Re: [PATCH 6/6] hash-object: use fsck for object checks
- From
Taylor Blau <me@ttaylorr.com>
- Date
- Jan 18, 2023, 21:34 UTC
- Message-ID
- <Y8hlyr0o6gs9omI5@nand.local>
- In-Reply-To
- <Y8haHL9xIWntSm0/@coredump.intra.peff.net>
On Wed, Jan 18, 2023 at 03:44:12PM -0500, Jeff King wrote:
Show 18 quoted lines
> This is obviously going to be a user-visible behavior change, and the > test changes earlier in this series show the scope of the impact. But > I'd argue that this is OK: > > - the documentation for hash-object is already vague about which > checks we might do, saying that --literally will allow "any > garbage[...] which might not otherwise pass standard object parsing > or git-fsck checks". So we are already covered under the documented > behavior. > > - users don't generally run hash-object anyway. There are a lot of > spots in the tests that needed to be updated because creating > garbage objects is something that Git's tests disproportionately do. > > - it's hard to imagine anyone thinking the new behavior is worse. Any > object we reject would be a potential problem down the road for the > user. And if they really want to create garbage, --literally is > already the escape hatch they need.
This is the discussion I was pointing out earlier in the series as evidence for making this behavior the new default without "--literally".
That being said, let me play devil's advocate for a second. Do the new fsck checks slow anything in hash-object down significantly? If so, then it's plausible to imagine a hash-object caller who (a) doesn't use `--literally`, but (b) does care about throughput if they're writing a large number of objects at once.
I don't know if such a situation exists, or if these new fsck checks even slow hash-object down enough to care. But I didn't catch a discussion of this case in your series, so I figured I'd bring it up here just in case.
Show 11 quoted lines
> - the resulting messages are much better. For example: > > [before] > $ echo 'tree 123' | git hash-object -t commit --stdin > error: bogus commit object 0000000000000000000000000000000000000000 > fatal: corrupt commit > > [after] > $ echo 'tree 123' | git.compile hash-object -t commit --stdin > error: object fails fsck: badTreeSha1: invalid 'tree' line format - bad sha1 > fatal: refusing to create malformed object
Much nicer, well done.
Show 48 quoted lines
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> object-file.c | 55 ++++++++++++++++++------------------------
> t/t1007-hash-object.sh | 11 +++++++++
> 2 files changed, 34 insertions(+), 32 deletions(-)
>
> diff --git a/object-file.c b/object-file.c
> index 80a0cd3b35..5c96384803 100644
> --- a/object-file.c
> +++ b/object-file.c
> @@ -33,6 +33,7 @@
> #include "object-store.h"
> #include "promisor-remote.h"
> #include "submodule.h"
> +#include "fsck.h"
>
> /* The maximum size for an object header. */
> #define MAX_HEADER_LEN 32
> @@ -2298,32 +2299,21 @@ int repo_has_object_file(struct repository *r,
> return repo_has_object_file_with_flags(r, oid, 0);
> }
>
> -static void check_tree(const void *buf, size_t size)
> -{
> - struct tree_desc desc;
> - struct name_entry entry;
> -
> - init_tree_desc(&desc, buf, size);
> - while (tree_entry(&desc, &entry))
> - /* do nothing
> - * tree_entry() will die() on malformed entries */
> - ;
> -}
> -
> -static void check_commit(const void *buf, size_t size)
> -{
> - struct commit c;
> - memset(&c, 0, sizeof(c));
> - if (parse_commit_buffer(the_repository, &c, buf, size, 0))
> - die(_("corrupt commit"));
> -}
> -
> -static void check_tag(const void *buf, size_t size)
> -{
> - struct tag t;
> - memset(&t, 0, sizeof(t));
> - if (parse_tag_buffer(the_repository, &t, buf, size))
> - die(_("corrupt tag"));OK, here we're getting rid of all of the lightweight checks that hash-object used to implement on its own.
Show 36 quoted lines
> +/*
> + * We can't use the normal fsck_error_function() for index_mem(),
> + * because we don't yet have a valid oid for it to report. Instead,
> + * report the minimal fsck error here, and rely on the caller to
> + * give more context.
> + */
> +static int hash_format_check_report(struct fsck_options *opts,
> + const struct object_id *oid,
> + enum object_type object_type,
> + enum fsck_msg_type msg_type,
> + enum fsck_msg_id msg_id,
> + const char *message)
> +{
> + error(_("object fails fsck: %s"), message);
> + return 1;
> }
>
> static int index_mem(struct index_state *istate,
> @@ -2350,12 +2340,13 @@ static int index_mem(struct index_state *istate,
> }
> }
> if (flags & HASH_FORMAT_CHECK) {
> - if (type == OBJ_TREE)
> - check_tree(buf, size);
> - if (type == OBJ_COMMIT)
> - check_commit(buf, size);
> - if (type == OBJ_TAG)
> - check_tag(buf, size);
> + struct fsck_options opts = FSCK_OPTIONS_DEFAULT;
> +
> + opts.strict = 1;
> + opts.error_func = hash_format_check_report;
> + if (fsck_buffer(null_oid(), type, buf, size, &opts))
> + die(_("refusing to create malformed object"));
> + fsck_finish(&opts);
> }And here's the main part of the change, which is delightfully simple and appears correct to me.
Show 19 quoted lines
> diff --git a/t/t1007-hash-object.sh b/t/t1007-hash-object.sh
> index 2d2148d8fa..ac3d173767 100755
> --- a/t/t1007-hash-object.sh
> +++ b/t/t1007-hash-object.sh
> @@ -222,6 +222,17 @@ test_expect_success 'empty filename in tree' '
> grep "empty filename in tree entry" err
> '
>
> +test_expect_success 'duplicate filename in tree' '
> + hex_oid=$(echo foo | git hash-object --stdin -w) &&
> + bin_oid=$(echo $hex_oid | hex2oct) &&
> + {
> + printf "100644 file\0$bin_oid" &&
> + printf "100644 file\0$bin_oid"
> + } >tree-with-duplicate-filename &&
> + test_must_fail git hash-object -t tree tree-with-duplicate-filename 2>err &&
> + grep "duplicateEntries" err
> +'
> +For what it's worth, I think that this is sufficient coverage for the new fsck checks.
Thanks, Taylor