Re: BUG #15449: file_fdw using program cause exit code error when using LIMIT

I wrote:
> I just had a thought about that: suppose we add a flag to CopyState
> to indicate whether we reached EOF while reading. ...
> Then the logic in ClosePipeToProgram could be "if we did not reach
> EOF, then a SIGPIPE termination is unsurprising. If we did reach
> EOF, then SIGPIPE is an error." If the called program gets SIGPIPE
> for some reason other than us closing the pipe early, then we would
> see EOF next time we try to read, and correctly report that there's
> a problem.

Concretely, something like the attached.

I'm not quite sure whether the reached_eof test should be
"if (bytesread == 0)" or "if (bytesread < maxread)". The former
seems more certain to indicate real EOF; are there other cases where
the fread might return a short read? On the other hand, if we
support in-band EOF indicators (\. for instance) then we might
stop without having made an extra call to CopyGetData that would
see bytesread == 0. On the third hand, if we do do that it's
not quite clear to me whether SIGPIPE is ignorable or not.

regards, tom lane