Try as a separate workflow #2
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| --- | |
| name: Prepare Build | |
| description: | | |
| This action prepares the build environment by setting up the matrix for platforms, | |
| extracting the upstream image, and verifying its signature if provided. | |
| inputs: | |
| platforms: | |
| description: Comma-separated list of platforms to build for (e.g., "amd64,arm64") | |
| required: true | |
| containerfile: | |
| description: Path to the Containerfile to use for extracting the upstream image | |
| required: true | |
| upstream-public-key: | |
| description: Public key for verifying the upstream image signature (optional) | |
| required: false | |
| outputs: | |
| matrix: | |
| description: The matrix of platforms to build for | |
| value: ${{ steps.set-matrix.outputs.matrix }} | |
| tag: | |
| description: The working tag derived from the Git reference name | |
| value: ${{ steps.set-matrix.outputs.WORKING_TAG }} | |
| runs: | |
| using: "composite" | |
| steps: | |
| - name: Set matrix | |
| id: set-matrix | |
| shell: bash | |
| run: | | |
| # turn the comma separated string into a list | |
| platforms=() | |
| IFS=',' read -r -a platforms <<< "${{ inputs.platforms }}" | |
| MATRIX="{\"include\":[]}" | |
| for platform in "${platforms[@]}"; do | |
| MATRIX=$(echo $MATRIX | jq ".include += [{\"platform\": \"$platform\"}]") | |
| done | |
| echo "matrix=$(echo $MATRIX | jq -c '.')" >> $GITHUB_OUTPUT | |
| WORKING_TAG="${{ github.ref_name }}" | |
| echo "WORKING_TAG=${WORKING_TAG//\//_}" >> "$GITHUB_OUTPUT" | |
| - name: Install Cosign | |
| if: ${{ inputs.upstream-public-key != '' }} | |
| uses: sigstore/cosign-installer@3454372f43399081ed03b604cb2d021dabca52bb # v3.8.2 | |
| - name: Extract upstream | |
| if: ${{ inputs.upstream-public-key != '' }} | |
| id: extract | |
| shell: bash | |
| run: | | |
| # Install Dockerfile parser | |
| pip3 install dockerfile-parse | |
| # Extract the last FROM image using Python | |
| upstream=$(python3 - << 'EOF' | |
| from dockerfile_parse import DockerfileParser | |
| with open("${{ inputs.containerfile }}", "r") as f: | |
| dfp = DockerfileParser(fileobj=f) | |
| froms = [s['value'].split()[0] for s in dfp.structure if s['instruction'] == 'FROM'] | |
| print(froms[-1]) | |
| EOF | |
| ) | |
| echo "upstream-image=$upstream" >> $GITHUB_OUTPUT | |
| - name: Verify signature | |
| if: ${{ inputs.upstream-public-key != '' }} | |
| id: verify | |
| shell: bash | |
| run: | | |
| echo "Verifying signature for ${{ steps.extract.outputs.upstream-image }}" | |
| cosign verify --key ${{ inputs.upstream-public-key }} ${{ steps.extract.outputs.upstream-image }} | jq . |