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feat(checksum): --checksum-choice/--cc and --checksum-seed for whole-file digest

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Adds real algorithm selection (xxh64 default, plus md5 via OpenSSL EVP) and a
64-bit seed for the per-file whole-file digest used by the --incremental/
--checksum handshake and basis-dir content verification. The seed also feeds
the delta path's per-block xxHash32 strong checksum (low 32 bits) so an
explicit seed deterministically changes those digests too. Sender and receiver
hash identically: the algorithm id and seed cross the config wire frame and the
STATUS_CHECK handshake now carries a length-prefixed, bounded digest instead of
a fixed 64-bit value. Unsupported algorithm names are rejected at parse time
(never a silent no-op). PROTOCOL_VERSION bumped 2.9.0 -> 2.10.0; defaults
(xxh64, seed 0) preserve prior byte-for-byte behavior.
This commit is contained in:
TapTap
2026-09-07 17:42:47 +02:00
parent 6701c103cb
commit 0afda6b094
12 changed files with 316 additions and 43 deletions
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src/client/client_send.c
+13 -6
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@@ -733,12 +733,18 @@ static int incremental_check(Client* client, File* file, const Config* config,
if (!send_n_data(client->file_descriptor, &mtime_nsec, sizeof(mtime_nsec)))
return -1;
/* With alternate basis directories the receiver must be able to verify the
* content of every candidate basis file, so the sender supplies its xxHash64
* for every file even when --checksum was not requested. */
* content of every candidate basis file, so the sender supplies its whole-file
* digest (computed with the negotiated --checksum-choice algorithm and
* --checksum-seed) for every file even when --checksum was not requested. */
if (config->checksum || config_has_basis(config)) {
uint64_t checksum;
if (!file_checksum(file, &checksum) ||
!send_n_data(client->file_descriptor, &checksum, sizeof(checksum)))
uint8_t digest[CHECKSUM_MAX_DIGEST_LEN];
size_t digest_len = 0;
if (!file_checksum(file, (ChecksumAlgo)config->checksum_algo, config->checksum_seed, digest,
sizeof(digest), &digest_len))
return -1;
uint8_t wire_len = (uint8_t)digest_len;
if (!send_n_data(client->file_descriptor, &wire_len, sizeof(wire_len)) ||
!send_n_data(client->file_descriptor, digest, wire_len))
return -1;
}
Status s;
@@ -774,7 +780,8 @@ static int incremental_check(Client* client, File* file, const Config* config,
}
static int send_delta(Client* client, File* file, DeltaSignature* sig, Config* config) {
Delta* delta = delta_compute(file->data->data, file->data->size, sig, config->delta_block_size);
Delta* delta = delta_compute_seeded(file->data->data, file->data->size, sig,
config->delta_block_size, (uint32_t)config->checksum_seed);
/* The receiver is blocked after sending the signature. Every local
fallback therefore needs the explicit NEXT response before full data. */
if (!delta)