ARW

HTTP Caching Semantics (Digest Blobs)

Updated: 2025-09-16 Type: Reference

For endpoints that serve immutable, digest‑addressed blobs (e.g., /admin/models/by-hash/{sha256}):

• Validators: strong ETag and Last‑Modified
  • ETag: "{sha256}" (quoted, strong)
  • Last-Modified: <RFC 2822>
  • Accept-Ranges: bytes
• Cache policy: long‑lived and immutable
  • Cache-Control: public, max-age=31536000, immutable
• Conditional requests
  • If-None-Match → 304 Not Modified when it matches the ETag
  • If-Modified-Since → 304 Not Modified when not newer than Last‑Modified
  • Precedence: ETag checks (If‑None‑Match) take precedence over Last‑Modified
• Partial content
  • Range: bytes=start-end | start- | -suffix
  • Returns 206 Partial Content with Content-Range: bytes start-end/total
  • Invalid/unsatisfiable ranges → 416 Range Not Satisfiable with Content-Range: bytes */total
• HEAD behavior
  • Mirrors GET headers (validators, caching); no body
  • Honors If-None-Match / If-Modified-Since

Examples:

# HEAD with ETag validator; 304 if unchanged
curl -I \
  -H 'If-None-Match: "<sha256>"' \
  http://localhost:8091/admin/models/by-hash/<sha256>

# GET a slice (first 1KB)
curl -H 'Range: bytes=0-1023' \
  http://localhost:8091/admin/models/by-hash/<sha256>

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