I'm at the laundromat. I have a 20mb epub in my Dropbox. I try to open it in the Dropbox app. It goes, I can't open this, but here's a button to upload it to Google Play Books. That's convenient, I think; I tap it. It spends something like twenty minutes downloading the epub to the phone over a cell connection, then another twenty minutes uploading it to Google Play Books. Eventually it finishes. I open Google Play Books. The book is not there. Nor is it in Files. There is no error message.
This story has no moral.

*Later, trying again from the computer*

Google what the fuck does "Processing" mean. What does it mean to process a book. I just want you to sync it to my phone and open it. I mean it's already on my phone but you won't open it on my phone unless you first sync it from my phone to your server back to my phone so I'm trying to be accommodating.

If I click on the book all it does is open a new tab containing this help page https://support.google.com/googleplay/answer/185545?visit_id=638955591931852971-3016000300&rd=2

Has anyone ever seen Google Play Books do this, and if it does, is there a way to get an error message? I am in contact with¹ the publisher but there is not enough information to tell the publisher what is wrong.

¹ Married to

Alternately I am now looking for recommendations for a good basic epub reader for Android. All I want is for it to have text search, have a good upper range of font sizes, and not display "noise" such as page numbers or the current time while I am reading. I have never needed anything besides Google Play Books before this.
@mcc Have you tried http://librera.mobi ?
Librera

@glyph What does it mean that google play says this "contains ads"
@mcc Oh. It's "remove ads" software. Open source though so if you don't want to pay for it, you can build your own copy: https://github.com/foobnix/LibreraReader
GitHub - foobnix/LibreraReader: Book Reader for Android

Book Reader for Android. Contribute to foobnix/LibreraReader development by creating an account on GitHub.

GitHub
@glyph I think the intersection of "running an ad engine, which does goodness knows what" and "requires full access to all files to run" might be over my risk budget… maybe I'll look at self compiling later :/
@mcc I was just looking for open source ones with reasonable presentation. I would not heavily endorse it particularly if you have lots of other options. Sadly the one I actually used to use has been dead for many years now. (I still fondly remember it using the volume buttons for pagination and I am *still* kind of mad that no iOS e-reader does this yet.)
@glyph So far I don't appear to have even a single option. I am also noticing an unusual trend where open source ebook readers don't seem to support the modern android file security model
@mcc ah I assumed that this is just how open source apps roll these days. 80% of open source mac apps I use at this point begin their README with a screed about how apple is just greedily trying to get their $99 which is why they aren't codesigned and have instructions for disabling signature verification. I just found an open source *window manager* that asks for super-root access to do arbitrary modifications of the system partition yesterday
@mcc meanwhile I'm over here feeling shame that I haven't enabled app sandbox yet, like a loser
@glyph well, I will go to any lengths to avoid giving an operating system vendor money for signing keys, but I don't think an ereader needs root access
@mcc fair enough, needing to pay $100 to do volunteer work is an actual reason to not want to do something (not to mention that the vendors maybe aren't the most responsible stewards of those roots). disabling SIP for a slightly fancier maximize button is bananas, though.
@mcc @glyph Lithium. While reading, it shows only the text, no faff. The only ads are for itself, or rather its "pro" version which has some extra features. It does need file access permissions to find and read them.
@glyph The volume buttons on one of my handheld devices literally wore out and stopped working after a year or two of excessive reading, so I think it may not be a great idea to use them for page turning.
@mgedmin that's the great tragedy: we need iPhone-quality hardware that won't break after a year and Android-style APIs that you can actually call without a hall monitor standing over your shoulder

@mcc @glyph You don't have to compile, the F-Droid version (aka Librera FD) comes without google stuff: https://f-droid.org/en/packages/com.foobnix.pro.pdf.reader/

It's really a fantastic app.

Librera Reader | F-Droid - Free and Open Source Android App Repository

Book and PDF reader

@glyph @mcc it is present on fdroid