Check for unmatched doc.restore() calls?

[realtaraharris]

It's easy to produce a corrupt PDF by inserting a stray unpaired doc.restore() into code that uses pdfkit.

Is checking for stuff like this something pdfkit should try to do?

These errors are hard to detect because the resulting file renders without error in the better PDF viewers out there, including Preview and pdf.js. Unfortunately, Acrobat stops rendering after encountering errors such as these and makes no attempt to explain what's wrong.

[devongovett]

Hmm, yes. Right now most commands get rendered directly into the document as soon as you call them, but I'm thinking of moving to a model where calls are batched and can be more easily checked for user error. Thanks for reporting. I didn't know Acrobat complained about this.

[sly7-7]

I just encounter this error as well, seems like acrobat still fails on it. (browsers are ok, OS X preview too, as well as affinity publisher).
Fortunately, it's a quite small document, so it was quite easy to find out the restore() call without previous save().

[backspace]

This happened to me recently, I found that:

• Illustrator would not open certain pages from a PDF
• Ghostscript said encountered more Q than q (or the opposite)
• pdftocairo said Restoring state when no valid states to pop

I tried printing at a chain printshop and it choked on the pages:

The code to generate the PDF is quite involved and superficially I see an equal number of save() and restore() calls, though there’s a lot of nesting so something’s surely wrong somewhere. It would be nice to have something to ease tracking this down.

Regardless, thanks for all the work on this, it’s much nicer to work with than the hideous hacks I was using in the past 😬

ETA: I added this hack to track the save/restore stack:

    let oldSave = doc.save;
    let oldRestore = doc.restore;

    let stack = 0;

    doc.save = function () {
      stack++;
      console.log(`save called, stack: ${stack}`);
      oldSave.call(doc);
    };

    doc.restore = function () {
      stack--;
      console.log(`restore called, stack: ${stack}`);
      oldRestore.call(doc);
    };

The last line logged is this: restore called, stack: 0

So it does seem like they balance out! I’m sure I did something wrong somewhere but I’m not sure how to track it down.