Complete the encrypted-object replication series (backlog#1783, PR-C of
3, after #5872 and #5885): SSE-C objects replicate as ciphertext
passthrough — the source holds no customer key, so the stored bytes and
their encryption metadata travel verbatim and the replica decrypts only
with the original customer key, single-part and multipart.
- Sender: SSE-C objects read raw (raw_data_movement_read), transfer at
ciphertext size, and range multipart parts over stored part sizes.
- Receiver: authorized replication PUTs restore the stored SSE-C keys
from the transport headers (exact lowercase forms - the read-path
check is case-sensitive), set ObjectOptions.preserve_ciphertext, and
skip compression, bucket-default SSE, and sse_encryption behind one
restore-derived gate. Multipart uses an internal session marker to
store parts verbatim and strips it on complete.
- Convergence: the replication HEAD sends
x-rustfs-source-replication-check; the target authorizes it as
ReplicateObjectAction and skips SSE-C read validation for that
request only, so keyless convergence HEADs see etag/size/mtime
instead of 400 and SSE-C replicas stop re-driving forever.
- e2e: SSE-C contract flips to a key-gated readable replica (no-key and
wrong-key GETs fail - the direct silent-plaintext detector); new
multipart passthrough contract with ETag/marker/stability assertions.
