fix: store raw SSE-C replicas verbatim on the destination

A raw SSE-C replica write carries the source ciphertext and the source seal
in X-Minio-Replication-Server-Side-Encryption-* headers but no public SSE-C
request headers, so crypto.Requested() was false and PutObjectHandler and
NewMultipartUploadHandler applied the destination's default encryption and
compression to bytes that were already ciphertext (upstream 468a9fae8,
"Enable replication of SSE-C objects", never exempted the raw path). With
destination default SSE-S3 the replica's IV and seal were overwritten and
GET returned 400; with destination compression the replica stored
compress(ciphertext) and GET failed, while the source reported COMPLETED.

Recognize a validated raw SSE-C replica (replicaTrusted plus a seal header,
shared helper isRawSSECReplica) and skip bucket default encryption,
compression and the encryption branch on the single PUT path, and default
encryption plus compression on the multipart initiation path, which already
skipped key generation. On the sender, reject replication of an object that
is both compressed and SSE-C, since the wire carries no compression state
and the destination would otherwise store an undetectable S2 stream, and
make replicateObject/replicateAll report a putReplicationOpts failure as
Failed instead of Completed.

Tests: TestAPISSECReplicaSkipsDestinationTransforms (single PUT and
multipart under destination default SSE-S3, compression and an explicit SSE
header, plus an untrusted control), TestAPISSECMultipartReplicaRoundTripWith
Compression, and TestPutReplicationOptsRejectsCompressedSSEC fail on main
and pass with the fix on ErasureSD and Erasure; the replication-trust,
multipart and PutObject suites stay green. Compatibility: no wire, API or
metadata change; the destination change applies only to trusted replica
writes carrying a source seal; replicas already transformed must be
rewritten from an intact source (see pgsty/silo#120 for why a resync does
not do that yet).

Fixes pgsty/silo#109

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L7qJqWwy8oFA6aCXWRzXQe
Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/object-handlers.go

@@ -2087,11 +2087,18 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 		delete(metadata, xhttp.AmzBucketReplicationStatus)
 	}
 
-	// Check if bucket encryption is enabled
-	sseConfig, _ := globalBucketSSEConfigSys.Get(bucket)
-	sseConfig.Apply(r.Header, sse.ApplyOptions{
-		AutoEncrypt: globalAutoEncryption,
-	})
+	// A validated raw SSE-C replica carries the source ciphertext and the
+	// source seal. Its bytes must be stored verbatim: default encryption would
+	// overwrite the SSE-C IV and compression would invalidate the ciphertext.
+	rawSSECReplica := isRawSSECReplica(r.Header, replicaTrusted)
+
+	if !rawSSECReplica {
+		// Check if bucket encryption is enabled
+		sseConfig, _ := globalBucketSSEConfigSys.Get(bucket)
+		sseConfig.Apply(r.Header, sse.ApplyOptions{
+			AutoEncrypt: globalAutoEncryption,
+		})
+	}
 
 	var reader io.Reader
 	reader = rd
@@ -2105,7 +2112,7 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 
 	actualSize := size
 	var idxCb func() []byte
-	if isCompressible(r.Header, object) && size > minCompressibleSize {
+	if !rawSSECReplica && isCompressible(r.Header, object) && size > minCompressibleSize {
 		// Storing the compression metadata.
 		metadata[ReservedMetadataPrefix+"compression"] = compressionAlgorithmV2
 		metadata[ReservedMetadataPrefix+"actual-size"] = strconv.FormatInt(size, 10)
@@ -2200,7 +2207,10 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 		metadata[ReservedMetadataPrefixLower+ReplicationStatus] = dsc.PendingStatus()
 	}
 	var objectEncryptionKey crypto.ObjectKey
-	if crypto.Requested(r.Header) {
+	// rawSSECReplica also gates the branch itself, not just the default-SSE
+	// header that would normally reach it: a trusted peer that sends an
+	// explicit public SSE header alongside a source seal must not re-encrypt.
+	if !rawSSECReplica && crypto.Requested(r.Header) {
 		if crypto.SSECopy.IsRequested(r.Header) {
 			writeErrorResponse(ctx, w, toAPIError(ctx, errInvalidEncryptionParameters), r.URL)
 			return