Calibre and GNU GPL

[Stodder]

Hi guys,

From what I understand a project becomes GPL when the output contains sections of the program's code--correct me if I'm wrong. So I would like to ask if the files that Calibre outputs, specifically the mobi and prc files, contain any Calibre-specific GPL'd code in them.

I probably sound a bit nutty, but I just wanted to double check that no portions of Calibre's actual source code got output into the files it makes.

Any help would be great
Stodder

[Manichean]

I really doubt it. Embedding Python code into ebook files doesn't make any sense.

[mwheinz]

No. Consider - Calibre supports copying DRM'ed books which, by definition, Calibre does not and cannot alter.

[Stodder]

Thanks for the responses. I just wanted to be sure, as I'm not a programmer and can't check for myself or see what's not visible to the end user.

As for DRM and Calibre, I did not know that Calibre could copy DRM'd books.

[Manichean]

Originally Posted by Stodder

As for DRM and Calibre, I did not know that Calibre could copy DRM'd books.

Copy, organize and send to devices: Yes. Change metadata or convert: No.

[Stodder]

As a matter of interest, can you even tell if a file was made with Calibre? Or Mobipocket, or any of these software packages?

[Stodder]

Originally Posted by Manichean

Copy, organize and send to devices: Yes. Change metadata or convert: No.

Ah, thanks for clarifying

[user_none]

Some DRMed formats can have the metadata updated *.

The GPL license does not extend to calibre produced ebook files.

I believe calibre's MOBI output puts the calibre version in the metadata *. Use ebook-meta to see.

* Can't remember off the top of my head and I'm not at my computer to check.

[Agama]

Originally Posted by Stodder

As a matter of interest, can you even tell if a file was made with Calibre? Or Mobipocket, or any of these software packages?

Calibre puts entries into the metadata of an ePub's OPF.

For example:

<dc:contributor opf:file-as="calibre" opf:role="bkp">calibre (0.7.28) [http://calibre-ebook.com]</dc:contributor>

<meta content="2010-12-07T07:18:36.758000+00:00" name="calibre:timestamp"/>
<meta content="Pride and Prejudice" name="calibre:title_sort"/>

This is quite an old conversion so things might have been changed in 0.8. I usually edit out the <meta content ... > lines but keep the <dc:contributor ...>

Update: There's also an entry in the OPF's XML namespace section -

xmlns:calibre="http://calibre.kovidgoyal.net/2009/metadata"

[Starson17]

Originally Posted by user_none

The GPL license does not extend to calibre produced ebook files.

I agree, but it would take some research to point to the exact part of the GPL that applies and explain why the GPL doesn't apply to output.

The OP seems to be worried that the GPL is "viral" and will somehow infect an e-book so that it can be copied/used/distributed by everyone. If that was really a concern, with respect to conversions, you couldn't use Calibre for much of anything as most e-books are copyrighted by third parties.

As to his specific question "I would like to ask if the files that calibre outputs, specifically the mobi and prc files, contain any Calibre-specific GPL'd code in them." The answer has just the tiniest bit of gray. In some circumstances, html/xml/xhtml/css will be considered "code," particularly when integrated into other code. By necessity, calibre, puts in some formatting and/or html/xml/xhtml/css content into recipe-created e-books (in particular) and during other conversions.

Calibre's "code" is all subject to the GPL and in some very limited circumstances, the code added, for example by a recipe, might be considered to be subject to the GPL. I suspect the likelihood that this would fall within the scope of the GPL, and that it would cause the OP any trouble to be less than the likelihood of being struck by a meteorite in the next 5 seconds, but it's always interesting to explore the limits of the horrible hypothetical. IOW, he's got absolutely nothing to worry about, and he should ignore the FUD that is spread by others about the GPL.

[theducks]

Originally Posted by Stodder

As a matter of interest, can you even tell if a file was made with Calibre? Or Mobipocket, or any of these software packages?

When Calibre converts, some of the stylsheet selectors used in "tags" have "calibre" in its name.
Up until recently, Baen e-books, all had Calibre fingerprints on them

[user_none]

Originally Posted by Starson17

I agree, but it would take some research to point to the exact part of the GPL that applies and explain why the GPL doesn't apply to output.

See http://gnu.org/licenses/gpl-faq.html#GPLOutput and http://gnu.org/licenses/gpl-faq.html#WhatCaseIsOutputGPL for an explanation.
In regard to the first link, even though things like style sheets are added by calibre to some ebook types they do not constitute a substantial amount of the output.

[kacir]

Originally Posted by Stodder

As for DRM and Calibre, I did not know that Calibre could copy DRM'd books.

Calibre can put DRMed book on disk. It doesn't need to be able to open it in order to copy it from disk to your devices.

As other posters said, Calibre can even write metadata to some DRMed files, because in some formats metadata is not encrypted.

Calibre can even work with DRMed files, even remove DRM. But for that you need third party plugins. Kovid doesn't provide any help with DRM removal (he even says so in his signature). But, the plugin infrastructure in Calibre is so well designed, that various other hackers can develop plugins for many, many things.

Here on this forum I can't provide better instructions, and besides, I have no personal experience with DRM removal using Calibre plugins. I have very limited experience from removal DRM in general (I removed from a book I have purchased). If you were to google for better answer, you might want to ask aprentice alf.

[Starson17]

Originally Posted by user_none

See http://gnu.org/licenses/gpl-faq.html#GPLOutput and http://gnu.org/licenses/gpl-faq.html...aseIsOutputGPL for an explanation.
In regard to the first link, even though things like style sheets are added by calibre to some ebook types they do not constitute a substantial amount of the output.

Yes, I'm familiar with the many FAQs on the GPL. I'm really not trying to argue that there is any reasonable likelihood that the GPL applies to any calibre output. Even if there is the barest such possibility, there's no reasonable likelihood that the GPL would be or could be enforced against anyone for that situation. It's just that I like to know the limits, even when it's just the limits of the universe that I'm interested in

For the record, from one of those FAQ questions:

In what cases is the output of a GPL program covered by the GPL too?
Only when the program copies part of itself into the output.

Again, I'm not arguing that the GPL does apply to the output just because some tiny bit of internal recipe formatting code of CSS/HTML, etc. got copied over into the output.

It's just that I find the subject interesting. I can imagine a hypothetical (and that's all it is) where a recipe author spends hundreds of hours authoring a complex recipe to produce complex output for displaying some complex data. His recipe extensively copies his work into the output. Then an evil entity comes along and copies that output. Under the right circumstances, there might (I emphasize the "might) be a GPL claim.

Time for me to take off the Devil's advocate robes and do some real work

[Stodder]

Thank you everyone for taking my question seriously and answering with thoughtful responses. I've had some great experiences on this forum, and appreciate the opinions

Do you think, just as a safeguard, Calibre should have a written "ebook exemption" added to its licensing? For example, some GPL fonts have a "font exemption", wherein these specific exempted fonts can be embedded without hypothetically turning their overall project into a GPL project.

I think the whole output thing is a lot simpler when the output is non-code. I.e. using OpenOffice.org to print out a letter on a physical piece of paper. There's no gray there, right?