Faster (and smaller) uploads in Discourse with Rust, WebAssembly and MozJPEG | Blog

As of a few weeks ago, image uploads in Discourse are faster AND smaller thanks to a technique that compresses and optimizes the images clientside before they are uploaded. This blog post will describe how this feature works and how we implemented it in Discourse.

This is a companion discussion topic for the original entry at

Amazing! :heart_eyes: This is an incredible improvement. Really great work. It’s so much more fun to upload and share photos in discussions now.

And an added benefit - people on slow connections are going to be able to upload a bunch of photos at a time now without the dreaded “Uploading…” appearing instead of the photo. :+1:


Nice improvement… and Happy Birthday, Rafael!


Super psyched to see Discourse playing more with the power of Rust! :crab: :muscle:

imageflow is another impressive Rust lib in this space.

I took the liberty of sharing the news here:


This is something I have on my site right now? Meaning y’all shipped this level of improved functionality out to everyone just because you want a better product?

Part of me knows that’s true. I’ve been around enough to know how y’all roll, but damn. Part of me feels like I missed the part where this is an advanced optimization play.


Yes and yes. :smiley:


Freakin’ radical, man.

Bill Murray Thank You GIF by filmeditor


Getting lots of complaints from Android users about jumping cursors and degraded upload performance, unfortunately.

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I have a PR open that will greatly improve the cursor/placeholder handling during multiple file uploads

If all of the following are true:

  • You don’t care about storage costs
  • Most of your user base has good internet upload
  • Most of your audience browses from average or worse Android phones

You may want to either disable the feature or tweak the threshold for minimum size up a few megabytes.


That’s great to hear!

Sadly, many of my users have cheap-ish/older Android phones, so I won’t be re-enabling the feature any time soon. Haven’t had any problems myself on my iPhone 12.

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Falco, would it be possible or of interest to provide a user setting for this, so people who want it can choose to use it? Or an option to “use classing image uploader” as craigslist does it? Selecting that button toggles the upload method.

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Maybe tweak the minimum size for it, so it’s only triggers on file larger than 3MB, so old phones won’t reach it on their own camera pictures.

That was included in the original RFC but it was removed according to the comments received.


Hi Rafael,

I think we have a little problem with the new placeholder handling. It seems the images goes inline not a new line. Not just on composer pre optimization but regular uploads too. Thanks :slightly_smiling_face:


This should fix it


Hello Rafael,

Sorry I am late but tested just now. :confused: It works fine on multiple uploads if i drag images in new line but it seems the issue still there if drag image(s) the end of a text. Thank you :slightly_smiling_face:

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Is it all good now @dodesz?


It seems to this one still happening.

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