Attach/Detach to/from PDFs

[sebastianludwig]

Hey, awesome project! Will probably end up using it some time soon. In the README you write

This does not contain any code to attach the XML to a PDF file, mainly because I have yet to find a ruby library to do that.

HexaPDF can do that.

Attaching is easy. See the documentation or unit tests.

Extraction:

irb(main):001> require "hexapdf"
=> true
irb(main):002> pdf = HexaPDF::Document.open("corpus-master/ZUGFeRDv2/correct/Mustangproject/MustangGnuaccountingBeispielRE-20190610_507.pdf")
=> <HexaPDF::Document:21960>
irb(main):003> pdf.files
=> #<HexaPDF::Document::Files:0x000000010337fbf0 @document=<HexaPDF::Document:21960>>
irb(main):004> pdf.files.each { |f| puts f }
#<HexaPDF::Type::FileSpecification:0x000000010337cc70>
=> #<HexaPDF::Document::Files:0x000000010337fbf0 @document=<HexaPDF::Document:21960>>
irb(main):005> pdf.files.first
=> #<HexaPDF::Type::FileSpecification [8, 0] value={:Type=>:Filespec, :F=>"zugferd-invoice.xml", :AFRelationship=>:Alternative, :UF=>"zugferd-invoice.xml", :Desc=>"Invoice metadata conforming to ZUGFeRD standard (http://www.ferd-net.de/front_content.php?idcat=231&lang=4)", :EF=>#<HexaPDF::Reference [17, 0]>}>
irb(main):006> pdf.files.first.embedded_file_stream
=> #<HexaPDF::Type::EmbeddedFile [107, 0] value={:Length=>10338, :Type=>:EmbeddedFile, :Subtype=>:"text/xml", :Params=>#<HexaPDF::Reference [239, 0]>}>

and then

fiber = obj.embedded_file_stream.stream_decoder
while fiber.alive? && (data = fiber.resume)
    file << data
end

I don't think it should be secretariat's job to do that, just wanted to let you (and others) know.

[halfbyte]

Hi @sebastianludwig Thanks for the pointer! I've been scanning rubygems.org again when I did the push for the latest ZUGFeRD versions but did not find HexaPDF. I think it would be useful to add this functionality to this library, but it'll probably take me a couple of weeks to get to that.

[sebastianludwig]

Hey, I understand the temptation but would argue that it's best left to the user of this library. Either they are already using HexaPDF, then an example in the README would be all they need. Or they are using a different PDF library in which case ruby-secretariat would add another PDF library as dependency (not a lightweight one - HexaPDF depends on OpenSSL 🙄) just for the attach functionality. Also not being required to maintaining compatibility with HexaPDF will also reduce the long term maintenance effort and give you more time to focus on the core functionality. </2c> ;-)

[mck9]

HexaPDF is AGPL, so not everybody would like that. Like @sebastianludwig said, PDF handling should not be part of this lib.