Re: [PATCH v2 1/2] sequencer: handle errors in read_author_ident()

[Eric Sunshine <sunshine@sunshineco.com>]

On Tue, Jul 31, 2018 at 7:15 AM Phillip Wood <phillip.wood@talktalk.net> wrote:
> The calling code treated NULL as a valid return value, so fix this by
> returning and integer and passing in a parameter to receive the author.

It might be difficult for future readers (those who didn't follow the
discussion) to understand how/why NULL is not sufficient to signal an
error. Perhaps incorporating the explanation from your email[1] which
discussed that the author name, email, and/or date might change
unexpectedly would be sufficient. This excerpt from [1] might be a
good starting point:

    ... the caller does not treat NULL as an error, so this will
    change the date and potentially the author of the commit
    ... [which] does corrupt the author data compared to its
    expected value.

[1]: https://public-inbox.org/git/c80cf729-1bbe-10f5-6837-b074d371b91c@talktalk.net/

> Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> ---
> diff --git a/sequencer.c b/sequencer.c
> @@ -701,57 +701,58 @@ static char *get_author(const char *message)
> -static const char *read_author_ident(struct strbuf *buf)
> +static int read_author_ident(char **author)

So, the caller is now responsible for freeing the string placed in
'author'. Okay.

>  {
> -       if (strbuf_read_file(buf, rebase_path_author_script(), 256) <= 0)
> -               return NULL;
> +       if (strbuf_read_file(&buf, rebase_path_author_script(), 256) <= 0)
> +               return -1;

I think you need to strbuf_release(&buf) in this error path since
strbuf_read_file() doesn't guarantee that the strbuf hasn't been
partially populated when it returns an error. (That is, this is
leaking.)

>         /* dequote values and construct ident line in-place */

Ugh, this comment should have been adjusted in my series. A minor
matter, though, which can be tweaked later.

>         /* validate date since fmt_ident() will die() on bad value */
>         if (parse_date(val[2], &out)){
> -               warning(_("invalid date format '%s' in '%s'"),
> +               error(_("invalid date format '%s' in '%s'"),
>                         val[2], rebase_path_author_script());
>                 strbuf_release(&out);
> -               return NULL;
> +               strbuf_release(&buf);
> +               return -1;

You were careful to print the error, which references a value from
'buf', before destroying 'buf'. Good.

(A simplifying alternative would have been to not print the actual
value and instead say generally that "the date" was bad. Not a big
deal.)

>         }
> -       strbuf_swap(buf, &out);
> -       strbuf_release(&out);
> -       return buf->buf;
> +       *author = strbuf_detach(&out, NULL);

And, 'author' is only assigned when 0 is returned, so the caller only
has to free(author) upon success. Fine.

> +       strbuf_release(&buf);
> +       return 0;
>  }
>
>  static const char staged_changes_advice[] =
> @@ -794,12 +795,14 @@ static int run_git_commit(const char *defmsg, struct replay_opts *opts,
> -               struct strbuf msg = STRBUF_INIT, script = STRBUF_INIT;
> -               const char *author = is_rebase_i(opts) ?
> -                       read_author_ident(&script) : NULL;
> +               struct strbuf msg = STRBUF_INIT;
> +               char *author = NULL;
>                 struct object_id root_commit, *cache_tree_oid;
>                 int res = 0;
>
> +               if (is_rebase_i(opts) && read_author_ident(&author))
> +                       return -1;

Logic looks correct, and it's nice to see that you went with 'return
-1' rather than die(), especially since the caller of run_git_commit()
is already able to handle -1.