fix(replication): forward single-part object checksums as headers

crates/e2e_test/src/replication_extension_test.rs

@@ -3837,6 +3837,164 @@ async fn test_bucket_replication_converges_delete_marker_and_version_purge() ->
     Ok(())
 }
 
+/// Regression for rustfs/backlog#2340 (not Wasabi specific): a directory
+/// marker (`prefix/` with a body) in a versioned bucket is stored as the null
+/// version, like MinIO (`putOpts`: "for directory objects skip creating new
+/// versions"), and must still replicate to completion instead of staying
+/// `PENDING`.
+#[tokio::test]
+async fn test_bucket_replication_replicates_directory_marker_in_versioned_bucket() -> TestResult {
+    init_logging();
+
+    let mut source_env = RustFSTestEnvironment::new().await?;
+    let mut source_env_vars = replication_fast_env();
+    source_env_vars.extend_from_slice(LOOPBACK_REPLICATION_TARGET_ENV);
+    source_env.start_rustfs_server_with_env(vec![], &source_env_vars).await?;
+
+    let mut target_env = RustFSTestEnvironment::new().await?;
+    target_env.start_rustfs_server_without_cleanup(vec![]).await?;
+
+    let source_bucket = "replication-dir-marker-src";
+    let target_bucket = "replication-dir-marker-dst";
+    let source_client = source_env.create_s3_client();
+    let target_client = target_env.create_s3_client();
+
+    source_client.create_bucket().bucket(source_bucket).send().await?;
+    target_client.create_bucket().bucket(target_bucket).send().await?;
+    enable_bucket_versioning(&source_env, source_bucket).await?;
+    enable_bucket_versioning(&target_env, target_bucket).await?;
+    let target_arn = set_replication_target(&source_env, source_bucket, &target_env, target_bucket).await?;
+    put_bucket_replication(&source_env, source_bucket, &target_arn).await?;
+
+    let marker_key = "dir/trailing/";
+    let body = b"directory marker body";
+    let put = source_client
+        .put_object()
+        .bucket(source_bucket)
+        .key(marker_key)
+        .body(ByteStream::from_static(body))
+        .send()
+        .await?;
+    assert!(
+        put.version_id()
+            .is_none_or(|id| id == "null" || id == uuid::Uuid::nil().to_string()),
+        "a directory marker is the null version even in a versioned bucket: {:?}",
+        put.version_id()
+    );
+
+    wait_for_source_replication_status(&source_client, source_bucket, marker_key, "COMPLETED", false).await?;
+
+    let replica = target_client
+        .get_object()
+        .bucket(target_bucket)
+        .key(marker_key)
+        .send()
+        .await?;
+    assert_eq!(replica.body.collect().await?.into_bytes().as_ref(), body);
+    let listed = target_client
+        .list_object_versions()
+        .bucket(target_bucket)
+        .prefix(marker_key)
+        .send()
+        .await?;
+    let marker_versions: Vec<_> = listed.versions().iter().filter(|v| v.key() == Some(marker_key)).collect();
+    assert_eq!(marker_versions.len(), 1, "the marker must land exactly once: {marker_versions:?}");
+    assert_eq!(
+        marker_versions[0].version_id(),
+        Some("null"),
+        "the replica keeps the null version identity"
+    );
+
+    Ok(())
+}
+
+/// Regression for rustfs/backlog#2340 (not Wasabi specific): a single-part
+/// object uploaded with `x-amz-checksum-*` must reach the target with the same
+/// checksum. The outbound options keyed the stored record by algorithm name,
+/// which the target client sent as `x-amz-meta-*` user metadata, so a replica
+/// never carried a checksum although the source HEAD returned one.
+#[tokio::test]
+async fn test_bucket_replication_forwards_single_part_object_checksums() -> TestResult {
+    init_logging();
+
+    let mut source_env = RustFSTestEnvironment::new().await?;
+    let mut source_env_vars = replication_fast_env();
+    source_env_vars.extend_from_slice(LOOPBACK_REPLICATION_TARGET_ENV);
+    source_env.start_rustfs_server_with_env(vec![], &source_env_vars).await?;
+
+    let mut target_env = RustFSTestEnvironment::new().await?;
+    target_env.start_rustfs_server_without_cleanup(vec![]).await?;
+
+    let source_bucket = "replication-checksum-src";
+    let target_bucket = "replication-checksum-dst";
+    let source_client = source_env.create_s3_client();
+    let target_client = target_env.create_s3_client();
+
+    source_client.create_bucket().bucket(source_bucket).send().await?;
+    target_client.create_bucket().bucket(target_bucket).send().await?;
+    enable_bucket_versioning(&source_env, source_bucket).await?;
+    enable_bucket_versioning(&target_env, target_bucket).await?;
+    let target_arn = set_replication_target(&source_env, source_bucket, &target_env, target_bucket).await?;
+    put_bucket_replication(&source_env, source_bucket, &target_arn).await?;
+
+    let body = b"123456789";
+    let crc32_key = "checksum-crc32.txt";
+    let sha256_key = "checksum-sha256.txt";
+    let crc32_put = source_client
+        .put_object()
+        .bucket(source_bucket)
+        .key(crc32_key)
+        .body(ByteStream::from_static(body))
+        .checksum_algorithm(aws_sdk_s3::types::ChecksumAlgorithm::Crc32)
+        .send()
+        .await?;
+    let expected_crc32 = crc32_put.checksum_crc32().ok_or("source PUT omitted CRC32")?.to_string();
+    let sha256_put = source_client
+        .put_object()
+        .bucket(source_bucket)
+        .key(sha256_key)
+        .body(ByteStream::from_static(body))
+        .checksum_algorithm(aws_sdk_s3::types::ChecksumAlgorithm::Sha256)
+        .send()
+        .await?;
+    let expected_sha256 = sha256_put.checksum_sha256().ok_or("source PUT omitted SHA256")?.to_string();
+
+    for key in [crc32_key, sha256_key] {
+        wait_for_source_replication_status(&source_client, source_bucket, key, "COMPLETED", false).await?;
+    }
+
+    let replica = target_client
+        .head_object()
+        .bucket(target_bucket)
+        .key(crc32_key)
+        .checksum_mode(aws_sdk_s3::types::ChecksumMode::Enabled)
+        .send()
+        .await?;
+    assert_eq!(replica.checksum_crc32(), Some(expected_crc32.as_str()), "replica lost the CRC32 checksum");
+    let replica = target_client
+        .head_object()
+        .bucket(target_bucket)
+        .key(sha256_key)
+        .checksum_mode(aws_sdk_s3::types::ChecksumMode::Enabled)
+        .send()
+        .await?;
+    assert_eq!(
+        replica.checksum_sha256(),
+        Some(expected_sha256.as_str()),
+        "replica lost the SHA256 checksum"
+    );
+    // The bare algorithm name must not leak as user metadata either.
+    assert!(
+        replica
+            .metadata()
+            .is_none_or(|meta| !meta.keys().any(|k| k.eq_ignore_ascii_case("sha256"))),
+        "replica carries the checksum as user metadata: {:?}",
+        replica.metadata()
+    );
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_bucket_replication_disabled_delete_marker_does_not_propagate() -> TestResult {
     init_logging();

crates/e2e_test/src/replication_target_matrix_test.rs

@@ -42,7 +42,8 @@ use crate::replication_extension_test::{
 use aws_sdk_s3::Client;
 use aws_sdk_s3::primitives::{ByteStream, DateTime};
 use aws_sdk_s3::types::{
-    Checksum, CompletedMultipartUpload, CompletedPart, ObjectAttributes, ObjectLockLegalHoldStatus, ObjectLockMode,
+    Checksum, ChecksumAlgorithm, CompletedMultipartUpload, CompletedPart, ObjectAttributes, ObjectLockLegalHoldStatus,
+    ObjectLockMode,
 };
 use bytes::Bytes;
 use std::error::Error;
@@ -114,10 +115,13 @@ enum ObjectShape {
     LockedMultipart,
     /// ODM stores two local parts while preserving a single-PUT source's MD5 ETag.
     OdmPreservedMd5Multipart,
+    /// Single-part object uploaded with `x-amz-checksum-sha256`; the replica
+    /// must carry the same header (rustfs/backlog#2340).
+    Checksummed,
 }
 
 impl ObjectShape {
-    const ALL: [ObjectShape; 7] = [
+    const ALL: [ObjectShape; 8] = [
         ObjectShape::Empty,
         ObjectShape::Plain,
         ObjectShape::Retention,
@@ -125,6 +129,7 @@ impl ObjectShape {
         ObjectShape::Multipart,
         ObjectShape::LockedMultipart,
         ObjectShape::OdmPreservedMd5Multipart,
+        ObjectShape::Checksummed,
     ];
 
     fn key(self) -> &'static str {
@@ -136,6 +141,16 @@ impl ObjectShape {
             ObjectShape::Multipart => "matrix/multipart.bin",
             ObjectShape::LockedMultipart => "matrix/locked-multipart.bin",
             ObjectShape::OdmPreservedMd5Multipart => "matrix/odm-preserved-md5.bin",
+            ObjectShape::Checksummed => "matrix/checksummed.bin",
+        }
+    }
+
+    /// The `x-amz-checksum-*` header the source stored and every upload of
+    /// the replica must repeat.
+    fn forwarded_checksum_header(self) -> Option<&'static str> {
+        match self {
+            ObjectShape::Checksummed => Some("x-amz-checksum-sha256"),
+            _ => None,
         }
     }
 
@@ -198,6 +213,18 @@ impl ObjectShape {
             ObjectShape::Multipart => multipart_put(client, bucket, key, 0x44, false).await,
             ObjectShape::LockedMultipart => multipart_put(client, bucket, key, 0x55, true).await,
             ObjectShape::OdmPreservedMd5Multipart => odm_preserved_md5_multipart(env, bucket, key).await,
+            ObjectShape::Checksummed => {
+                let body = payload(40 * 1024, 0x66);
+                client
+                    .put_object()
+                    .bucket(bucket)
+                    .key(key)
+                    .body(ByteStream::from(body.clone()))
+                    .checksum_algorithm(ChecksumAlgorithm::Sha256)
+                    .send()
+                    .await?;
+                Ok(body)
+            }
         }
     }
 }
@@ -450,6 +477,19 @@ async fn check_completed_cell(
     }) {
         return Err(format!("a locked PutObject went out without any integrity header (rustfs#7082): {bare:?}").into());
     }
+    // rustfs/backlog#2340 contract: a source checksum reaches the target as
+    // the `x-amz-checksum-*` header, not as user metadata; every PutObject of
+    // the shape carries it.
+    if let Some(header) = shape.forwarded_checksum_header()
+        && let Some(missing) = uploads.iter().find(|record| {
+            record.operation == FakeTargetOperation::PutObject
+                && !record.transport.checksum_headers.iter().any(|name| name == header)
+        })
+    {
+        return Err(
+            format!("a PutObject went out without the source's {header} header (rustfs/backlog#2340): {missing:?}").into(),
+        );
+    }
     Ok(())
 }
 

crates/ecstore/src/bucket/bucket_target_sys.rs

@@ -2064,7 +2064,15 @@ impl TargetClient {
             }
         }
 
-        match builder
+        // A forwarded source checksum is this PUT's integrity header. In
+        // streaming-checksum mode (`RUSTFS_REPLICATION_STREAMING_CHECKSUMS`)
+        // the SDK would still add its default CRC32 trailer, and a target that
+        // receives both keeps the trailer's algorithm: a forwarded SHA256
+        // vanished from the replica while the source reported COMPLETED. Pin
+        // this request to WhenRequired so nothing is sent beside the source's
+        // own checksum.
+        let forwards_source_checksum = headers.keys().any(|name| name.as_str().starts_with("x-amz-checksum-"));
+        let mut operation = builder
             .bucket(bucket)
             .key(object)
             .content_length(size)
@@ -2084,10 +2092,14 @@ impl TargetClient {
                 }
 
                 Result::<_, aws_smithy_types::error::operation::BuildError>::Ok(req)
-            })
-            .send()
-            .await
-        {
+            });
+        if forwards_source_checksum {
+            operation = operation.config_override(
+                aws_sdk_s3::config::Builder::new()
+                    .request_checksum_calculation(aws_sdk_s3::config::RequestChecksumCalculation::WhenRequired),
+            );
+        }
+        match operation.send().await {
             Ok(output) => {
                 // Under SSE-KMS/DSSE or SSE-C the target's ETag is not the MD5
                 // of the stored plaintext, so it cannot be compared against the
@@ -2507,13 +2519,21 @@ mod tests {
     }
 
     fn header_recording_target_client(response_headers: Vec<(String, String)>) -> (TargetClient, RecordedHeaders) {
+        header_recording_target_client_with_checksums(response_headers, replication_request_checksum_calculation())
+    }
+
+    fn header_recording_target_client_with_checksums(
+        response_headers: Vec<(String, String)>,
+        checksums: RequestChecksumCalculation,
+    ) -> (TargetClient, RecordedHeaders) {
         let request_headers: RecordedHeaders = Arc::new(std::sync::Mutex::new(Vec::new()));
         let connector = SharedHttpConnector::new(RecordingHeaderConnector {
             request_headers: Arc::clone(&request_headers),
             response_headers,
         });
         let http_client = http_client_fn(move |_settings, _components| connector.clone());
-        let client = s3_client_for_test(443, Some(http_client));
+        let client =
+            s3_client_for_endpoint_test_with_checksums("https://localhost:443".to_string(), Some(http_client), checksums);
         (
             TargetClient {
                 endpoint: "https://localhost:443".to_string(),
@@ -2680,6 +2700,47 @@ mod tests {
         }
     }
 
+    /// With streaming checksums enabled the SDK adds a CRC32 trailer to every
+    /// upload. A PUT that forwards the source's checksum must not get that
+    /// second algorithm: a target that receives both keeps the trailer's and
+    /// the forwarded SHA256 never reaches the replica (rustfs/backlog#2340).
+    #[tokio::test]
+    async fn streaming_put_object_with_forwarded_checksum_sends_no_sdk_checksum() {
+        let (client, recorded) =
+            header_recording_target_client_with_checksums(Vec::new(), RequestChecksumCalculation::WhenSupported);
+        let mut forwarded = PutObjectOptions::default();
+        forwarded.user_metadata.insert(
+            "x-amz-checksum-sha256".to_string(),
+            "OoJ3yNhRwv3wwtZoGqEIPrPX9xwTnfLl+ka0wStN1g0=".to_string(),
+        );
+        client
+            .put_object("target-bucket", "object", 4, streaming_test_body(b"data"), &forwarded)
+            .await
+            .expect("recorded put_object should succeed");
+        client
+            .put_object("target-bucket", "object", 4, streaming_test_body(b"data"), &PutObjectOptions::default())
+            .await
+            .expect("recorded put_object should succeed");
+        let recorded = recorded.lock().expect("recorded header lock should not be poisoned");
+        let with_forwarded = &recorded[0];
+        assert_eq!(
+            recorded_header(with_forwarded, "x-amz-checksum-sha256"),
+            Some("OoJ3yNhRwv3wwtZoGqEIPrPX9xwTnfLl+ka0wStN1g0=")
+        );
+        assert_eq!(
+            recorded_header(with_forwarded, "x-amz-trailer"),
+            None,
+            "the SDK must not add a trailer checksum"
+        );
+        assert_eq!(recorded_header(with_forwarded, "x-amz-sdk-checksum-algorithm"), None);
+        // Control: the same client still streams a trailer when nothing is forwarded.
+        let without_forwarded = &recorded[1];
+        assert!(
+            recorded_header(without_forwarded, "x-amz-trailer").is_some(),
+            "streaming mode must still apply to uploads without a forwarded checksum: {without_forwarded:?}"
+        );
+    }
+
     /// A forwarded source checksum already satisfies the rule; nothing is added.
     #[tokio::test]
     async fn locked_put_object_keeps_a_forwarded_source_checksum() {
@@ -3045,6 +3106,14 @@ mod tests {
     }
 
     fn s3_client_for_endpoint_test(endpoint: String, http_client: Option<SharedHttpClient>) -> S3Client {
+        s3_client_for_endpoint_test_with_checksums(endpoint, http_client, replication_request_checksum_calculation())
+    }
+
+    fn s3_client_for_endpoint_test_with_checksums(
+        endpoint: String,
+        http_client: Option<SharedHttpClient>,
+        checksums: RequestChecksumCalculation,
+    ) -> S3Client {
         let credentials = SdkCredentials::builder()
             .access_key_id("test-access")
             .secret_access_key("test-secret")
@@ -3058,7 +3127,7 @@ mod tests {
             .behavior_version(aws_sdk_s3::config::BehaviorVersion::latest())
             // Mirror the production remote-target builder so recorded requests
             // exercise the same checksum/framing behavior (#6853).
-            .request_checksum_calculation(replication_request_checksum_calculation());
+            .request_checksum_calculation(checksums);
         if let Some(http_client) = http_client {
             config = config.http_client(http_client);
         }

crates/ecstore/src/bucket/replication/replication_target_boundary.rs

@@ -281,12 +281,6 @@ pub(crate) fn replication_put_object_options(sc: &str, object_info: &ObjectInfo)
             // record may only add multipart-ness, never take it away.
             is_multipart = base_is_multipart || checksum_record_is_multipart;
 
-            for (key, value) in checksum_meta.iter() {
-                if key != AMZ_CHECKSUM_TYPE {
-                    meta.insert(key.clone(), value.clone());
-                }
-            }
-
             if !base_is_multipart
                 && checksum_meta
                     .get(AMZ_CHECKSUM_TYPE)
@@ -294,6 +288,26 @@ pub(crate) fn replication_put_object_options(sc: &str, object_info: &ObjectInfo)
             {
                 is_multipart = false;
             }
+
+            // The record keys each checksum by algorithm name ("CRC32"); the
+            // target only reads `x-amz-checksum-<algorithm>`. Inserting the bare
+            // name here made `PutObjectOptions::header()` send it as user
+            // metadata (`x-amz-meta-crc32`), so no replica ever carried the
+            // source checksum (rustfs/backlog#2340). The object-level record
+            // describes one PUT body: a multipart replica is rebuilt part by
+            // part, and its CreateMultipartUpload must not announce a checksum
+            // the parts do not carry, so the record is forwarded on the
+            // single-PUT route only (MinIO `getCRCMeta` parity).
+            if !is_multipart {
+                for (key, value) in checksum_meta.iter() {
+                    if key == AMZ_CHECKSUM_TYPE {
+                        continue;
+                    }
+                    if let Some(header) = rustfs_rio::ChecksumType::from_string(key).key() {
+                        meta.insert(header.to_string(), value.clone());
+                    }
+                }
+            }
         }
     }
 
@@ -1468,12 +1482,63 @@ mod tests {
                 ..Default::default()
             };
 
-            let (opts, _is_multipart) = replication_put_object_options("", &object_info).expect("build replication put options");
+            let (opts, is_multipart) = replication_put_object_options("", &object_info).expect("build replication put options");
 
+            assert!(!is_multipart, "{name}: a single-part checksum record must keep the single-PUT route");
+            let header = ty.key().expect("every forwarded algorithm has an x-amz-checksum header");
             assert_eq!(
-                opts.user_metadata.get(name),
+                opts.user_metadata.get(header),
                 Some(&checksum.encoded),
-                "replication must forward the {name} checksum into user_metadata identically to the classic algorithms"
+                "replication must forward the {name} checksum as the {header} header"
+            );
+            assert!(
+                !opts.user_metadata.contains_key(name),
+                "{name}: the bare algorithm name would leave as x-amz-meta user metadata"
+            );
+        }
+    }
+
+    /// The object-level record of a multipart upload (composite or full-object)
+    /// must not become a PutObject checksum header: the replica is rebuilt
+    /// through CreateMultipartUpload/UploadPart, and a checksum announced there
+    /// that the parts do not carry would be rejected by the target.
+    #[test]
+    fn replication_put_object_options_keeps_multipart_checksum_records_off_the_wire() {
+        let mut composite_type = rustfs_rio::ChecksumType::from_string("crc32");
+        composite_type
+            .merge(rustfs_rio::ChecksumType::MULTIPART)
+            .merge(rustfs_rio::ChecksumType::INCLUDES_MULTIPART);
+        let mut combined = Vec::new();
+        for part in [b"part-one".as_slice(), b"part-two".as_slice()] {
+            let part_checksum =
+                rustfs_rio::Checksum::new_from_data(rustfs_rio::ChecksumType::from_string("crc32"), part).expect("part checksum");
+            combined.extend_from_slice(part_checksum.raw.as_slice());
+        }
+        let composite = rustfs_rio::Checksum::new_from_data(composite_type, &combined)
+            .expect("composite checksum")
+            .to_bytes(&combined);
+
+        for (label, checksum, etag) in [
+            ("composite", composite, "0123456789abcdef0123456789abcdef-2"),
+            (
+                "full-object",
+                full_object_multipart_checksum_record(),
+                "0123456789abcdef0123456789abcdef-3",
+            ),
+        ] {
+            let object_info = ObjectInfo {
+                etag: Some(etag.to_string()),
+                checksum: Some(checksum),
+                ..Default::default()
+            };
+            let (opts, is_multipart) = replication_put_object_options("", &object_info).expect("build replication put options");
+            assert!(is_multipart, "{label}: a multipart object must keep the multipart route");
+            assert!(
+                opts.user_metadata
+                    .keys()
+                    .all(|key| !key.starts_with("x-amz-checksum-") && key != "CRC32"),
+                "{label}: no object-level checksum may reach the target's CreateMultipartUpload: {:?}",
+                opts.user_metadata
             );
         }
     }

docs/architecture/s3-compatibility-matrix.md

@@ -62,6 +62,7 @@ Object keys are stored as file-system paths under each drive (`{drive}/{bucket}/
 | Behavior | RustFS | AWS S3 | Why |
 |---|---|---|---|
 | Object key with a `.` or `..` path segment, or an empty segment (`//`), such as `a//b/./c/../d` | `400 InvalidArgument` (`check_object_args` in `crates/ecstore/src/bucket/utils.rs`, mirroring MinIO `IsValidObjectPrefix`) | Accepted as an opaque key | A `..` segment would resolve to a parent directory and `.`/`//` segments would alias other keys on disk; encoding them would change the MinIO-compatible on-disk format. |
+| Directory marker (key ending in `/`, with or without a body) in a versioned bucket | Stored as the null version: `PutObject`/`HeadObject` report version id `00000000-0000-0000-0000-000000000000`, `ListObjectVersions` reports `null`, and a later PUT of the same key overwrites in place (`put_opts` in `rustfs/src/storage/options.rs`, mirroring MinIO `putOpts`: "for directory objects skip creating new versions") | A real version id per PUT, with a version history | The marker only exists to make an empty prefix listable; keeping a history for it would leave hidden versions behind every prefix delete. Replication still copies the marker as its null version (`test_bucket_replication_replicates_directory_marker_in_versioned_bucket` in `crates/e2e_test/src/replication_extension_test.rs`). |
 
 ## Update Rule
 

docs/operations/replication-outbound-transport.md

@@ -6,7 +6,7 @@
 ## What a replication PUT carries by default
 
 - A plain signed body with an exact `Content-Length`. The SDK does not add a streaming trailer checksum, so the body is never wrapped in `aws-chunked` framing (rustfs#6853: a target that does not decode that framing stored the frames verbatim while RustFS recorded COMPLETED).
-- Any object-level checksum the source object was uploaded with, forwarded as its `x-amz-checksum-*` header.
+- For a single-part object, the checksum the source object was uploaded with, forwarded as its `x-amz-checksum-<algorithm>` header (the value the source verified on upload). A multipart replica is rebuilt through CreateMultipartUpload/UploadPart and carries no object-level checksum header. Managed-SSE objects forward none.
 - On a PUT that carries Object Lock parameters and no forwarded checksum: `Content-MD5` derived from the source ETag, or an SDK CRC32 checksum when the ETag is not the MD5 of the wire bytes (rustfs#7082).
 - The source ETag, mtime and version id on `x-rustfs-source-*` headers (with `x-minio-source-*` twins), and the Object Lock mode, retain-until date and legal hold of the source version when present.
 - After the PUT, the target's ETag is compared with the source ETag when both are plain single-part MD5s; a mismatch fails the replication instead of reporting a corrupted replica as COMPLETED.
@@ -17,6 +17,7 @@
 | --- | --- | --- |
 | Rejects or mis-stores `aws-chunked` bodies (SeaweedFS 3.97) | Handled by the plain-payload default above. | Outbound target matrix, `RejectAwsChunked` mode |
 | Requires `Content-MD5` or `x-amz-checksum-*` on a PutObject with Object Lock parameters (AWS S3, MinIO, Impossible Cloud, most compatible stores) | Satisfied: a locked single PUT carries `Content-MD5` derived from the source ETag (plaintext objects whose ETag is the MD5 of the wire bytes) or an SDK CRC32 checksum (multipart-layout ETags, managed SSE, SSE-C passthrough — this one is an `aws-chunked` trailer, so a target that also rejects that framing cannot take such objects). Releases before this fix (`1.0.0-rc.5`) need `RUSTFS_REPLICATION_STREAMING_CHECKSUMS=true` as a workaround. | Outbound target matrix, `RequireChecksumWithObjectLock` mode |
+| Stores `x-amz-checksum-*` from a PutObject and returns it on `HEAD ?ChecksumMode=ENABLED` (AWS S3, Wasabi, RustFS) | Satisfied for single-part objects: the replica answers with the source's checksum. Before this fix (`1.0.0-rc.5`) the checksum left the source as `x-amz-meta-<algorithm>` user metadata and no replica carried it (rustfs/backlog#2340). | Outbound target matrix, `Checksummed` shape |
 | Mints its own version ids (AWS S3, Wasabi, Impossible Cloud) | Data lands; version-addressed convergence does not. See rustfs/backlog#2085 and `docs/operations/replication-check.md` (VersionFidelity). | `replication-check`, outbound target matrix, `MintOwnVersionIds` mode |
 | Returns an ETag that is not the content MD5 without announcing SSE | Every single-part object fails ETag verification. Set `RUSTFS_REPLICATION_REPLICA_ETAG_VERIFY=false`. | Replication status FAILED with `replica etag mismatch` |
 
@@ -24,7 +25,7 @@
 
 | Variable | Default | Meaning |
 | --- | --- | --- |
-| `RUSTFS_REPLICATION_STREAMING_CHECKSUMS` | unset (plain payloads) | `true` or `1` restores SDK trailer checksums (`RequestChecksumCalculation::WhenSupported`). Every streaming upload is then `aws-chunked` with an `x-amz-trailer`; use only when every target decodes that framing. |
+| `RUSTFS_REPLICATION_STREAMING_CHECKSUMS` | unset (plain payloads) | `true` or `1` restores SDK trailer checksums (`RequestChecksumCalculation::WhenSupported`). Every streaming upload is then `aws-chunked` with an `x-amz-trailer`, except a single-part PUT that forwards the source's `x-amz-checksum-*` header, which is sent plain so the target does not receive a second algorithm; use only when every target decodes that framing. |
 | `RUSTFS_REPLICATION_REPLICA_ETAG_VERIFY` | enabled | `false` or `0` disables the post-PUT ETag comparison for targets whose 32-hex ETags are legitimately not the content MD5. |
 
 Both knobs are read by the RustFS process that owns the replication target, at client build time; restart the server after changing them.