servewaf answers rproxy's question about each request and takes its report (closes #170)

`smallwebwaf servewaf` runs today's checks on the visitor's request each
question carries, answers rproxy, and passes nothing to an app. rproxy reports
every request servewaf answered. A report counts an allowed request's bytes and
writes servewaf's second log line. The table holds a copy of what a report
needs, never the request, so a report cannot reach a request being handled.

Judgement call: a question's body is read before any check; over 64 KiB gets 400.
Judgement call: a report's bytes and durations have ceilings, so they cannot overflow.
Judgement call: a `close` disposition for SWWAF_BAN_RESPONSE=close.

Model: opus-5-5

internal/metrics/metrics.go

@@ -403,28 +403,21 @@ func (m *Metrics) RequestEnded(
 	line *requestlog.Line, limit string, duration, upstreamDuration time.Duration,
 ) {
 	m.inFlight.Dec()
+	m.count(line, limit, duration, upstreamDuration)
+}
 
-	class := statusClass(line.Status)
-	m.requests.WithLabelValues(class, line.Action).Inc()
-	m.requestBytes.WithLabelValues(class, line.Action).Add(float64(line.RequestBytes))
-	m.responseBytes.WithLabelValues(class, line.Action).Add(float64(line.ResponseBytes))
-	m.requestDuration.Observe(duration.Seconds())
+// RequestAllowed counts a question of rproxy's, answered allow, as no longer
+// under way. RequestReported counts the request it was about.
+func (m *Metrics) RequestAllowed() {
+	m.inFlight.Dec()
+}
 
-	if upstreamDuration > 0 {
-		m.upstreamDuration.Observe(upstreamDuration.Seconds())
-	}
-
-	if limit != "" {
-		m.sizeAndTimeLimitHits.WithLabelValues(limit).Inc()
-	}
-
-	if line.Country != "" {
-		m.countries.add(line.Country, line)
-	}
-
-	if line.ASN != "" {
-		m.asns.add(line.ASN, line)
-	}
+// RequestReported counts a request rproxy passed to the app, as RequestEnded
+// does, from what its report says, which line holds.
+func (m *Metrics) RequestReported(
+	line *requestlog.Line, duration, upstreamDuration time.Duration,
+) {
+	m.count(line, "", duration, upstreamDuration)
 }
 
 // LimitHit counts a request that broke a rate limit, a byte limit or the
@@ -493,6 +486,33 @@ func (m *Metrics) StateFileEditSetAside(name string) {
 	m.stateFileEditsSetAside.WithLabelValues(name).Inc()
 }
 
+// count counts a request that has ended, as RequestEnded describes.
+func (m *Metrics) count(
+	line *requestlog.Line, limit string, duration, upstreamDuration time.Duration,
+) {
+	class := statusClass(line.Status)
+	m.requests.WithLabelValues(class, line.Action).Inc()
+	m.requestBytes.WithLabelValues(class, line.Action).Add(float64(line.RequestBytes))
+	m.responseBytes.WithLabelValues(class, line.Action).Add(float64(line.ResponseBytes))
+	m.requestDuration.Observe(duration.Seconds())
+
+	if upstreamDuration > 0 {
+		m.upstreamDuration.Observe(upstreamDuration.Seconds())
+	}
+
+	if limit != "" {
+		m.sizeAndTimeLimitHits.WithLabelValues(limit).Inc()
+	}
+
+	if line.Country != "" {
+		m.countries.add(line.Country, line)
+	}
+
+	if line.ASN != "" {
+		m.asns.add(line.ASN, line)
+	}
+}
+
 // addReputationQueries adds the counter of the queries to source, a DNSBL
 // zone, or of the checks of clients with AbuseIPDB, which count tells.
 func (m *Metrics) addReputationQueries(source prometheus.Labels, count func() int) {