Documents without /Info reference in trailer will result in 0 when calling FPDF_GetMetaText

[Jeroen Bobbeldijk]

Hi there,

In go-pdfium, I use the response of FPDF_GetMetaText to detect whether something went wrong or not, mainly because FPDF_GetMetaText return 2 (string), whether the tag exists or not. However, when opening a PDF without any /Info reference in the trailer always returns 0, which doesn't really match the behavior of other PDF's in my opinion that do have /Info but do not have that specific Tag.

My proposal would be to also return 2 (empty string) when the /Info reference doesn't exist.

I attched a demo PDF, created with the commands:

exiftool -all:all= foo.pdf

qpdf --linearize foo.pdf bar.pdf

It would also be great to have some method to list the available tags in a document.

Kind regards,

Jeroen Bobbeldijk

[Jeroen Bobbeldijk]

Correction:

  mainly because FPDF_GetMetaText return 2 (empty string), when the tag is actually empty, but also when it doesn't exist

Also, I could also live with having 0 being that the tag doesn't exist or that there is no info at all in the document, but that would break how it currently works.

[Lei Zhang]

Would adding FPDF_BOOL FPDF_HasMetaText(FPDF_DOCUMENT document,
FPDF_BYTESTRING tag) help?

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[Jeroen Bobbeldijk]

Yes, I think it would :) A method to get all the meta tags of a document would also work, since you can basically add anything to the Info tag right?

[geisserml]

On comment 2: I agree. We noticed this problem, too, while implementing a python wrapper for FPDF_GetMetaText().
With the current API, it's not possible to distinguish between "empty" and "not set".

[Jeroen Bobbeldijk]

@Lei, are there any plans to add the FPDF_HasMetaText and/or a method to list the tags of a document?

[Jeroen Bobbeldijk]

I'd still like to see this implemented, also willing to build it myself. 

@Lei can you confirm whether adding "FPDF_HasMetaText" and making "FPDF_GetMetaText" always return a buflen of at least 2 (empty string), even if /Info doesn't exist, is something that would be merged?