FPDF_LoadPage returns NULL meaning

[Markoce]

We recently ran into a case where calling FPDF_LoadPage returned NULL. What are some ways we can interpret this? Also, is it valid to FPDF_GetLastError when that function returns NULL? Many functions explicitly say to call FPDF_GetLastError if there was an issue, and this one does not, so I am assuming the error code would me meaningless if we did?

We are sure we gave a page index that is in bounds as it is a 1 page PDF and we passed in 0.. We also already checked if the Document object being passed in is NULL.

[geisserml]

There is the error code FPDF_ERR_PAGE ("Page not found or content error") [1], so I would assume a meaningful return value of FPDF_GetLastError() in this case.

If possible, could you please share the document in question? It sounds like an interesting test case.

[1]: https://pdfium.googlesource.com/pdfium/+/15d326e3d3fbbf178fde4c22ec8860f08b54362c/public/fpdfview.h#560

[Lei Zhang]

Some PDFs contain bad pages. e.g. 3 page document with valid pages 1
and 3, but page 2 points at a non-existent object. In which case,
FPDF_LoadPage() would return NULL for page 2.

On Tue, Jun 7, 2022 at 11:04 AM Markoce <abacefabm...@gmail.com> wrote:
>
> We recently ran into a case where calling FPDF_LoadPage returned NULL. What are some ways we can interpret this? Also, is it valid to FPDF_GetLastError when that function returns NULL? Many functions explicitly say to call FPDF_GetLastError if there was an issue, and this one does not, so I am assuming the error code would me meaningless if we did?
>
> We are sure we gave a page index that is in bounds as it is a 1 page PDF and we passed in 0.. We also already checked if the Document object being passed in is NULL.
>

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[Bupo Zhuang]

I had the same problem， FPDF_LoadPage returns NULL but FPDF_GetLastError return success.  what's the meaning?

[Lei Zhang]

Same answer as before. Assuming the input parameters are correct, a
NULL return value means the page failed to load, as defined in the
FPDF_LoadPage() documentation.

IIRC, FPDF_GetLastError() only works for the document loading APIs,
and not in the general case for any arbitrary API.

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[geisserml]

The outdated Foxit documentation still mentions FPDF_GetLastError() in
FPDF_LoadPage(). Does this mean the error handling behaviour has changed
throughout the history of PDFium?

[Lei Zhang]

Not much has changed throughout the history of PDFium w.r.t.
FPDF_GetLastError(). One can sync PDFium back to 2014, examine the
code, and see FPDF_GetLastError() behaves similar to the way it does
today. The Foxit documentation is simply incorrect when it talks about
FPDF_GetLastError().

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