Fix missing thumbnail on MacOS

[gonejack]

Hi, author.

This PR addresses both #19 and #18

[coveralls]

Coverage increased (+0.2%) to 81.926% when pulling 29bfce9 on gonejack:fix/thumbnail into 2a8f9fd on bmaupin:master.

[bmaupin]

@gonejack Thanks for the PR!

Unfortunately it seems to be failing the EPUBCheck test (I'm using v4.2.2).

To see the results for yourself, you can either:

• Set doCleanup = false in epub_test.go and then upload the generated My EPUB.epub to http://validator.idpf.org/
• Or you can download EPUBCheck from https://github.com/w3c/epubcheck/releases/download/v4.2.2/epubcheck-4.2.2.zip and then unzip it in the current directory and re-run go test
  • This requires Java to be installed and I haven't tested it in Windows

I'll try to document this a bit better for contributors to make it easier to submit PRs.

Here is the output I'm getting:

$ go test
Validating using EPUB version 3.2 rules.
ERROR(RSC-005): My EPUB.epub/EPUB/package.opf(10,63): Error while parsing file: value of attribute "property" is invalid; must be an XML NMTOKEN
ERROR(RSC-005): My EPUB.epub/EPUB/package.opf(10,63): Error while parsing file: attribute "name" not allowed here; expected attribute "dir", "id", "refines", "scheme" or "xml:lang"
ERROR(RSC-005): My EPUB.epub/EPUB/package.opf(10,63): Error while parsing file: attribute "content" not allowed here; expected attribute "dir", "id", "refines", "scheme" or "xml:lang"
ERROR(RSC-005): My EPUB.epub/EPUB/package.opf(10,70): Error while parsing file: character content of element "meta" invalid; must be a string with length at least 1 (actual length was 0)

Check finished with errors
Messages: 0 fatals / 4 errors / 0 warnings / 0 infos

EPUBCheck completed

--- FAIL: TestEpubValidity (3.62s)
    epub_test.go:652: EPUB validation failed
FAIL
exit status 1
FAIL	github.com/bmaupin/go-epub	4.153s

If you want to send a separate PR just for #19 I can merge that now, or if you'd like you can just fix this one.

Thanks!

[bmaupin]

@gonejack I just added more information on EPUBCheck to the readme. Hope that helps!

[bmaupin]

@gonejack I just updated the CI/CD tests in Travis to run EPUBCheck so it should help catch this sooner.

[gonejack]

I notice that sigil sets cover meta the same way and O'reilly books contain this meta as well.

It's interesting why sigil and macOS support something not following the specification.

[bmaupin]

@gonejack I'll try to take a closer look at this PR this coming week. If you're able to split the fixes for #18 and #19 into separate PRs it might be a little bit easier. But if not I'll see what I can do. Thanks!

[gonejack]

@coveralls it's my fault that mixed them, fix for #19 is too short for a PR, could you include it in your later commits?

[bmaupin]

@gonejack

I did some research regarding the thumbnail issue and the new element you added, and it seems that this is an old EPUB 2 element that a lot of companies still use. This page in particular was helpful: http://idpf.org/forum/topic-715

This was the example given on that page:

<meta name="cover" content="My_Cover_ID" />

According to that page, this should still be valid even in EPUB 3 (which this library generates), so I compared it to the meta element from the change you made:

<meta property="" name="cover" content="testfromfile.png"></meta>

The biggest difference seems to be that they left out the property attribute.

So I made one small tweak in pkg.go, and it passes validation now!

	Property string `xml:"property,attr,omitempty"`

Since I couldn't modify this PR, I created a new one (#38) and rebased it on your commit so you'll be listed as a contributor.

Thanks for your help and I'm sorry it took me so long to look into this. I don't have a Mac that's easily accessible now, but hopefully this fixes #18. Feel free to reopen it if it doesn't.

[gonejack]

Good done, I will try it later.