fetchFromUpstream read every upstream response fully into memory before
storing and serving it, so a large blob (or several concurrent ones) could
OOM the process. Immutable artifacts now stream through the tempfile-backed
CAS (tee to sha256 + S3), keeping memory bounded regardless of size, and
are served back from the store. Mutable indexes are small and may be
rewritten, so they keep the in-memory path. Immutable content is never
rewritten in the proxy path (proxyBaseURL is empty), so skipping
RewriteResponse there is behaviour-preserving.
Refs #66
## Problems
1. Docker daemon sends specific Accept headers to negotiate manifest format, but the proxy dropped them — registries defaulted to OCI format, causing "mediaType should be manifest.v2+json not oci.image.index" errors
2. Upstream Content-Type was only used when the provider returned "application/octet-stream" — Docker manifests got the wrong Content-Type
## Fixes
- Forward client Accept header to upstream (both initial request and Bearer token retry)
- Always prefer upstream Content-Type when present
- Fetch signature now accepts variadic clientHeaders for backwards compat
## E2E tested
- DockerHub: redis:7-alpine, alpine:3 — skopeo inspect OK
- GHCR: OCI-only images work with docker pull (GHCR 404s Docker v2 Accept, which is expected)
- Quay: prometheus/node-exporter — skopeo inspect OK
Reviewed-on: #62
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>
Docker Hub (and other registries) return 401 with a `Www-Authenticate: Bearer realm=...` challenge even for public images. The proxy now:
1. Detects 401 + Bearer challenge
2. Parses realm/service/scope from the header
3. Fetches an anonymous token (or authenticated if username/password configured)
4. Retries the original request with the Bearer token
Fixes: `docker pull artifactapi.../dockerhub/library/redis:latest` returning "unauthorized: upstream returned 401"
Reviewed-on: #60
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>
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