fix(mirror): skip recopies when source ETag is preserved in metadata - #351
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S3-to-S3 mirror uploads through a temporary file, so multipart completion stores a different ETag than the source. Auto compare now records the source ETag in x-amz-meta-rc-source-etag and HeadObject fills that identity when listed ETags differ, so unchanged objects are skipped on the next run. Co-authored-by: RustFS <hello@rustfs.com>
…pare Auto compare recopies when destination identity is absent or wrong, and size mismatches skip HeadObject. Mark the protected mirror contract with a BREAKING migration note for the additive change. Co-authored-by: RustFS <hello@rustfs.com>
The previous synchronize event ran before the PR body included BREAKING. This empty commit re-runs CI against the updated description. Co-authored-by: RustFS <hello@rustfs.com>
houseme
marked this pull request as ready for review
August 25, 2026 02:37
cxymds
reviewed
Aug 25, 2026
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Related issue
Fixes #342
Background
rc mirrorcopies S3-to-S3 objects through a download-then-upload path. Multipart completion on the destination stores a different ETag than the source (hash-2vshash-1in the report). The planner compared ListObjects ETags, so a second--overwriterun recopied every object even when the bytes were unchanged.mc cp --preservekeeps the source ETag via server-side copy. Cross-alias mirror cannot do that, and ListObjects does not return user metadata, so ETag-only planning cannot see a client-recorded identity.Solution
x-amz-meta-rc-source-etag.--compare auto|etag|size(defaultauto):auto: skip when ETags match, or when size matches and destination metadata records the source ETagetag: skip only on identical stored ETagssize: skip when sizes matchautomode, destinations with the same size but a different listed ETag are inspected with HeadObject so the identity metadata can be read.This is additive. Existing flags and default skip-on-matching-ETag behavior are unchanged. Objects copied before this change still recopy once; after that they skip.
This PR must be marked BREAKING because
docs/reference/rc/mirror.mdis a protected CLI behavior contract. The change is additive; no JSON schema or configschema_versionbump applies.Tests
--comparescripts/regression/mirror-identity.shValidation
cargo fmt --all cargo clippy --workspace -- -D warnings cargo test --workspace ./scripts/regression/mirror-identity.sh