Add a `mode` to the urltest group so it can distribute traffic instead of only
picking the lowest-delay node, with optional per-flow stickiness.
- mode: least_test (default, unchanged) | round_robin (rotate across live nodes)
| least_connection (reserved, phase 2 — rejected at config time).
- round_robin selects once per connection over the tag-sorted live set (nodes with
a fresh URL-test result supporting the network); UDP/QUIC sessions stay on one
node; first usable outbound is the fallback when nothing is live. The legacy
selectedOutbound* cache path is untouched — balancing is a separate branch in
DialContext/ListenPacket.
- sticky {mode, timeout, cap, hash}: binds one flow to one node. hash components
process|domain|source_ip|dest_ip|dest_port concatenate in order; absent -> "",
all-empty key -> one fixed node (keyless flows never rotate). mode jumphash
(default, stateless consistent hash — ~1/n remap on node-set change) or ttlmap
(key->node table, lazy + ticker eviction, 2000 LRU cap, 10m TTL, dead-node re-pin).
Reuses the existing urltest health ticker/history as the single liveness source;
no new probing. Now() reports the last-picked tag in balanced modes.
Tests (go test -race, 15 cases): distribution, dead-node skip, all-dead fallback,
jumphash stability + empty-key fixed node, ttlmap stick/expire/cap/dead-repick,
key building, validation. The race detector caught a real bug in the sticky
sweeper (read t.ticker unlocked while close() nilled it) — fixed by passing the
channels into the goroutine, mirroring URLTestGroup.loopCheck.
Also folds the SPEC 016 connections-map mutex (ebf9cc07) into the rc.11 changelog
section, which had not yet shipped in a release.
Leadaxe
5ebff914fc