go-epub's ReadBook parses every spine chapter and fails the entire call
if any single chapter (or the TOC) is malformed, discarding already-parsed
OPF metadata. For books like Pragmatic's 'A Common-Sense Guide' the OPF
holds good title/author/publisher/ISBN metadata that rescans then wrote
as blanks - success toast, no (visible) change.
Refactor to parse the EPUB's own OPF document with the same Dublin Core
machinery used for Calibre sidecars: parseCalibreMetadataOPF is now a thin
file wrapper around a reusable parseOPFContent([]byte), and the OPF lookup
previously inline in extractEPUBCover is shared via findOPFPathInZip. Since
metadata never touches chapter bodies, chapter damage cannot blank it.
Also picked up along the way: dc:language mapping and scheme-less
dc:identifier values that normalize to a valid ISBN (EPUB3 style).
Tests cover a Pragmatic-style EPUB (dc namespace on <metadata>, no
identifier scheme, deliberately malformed chapter) that must still yield
full metadata, plus series/date/subject OPF parsing.
John O'Keefe
61681aac23