Tag latest release of Docker image

.github/actions/get-latest-release/action.yml

@@ -0,0 +1,21 @@
+name: Get latest release
+description: Gets the latest (non-prerelease) version of a PyPI package.
+inputs:
+  package:
+    description: Name of the the package.
+    required: true
+outputs:
+  latest_version:
+    description: Latest version of the package.
+    value: ${{ steps.get-latest.outputs.VERSION }}
+runs:
+  using: composite
+  steps:
+    - name: Install packaging
+      run: pip install packaging requests
+      shell: bash
+
+    - name: Get latest version
+      id: get-latest
+      run: ./.github/actions/get-latest-release/get_latest_release.py ${{ inputs.package }} >> "$GITHUB_OUTPUT"
+      shell: bash

.github/actions/get-latest-release/get_latest_release.py

@@ -0,0 +1,24 @@
+#!/usr/bin/env python3
+
+import argparse
+
+import requests
+from packaging.version import parse as parse_version
+
+if __name__ == "__main__":
+    arg_parser = argparse.ArgumentParser(
+        description="Get the latest non-prerelease version of a package according to PEP440."
+    )
+    arg_parser.add_argument("package")
+    args = arg_parser.parse_args()
+
+    r = requests.get(
+        f"https://pypi.org/simple/{args.package}",
+        headers={"Accept": "application/vnd.pypi.simple.v1+json"},
+        timeout=30,
+    )
+    r.raise_for_status()
+    versions = [parse_version(v) for v in r.json().get("versions", [])]
+    latest = max(v for v in versions if not v.is_prerelease)
+    if latest:
+        print(f"VERSION={latest}")

.github/workflows/docker-publish.yml

@@ -65,14 +65,40 @@ jobs:
         with:
           images: ${{ env.IMAGE_NAME }}
 
+      - name: Check if prerelease
+        id: check-prerelease
+        uses: ./.github/actions/check-prerelease
+        with:
+          version: ${{ steps.version.outputs.version }}
+
+      - name: Get latest release
+        id: latest-version
+        uses: ./.github/actions/get-latest-release
+        with:
+          package: dmarc-metrics-exporter
+
+      - name: Set tags
+        id: set-tags
+        shell: bash
+        run: |
+          {
+            echo 'TAGS<<EOF'
+            echo ${{ env.IMAGE_NAME }}:${{ steps.version.outputs.version }}
+            [ ${{ steps.version.outputs.version }} = ${{ steps.latest-version.outputs.latest_version }} ] \
+              && [ ${{ steps.check-prerelease }} != true ] \
+              && echo ${{ env.IMAGE_NAME }}:latest
+            echo EOF
+          }
+
+
       # Build and push Docker image with Buildx (don't push on PR)
       # https://github.com/docker/build-push-action
       - name: Build and push Docker image
         uses: docker/build-push-action@v5
         with:
           context: .
           push: ${{ github.event_name != 'pull_request' }}
-          tags: ${{ env.IMAGE_NAME }}:${{ steps.version.outputs.version }}
+          tags: ${{ steps.set-tags.outputs.TAGS }}
           platforms: linux/amd64,linux/arm64
           labels: ${{ steps.meta.outputs.labels }}
           build-args: "version=${{ steps.version.outputs.version }}"