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csum-file: introduce checksum_valid() 

Introduce a new function which checks the validity of a file's trailing
checksum. This is similar to hashfd_check(), but different since it is
intended to be used by callers who aren't writing the same data (like
`git index-pack --verify`), but who instead want to validate the
integrity of data that they are reading.

Rewrite the first of two callers which could benefit from this new
function in pack-check.c. Subsequent callers will be added in the
following patches.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau 2021-06-23 14:39:07 -04:00 committed by Junio C Hamano
parent ebf3c04b26
commit f9221e2cf5
3 changed files with 20 additions and 10 deletions
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16
csum-file.c
View File

@ -187,3 +187,19 @@ uint32_t crc32_end(struct hashfile *f)
f->do_crc = 0;
return f->crc32;
}
int hashfile_checksum_valid(const unsigned char *data, size_t total_len)
{
unsigned char got[GIT_MAX_RAWSZ];
git_hash_ctx ctx;
size_t data_len = total_len - the_hash_algo->rawsz;
if (total_len < the_hash_algo->rawsz)
return 0; /* say "too short"? */
the_hash_algo->init_fn(&ctx);
the_hash_algo->update_fn(&ctx, data, data_len);
the_hash_algo->final_fn(got, &ctx);
return hasheq(got, data + data_len);
}

3
csum-file.h
View File

@ -42,6 +42,9 @@ void hashflush(struct hashfile *f);
void crc32_begin(struct hashfile *);
uint32_t crc32_end(struct hashfile *);
/* Verify checksum validity while reading. Returns non-zero on success. */
int hashfile_checksum_valid(const unsigned char *data, size_t len);
/*
* Returns the total number of bytes fed to the hashfile so far (including ones
* that have not been written out to the descriptor yet).

11
pack-check.c
View File

@ -164,22 +164,13 @@ static int verify_packfile(struct repository *r,
int verify_pack_index(struct packed_git *p)
{
size_t len;
const unsigned char *index_base;
git_hash_ctx ctx;
unsigned char hash[GIT_MAX_RAWSZ];
int err = 0;
if (open_pack_index(p))
return error("packfile %s index not opened", p->pack_name);
index_base = p->index_data;
len = p->index_size - the_hash_algo->rawsz;
/* Verify SHA1 sum of the index file */
the_hash_algo->init_fn(&ctx);
the_hash_algo->update_fn(&ctx, index_base, len);
the_hash_algo->final_fn(hash, &ctx);
if (!hasheq(hash, index_base + len))
if (!hashfile_checksum_valid(p->index_data, p->index_size))
err = error("Packfile index for %s hash mismatch",
p->pack_name);
return err;