Handling Images

OpenFn jobs run in Javascript, and most commonly we're handling JSON data from REST APIs or webhooks. We receive JSON, manipulate it with Javascript, then send JSON to some other REST API. Sometimes, however, you need to work with images or other binaries. This page explains how you do it.

The tl;dr:

Images and other binaries mostly Just Work™️. Edges cases might need additions to adaptors.

Base64 (standard handling)

In essence, the way to deal with images/PDFs/other files and be able to save them to state and pass them from step to step in an OpenFn workflow is to encode them as base64 and then turn them back into Buffers before sending them to a downstream system's API.

The HTTP adaptor already contains everything you need to do this. Check out:

1. Request Options (parseAs)
2. Encode a given string into Base64 format.
3. Decode a Base64 encoded string back to its original format.

Adaptor Native Support

Some adaptors (DHIS2, FHIR-4, Sunbird-RC) have built in binary handling for known image/file endpoints. When you request a file (and image, a PDF, etc.) the response will be automatically converted to a base64 encoded string.

Working with Buffers

You can also work directly with buffers in OpenFn job code via code like:

fn(state => {
  const encoded = Buffer.from(state.data.myBase64string, 'base64');
  return { ...state, encodedImage };
});

or...

fn(state => {
  const decoded = state.data.myBuffer.toString('base64');
  return { ...state, decoded };
});

Summary

Most use cases should Just Work ™️. If you have a specific need involving large file sizes or high volumes and you need to process images, rather than just moving them from place to place, you might need to make a change to your adaptor.