The old ParseConf opened the file itself, which the name did not
convey. Now it parses the config text directly, matching
encoding/json.Unmarshal-style conventions: callers read the file (or
source the string however they like) and pass it in. Also introduce
errors.ErrMissingCredentials for the credential-missing case so callers
can branch on it.
- httpcache.Cacher loses Transform (always atomic copy to Path); adds
BasicAuth and Bearer helpers for Authorization header values.
- geoip.Open now reads <dir>/GeoLite2-City.tar.gz and GeoLite2-ASN.tar.gz
directly: extracts the .mmdb entry in memory and opens via
geoip2.FromBytes. No .mmdb files written to disk.
- geoip.Downloader/New/NewCacher/Fetch/ExtractMMDB removed — geoip is
purely read/lookup; fetching is each caller's concern.
- cmd/check-ip/main.go is a single main() again: blocklists via
gitshallow+dataset, geoip via two httpcache.Cachers (if GeoIP.conf
present) + geoip.Open. No geo refresh loop, no dataset.Group for geo.
- cmd/geoip-update and the integration test construct httpcache.Cachers
directly against geoip.DownloadBase + edition IDs, writing .tar.gz.
httpcache: write <path>.meta JSON sidecar after each successful download;
load it on first Fetch so conditional GETs work after process restarts.
Tests verify: download, sidecar written, same-cacher 304, fresh-cacher 304
(the last being the key case — no in-memory state, sidecar drives ETag).
MaxMind integration test reads GeoIP.conf, downloads City+ASN, verifies
fresh-cacher conditional GET skips re-download via sidecar ETag.
