Multipart download enhancements by andaaron · Pull Request #4021 · project-zot/zot

andaaron · 2026-04-27T07:53:52Z

As a follow-up to #3995, to include enhancements in #3976

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Blob HEAD responses had no Content-Type and GET responses echoed the request's Accept header verbatim, which produced missing or malformed media types and left multipart/byteranges parts without a per-part Content-Type. This breaks OCI distribution-spec conformance and consumers like stargz-snapshotter that need a well-formed layer media type. Add a blobResponseMediaType helper that resolves the descriptor's MediaType via GetBlobDescriptorFromRepo and falls back to application/octet-stream. Use it in CheckBlob (HEAD), GetBlob full (200), GetBlob single-range (206), and per-part in writeMultipartRanges (206 multipart). Lookup is deferred until after the blob is known to exist. Cover the new behaviour with mock-based unit tests in routes_test.go and end-to-end assertions in TestPullRange. Signed-off-by: Andrei Aaron <andreifdaaron@gmail.com>

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Pull request overview

Follow-up to earlier multipart range blob pull work, improving blob download responses to be descriptor-aware for Content-Type and optimizing multipart range delivery to reduce concurrent reader usage.

Changes:

Add descriptor-aware Content-Type resolution for blob HEAD/GET with application/octet-stream fallback.
Rework multipart range responses to stream ranges lazily (one reader at a time) and advertise a precomputed Content-Length.
Expand test coverage for descriptor-derived Content-Type, multipart part headers, streaming behavior, and truncation on mid-stream read errors.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
pkg/api/routes.go	Adds `blobResponseMediaType`, sets `Content-Type` for blob responses, and rewrites multipart range streaming to be lazy with precomputed `Content-Length`.
pkg/api/routes_test.go	Adds unit tests for descriptor-aware `Content-Type` and multipart range response behavior (per-part headers, content-length correctness, sequential reader opens, truncation on error).
pkg/api/controller_test.go	Extends existing range-pull integration tests to assert correct fallback/per-part `Content-Type` behavior.

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codecov · 2026-04-27T08:14:19Z

Codecov Report

❌ Patch coverage is 90.69767% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.48%. Comparing base (bb5b77a) to head (c2987f6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/api/routes.go	90.69%	4 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4021      +/-   ##
==========================================
+ Coverage   91.39%   91.48%   +0.09%     
==========================================
  Files         197      197              
  Lines       28308    28353      +45     
==========================================
+ Hits        25872    25940      +68     
+ Misses       1581     1561      -20     
+ Partials      855      852       -3

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Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

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…nt-Length writeMultipartRanges previously opened every range reader up front and emitted no Content-Length, so an N-range request held N concurrent storage readers (and their fds / read buffers) per response window and forced chunked encoding on HTTP/1.1 — neither friendly to proxies nor to fan-out scenarios like stargz lazy pulls. Signed-off-by: Andrei Aaron <andreifdaaron@gmail.com>

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Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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andaaron · 2026-04-27T17:31:58Z

@jezell I have added the enhancements in #3976 on top of main (after #3995 was merged).
@jezell, @invy, do you want to try it out?

rchincha · 2026-04-28T05:37:54Z

code coverage is dropping and trending in the wrong direction :(

andaaron · 2026-04-28T05:40:41Z

Something is wrong with coverage reporting in this case.

vrajashkr · 2026-05-01T06:20:07Z

+// distribution-spec conformance and consumers like stargz-snapshotter that
+// require a non-empty, well-formed media type.


nit: specific tools probably shouldn't be mentioned in the source code as the implementation is aligned to dist-spec.

Suggested change

// distribution-spec conformance and consumers like stargz-snapshotter that

// require a non-empty, well-formed media type.

// distribution-spec conformance that

// requires a non-empty, well-formed media type.

invy · 2026-05-26T13:16:35Z

@jezell I have added the enhancements in #3976 on top of main (after #3995 was merged). @jezell, @invy, do you want to try it out?

We've tested newest ZOT 2.1.17 release, our stargz and zstd-chunked images work now perfectly (and reduce pull times significantly) :)

andaaron requested a review from Copilot April 27, 2026 07:54

andaaron changed the title ~~Multipart download changes.~~ Multipart download enhancements Apr 27, 2026

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Comment thread pkg/api/routes.go Outdated

Comment thread pkg/api/routes.go Outdated

Comment thread pkg/api/routes_test.go

This was referenced Apr 27, 2026

Fix OCI conformity, add support for HTTP multi-range requests #3879

Closed

fixes zot to properly return media types / content types and support lazy pulls #3976

Closed

andaaron force-pushed the multipart branch 3 times, most recently from d552e1a to e96ba0a Compare April 27, 2026 16:26

andaaron requested a review from Copilot April 27, 2026 16:27

Copilot started reviewing on behalf of andaaron April 27, 2026 16:28 View session

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Comment thread pkg/api/routes.go

Comment thread pkg/api/routes.go Outdated

Comment thread pkg/api/routes.go Outdated

andaaron force-pushed the multipart branch from e96ba0a to c2987f6 Compare April 27, 2026 17:05

andaaron requested a review from Copilot April 27, 2026 17:06

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andaaron marked this pull request as ready for review April 27, 2026 17:28

andaaron requested a review from rchincha as a code owner April 27, 2026 17:28

rchincha approved these changes Apr 28, 2026

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andaaron merged commit 1a1f84d into project-zot:main Apr 28, 2026
48 of 49 checks passed

andaaron deleted the multipart branch April 28, 2026 05:43

vrajashkr reviewed May 1, 2026

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		// distribution-spec conformance and consumers like stargz-snapshotter that
		// require a non-empty, well-formed media type.

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andaaron commented Apr 27, 2026

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invy commented May 26, 2026

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