Trap paths, and the error burst banning a client refused too often (closes #115)

SWWAF_TRAP_PATHS: a request whose path, as a path rule sees it, is one
of them is a clear sign of attack, banned as a ban rule's match is; the
ban's notes give its trap_path. Checked after the rate limits, before the
rule files.

SWWAF_ERROR_BURST_THRESHOLD (default 30, or off): more refusals in a
minute after a block or ban rule or a trap path, or for a missing or
wrong token, ban the client as a broken limit does. Counted in
clients.json's minute_refusals; limit_hit error_burst, notes kind
refusals.

A token refusal is now the offence token_refused, and
smallwebwaf_offences_total counts every kind the history does.

Judgement call: the threshold is not lowered by a client's limit percentage.

Model: opus-5-5

internal/state/state.go

@@ -679,8 +679,8 @@ func (f *bansFile) check(data []byte) error {
 }
 
 // check refuses a client without its address, which would count nobody's
-// requests, or with requests or bytes in a window but no start, which
-// would drop them and give the client a fresh allowance.
+// requests, or with requests, bytes or refusals in a window but no start,
+// which would drop them and give the client a fresh allowance.
 func (f *clientsFile) check([]byte) error {
 	for i, client := range f.Clients {
 		switch {
@@ -698,6 +698,8 @@ func (f *clientsFile) check([]byte) error {
 			return missing(i, "hour_bytes.start")
 		case countsWithoutStart(client.DayBytes):
 			return missing(i, "day_bytes.start")
+		case countsWithoutStart(client.MinuteRefusals):
+			return missing(i, "minute_refusals.start")
 		}
 	}
 
@@ -898,8 +900,8 @@ func missingFromCounter(counter anomaly.Counter) string {
 	}
 }
 
-// countsWithoutStart reports whether b holds requests, or bytes, but no
-// start, which places them in time.
+// countsWithoutStart reports whether b holds requests, bytes or refusals
+// but no start, which places them in time.
 func countsWithoutStart(b ratelimit.Buckets) bool {
 	return b.Start.IsZero() && (b.Current != 0 || b.Previous != 0)
 }

internal/state/state_test.go

@@ -639,6 +639,15 @@ func TestEntryWithoutAFieldItNeedsStopsTheStart(t *testing.T) {
 	}
 }
 
+func TestClientWithRefusalsInTheMinuteWithoutTheirStartStopsTheStart(t *testing.T) {
+	t.Parallel()
+
+	wantRefused(t, clientsJSON,
+		`{"version": 1, "clients": [{"client": "203.0.113.9/32", `+
+			`"minute_refusals": {"current": 2}}]}`,
+		`: entry 1 has no "minute_refusals.start"`)
+}
+
 func TestReputationJSONEntryWithoutAFieldItNeedsStopsTheStart(t *testing.T) {
 	t.Parallel()