feat: misina/digest — RFC 9530 Repr-Digest / Content-Digest

[productdevbook]

Problem

RFC 9530 (Feb 2024, replaces RFC 3230) defines Repr-Digest and Content-Digest for verifying body integrity. Storage backends (S3-style) and bot-auth (Cloudflare) ecosystems are adopting it. Without a helper, users hand-roll WebCrypto + base64 + SF formatting.

Proposal

New subpath misina/digest:

import { withDigest, verifyDigest } from 'misina/digest'

// Auto-add Content-Digest on outgoing requests with body
const api = withDigest(misina, { algorithm: 'sha-256' })

// Verify response Content-Digest
await verifyDigest(response)  // throws DigestMismatchError on failure

Implementation:

• crypto.subtle.digest (cross-runtime)
• Base64 encode (RFC 9530 SF byte-sequence)
• TransformStream for streaming bodies (don't buffer huge requests)

Depends on RFC 9651 SF parser (#20) for output formatting.

Acceptance criteria

• withDigest(misina, opts) adds Content-Digest: sha-256=:...: header
• verifyDigest(response) validates and throws on mismatch
• Streaming digest for non-buffered bodies
• Test against RFC 9530 examples
• Doc

Refs

• https://www.rfc-editor.org/rfc/rfc9530.html

[productdevbook]

Shipped in 2e0dc2c. withDigest for outgoing, verifyDigest for incoming, sha-256/sha-512, RFC 9530 §6 vector pinned in tests.