Create in-memory image blob processing via `express`

[Vitold S.]

How to processing image in-memory and delivery user without save on disk? i.e. convert image to Blob or ArrayBuffer to delivery with express server handler?

[Vincent Bruijn]

Hi, the function pngPtr for example will return a Buffer which you can send directly to the client via res.send(). Be aware to add the proper Content-Type HTTP header in the response so that the client knows it is dealing with an image.

The function pngPtr and jpegPtr and gifPtr are not (yet) well documented in the docs, but you can see for example from https://github.com/y-a-v-a/node-gd/blob/master/src/node_gd.cc#L562 that the macro RETURN_DATA (available here: https://github.com/y-a-v-a/node-gd/blob/master/src/node_gd.h#L214 ) returns a Buffer.

I haven't tested this out but I think this could be more or less the solution:

const gd = require('node-gd');

app.get('/', async (req, res, next) => {
  try {
    const img = await gd.create(100,100);

    // do other stuff with img

    res.set('Content-Type', 'image/png');
    res.send(img.pngPtr());
  } catch(e) {
    next();
  }
});

[Vitold S.]

Your code cause an segmentation error:

GD Warning: gd-png error: no colors in palette
Segmentation fault (core dumped)

But correct gd source code sequence provide well image content. Thanks.

[Vincent Bruijn]

Cool to hear. I will review what causes that error but probably because an empty created paletted images does not contain any image actually.

[Vitold S.]

Cool to hear. I will review what causes that error but probably because an empty created paletted images does not contain any image actually.

Yep. But await an exception instead Segfault with coredump entire express server.