On Tue, Apr 28, 2015 at 10:07:43PM +0200, erik elfström wrote:
> On Tue, Apr 28, 2015 at 8:17 AM, Jeff King <[email protected]> wrote:
> >
> > There was a discussion not too long ago on strategies for returning
> > errors, and one of the suggestions was to return an "error strbuf"
> > rather than a code[1]. That's less flexible, as the caller can't react
> > differently based on the type of error. But for cases like this, where
> > the only fate for the code is to get converted back into a message,
> > it can reduce the boilerplate.
> >
> > What you have here is OK to me, and I don't want to hold up your patch
> > series in a flamewar about error-reporting techniques. But I think it's
> > an interesting case study.
> >
> > -Peff
>
> Thanks. I haven't had time to look through that thread yet, I'll try
> to get to that later.
>
> My initial reaction is a bit skeptical though. For this case we
> currently don't want any error reporting, the NULL return is
> sufficient and even allocating and sending in the int* is pure noise.
> Allocating and releasing a strbuf seems like a lot more overhead for
> this type of caller? The one other potential candidate caller for
> read_gitfile_gently that I have seen (clone.c:get_repo_path) don't
> want any error code or message either as far as i can tell.
I had envisioned that the strbuf would be optional. I.e., you would
have:
/* like error(), but dump the message in a strbuf instead of stderr */
int error_buf(struct strbuf *buf, const char *fmt, ...)
{
if (buf) {
va_list ap;
va_start(ap, fmt);
strbuf_vaddf(buf, fmt, ap);
va_end(ap);
}
return -1;
}
and then in the error-reporting function:
const char *read_gitfile_gently(const char *path, struct strbuf *err)
{
...
fd = open(path, O_RDONLY);
if (fd < 0) {
error_buf(err, "unable to open %s: %s", path, strerror(errno));
return NULL; /* or goto cleanup if necessary */
}
}
and then one caller can do:
if (!read_gitfile_gently(path, NULL)) {
/* we know there was an error, but we did not ask for details */
...
}
and the non-gentle read_gitfile() becomes:
const char *read_gitfile(const char *path)
{
struct strbuf err = STRBUF_INIT;
const char *ret = read_gitfile_gently(path, &err);
if (!ret)
die("%s", err.buf);
/* no need to free err; if there was no error, nothing was written */
return path;
}
Note that the "return -1" from error_buf() is not useful here, but it
might be used as a shortcut in other situations (e.g., the same places
we call "return error()" now).
> Also if it turns out that we actually need to treat the "file too
> large" error differently in clean (as discussed in thread on the file
> size check) then we can no longer communicate that back using the
> strbuf interface.
Yeah, agreed. This system breaks down as soon as you need to
programatically know which error happened.
-Peff
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