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Posted to commits@opendal.apache.org by "matt-goroff (via GitHub)" <gi...@apache.org> on 2026/08/12 15:19:03 UTC
[I] Include user-defined metadata in S3Backend read response [opendal]
matt-goroff opened a new issue, #8059:
URL: https://github.com/apache/opendal/issues/8059
The `S3Backend` supports storing and fetching S3 user-defined metadata (`x-amz-meta-*` metadata). It is set as part of the [`OpWrite`](https://github.com/apache/opendal/blob/c5d6049f733889fcbba2c49ff1d7d9451016cbcd/core/core/src/raw/ops.rs#L691) when writing and [included as headers](https://github.com/apache/opendal/blob/c5d6049f733889fcbba2c49ff1d7d9451016cbcd/core/services/s3/src/core.rs#L362-L367). The only way to fetch it is via the [`stat()`](https://github.com/apache/opendal/blob/c5d6049f733889fcbba2c49ff1d7d9451016cbcd/core/services/s3/src/backend.rs#L1090-L1113) method. S3 includes this metadata as headers in the response to regular get requests, but the opendal `S3Backend` currently ignores them. This means that to read user-defined metadata + content, one must make two HTTP requests and correctly handle a possible race condition.
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Re: [I] Include user-defined metadata in S3Backend read response [opendal]
Posted by "dosubot[bot] (via GitHub)" <gi...@apache.org>.
dosubot[bot] commented on issue #8059:
URL: https://github.com/apache/opendal/issues/8059#issuecomment-5268808697
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<!-- Answer -->
Hi @matt-goroff! I'm [Dosu](https://go.dosu.dev/dosubot) and I'm helping the Apache OpenDAL team.
This exact problem was called out in [RFC-5871 ("Read Returns Metadata")](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/docs/rfcs/5871_read_returns_metadata.md#L10-L18), which was designed so that `read` responses carry metadata directly, eliminating the extra `stat()` call and the race condition you describe. The RFC was implemented and merged in [PR #7624](https://github.com/apache/opendal/pull/7624) as part of v0.57.0 [[1]](https://github.com/apache/opendal/pull/7628). The key changes are:
- **`RpRead` now carries `Option<Metadata>`** populated from the GET response headers [[2]](https://github.com/apache/opendal/pull/7624).
- **`Reader::metadata()`** exposes observed metadata (ETag, content-type, last-modified, etc.) without a separate `stat()` call [[3]](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/docs/rfcs/5871_read_returns_metadata.md#L22-L39).
- The S3 backend was updated so that on `200 OK` / `206 Partial Content`, it returns `RpRead::new(parse_into_metadata(path, resp.headers())?)` alongside the body [[2]](https://github.com/apache/opendal/pull/7624).
However, looking at the **current S3 `read` implementation on the `main` branch**, it still returns `RpRead::default()` rather than parsing metadata from the response [[4]](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/services/s3/backend.rs#L1055-L1068). This suggests the v0.57.0 changes haven't landed on the branch you're looking at, or there's still a gap. More importantly for your specific request: the `stat` path explicitly calls [`parse_prefixed_headers`](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/services/s3/backend.rs#L1040-L1043) to extract `x-amz-meta-*` user-defined metadata and attach it via `with_user_metadata`, but the PR description for #7624 only mentions `parse_into_metadata` for the read path — it does **not** mention `parse_prefixed_headers`. So even once #7624 ships, `x-amz-meta-*` user-defined metadata may not be included in the read response metadata unless `parse_prefi
xed_headers` is also called in the read path.
In short: the general "read returns metadata" infrastructure exists, but you may want to verify (or request) that the S3 read path also calls `parse_prefixed_headers` to include `x-amz-meta-*` headers — that appears to be the remaining gap this issue highlights.
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Re: [I] Include user-defined metadata in S3Backend read response [opendal]
Posted by "Xuanwo (via GitHub)" <gi...@apache.org>.
Xuanwo closed issue #8059: Include user-defined metadata in S3Backend read response
URL: https://github.com/apache/opendal/issues/8059
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