer.v1.tar"),select(.mediaType == "application/vnd.docker.image.rootfs.diff.tar.gzip")) | .[] | .digest' "${image_dir}"/blobs/"${mnfst_dgst/:/\/}" | tr -d \")"
     ret=$?
     if [ ${ret} -ne 0 ] ; then
         return ${ret}
@@ -1026,8 +1062,9 @@ main() {
     local work_dir
 
     _init "${@}"
+    _subcommand "${@}"
 
-    base_dir="$(pwd)/${ABV_NAME}"
+    base_dir="${BASE_DIR:-$(pwd)/${ABV_NAME}}"
     # using the bash builtin to parse
     while getopts ":hlvDi:c:s:e:o:b:d:p:" opts; do
         case "${opts}" in

Dockerfile

@@ -4,4 +4,6 @@ RUN dnf install -y jq skopeo findutils file 'dnf-command(download)'
 
 COPY ./BuildSourceImage.sh /usr/local/bin/BuildSourceImage.sh
 
-ENTRYPOINT ["/usr/local/bin/BuildSourceImage.sh", "-b", "/tmp/"]
+ENV BASE_DIR=/tmp
+
+ENTRYPOINT ["/usr/local/bin/BuildSourceImage.sh"]

test/02-from_image_ref.bats

@@ -3,6 +3,7 @@
 load helpers
 
 @test "Build from image reference" {
+	#skip "this takes like 20min ..."
     local d
     d=$(mktemp -d)
     echo "temporary directory: ${d}"

test/03-unpack.bats

@@ -0,0 +1,32 @@
+#!/usr/bin/env bats -t
+
+load helpers
+
+@test "unpack - no args" {
+	run_ctr $CTR_IMAGE unpack
+	[ "$status" -eq 1 ]
+	[[ ${lines[0]} =~ "[SrcImg][ERROR] [unpack_img] blank arguments provided" ]]
+}
+
+@test "unpack - Help" {
+	run_ctr $CTR_IMAGE unpack -h
+	[ "$status" -eq 1 ]
+	[[ ${lines[0]} =~ "BuildSourceImage.sh unpack <oci layout path> <unpack path>" ]]
+}
+
+@test "unpack - from a SRPM build" {
+	local d
+	local r
+
+	d=$(mktemp -d)
+	echo "temporary directories: output - ${d}"
+	run_ctr -v $(pwd)/.testprep/srpms/:/src:ro --mount type=bind,source=${d},destination=/output $CTR_IMAGE -s /src -o /output
+	[ "$status" -eq 0 ]
+	[ -f "${d}/index.json" ]
+
+	r=$(mktemp -d)
+	echo "temporary directories: unpacked - ${r}"
+	run_ctr --mount type=bind,source=${d},destination=/output -v ${r}:/unpacked/ $CTR_IMAGE unpack /output/ /unpacked/
+	[ "$(find ${r} -type f | wc -l)" -eq 3 ] # regular files
+	[ "$(find ${r} -type l | wc -l)" -eq 3 ] # and symlinks
+}

test/helpers.bash

@@ -1,3 +1,8 @@
+#!/bin/bash
+
+export CTR_IMAGE="${CTR_IMAGE:-localhost/containers/buildsourceimage}"
+export CTR_ENGINE="${CTR_ENGINE:-podman}"
+
 function run_ctr() {
 	run $CTR_ENGINE run --security-opt label=disable --rm "$@"
 }