Calibre in mobile

avnermoshkovitz · 07-13-2021, 03:16 PM

Hi,
I'm new to ebook world, and calibre, so excuse me for the beginner and naieve questions.

I have a html5+javascript+css code that I want to run in mobile (Android).
Typically this kind of code is run with:

an online webserver, or
an local webserver (e.g. if someone wants to work offline)

Using a local webserver is possible, but not straight-forward:

it is usually easier to run on a desktop compared to mobile.
it requires some basic knowledge, and interaction with the computer (my grandmother can't do it).

I recently discovered that the epub format supports html5+javascript+css which theoretically means (if I understand correctly) that the ebook/epub platform can be used to run typical web code without a web server.

So I wrapped my html5+javascript+css code into a file in epub format, and was pleasantly surprised that Calibre on desktop (Ubuntu 20.04) opened the ebook and "read" my code properly.
I'm placing "read" in quotation marks because this is not a typical book with mostly text, but some javascript that displays images.

Because I want to read the ebook in mobile, I followed the path to use the Calibre Content Server.
I started with Calibre Content Server on the desktop (by using e.g. http://localhost:8080),
and also tested with Calibre Content Server on mobile (by using e.g. http://192.168.1.75:8080)

According to the the documentation Calibre Content Server is expected to work similar to Calibre, but I did find that I had to make some adjustments.
Here are 2 examples:

Example1 - seeing a button icon image
I have a button with an icon.
In regular (non-ebook) web code, the icon image is fetched from the webserver via e.g. http://localhost/static/img1.png
But for the Calibre Content Server, I need to provide the image via data URI, which reduces the flexibility of the code.

Example2 - interaction with a button
When the ebook is viewed by Calibre, the button responds properly, i.e. clicking on a button opens a input file dialog.
This also works in Calibre Content Server on the desktop.
But when using Calibre Content Server on the mobile, the buttons do not respond.

I assume that the differences in behaviour are because Calibre Content Server uses the web browser (e.g. Chrome) and the lack of a webserver,
which adds restrictions such as:

cannot make a GET request (Calibre, or Calibre Content Server does not provide static assets, such as the button icon image?)
CORS requests (preventing from doing GET requests)
other security restrictions (which could be what causes the button interaction problems)

So I have a general question: is it possible to implement Calibre as a mobile app?
I'm sure this can be a big task. I looked at the calibre code and it's huge. I also see the span of the project in years, and the amount of ongoing activity (commits, releases, etc...)
My question is more about the technical limit.
I basically want to understand what are the limits of ebook/epub to execute html5+javascript+css offline, without many limitations (assuming that requests to external resources are eliminated).

Thank you
Avner

kovidgoyal · 07-13-2021, 10:02 PM

There are no limitations, the in browser viewer uses the same code as the desktop viewer and they both run in browsers. The only difference is the in browser viewer loads resources from indexeddb so that means trying to load things dynamically via javascript is not going to work.

avnermoshkovitz · 07-19-2021, 05:32 PM

Apparently, the mobile in-browser viewer (via Calibre Content Server) is not the same as the desktop in-browser viewer.
The desktop responds to mouse events, but the mobile does not respond to touch events.
The touch events are recognized by other mobile ereaders, so clearly there is something in Calibre or Calibre Content Server that is problematic.
I described the problem, and attached a small video clip and a small ebook that demonstrates the problem in
https://www.mobileread.com/forums/sh...5&postcount=15

@kovidgoyal, can you please take a look there and confirm my observation?

Thanks
Avner

kovidgoyal · 07-19-2021, 10:28 PM

Touch events are used for the viewers own UI. And they wont work in either the desktop or the mobile. Mouse events will work in both.

kovidgoyal · 07-19-2021, 10:28 PM

You seem to be trying to create an application, not a book, I suggest you do that. Use a website or a mobile application, not an ebook.

07-13-2021, 03:16 PM	#1
avnermoshkovitz Member Posts: 22 Karma: 10 Join Date: Jun 2021 Device: Any ereader for Android or iOS	Calibre in mobile Hi, I'm new to ebook world, and calibre, so excuse me for the beginner and naieve questions. I have a html5+javascript+css code that I want to run in mobile (Android). Typically this kind of code is run with: an online webserver, or an local webserver (e.g. if someone wants to work offline) Using a local webserver is possible, but not straight-forward: it is usually easier to run on a desktop compared to mobile. it requires some basic knowledge, and interaction with the computer (my grandmother can't do it). I recently discovered that the epub format supports html5+javascript+css which theoretically means (if I understand correctly) that the ebook/epub platform can be used to run typical web code without a web server. So I wrapped my html5+javascript+css code into a file in epub format, and was pleasantly surprised that Calibre on desktop (Ubuntu 20.04) opened the ebook and "read" my code properly. I'm placing "read" in quotation marks because this is not a typical book with mostly text, but some javascript that displays images. Because I want to read the ebook in mobile, I followed the path to use the Calibre Content Server. I started with Calibre Content Server on the desktop (by using e.g. http://localhost:8080), and also tested with Calibre Content Server on mobile (by using e.g. http://192.168.1.75:8080) According to the the documentation Calibre Content Server is expected to work similar to Calibre, but I did find that I had to make some adjustments. Here are 2 examples: Example1 - seeing a button icon image I have a button with an icon. In regular (non-ebook) web code, the icon image is fetched from the webserver via e.g. http://localhost/static/img1.png But for the Calibre Content Server, I need to provide the image via data URI, which reduces the flexibility of the code. Example2 - interaction with a button When the ebook is viewed by Calibre, the button responds properly, i.e. clicking on a button opens a input file dialog. This also works in Calibre Content Server on the desktop. But when using Calibre Content Server on the mobile, the buttons do not respond. I assume that the differences in behaviour are because Calibre Content Server uses the web browser (e.g. Chrome) and the lack of a webserver, which adds restrictions such as: cannot make a GET request (Calibre, or Calibre Content Server does not provide static assets, such as the button icon image?) CORS requests (preventing from doing GET requests) other security restrictions (which could be what causes the button interaction problems) So I have a general question: is it possible to implement Calibre as a mobile app? I'm sure this can be a big task. I looked at the calibre code and it's huge. I also see the span of the project in years, and the amount of ongoing activity (commits, releases, etc...) My question is more about the technical limit. I basically want to understand what are the limits of ebook/epub to execute html5+javascript+css offline, without many limitations (assuming that requests to external resources are eliminated). Thank you Avner

07-19-2021, 05:32 PM	#3
avnermoshkovitz Member Posts: 22 Karma: 10 Join Date: Jun 2021 Device: Any ereader for Android or iOS	Apparently, the mobile in-browser viewer (via Calibre Content Server) is not the same as the desktop in-browser viewer. The desktop responds to mouse events, but the mobile does not respond to touch events. The touch events are recognized by other mobile ereaders, so clearly there is something in Calibre or Calibre Content Server that is problematic. I described the problem, and attached a small video clip and a small ebook that demonstrates the problem in https://www.mobileread.com/forums/sh...5&postcount=15 @kovidgoyal, can you please take a look there and confirm my observation? Thanks Avner Last edited by avnermoshkovitz; 07-19-2021 at 05:35 PM.

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07-13-2021, 10:02 PM	#2
kovidgoyal creator of calibre Posts: 45,345 Karma: 27182818 Join Date: Oct 2006 Location: Mumbai, India Device: Various	There are no limitations, the in browser viewer uses the same code as the desktop viewer and they both run in browsers. The only difference is the in browser viewer loads resources from indexeddb so that means trying to load things dynamically via javascript is not going to work.

07-19-2021, 10:28 PM	#4
kovidgoyal creator of calibre Posts: 45,345 Karma: 27182818 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Touch events are used for the viewers own UI. And they wont work in either the desktop or the mobile. Mouse events will work in both.

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