@dwk/safe-fetch

SSRF-safe outbound fetch and capped body reads, shared across every @dwk package that fetches an attacker- or user-supplied URL.

Provides:

• safeFetch / safeFetchJson — private/reserved-host blocking (including the RFC 7686 .onion special-use TLD, unreachable from Workers), bounded manual redirects with per-hop re-validation, a single overall timeout, and cross-origin credential-header stripping on redirect.
• readBodyCapped / readBytesCapped — a response body reader that refuses to buffer past a byte cap, ignoring a lying Content-Length.

Local development (allowedHosts)

The host block is deny-by-default. For local debugging only (e.g. a composed Worker under wrangler dev --local fetching the dev site it sits next to), allowedHosts accepts exact host[:port] entries (case-insensitive, bracketed IPv6) exempted from the private/loopback block:

await safeFetch(fetch, "http://localhost:4321/post", init, {
  allowedHosts: ["localhost:4321"],
});

Scheme checks, redirect caps (each hop re-validated against the same list), timeouts, and body caps still apply. Never enable this in a production composition — inject it only into local-dev config, never from the environment. Every use is logged/counted as safe_fetch.ssrf.allowed_host (ALLOWED_HOST_EVENT). Consuming packages expose it as fetchAllowedHosts in their options/config.

See spec/packages/safe-fetch.md for the full contract.