Stop throwing away the files a document carries

[tannevaled]

A PDF can hold whole files inside it — the spreadsheet a report was drawn from, the XML a form was filled from, the source of a figure. Every verb here dropped them.

Not out of carelessness: the catalogue's /Names was dropped whole, on the ground that a name tree points into the document rather than describing it. That is true of /Dests, whose names point at pages this reorders and removes, and of /JavaScript, which is code. It is not true of /EmbeddedFiles: a file inside a document belongs to no page, so nothing here can invalidate it — and nothing on the page says it is there, so nobody notices it went until the file is wanted.

45 of the 3 215 documents in the forms and scans corpora carry one, 50 files between them.

So they are carried, and three verbs follow from having to read them anyway: Attachments lists what a document holds, Attach puts one in, Detach takes one out. Two files under one name is a document that has lost one of them, so a name already used is refused rather than quietly replacing what is there. A sanitised file still carries nothing inside it — that is what sanitising is for.

What the tests found

Files from several documents are all kept, unlike everything else in the catalogue: two forms cannot be merged and two catalogues cannot be chosen between, but two sets of files can simply both be carried. Writing that test is what found the bug — Attachments read the single source, and a merged document has none.

Two things a specification can point at are not files, and both are left out rather than handed over empty: one that names no stream, and one whose stream is still in a filter nothing here unpacks. DecodeStream hands those back as they were stored and names what they are in, so passing them on gives somebody a spreadsheet that is not one.

Judged by poppler rather than by ourselves

pdfdetach -list says 1 file before and 2 after a rotation and an addition, and -saveall writes both with the right bytes.

Parity: BentoPDF's Add Attachments, Extract Attachments and Edit Attachments.

100% statement coverage, go vet and -race clean, nine cross-compile targets.