/metrics was Prometheus-ish name/value text with a custom banner and
text/plain Content-Type, so strict scrapers could fail.
Emit Prometheus text 0.0.4 (# HELP, # TYPE, counter|gauge) with stable
metric names, and set Content-Type to text/plain; version=0.0.4; charset=utf-8.
Steam clients lean on Range requests. Hit/miss looked fine while downloads
still felt cold when a Range miss returned the full upstream body as 200.
Add range_cache / range_upstream metrics. HIT path already sliced 206 from
the cached full object; count range_cache there. On MISS, keep stripping
Range for the upstream fetch (full object still cached) but serve the
client's requested slice as 206 and count range_upstream.
Tests in steamcache/range_test.go cover Range HIT (local, no upstream),
Range MISS (206 + full object cached), and /metrics emission.
pike
moss