PDF to PNG Service

This is the result of a long, painful and embarrassing journey to resolve a very simple task: get pngs and webp files from a PDF. Here are a few alternatives we tried:

• pdf-to-png-converter - great, simple solution, but limited pdf render functions
• gm - tried many different variations but we couldn't get this to work
• sharp - built on libvips it's the fastest image conversion library, but doesn't come with PDF support out of the box. pdfium is required and it's a nightmare to try to build a somewhat up-to-date Dockerfile with libvips and libpdfium.

Cloud Functions / Lambda have ImageMagick pre-installed which should be capbable, but:

• on Google Cloud Functions, ImageMagick is only installed on the Node 12 and 14 runtime. Not on Node 16 🤦
• In order to read PDF, ImageMagick requires a change in a policy.xml which we don't have access to in the Functions environment

Setup

The Dockerfile has everything you need. You can build it locally or in the cloud and use the Cloud Run environment to start the container. There are two environment variables needed:

    SOURCE_BUCKET=source-bucket
    DEST_BUCKET=destination-bucket

This service is currently designed for Google Cloud EventArc triggers. You should create a trigger on the source bucket when new files are uploaded/finalized. The trigger will then call the Cloud Run instance and execute this service. There'll be various versions:

• original png: full size, 90% quality
• preview png: 1920px width, 75% quality, interlace
• thumbnail png: 1024px width, 70% quality, interlace
• lossless webp: full size, 100% quality
• preview webp: 1920px width, 75% quality

All versions will be stored on the destination bucket with the same filename as the source (including folders), and a prefix for the version.

Local Development

To build and run locally, you need to create a service account and place the keyfile in the same folder. You'll need to add:

GOOGLE_APPLICATION_CREDENTIALS=keyfile.json

As an environment variable. vips is linked statically:

RUSTFLAGS="-C target-feature=-crt-static $(pkg-config vips --libs)" cargo build && ./target/debug/pdf-service

Feel free to fork to adjust this to your own needs.

Happy converting.

Acknowledgements & Thanks

• Federico Rampazzo for the help with Rust and putting the libraries together.
• Lachezar Lechev for the final touches and getting the http wrapper to work.
• Naohiro Yoshida for the Google Cloud libraries in Rust

License

Licensed under MIT.

Built with 💌 in Cyprus 🇨🇾