Am Sat, 29 Jul 2023 12:12:12 +0200 schrieb LARONDE Thierry:

> OK, let's go to "TeX: The Program": m.537 (p 214):

Your concrete problem is not the implementation of \input, your
problem is that your implementation of \pdffilesize (which by the
way is not mentioned in "TeX: The Program") doesn't use the same
method to find a file as your \input/\openin. 

It is  -- as David already wrote -- quite a problem if "\pdffilesize
filename" reports a size that differs from the size of the file that
is input with "\input filename". 

It doesn't make much sense therefore to muse on if or if not the
current engines implement exactly what "TeX: The Program" says. 
Simply get \pdffilesize etc in sync with \input, \openin etc.

Ulrike Fischer