Tests: new tool to build a no-history image

Script crafts a custom image with multiple layers but
no history; used in tests/bud.bats:bud-implicit-no-history test.

Signed-off-by: Ed Santiago <santiago@redhat.com>

tests/make-nohistory-image

@@ -0,0 +1,98 @@
+#!/bin/bash
+#
+# make-no-history-image - craft a custom image used in bud-implicit-no-history test
+#
+# See https://github.com/containers/buildah/pull/5473/files
+#
+set -e
+
+# Name of the resulting image. (Never pushed automatically).
+# If image build is successful, a human can push it to quay.
+IMAGE=quay.io/libpod/buildah-testimage-nohistory:$(date +%Y%m%d)
+
+function createrandom() {
+    outfile=${1?Missing OUTFILE arg to createrandom()}
+    if [[ ! -e $outfile ]]; then
+        dd if=/dev/urandom bs=1 count=${2:-256} of=$outfile status=none
+    fi
+}
+
+workdir=$(mktemp -d)
+
+# First layer is a copy of this script
+# FIXME: find some way to add a label or annotation or something to indicate that
+cp $0 $workdir/file01
+cd $workdir
+
+mkdir -p oci/blobs/sha256
+
+# Build an image config and image manifest in parallel
+# FIXME: find some way to create images for other arches?
+echo '{"architecture": "amd64", "os": "linux", "rootfs": {"type": "layers", "diff_ids": [' > config.json
+echo '{"schemaVersion": 2, "mediaType": "application/vnd.oci.image.manifest.v1+json", "layers": [' > manifest.json
+
+# Create some layers
+for layer in $(seq 16) ; do
+    # Content for the layer
+    createrandom file$layer $((RANDOM+1024))
+    # Layer blob
+    tar -cf layer$layer.tar file$layer
+    # Get the layer blob's digest and size
+    diffid=$(sha256sum layer$layer.tar | awk '{print $1}')
+    diffsize=$(wc -c layer$layer.tar | awk '{print $1}')
+    # Link the blob into where an OCI layout would put it.
+    ln layer$layer.tar oci/blobs/sha256/$diffid
+    # Try to keep the resulting files at least kind of readable.
+    if test $layer -gt 1 ; then
+      echo "," >> config.json
+      echo "," >> manifest.json
+    fi
+
+    # Add the layer to the config blob's list of diffIDs for its rootfs.
+    echo -n '  "sha256:'${diffid}'"' >> config.json
+    # Add the layer blob to the manifest's list of blobs.
+    echo -n '  {"mediaType": "application/vnd.oci.image.layer.v1.tar", "digest": "sha256:'${diffid}'", "size": '${diffsize}'}' >> manifest.json
+done
+
+# Finish the diffID and layer blob lists.
+echo >> config.json
+echo >> manifest.json
+# Finish the config blob with some boilerplate stuff.
+echo ']}, "config": { "Cmd": ["/bin/sh"], "Env": [ "PATH=/usr/local/sbin:/usr/sbin:/sbin:/usr/local/bin:/usr/bin:/bin" ]}}' >> config.json
+
+# Compute the CONFIG BLOB'S digest and size, so that we can list it in the manifest.
+configsize=$(wc -c config.json | awk '{print $1}')
+configdigest=$(sha256sum config.json | awk '{print $1}')
+# Finish the manifest with information about the config blob.
+echo '], "config": { "mediaType": "application/vnd.oci.image.config.v1+json", "digest": "sha256:'${configdigest}'", "size": '${configsize}'}}' >> manifest.json
+
+# Compute the MANIFEST'S digest and size, so that we can list it in the OCI layout index.
+manifestsize=$(wc -c manifest.json | awk '{print $1}')
+manifestdigest=$(sha256sum manifest.json | awk '{print $1}')
+# Link the config blob and manifest into where an OCI layout would put them.
+ln config.json   oci/blobs/sha256/$configdigest
+ln manifest.json oci/blobs/sha256/$manifestdigest
+# Write the layout index with just the one image manifest in it.
+echo '{"schemaVersion": 2, "manifests": [ {"mediaType": "application/vnd.oci.image.manifest.v1+json", "digest": "sha256:'${manifestdigest}'", "size": '${manifestsize}' } ]}' > oci/index.json
+# Write the "this is an OCI layout directory" identifier.
+echo '{"imageLayoutVersion":"1.0.0"}' > oci/oci-layout
+
+# Import the image from the OCI layout into buildah's normal storage.
+skopeo copy oci:oci containers-storage:$IMAGE
+
+# Double-check that the image has no history, which is what we wanted to get
+# out of all of this.
+inspect_history=$(buildah inspect --format '{{.History}}' $IMAGE)
+if [[ "$inspect_history" != '[]' ]]; then
+    echo "base image generated for test had history field that was not an empty slice:" >&2
+    echo "$inspect_history" >&2
+    exit 1
+fi
+
+# Worked. Clean up working directory
+cd /
+rm -rf $workdir
+
+echo
+echo "You may now run:"
+echo "   skopeo copy containers-storage:$IMAGE docker://$IMAGE"