Re: [PATCH 14/17] midx: use chunk-format read API

On 1/26/2021 10:06 PM, Taylor Blau wrote:

On Tue, Jan 26, 2021 at 04:01:23PM +0000, Derrick Stolee via GitGitGadget wrote:

quoted

From: Derrick Stolee <redacted>

Instead of parsing the table of contents directly, use the chunk-format
API methods read_table_of_contents() and pair_chunk(). In particular, we
can use the return value of pair_chunk() to generate an error when a
required chunk is missing.

Signed-off-by: Derrick Stolee <redacted>
---
 midx.c                      | 103 ++++++++++++++++++++----------------
 t/t5319-multi-pack-index.sh |   6 +--
 2 files changed, 60 insertions(+), 49 deletions(-)

diff --git a/midx.c b/midx.c
index 0bfd2d802b6..dd019c00795 100644
--- a/midx.c
+++ b/midx.c

@@ -54,6 +54,51 @@ static char *get_midx_filename(const char *object_dir)
 	return xstrfmt("%s/pack/multi-pack-index", object_dir);
 }

+static int midx_read_pack_names(const unsigned char *chunk_start,
+				size_t chunk_size, void *data)
+{
+	struct multi_pack_index *m = (struct multi_pack_index *)data;
+	m->chunk_pack_names = chunk_start;
+	return 0;
+}

There are a lot of these callbacks that just assign some 'void **' to
point at chunk_start.

Maybe a good use of the "pair_chunk" name would be something like:

    int pair_chunk(struct chunkfile *cf, uint32_t id, const unsigned char **p);

which does the same as what you wrote here. So instead of what you
wrote, you could instead:

    pair_chunk(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names);

This would be in addition to the richer callback-style function which
allows the caller greater flexibility (e.g., for the Bloom filter
related readers in the commit-graph code).

You're right that _most_ callers just want to assign a pointer,
so this mechanism would be better. I'll make a different function,
read_chunk() perhaps, that relies on a callback for advanced users.

Thanks,
-Stolee