Using exifr.parse on a buffer that contains just exif data

[rijkvanzanten]

Heya!

Is it possible to have exifr.parse function on a buffer that just contains exif data rather than a whole file?

I'm currently relying on Sharp to gather some file metadata (like width/height/orientation), and would like to use Exifr to (optionally) parse the Exif information if Sharp returns it. I do not have a Buffer with the full file contents available (nor am I able to get it), so I was hoping I could stream the file to sharp, have sharp prepare an Exif buffer, and parse that out with Exifr.
For example:

import { createReadStream } from 'node:fs';
import { pipeline } from 'node:stream/promises';
import sharp from 'sharp';
import { parse } from 'exifr';

const stream = createReadStream('./path/to/large/file.jpg');

const getMetadata = (stream) => new Promise((resolve, reject) => {
  pipeline(stream, sharp().metadata(async (err, sharpMetadata) => {
    if (err) return reject(err);
    
    // Do stuff with sharp metadata

    if (sharpMetadata.exif) {
      const exifData = await parse(sharpMetadata.exif);
      //               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    }

    // etc
  });
});

At the moment, the highlighted section errors with an error: Error: Unknown file format, which I believe stems from the fact that exifr expects the buffer to contain all file data, rather than just the exif information.

[paescuj]

For now, we might be able to extend the Exifr class and inject the corresponding parser manually (based on image type detected by sharp).

Super dirty examplary code:

import { Exifr } from 'exifr';

const formatMap = {
  jpeg: 'JpegFileParser'
  // ...
};

class CustomExifr extends Exifr {
  constructor(parser, options) {
    this.fileParser = parser;
    super(options);
  }
}

// sharp stuff

    if (sharpMetadata.exif) {
      const parserType = formatMap[sharpMetadata.format];
      if (parserType) {
        // try...catch
        const Parser = (await import(`exifr/file-parsers/${sharpMetadata.format}`)).[parserType];
        const exifr = new CustomExifr(new Parser(/* <need to look into parser options> */), exifrOptions);
        await exifr.read(sharpMetadata.exif);
        const exifData = await exifr.parse();
        //
      }
      //
    }

//

No idea whether a) those classes are indeed exported and available b) this would be sufficient or still too few / wrong data for exifr to process...

Obivously, if this approach would work and with the agreement of @MikeKovarik, we could then handle this in exifr itself (happy to come up with a PR in that case).