Implementation of file-embed link.

[danfickle]

#508 #509 #636

Based heavily on code by @syjer whom I'm indebted to. Thanks.

Still todo:

• Prevent duplicate file embeds. Possibly create a map of uris to PDComplexFileSpecification and reuse if encountered again. I have to peruse the PDF spec to see if this is allowed.
• Logging on fail.

[syjer]

Thank you @danfickle , I'll close the old PR :)

[danfickle]

OK, here is a valid file embed link for PDF/A3 standards:

   <a href="file-embed.html"
      download="source.html"
      data-content-type="text/html"
      title="File embedded"
      relationship="Source">

      Link to source code

   </a>

The attributes are:

• href: The file source. Required.
• download: The file name as presented in the PDF viewer. Required.
• data-content-type: The mime type of the embedded file. Defaults to application/octet-stream.
• title: Optional short description of the file. Strongly recommended for PDF/A3 documents.
• relationship: Should only be used in PDF/A3 documents. The relationship of the embedded file to the link. Must be one of the following:
  • Source - Example: source markup of the document.
  • Supplement
  • Data - Example tabular data.
  • Alternative - Example audio providing an alternative view of the material.
  • Unspecified - Fallback catch all.

NOTE: If the relationship attribute is present the files modification date is set to the servers current date (Calendar.getInstance()). The modification date is required by PDF/A3.

Useful links in writing this implementation:

• PDF/A-3u as an archival format for Accessible mathematics (large PDF)
• Library of Congress on PDF/A3

[houssainy]

@danfickle
I want to embed an XML file to the generated PDF/A3 file but I don't really want the tag to appear in the generated PDF. So is there a way to hide the <a> tag?

I tried multiple ways to hide the tag but all of them were failing. Also i tried to have an empty tag

 <a href="file-embed.html"
      download="source.html"
      data-content-type="text/html"
      title="File embedded"
      relationship="Source">
   </a>

but this also didn't work and generated PDF didn't contain the expected attachment.

[maciejtoporowicz]

Hello, does it work in fast mode? It only works for me in slow mode.

In fast mode I can see these logs:

com.openhtmltopdf.load WARNING:: URI file:///<path> with type FILE_EMBED was rejected by resource access controller
com.openhtmltopdf.load WARNING:: Was not able to load an embedded file for embedding with uri file:///<path>

The PDF is created and the link is rendered, but it's not clickable.

[maciejtoporowicz]

Ok, figured it out. The DefaultAccessController used in com.openhtmltopdf.swing.NaiveUserAgent rejects embedding files.
I don't really understand this mechanism, but I found out that it's configurable. I created my own "AccessController":

private static class AllowAllAccessController implements BiPredicate<String, ExternalResourceType> {
  public boolean test(String uri, ExternalResourceType resourceType) {
    return true;
  }
}

and then configured the pdf renderer to use it:

new PdfRendererBuilder()
    .useExternalResourceAccessControl(new AllowAllAccessController(), ExternalResourceControlPriority.RUN_BEFORE_RESOLVING_URI)
    .useExternalResourceAccessControl(new AllowAllAccessController(), ExternalResourceControlPriority.RUN_AFTER_RESOLVING_URI)
    (...)
    .run();

Now it works fine.