Re: [PATCH 1/2] config: check if config path is a file before parsing it

On Fri, Mar 3, 2017 at 4:53 PM, Jeff King [off-list ref] wrote:

I'm mildly negative on this approach for two reasons:

  1. It requires doing an _extra_ check anywhere we want to care about
     this. So if we care about file/directory confusion, we're going to
     sprinkle these is_not_file() checks all over the code base.

     I think we're much better to just do the thing we want to do (like
     open the file), and deal with the error results. I'm on the fence
     on whether we want to care about the fopen behavior on Linux here
     (where reading a directory essentially behaves like an empty file,
     because the first read() gives an error and we don't distinguish
     between error and EOF).

I can't fix problems of my series on Windows because I don't use
Windows (because I will not be able to verify it). So I'm definitely
on the side that makes behavior consistent across platforms. Then I
can at least verify some (assuming that the consistent behavior is the
right one).

I didn't go with yours because I would have to handle two separate
code paths (fopen returns NULL and read returns EISDIR). But yeah it
should be that way even if it takes more time and effort. At least
we're now back on the mailing list and I didn't have to hurry to get
something out, to get off github.

But if we do, I think we'd either want to:

       a. actually check ferror() after getting EOF and report the read
          error. That catches EISDIR, along with any other unexpected
          errors.

       b. use an fopen wrapper that checks fstat(fileno(fh)) after the
          open, and turns fopen(some_dir) into an error.

If you don't like extra check, I guess you're negative on b as well
since it is an extra check on Windows. That leaves us with option a.

  2. It doesn't address the root problem for git_config_from_file(),
     which is that it is quiet when fopen fails, even if the reason is
     something interesting besides ENOENT. The caller can't check errno
     because it doesn't know if fopen() failed, or if the config
     callback returned an error.

     There's an attempt to protect the call to git_config_from_file() by
     checking access(), but that breaks down when access() and fopen()
     have two different results (which is exactly what happens on
     Windows in this case).

-Peff

-- 
Duy