scripts/update-gh-pages: manage a Helm repo

Make the update-gh-pages.sh script to maintain a Helm charts repository
under charts/ subdirectory in gh-pages. The script now (always) scans
throught all release assets and injects any found Helm chart archives
into the Helm repo. In practice, new assets in all Github releases are
scanned and the Helm repo is updated on any update of the master or
release branches or on any new tags. Asset ids are tracked/cached in
order to avoid unnecessary downloads, but also, to capture any changes
in assets that were already merged in the repo index.

After this a user is able to do something like

$ helm repo add nfd http://kubernetes-sigs.github.io/node-feature-discovery/charts
  ...
$ helm repo update
  ...
$ helm install nfd/node-feature-discovery --namespace nfd --create-namespace --generate-name
  ...

.github/workflows/gh-pages.yml

@@ -12,6 +12,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
+    - name: Install dependencies
+      run: |
+        sudo apt-get install -y jq curl
+        curl -sfL https://raw.githubusercontent.com/helm/helm/master/scripts/get-helm-3 | bash -s -- --version v3.5.2
+
     - name: Check out repo
       uses: actions/checkout@v1
       with:

scripts/github/update-gh-pages.sh

@@ -22,11 +22,59 @@ create_versions_js() {
     # 'stable' is a symlink pointing to the latest version
     [ -f stable ] && echo "    { name: 'stable', url: '$_baseurl/stable' },"
     for f in `ls -d */  | tr -d /` ; do
-        echo "    { name: '$f', url: '$_baseurl/$f' },"
+        if [ -f "$f/index.html" ]; then
+            echo "    { name: '$f', url: '$_baseurl/$f' },"
+        fi
     done
     echo -e "  ];\n}"
 }
 
+# Helper for updating help repo index
+update_helm_repo_index() {
+    echo "Updating Helm repo index"
+
+    # TODO: with a lot of releases github API will paginate and this will break
+    releases="`curl -sSf -H 'Accept: application/vnd.github.v3+json' \
+        $GITHUB_API_URL/repos/$GITHUB_REPOSITORY/releases | jq -c '.[]'`"
+
+    for release_meta in $releases; do
+        # Set fields we're interested in as shell variables
+        eval `echo $release_meta | jq -r '{tag_name, url, assets} | keys[] as $k | "\($k)='"'"'\(.[$k])'"'"'"'`
+
+        for asset_meta in `echo $assets | jq -c '.[]'`; do
+            # Set fields we're interested in as "asset_<field>" shell variables
+            eval `echo $asset_meta | jq -r '{id, name, url, browser_download_url} | keys[] as $k | "local asset_\($k)=\(.[$k])"'`
+
+            if [[ "$asset_name" != node-feature-discovery-chart-*tgz ]]; then
+                echo "Asset $asset_name does not look like a Helm chart archive, skipping..."
+                continue
+            fi
+
+            # Check if the asset has changed
+            asset_id_old=`cat "$asset_name".id 2> /dev/null || :`
+            if [[ $asset_id_old == $asset_id ]]; then
+                echo "$asset_name (id=$asset_id) unchanged, skipping..."
+                continue
+            fi
+
+            # Update helm repo index
+            local tmpdir="`mktemp -d`"
+
+            echo "Downloading $asset_name..."
+            curl -sSfL -H "Accept:application/octet-stream" -o "$tmpdir/$asset_name" $asset_url
+
+            echo "Updating helm index for $asset_name..."
+            local download_baseurl=`dirname $asset_browser_download_url`
+            helm repo index "$tmpdir" --merge index.yaml --url $download_baseurl
+            cp "$tmpdir/index.yaml" .
+            rm -rf "$tmpdir"
+
+            # Update id cache file
+            echo $asset_id > "$asset_name".id
+        done
+    done
+}
+
 #
 # Argument parsing
 #
@@ -132,7 +180,7 @@ else
 fi
 
 # Switch to work in the gh-pages worktree
-cd "$build_dir"
+pushd "$build_dir"
 
 _stable=`(ls -d1 v*/ || :) | sort -n | tail -n1`
 [ -n "$_stable" ] && ln -sfT "$_stable" stable
@@ -140,10 +188,18 @@ _stable=`(ls -d1 v*/ || :) | sort -n | tail -n1`
 # Detect existing versions from the gh-pages branch
 create_versions_js > versions.js
 
+# Create index.html
 cat > index.html << EOF
 <meta http-equiv="refresh" content="0; URL='stable/'"/>
 EOF
 
+# Update Helm repo
+mkdir -p charts
+pushd charts
+update_helm_repo_index
+popd
+
+# Check if there were any changes in the repo
 if [ -z "`git status --short`" ]; then
     echo "No new content, gh-pages branch already up-to-date"
     exit 0
@@ -156,7 +212,7 @@ echo "Committing changes..."
 git add .
 git commit $amend -m "$commit_msg"
 
-cd -
+popd
 
 echo "gh-pages branch successfully updated"