Timeout not applying to encoding?

[rexxars]

Question about an existing feature

The .timeout() method seems to only apply to certain operations, not the actual encoding of the image - is that right? Is there a way one could abort an ongoing transform/encode operation? If so, would it be possible to make the timeout apply to this step as well?

What are you trying to achieve?

I'd like to "give up" on processing/encoding images if they take longer than a given threshold. Without having been able to reproduce this consistently, it seems processing sometimes gets "stuck" on an image for a very long time, and I'd love to be able to simply drop the operation entirely - eg prevent it from using any more resources, and explicitly fail.

While I can set a timeout in user-land code and proceed as if it timed out, I cannot abort the actual encoding process, so it will continue taking CPU time until it eventually finishes/errors.

Additionally, it would be nice to be able to abort transformations, eg:

import sharp from 'sharp'

const abortController = new AbortController()
setTimeout(() => abortController.abort(), 1000)

try {
  const image = await sharp('input.jpg')
    .resize(1000, 1000)
    .toFormat('avif', {
      signal: abortController.signal
    })
    .toBuffer()
} catch (err) {
  console.log(err instanceof AbortError) // true
}

When you searched for similar issues, what did you find that might be related?

• Timeout doesn't work #3331 lead me to understand that it was the encoding step that does not respect the timeout
• Is there a way to set a timeout for a conversion? #2239 seems to have been raised prior to timeout() being added, but also calls out that there is no way to cancel/abort an ongoing process

Please provide a minimal, standalone code sample, without other dependencies, that demonstrates this question

Repository that illustrates the problem: https://github.com/rexxars/sharp-timeout-issue

Please provide sample image(s) that help explain this question

See repo above, but any sufficiently large image will do

[lovell]

Almost all libvips operations support timeout, however the HEIF writer does not as the API of the underlying libheif library exposes a "one shot" encoder.

https://github.com/libvips/libvips/blob/b27b8e450e6508f3d7e840da8212ec59695b632d/libvips/foreign/heifsave.c#L321-L322

There is a brand new feature in the latest libheif v0.19.x that exposes HEIF's grid feature, which might allow for tile-based output, but support for this would need to be added to libvips (mapping its concept of an image region to HEIF's concept of a grid image). This would increase file size a little, but should reduce memory consumption and I would guess slightly improve performance as encoding can start sooner.

[kleisauke]

FWIW, the comment at kleisauke/wasm-vips#78 (comment) provides more details on why this occurs with the HEIF saver (or any saver that doesn't support streaming/chunk-wise encoding).

[rexxars]

For what it's worth, in the repo I linked I am seeing the same behavior as AVIF (heif) when encoding PNGs and GIFs, eg if I set the timeout to 2 seconds:

  [avif]
    ❌ Exceeded timeout by 4293 milliseconds without failing
  [webp]
    ✅ Processed image in less than 2 seconds
  [jpeg]
    ✅ Processed image in less than 2 seconds
  [png]
    ❌ Exceeded timeout by 665 milliseconds without failing
  [gif]
    ❌ Exceeded timeout by 1297 milliseconds without failing

I am completely unfamiliar with the internals of libvips and how it uses threads, but would it be possible to forcefully "kill"/abort an ongoing encoding operation?

[lovell]

To improve things for PNG writing, I think we'd need to add a call to vips_image_eval then check vips_image_iskilled to see if we should exit within the loop that calls spng_encode_row here:

https://github.com/libvips/libvips/blob/e38953c5dfa302875c4578ad1222b114ee6eac69/libvips/foreign/spngsave.c#L353

(Could probably limit this check to every N iterations of the loop.)