feat: add use-inbuild-sbom input defaulting to false

action.yaml

@@ -24,6 +24,10 @@ inputs:
     description: Whether to append the generated reports to the job summary ($GITHUB_STEP_SUMMARY)
     required: false
     default: 'true'
+  use-inbuild-sbom:
+    description: Whether to inspect and use built-in image SBOM attestations. If false, generates SBOM directly from images with Trivy.
+    required: false
+    default: 'false'
 
 outputs:
   delta-report:
@@ -58,14 +62,15 @@ runs:
   - name: Install and Verify Trivy
     shell: bash
     run: |
-      mkdir -p "$HOME/.cache/trivy-bin" "$HOME/.local/bin"
-      echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+      set -euo pipefail
 
-      ARCH=$(uname -m)
-      case "$ARCH" in
+      mkdir -p "$HOME/.local/bin" "$HOME/.cache/trivy-bin"
+      echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+      ARCH="$(uname -m)"
+      case "${ARCH}" in
         x86_64) T_ARCH="64bit" ;;
         aarch64|arm64) T_ARCH="ARM64" ;;
-        *) echo "Unsupported architecture: $ARCH"; exit 1 ;;
+        *) echo "::error::Unsupported architecture: ${ARCH}"; exit 1 ;;
       esac
 
       checksums_file="${{ github.action_path }}/checksums.txt"
@@ -100,9 +105,11 @@ runs:
 
       head_sbom_err=""
       target_sbom_err=""
+      use_inbuild="${{ inputs.use-inbuild-sbom }}"
 
       # --- Head Image SBOM Extraction ---
-      echo "Extracting platform SBOMs for head image: ${{ inputs.head-image }}..."
+      if [ "$use_inbuild" = "true" ]; then
+        echo "Attempting extraction of built-in SBOM attestations for head image: ${{ inputs.head-image }}..."
         docker buildx imagetools inspect "${{ inputs.head-image }}" \
           --format '{{ json (index .SBOM "linux/amd64").SPDX }}' > sboms/head/sbom-amd64.spdx.json 2>/dev/null || true
         cleanup_file sboms/head/sbom-amd64.spdx.json
@@ -117,22 +124,24 @@ runs:
             --format '{{ json .SBOM.SPDX }}' > sboms/head/sbom-amd64.spdx.json 2>/dev/null || true
           cleanup_file sboms/head/sbom-amd64.spdx.json
         fi
+      fi
 
-      # Fallback to generating head SBOM with Trivy if attestation missing
+      # Generate head SBOM with Trivy if attestation not used or missing
       if [ ! -f sboms/head/sbom-amd64.spdx.json ] && [ ! -f sboms/head/sbom-arm64.spdx.json ]; then
-        echo "Head image lacks SBOM attestation; generating with Trivy..."
+        echo "Generating SBOM for head image directly with Trivy: ${{ inputs.head-image }}..."
         if ! trivy image --skip-version-check --format spdx-json --output sboms/head/sbom-amd64.spdx.json "${{ inputs.head-image }}"; then
-          head_sbom_err="Failed to generate fallback SBOM with Trivy for head image"
+          head_sbom_err="Failed to generate SBOM with Trivy for head image"
         fi
         cleanup_file sboms/head/sbom-amd64.spdx.json
       fi
 
       if [ ! -f sboms/head/sbom-amd64.spdx.json ] && [ ! -f sboms/head/sbom-arm64.spdx.json ] && [ -z "$head_sbom_err" ]; then
-        head_sbom_err="No SBOM attestation found and head image could not be inspected"
+        head_sbom_err="No SBOM generated and head image could not be inspected"
       fi
 
       # --- Target Image SBOM Extraction ---
-      echo "Extracting platform SBOMs for target image: ${{ inputs.target-image }}..."
+      if [ "$use_inbuild" = "true" ]; then
+        echo "Attempting extraction of built-in SBOM attestations for target image: ${{ inputs.target-image }}..."
         docker buildx imagetools inspect "${{ inputs.target-image }}" \
           --format '{{ json (index .SBOM "linux/amd64").SPDX }}' > sboms/target/sbom-amd64.spdx.json 2>/dev/null || true
         cleanup_file sboms/target/sbom-amd64.spdx.json
@@ -146,18 +155,19 @@ runs:
             --format '{{ json .SBOM.SPDX }}' > sboms/target/sbom-amd64.spdx.json 2>/dev/null || true
           cleanup_file sboms/target/sbom-amd64.spdx.json
         fi
+      fi
 
-      # Fallback to generating target SBOM with Trivy if attestation missing
+      # Generate target SBOM with Trivy if attestation not used or missing
       if [ ! -f sboms/target/sbom-amd64.spdx.json ] && [ ! -f sboms/target/sbom-arm64.spdx.json ]; then
-        echo "Target image lacks SBOM attestation; attempting to generate with Trivy..."
+        echo "Generating SBOM for target image directly with Trivy: ${{ inputs.target-image }}..."
         if ! trivy image --skip-version-check --format spdx-json --output sboms/target/sbom-amd64.spdx.json "${{ inputs.target-image }}"; then
-          target_sbom_err="Failed to generate fallback SBOM with Trivy for target image"
+          target_sbom_err="Failed to generate SBOM with Trivy for target image"
         fi
         cleanup_file sboms/target/sbom-amd64.spdx.json
       fi
 
       if [ ! -f sboms/target/sbom-amd64.spdx.json ] && [ ! -f sboms/target/sbom-arm64.spdx.json ] && [ -z "$target_sbom_err" ]; then
-        target_sbom_err="No SBOM attestation found and target baseline image could not be inspected"
+        target_sbom_err="No SBOM generated and target baseline image could not be inspected"
       fi
 
       # Report on both sides