Re: [PATCH 2/8] builtin/multi-pack-index.c: support --stdin-packs mode

On Sat, Sep 11, 2021 at 10:08:44PM -0400, Eric Sunshine wrote:

On Sat, Sep 11, 2021 at 12:25 PM Taylor Blau [off-list ref] wrote:

quoted

On Sat, Sep 11, 2021 at 12:05:05PM +0200, Ævar Arnfjörð Bjarmason wrote:

quoted

Before calling string_list_clear(). I.e. we didn't strdup(), but during
free() we pretend that we did, because we did, just not in
string_list_append().

Good catch. It's kind of gross, but the result is:

 static void read_packs_from_stdin(struct string_list *to)
 {
-       struct strbuf buf = STRBUF_INIT;
+       struct strbuf buf = STRBUF_INIT_NODUP;
        while (strbuf_getline(&buf, stdin) != EOF) {
                string_list_append(to, strbuf_detach(&buf, NULL));
        }

@@ -107,6 +107,11 @@ static int cmd_multi_pack_index_write(int argc, const char **argv)
                ret = write_midx_file_only(opts.object_dir, &packs,
                                           opts.preferred_pack, opts.flags);

+               /*
+                * pretend strings are duplicated to free the memory allocated
+                * by read_packs_from_stdin()
+                */
+               packs.strdup_strings = 1;
                string_list_clear(&packs, 0);

An alternative is to do this:

    struct strbuf buf = STRBUF_INIT;
    ...
    while (...) {
        string_list_append_nodup(to, strbuf_detach(&buf, NULL));
        ...
    }
    ...
    string_list_clear(&packs, 0);

That is, use string_list_append_nodup(), which is documented as
existing precisely for this sort of use-case:

    Like string_list_append(), except string is never copied.  When
    list->strdup_strings is set, this function can be used to hand
    ownership of a malloc()ed string to list without making an extra
    copy.

(I mention this only for completeness but don't care strongly which
approach is used.)

Thanks for a great suggestion; I do prefer using the existing APIs where
possible, and it seems like string_list_append_nodup() was designed
exactly for this case.

Thanks,
Taylor