Full --fast crawl of russell.ballestrini.net (242 URIs): 26s -> ~5s.
Three changes, biggest first:
1. fast_mode now actually ignores crawl-delay (the ~5x). The delay was
only zeroed on the robots-200 path; a site with no robots.txt (404)
or a robots fetch error fell back to default_crawl_delay (2s). Under
--fast that made every concurrent fetch wave sleep ~2s — ~10 waves
x 2s dominated the wall time. _enforce_crawl_delay now short-circuits
when fast_mode, matching the documented "ignore crawl-delay"
contract regardless of robots status. Disallow is still honored
(separate path).
2. One shared ClientSession for the fetcher's lifetime (keepalive TCP
connector sized to page-worker width) instead of a fresh session per
fetch — ~3x on a 24-page wave. Lazily built in-loop via _get_session;
the bridge closes it in a finally (guarded on owning the fetcher).
3. Drop the per-page preflight HEAD. aiohttp exposes response headers
before the body is read, so the existing content-type binary guard
skips images/video/audio without downloading them — the HEAD was a
redundant round trip that doubled per-page latency.
Diverges arborist's AsyncWebFetcher from the agents.ai.unturf.com/core
verbatim lift (fox-approved); candidate to upstream. Regression tests
pin fast=no-delay / polite=delay, shared-session lifecycle, and bridge
session teardown (owned vs injected).
Two crawler-discovery changes surfaced while chasing fast-crawl wall
time on russell.ballestrini.net:
1. Feed-skip in BFS discovery: the bridge fetched feed/sitemap URLs
(a multi-MB atom.xml among them) only for ingest_crawled to discard
them. Gate enqueue on the existing _looks_like_feed_url so we never
fetch crawl-infrastructure URLs — less wasted work and one fewer
slow wave straggler.
2. lxml link extraction, DRY'd: the three duplicated BeautifulSoup
html.parser closures (fresh fetch + 2 cache paths) collapse into one
module-level extract_page_links() backed by lxml.html (C parser,
releases the GIL so to_thread actually parallelises) with a BS4
fallback for markup lxml rejects. Parse on a 24-page wave 3.5s->2.5s.
Honest scope: neither moves full-crawl wall time much — measurement
showed the dominant cost is the per-page HEAD+GET double round-trip on
a per-call ClientSession, not parsing. These are correct-and-cleaner
on their own; the wall-time lever (shared session + drop redundant
HEAD) is a separate change. lxml extraction is regression-pinned
against the BS4 fallback for parity.
