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http-resume-integrity

Skill0 starsChanged 39 days agoMITView on GitHub

Use when interrupted or parallel HTTP downloads resume with corrupt bytes, a server ignores Range, or decompression and file offsets disagree.

The file

We split this skill into the rules it gives an agent

3 rules. About 0 are common, 3 are distinctive, and 0 are very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈3

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 0

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Before promoting the assembled artifact, check its expected total and independently trusted digest/signature when available.

    line 29
  2. Distinctive:

    Run the original offline byte-splice fixture:

    line 33
  3. Distinctive:

    Never disable TLS verification to make a resume succeed.

    line 46

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

HTTP Resume Integrity

A checkpoint identifies a representation, not merely a URL and file length. Treat resumption as a conditional splice, not an append operation. Scope this recipe to sequential, single-range, identity-coded downloads.

Response gate

Send Range: bytes=N- with If-Range containing the saved strong ETag. A weak ETag is unsuitable. Byte offsets address the encoded representation; transparent decompression changes the coordinate system.

ResponseLocal action before publishing bytes
206Validate single-part byte range, start N, inclusive end, unchanged total, matching strong ETag, coding, and actual body length. A shorter valid interval needs another request.
200Never append. Stage a new full transfer with new metadata; replace only after validation.
416Reconcile metadata; bytes */L alone does not prove the local file is complete or correct.
Error, malformed range, changed identityPreserve the last verified checkpoint; stop or restart under the download policy.

These conservative gates intentionally reject some legal responses, including unknown totals and multipart ranges. Broader clients need separate handling, not relaxed checks.

Checkpoint recipe

  1. Persist effective resource identity, representation-selecting request context, ETag, total length, byte domain, and committed prefix together. Isolate destinations by job; do not store secrets in logs. Changes in redirect target or selection context invalidate this checkpoint unless equivalence is independently established.
  2. Request Accept-Encoding: identity, then inspect the response. Requests automatically decompresses through iter_content; a file length measured after decoding is not a safe resume offset. Verify the adapter exposes the intended bytes.
  3. Stage each bounded response separately. Validate headers, count bytes, and require successful transfer completion before advancing the checkpoint. A timeout, short body, or exhausted retry budget leaves the prior prefix intact. Limit total bytes, response size, elapsed time, and attempts independently.
  4. Serialize checkpoint commits or compare generations before committing; two successful concurrent retries must not append the same suffix twice. File length alone does not establish contiguous coverage for parallel downloads.
  5. Before promoting the assembled artifact, check its expected total and independently trusted digest/signature when available. An ETag is not an authenticity guarantee. Follow dependency-artifact-integrity before executing downloaded packages.

Example: old bytes AAAA1111, new bytes BBBB2222; resuming after four bytes without identity checks produces AAAA2222. Its length is correct, but it belongs to neither version.

Run the original offline byte-splice fixture:

python3 skills/engineering/http-resume-integrity/reproduce.py

See primary sources and validation limits. No HTTP-client integration or production downloader is supplied.

Pitfalls

  • Accept-Ranges advertises support, not a future response guarantee.
  • curl -C - derives an offset from local files; that does not establish their provenance.
  • A matching length or clean transport exit cannot authenticate artifact bytes.
  • Never disable TLS verification to make a resume succeed.

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