Take in an admin's edits of the state files while running (closes #68)

smallwebwaf watches SWWAF_STATE_DIR with fsnotify and takes in a saved
edit of a state file in place of what it held. It knows its own writes
by the SHA-256 of what it last read or wrote; each write first takes in
an edit made since. An edit that does not parse is renamed to
<name>.bad at the next write. Each edit taken in or set aside is logged
and counted. Every ban on a netblock is checked, and the next ban is
worked out from the one that ended last. README.md says how to add and
lift a ban.

Judgement call: a broken edit is set aside at the next write, since an
editor's file can be read half written.

Model: opus-5-5

internal/metrics/metrics.go

@@ -44,6 +44,8 @@ type Metrics struct {
 	stateFileWriteFailures *prometheus.CounterVec
 	stateFileLastWrite     *prometheus.GaugeVec
 	stateFileSize          *prometheus.GaugeVec
+	stateFileEditsTakenIn  *prometheus.CounterVec
+	stateFileEditsSetAside *prometheus.CounterVec
 }
 
 // New returns the metrics, with the Go runtime's and the process's own.
@@ -105,6 +107,11 @@ func New(topN int) *Metrics {
 			"When each state file was last written, in seconds since 1970.", byFile),
 		stateFileSize: gaugeVec("smallwebwaf_state_file_size_bytes",
 			"The size of each state file, as it was last written.", byFile),
+		stateFileEditsTakenIn: counterVec("smallwebwaf_state_file_edits_taken_in_total",
+			"Edits of each state file taken in while running.", byFile),
+		stateFileEditsSetAside: counterVec("smallwebwaf_state_file_edits_set_aside_total",
+			"Edits of each state file renamed to <name>.bad because they did not parse.",
+			byFile),
 	}
 
 	m.handler = promhttp.HandlerFor(m.registry, promhttp.HandlerOpts{})
@@ -120,6 +127,7 @@ func New(topN int) *Metrics {
 		m.GeoJSRequests, m.GeoJSFailures, m.GeoJSUnanswered,
 		m.stateFileWrites, m.stateFileWriteFailures,
 		m.stateFileLastWrite, m.stateFileSize,
+		m.stateFileEditsTakenIn, m.stateFileEditsSetAside,
 	)
 
 	return m
@@ -230,6 +238,18 @@ func (m *Metrics) StateFileWritten(name string, size int, err error) {
 	m.stateFileSize.WithLabelValues(name).Set(float64(size))
 }
 
+// StateFileEditTakenIn counts an admin's edit of the state file name
+// taken in while smallwebwaf runs.
+func (m *Metrics) StateFileEditTakenIn(name string) {
+	m.stateFileEditsTakenIn.WithLabelValues(name).Inc()
+}
+
+// StateFileEditSetAside counts an admin's edit of the state file name
+// renamed to name.bad because it did not parse.
+func (m *Metrics) StateFileEditSetAside(name string) {
+	m.stateFileEditsSetAside.WithLabelValues(name).Inc()
+}
+
 // statusClass returns the class of status, such as 2xx, or none when no
 // status was sent.
 func statusClass(status int) string {