Caches of outside APIs live in /var/cache/sww (closes #314)

Every cache of answers from an outside service has its own file in `SWW_CACHE_DIR` (default `/var/cache/sww`): `lookups.json` (GeoJS), `lists.json` (lists fetched by URL, CrowdSec's decisions included), `dnsbl.json`, `abuseipdb-scores.json` and `routewatch.json` (at most 100,000 answers, each kept an hour). `reputation.json` is gone; the AbuseIPDB checks spent today stay in `SWW_STATE_DIR` as `abuseipdb-checks-spent.json`, since losing them would spend the daily budget twice.

A cache file never stops the start: one that does not parse is set aside as `<name>.bad` with a `file_error` alert. An unwritable `SWW_CACHE_DIR` stops the start. The `run` script creates the cache directory and gives it to `sww`. The cache directory needs no volume and can be left out of backups.

Model: opus-5-5

internal/routewatch/routewatch_test.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/netip"
+	"slices"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -336,3 +337,96 @@ func TestRepeatedRequestsMakeOneQueryAndTheAnswerExpires(t *testing.T) {
 		t.Errorf("%d queries after the answer expired, want 2", got)
 	}
 }
+
+func TestSnapshotHoldsTheAnswerUntilItExpires(t *testing.T) {
+	t.Parallel()
+
+	f := newFixture(t, answering(routedAnswer))
+
+	f.route()
+	f.waitFor("")
+
+	want := []routewatch.Answer{{
+		Client:   netip.MustParsePrefix(clientAddr + "/32"),
+		Netblock: netip.MustParsePrefix("192.0.2.0/24"), ASN: 64496,
+		Answered: f.clk.Now(),
+	}}
+	if got := f.client.Snapshot(); !slices.Equal(got, want) {
+		t.Errorf("snapshot %+v, want %+v", got, want)
+	}
+
+	f.clk.advance(time.Hour)
+
+	if got := f.client.Snapshot(); len(got) != 0 {
+		t.Errorf("snapshot %+v an hour after the answer, want none", got)
+	}
+}
+
+func TestLoadedAnswersAreUsedForAnHourFromWhenTheyCame(t *testing.T) {
+	t.Parallel()
+
+	f := newFixture(t, answering(routedAnswer))
+	now := f.clk.Now()
+	kept := routewatch.Answer{
+		Client:   netip.MustParsePrefix(clientAddr + "/32"),
+		Netblock: netip.MustParsePrefix("198.51.100.0/24"), ASN: 64497,
+		Answered: now.Add(-time.Hour + time.Second),
+	}
+	stale := routewatch.Answer{
+		Client:   netip.MustParsePrefix("192.0.2.2/32"),
+		Netblock: netip.MustParsePrefix("192.0.2.0/24"), ASN: 64496,
+		Answered: now.Add(-time.Hour),
+	}
+
+	f.client.Load([]routewatch.Answer{kept, stale})
+
+	if got := f.client.Snapshot(); !slices.Equal(got, []routewatch.Answer{kept}) {
+		t.Errorf("kept %+v, want only the answer that came less than an hour ago", got)
+	}
+
+	route, missing := f.route()
+
+	want := routewatch.Route{Netblock: kept.Netblock, ASN: kept.ASN}
+	if route != want || missing != "" {
+		t.Errorf("route %+v (%q), want %+v", route, missing, want)
+	}
+
+	if got := f.queries.Load(); got != 0 {
+		t.Errorf("%d queries for a client with an answer loaded, want none", got)
+	}
+}
+
+func TestLoadDropsTheAnswerThatCameLongestAgoFirst(t *testing.T) {
+	t.Parallel()
+
+	const maxAnswers = 100000
+
+	f := newFixture(t, answering(routedAnswer))
+	now := f.clk.Now()
+
+	// routewatch.json lists the answers by client. Here each came a
+	// millisecond before the one listed before it, so the last listed is
+	// the one that came longest ago, and the one dropped.
+	answers := make([]routewatch.Answer, maxAnswers+1)
+	addr := netip.MustParseAddr("10.0.0.0")
+
+	for i := range answers {
+		answers[i] = routewatch.Answer{
+			Client:   netip.PrefixFrom(addr, addr.BitLen()),
+			Answered: now.Add(-time.Duration(i) * time.Millisecond),
+		}
+		addr = addr.Next()
+	}
+
+	f.client.Load(answers)
+
+	got := f.client.Snapshot()
+	if len(got) != maxAnswers {
+		t.Fatalf("%d answers kept, want %d", len(got), maxAnswers)
+	}
+
+	if got[0] != answers[0] || got[maxAnswers-1] != answers[maxAnswers-1] {
+		t.Errorf("answers kept from %s to %s, want from %s to %s", got[0].Client,
+			got[maxAnswers-1].Client, answers[0].Client, answers[maxAnswers-1].Client)
+	}
+}