EPUB file fails to open in KOReader on Onyx Boox Note Air 3 (opens fine in NeoReader)

[r777r]

Device

Onyx Boox Note Air 3

Firmware

Latest official firmware version installed

Issue

Some EPUB files cannot be opened in KOReader.
• Example: a specific EPUB book (attached)
• The same file opens perfectly with the default Onyx built-in reader (NeoReader) without any issues.
• In KOReader, it fails to open (no text is displayed / error message shown).

Steps to Reproduce
1. Open KOReader on Onyx Boox Note Air 3
2. Try to open the attached EPUB file
3. Observe that the book does not open properly

Expected Behavior

The EPUB file should open normally in KOReader, just like in the default Onyx NeoReader.

Actual Behavior

KOReader cannot open the EPUB file.

Attachment

EPUB file is attached for testing.

[Doitsu]

The Epub is invalid, because the OPF file contains multiple duplicate ids.
The OPF file also has a size of 40 MB(!) and contains 650K(!) lines.
I'm really surprised that you ware able to open it with Onyx NeoReader.

[r777r]

What is the solution to open it in KOReader?

There are many books like this that KOReader cannot open, while NeoReader can open them.

However, we don’t like using NeoReader because it does not properly support highlighting and text selection in RTL (right-to-left) languages if the highlight spans more than two lines (for example, Arabic is written from right to left).

Can you fix this issue and make KOReader able to open such files in the next update?

[DNSB]

That content.opf file is so far from compliant, you'd need a space telescope to set any hint of compliance. 2045 occurences of 'id="page_1"' for instance. Multiple pages of references to id for pages that do not exist. Multiple items in the main.css file with non-existent selectors such as sanad, mateen and sheer. Perhaps .sanad, .mateen and .sheer for those colour settings?

It's a bloody miracle that anything could open this abomination. The first time I've had an epub break epubcheck.

As for opening this in KOReader? The fastest answer is to use ePub ebooks that are valid ePub ebooks. Perhaps try an epub to epub conversion in calibre to see if calibre is able to fix enough to make this *&$*!@)# work with KOReader.

Edit: I've attached a calibre epub-epub conversion output to this message. The file size shrank drastically however the filename is now an ASCII transliteration of the original Arabic name.

[Frenzie]

The document in the OP actually does open in KOReader. It just takes a crazy amount of time and depending on the device in question far too much memory (a little over a gigabyte).

09/06/25-20:18:54 DEBUG CreDocument: rendering document...
[…]
09/06/25-20:24:43 DEBUG CreDocument: rendering done.

That was on a nearly decade-old i7-6560U laptop CPU, but for its time that was a pretty decent one and in any case probably orders of magnitude faster than any ereader.

Edit: forgot to say, but that EPUB to EPUB conversion opens in 306 milliseconds. (I'd estimate about 2-4 seconds on a device.)

Edit 2: quoting from https://github.com/koreader/koreader...ent-3263195394

As mentionned on mobileread, the .opf is crap:
There are only 89 HTML files in the .epub,
There are 6567 items in the .opf, with only 111 unique ones (which means that some of them are from 11- to 1800-plicated )

We trust the .opf, and so we open these 89 files but add them as 6567 copies.
May be other reader software do differently.
Nothing for us to fix. This EPUB is just crappy - and you could solve it by editing the .opf in that epub and removing duplicated stuff.

[DNSB]

For what it may be worth, I was watching a football game and spent the commercial breaks and half time running the original epub through Sigil and doing manual cleanup. Size is pretty much the same as the calibre epub=>epub conversion. During this, I found the footnotes links are broken.

I tried the original ePub on my Kobo Sage and it crashed with what I think is an out of memory error. Ditto for Nickel and KOReader on my Libra Colour. Either of my two modified versions will open in any of the renders I tested without taking excess memory or time.

For what it may be worth, the original opened in calibre's ebook-viewer on my i9 PC in ~1.25 minutes. The memory use peaked at 984MB.

[Frenzie]

13.3 seconds on my desktop AMD Ryzen 7 7800X3D in KOReader fwiw. A pleasing difference. But as previously stated, my old laptop is already much, much faster than a Kobo Libra something or other. To make up for it the battery lasts only 4-8 hours instead of weeks. (I put in a new battery earlier this year; it'd gone down to less than 2.)

09/07/25-21:22:18 DEBUG CreDocument: loading document... 
[…]
09/07/25-21:22:31 DEBUG CreDocument: loading done. 
09/07/25-21:22:31 DEBUG   loading took 13.305 seconds

Perhaps I should add that both of those tests were with debug builds. Release builds would be a fair bit faster.