Re: [PATCH 05/30] loose: add a mapping between SHA-1 and SHA-256 for loose objects

[Eric Sunshine <sunshine@sunshineco.com>]

On Wed, Sep 27, 2023 at 3:56 PM Eric W. Biederman <ebiederm@gmail.com> wrote:
> As part of the transition plan, we'd like to add a file in the .git
> directory that maps loose objects between SHA-1 and SHA-256.  Let's
> implement the specification in the transition plan and store this data
> on a per-repository basis in struct repository.
>
> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
> diff --git a/loose.c b/loose.c
> @@ -0,0 +1,245 @@
> +static int load_one_loose_object_map(struct repository *repo, struct object_directory *dir)
> +{
> +       struct strbuf buf = STRBUF_INIT, path = STRBUF_INIT;
> +       FILE *fp;
> +
> +       if (!dir->loose_map)
> +               loose_object_map_init(&dir->loose_map);
> +
> +       insert_oid_pair(dir->loose_map->to_compat, repo->hash_algo->empty_tree, repo->compat_hash_algo->empty_tree);
> +       insert_oid_pair(dir->loose_map->to_storage, repo->compat_hash_algo->empty_tree, repo->hash_algo->empty_tree);
> +
> +       insert_oid_pair(dir->loose_map->to_compat, repo->hash_algo->empty_blob, repo->compat_hash_algo->empty_blob);
> +       insert_oid_pair(dir->loose_map->to_storage, repo->compat_hash_algo->empty_blob, repo->hash_algo->empty_blob);
> +
> +       insert_oid_pair(dir->loose_map->to_compat, repo->hash_algo->null_oid, repo->compat_hash_algo->null_oid);
> +       insert_oid_pair(dir->loose_map->to_storage, repo->compat_hash_algo->null_oid, repo->hash_algo->null_oid);
> +
> +       strbuf_git_common_path(&path, repo, "objects/loose-object-idx");
> +       fp = fopen(path.buf, "rb");
> +       if (!fp)
> +               return 0;

This early return leaks `path`. At minimum, call
`strbuf_release(&path)` before returning.

> +       errno = 0;
> +       if (strbuf_getwholeline(&buf, fp, '\n') || strcmp(buf.buf, loose_object_header))
> +               goto err;
> +       while (!strbuf_getline_lf(&buf, fp)) {
> +               const char *p;
> +               struct object_id oid, compat_oid;
> +               if (parse_oid_hex_algop(buf.buf, &oid, &p, repo->hash_algo) ||
> +                   *p++ != ' ' ||
> +                   parse_oid_hex_algop(p, &compat_oid, &p, repo->compat_hash_algo) ||
> +                   p != buf.buf + buf.len)
> +                       goto err;
> +               insert_oid_pair(dir->loose_map->to_compat, &oid, &compat_oid);
> +               insert_oid_pair(dir->loose_map->to_storage, &compat_oid, &oid);
> +       }
> +
> +       strbuf_release(&buf);
> +       strbuf_release(&path);
> +       return errno ? -1 : 0;
> +err:
> +       strbuf_release(&buf);
> +       strbuf_release(&path);
> +       return -1;
> +}
> +
> +int repo_write_loose_object_map(struct repository *repo)
> +{
> +       kh_oid_map_t *map = repo->objects->odb->loose_map->to_compat;
> +       struct lock_file lock;
> +       int fd;
> +       khiter_t iter;
> +       struct strbuf buf = STRBUF_INIT, path = STRBUF_INIT;
> +
> +       if (!should_use_loose_object_map(repo))
> +               return 0;
> +
> +       strbuf_git_common_path(&path, repo, "objects/loose-object-idx");
> +       fd = hold_lock_file_for_update_timeout(&lock, path.buf, LOCK_DIE_ON_ERROR, -1);
> +       iter = kh_begin(map);
> +       if (write_in_full(fd, loose_object_header, strlen(loose_object_header)) < 0)
> +               goto errout;
> +
> +       for (; iter != kh_end(map); iter++) {
> +               if (kh_exist(map, iter)) {
> +                       if (oideq(&kh_key(map, iter), the_hash_algo->empty_tree) ||
> +                           oideq(&kh_key(map, iter), the_hash_algo->empty_blob))
> +                               continue;
> +                       strbuf_addf(&buf, "%s %s\n", oid_to_hex(&kh_key(map, iter)), oid_to_hex(kh_value(map, iter)));
> +                       if (write_in_full(fd, buf.buf, buf.len) < 0)
> +                               goto errout;
> +                       strbuf_reset(&buf);
> +               }
> +       }

Nit: If you call strbuf_reset() immediately before strbuf_addf(), then
you save the reader of the code the effort of having to scan backward
through the function to verify that `buf` is empty the first time
through the loop.

> +       strbuf_release(&buf);
> +       if (commit_lock_file(&lock) < 0) {
> +               error_errno(_("could not write loose object index %s"), path.buf);
> +               strbuf_release(&path);
> +               return -1;
> +       }
> +       strbuf_release(&path);
> +       return 0;
> +errout:
> +       rollback_lock_file(&lock);
> +       strbuf_release(&buf);
> +       error_errno(_("failed to write loose object index %s\n"), path.buf);
> +       strbuf_release(&path);
> +       return -1;
> +}
> +
> +int repo_loose_object_map_oid(struct repository *repo,
> +                             const struct object_id *src,
> +                             const struct git_hash_algo *to,
> +                             struct object_id *dest)
> +
> +{

Style: unnecessary blank line before opening `{`

> +       struct object_directory *dir;
> +       kh_oid_map_t *map;
> +       khiter_t pos;
> +
> +       for (dir = repo->objects->odb; dir; dir = dir->next) {
> +               struct loose_object_map *loose_map = dir->loose_map;
> +               if (!loose_map)
> +                       continue;
> +               map = (to == repo->compat_hash_algo) ?
> +                       loose_map->to_compat :
> +                       loose_map->to_storage;
> +               pos = kh_get_oid_map(map, *src);
> +               if (pos < kh_end(map)) {
> +                       oidcpy(dest, kh_value(map, pos));
> +                       return 0;
> +               }
> +       }
> +       return -1;
> +}