[Feature Request] Support for compressing PDFs

[karlhorky]

What problem would this feature solve?

Compress PDFs, which are often a lot larger than they need to be (recently converted a 10MB PDF to ~1MB)

Describe the solution you’d like to see

Support for PDF files

Are you willing to work on implementing this solution?

No

Describe alternatives you’ve considered

• Writing a separate GitHub Actions workflow manually to do this
• Finding a different Action that does this already, eg. some discussion of PDF support over in this Imgbot issue https://github.com/imgbot/Imgbot/issues/332

Additional context

No response

Code of Conduct

• [X] I agree to follow this project’s Code of Conduct

[karlhorky]

Alternative

A separate GitHub Actions workflow to do this using ghostscript (generate an access token for this and add it as a GitHub repo secret called PDF_COMPRESSION_GITHUB_TOKEN):

name: Compress PDFs
on:
  pull_request:
    # Run only when PDF files are added or changed
    paths:
      - '**.pdf'

jobs:
  build:
    # Only run on Pull Requests within the same repository, and not from forks.
    if: github.event.pull_request.head.repo.full_name == github.repository
    name: Compress PDFs
    runs-on: ubuntu-latest
    steps:
      - name: Run apt update
        run: sudo apt update
      - name: Install Ghostscript for compression
        run: sudo apt install -y ghostscript
      - name: Checkout Repo
        uses: actions/checkout@v3
        with:
          ref: ${{ github.head_ref }}

      - name: Compress PDFs
        run: |
          find . -type f -iname '*.pdf' -not -path "./node_modules/*" | while read file; do
            echo "Compressing $file"
            # Compress the file for screen using Ghostscript
            gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile="./temp.pdf" "$file"
            mv ./temp.pdf "$file"
          done
      - name: Commit files
        run: |
          git config user.email github-actions@github.com
          git config user.name github-actions

          # Discard modified compressed files that are not more
          # than 10KB smaller than the previous version
          git ls-files -z --modified '*.pdf' | while IFS= read -r -d '' file; do
            old_size=$(git cat-file -s "HEAD:$file")
            new_size=$(wc -c < "$file" | tr -d ' ')
            if [[ $(($old_size - $new_size)) -lt 10000 ]]; then
              echo "Discarding changes to $file, compressed file size $new_size is not >10KB smaller than old size $old_size"
              git checkout -- "$file"
              continue
            fi
            echo "Compressed $file from $old_size to $new_size bytes"
          done

          git add **/*.pdf
          if [ -z "$(git status --porcelain)" ]; then
            exit 0
          fi
          git commit -m "Compress PDFs"
          git push origin HEAD:${{ github.head_ref }}
        env:
          GITHUB_TOKEN: ${{ secrets.PDF_COMPRESSION_GITHUB_TOKEN }}

[benschwarz]

Thanks for sharing this recipe @karlhorky.

We're not interested in adding PDF support to image-actions.