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

The answers of GeoJS, the lists fetched by URL, the DNS blocklists,
AbuseIPDB and routewatch each go in a cache file in SWW_CACHE_DIR
(default /var/cache/sww): lookups.json, lists.json, dnsbl.json,
abuseipdb-scores.json and routewatch.json. reputation.json is gone. The
AbuseIPDB checks spent today are a count, not a cache, and stay in
SWW_STATE_DIR as abuseipdb-checks-spent.json.

A cache file never stops the start: one that does not parse is set
aside as an edit is, one that cannot be read is written over, and its
cache starts empty. An unwritable SWW_CACHE_DIR stops the start, as an
unwritable SWW_STATE_DIR does. Each directory is watched on its own.
The run script makes the cache directory and gives it to sww.

Model: opus-5-5

internal/state/state.go

@@ -1,13 +1,23 @@
-// Package state keeps sww's state in JSON files in
-// SWW_STATE_DIR, as the "Persistent state" section of SPEC.md requires
-// and docs/state-files.md lists them:
-// bans.json holds the bans, clients.json each client's counters and
-// history, lookups.json GeoJS's answers, reputation.json the last try and
-// last good copy of each list fetched from a URL, the DNSBL zones'
-// verdicts, and AbuseIPDB's scores and checks spent, and alerts.json the
-// cooldowns, the hour under way, the alerts waiting for each destination
-// and the anomaly counters. Load
-// reads them at start, Watch takes in an admin's edit of one while
+// Package state keeps sww's state in JSON files, as the "Persistent
+// state" section of SPEC.md requires and docs/state-files.md lists them.
+//
+// The state files are in SWW_STATE_DIR:
+//   - bans.json holds the bans;
+//   - clients.json holds each client's counters and history;
+//   - abuseipdb-checks-spent.json holds the AbuseIPDB checks spent today;
+//   - alerts.json holds the cooldowns, the hour under way, the alerts
+//     waiting for each destination and the anomaly counters.
+//
+// The cache files are in SWW_CACHE_DIR. Each keeps answers from an
+// outside service, which are fetched again when the file is lost:
+//   - lookups.json holds GeoJS's answers;
+//   - lists.json holds the last try and last good copy of each list
+//     fetched from a URL;
+//   - dnsbl.json holds the DNSBL zones' verdicts;
+//   - abuseipdb-scores.json holds AbuseIPDB's scores;
+//   - routewatch.json holds routewatch's answers.
+//
+// Load reads them at start, Watch takes in an admin's edit of one while
 // sww runs, and Run and WriteAll write them. The disk is read and
 // written outside the parts' locks, which are held only to take a
 // snapshot or to put in what a file holds, so that no request waits on
@@ -31,6 +41,7 @@ import (
 	"sync"
 	"time"
 
+	"cloud.google.com/go/civil"
 	"github.com/fsnotify/fsnotify"
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
 	"sneak.berlin/go/smallwebwaf/internal/anomaly"
@@ -39,6 +50,7 @@ import (
 	"sneak.berlin/go/smallwebwaf/internal/metrics"
 	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
 	"sneak.berlin/go/smallwebwaf/internal/reputation"
+	"sneak.berlin/go/smallwebwaf/internal/routewatch"
 )
 
 // version is the version of the files' format, the only one read.
@@ -48,15 +60,42 @@ const version = 1
 // hold visitors' addresses.
 const fileMode = 0o600
 
-// The state files' names.
+// The state files' names, in Dir.
 const (
-	bansJSON       = "bans.json"
-	clientsJSON    = "clients.json"
-	lookupsJSON    = "lookups.json"
-	reputationJSON = "reputation.json"
-	alertsJSON     = "alerts.json"
+	bansJSON                 = "bans.json"
+	clientsJSON              = "clients.json"
+	abuseIPDBChecksSpentJSON = "abuseipdb-checks-spent.json"
+	alertsJSON               = "alerts.json"
 )
 
+// The cache files' names, in CacheDir.
+const (
+	lookupsJSON         = "lookups.json"
+	listsJSON           = "lists.json"
+	dnsblJSON           = "dnsbl.json"
+	abuseIPDBScoresJSON = "abuseipdb-scores.json"
+	routeWatchJSON      = "routewatch.json"
+)
+
+// fileNames returns the names of the state files, then those of the
+// cache files, in the order they are written.
+func fileNames() []string {
+	return []string{
+		bansJSON, clientsJSON, abuseIPDBChecksSpentJSON, alertsJSON,
+		lookupsJSON, listsJSON, dnsblJSON, abuseIPDBScoresJSON, routeWatchJSON,
+	}
+}
+
+// isCacheFile reports whether name is the name of a cache file.
+func isCacheFile(name string) bool {
+	switch name {
+	case lookupsJSON, listsJSON, dnsblJSON, abuseIPDBScoresJSON, routeWatchJSON:
+		return true
+	default:
+		return false
+	}
+}
+
 var (
 	errVersion = errors.New("unknown version")
 	// errMissing is for an entry without a field it needs.
@@ -72,24 +111,29 @@ var (
 
 // Params are what Load needs.
 type Params struct {
-	// Dir is the directory of the state files (SWW_STATE_DIR).
-	Dir string
+	// Dir is the directory of the state files (SWW_STATE_DIR), and
+	// CacheDir that of the cache files (SWW_CACHE_DIR).
+	Dir      string
+	CacheDir string
 	// WriteDelay is how long after a ban is made bans.json is written
 	// (SWW_STATE_WRITE_DELAY), and CounterInterval how often every file
 	// is (SWW_STATE_COUNTER_INTERVAL).
 	WriteDelay      time.Duration
 	CounterInterval time.Duration
-	// Ledger, Limiter, GeoJS, Lists, DNSBL, AbuseIPDB, Alerts and Anomalies
-	// hold the state. Alerts also receive a file_error alert for an edit set
-	// aside, and for a write that fails while sww runs.
-	Ledger    *bans.Ledger
-	Limiter   *ratelimit.Limiter
-	GeoJS     *lookup.GeoJS
-	Lists     *reputation.Lists
-	DNSBL     *reputation.DNSBL
-	AbuseIPDB *reputation.AbuseIPDB
-	Alerts    *alerts.Queue
-	Anomalies *anomaly.Counters
+	// Ledger, Limiter, GeoJS, Lists, DNSBL, AbuseIPDB, RouteWatch, Alerts and
+	// Anomalies hold the state. RouteWatch is nil while SWW_ROUTEWATCH_URL is
+	// unset, and routewatch.json then holds no answers. Alerts also receive a
+	// file_error alert for an edit set aside, and for a write that fails while
+	// sww runs.
+	Ledger     *bans.Ledger
+	Limiter    *ratelimit.Limiter
+	GeoJS      *lookup.GeoJS
+	Lists      *reputation.Lists
+	DNSBL      *reputation.DNSBL
+	AbuseIPDB  *reputation.AbuseIPDB
+	RouteWatch *routewatch.Client
+	Alerts     *alerts.Queue
+	Anomalies  *anomaly.Counters
 	// Now tells the time by which the counters' buckets run out, normally
 	// time.Now in UTC.
 	Now func() time.Time
@@ -101,7 +145,7 @@ type Params struct {
 	Metrics *metrics.Metrics
 }
 
-// Files are the state files of a running sww.
+// Files are the state and cache files of a running sww.
 type Files struct {
 	params Params
 
@@ -147,13 +191,38 @@ type lookupsFile struct {
 	Lookups []lookup.Answer `json:"lookups"`
 }
 
-// reputationFile is reputation.json, indented for an admin to read and
-// edit, so that each line of a list's copy is on a line of its own.
-type reputationFile struct {
-	Version   int                  `json:"version"`
-	Lists     []reputation.List    `json:"lists"`
-	Verdicts  []reputation.Verdict `json:"verdicts"`
-	AbuseIPDB reputation.Checks    `json:"abuseipdb"`
+// abuseIPDBChecksSpentFile is abuseipdb-checks-spent.json, indented for an
+// admin to read and edit.
+type abuseIPDBChecksSpentFile struct {
+	Version int        `json:"version"`
+	Day     civil.Date `json:"day,omitzero"`
+	Spent   int        `json:"spent"`
+}
+
+// listsFile is lists.json, indented for an admin to read and edit, so
+// that each line of a list's copy is on a line of its own.
+type listsFile struct {
+	Version int               `json:"version"`
+	Lists   []reputation.List `json:"lists"`
+}
+
+// dnsblFile is dnsbl.json, with each verdict on a line of its own.
+type dnsblFile struct {
+	Version  int                  `json:"version"`
+	Verdicts []reputation.Verdict `json:"verdicts"`
+}
+
+// abuseIPDBScoresFile is abuseipdb-scores.json, with each score on a line
+// of its own.
+type abuseIPDBScoresFile struct {
+	Version int                `json:"version"`
+	Scores  []reputation.Score `json:"scores"`
+}
+
+// routeWatchFile is routewatch.json, with each answer on a line of its own.
+type routeWatchFile struct {
+	Version int                 `json:"version"`
+	Answers []routewatch.Answer `json:"answers"`
 }
 
 // alertsFile is alerts.json, indented for an admin to read and edit.
@@ -178,34 +247,45 @@ type stateFile interface {
 	toUTC()
 }
 
-// Load checks that files can be written in Dir, and reads the state files
-// in it into the parts of Params that hold the state. A missing file is
-// empty state, as on a first start. A file that does not parse, has an
-// unknown version, or has an entry without a field it needs, is an error
-// that names the file and, where the JSON decoder tells it, the line and
-// column, or else the entry.
+// Load checks that files can be written in Dir and CacheDir, and reads the
+// files in them into the parts of Params that hold the state. A missing
+// file is empty state, as on a first start. A state file that does not
+// parse, has an unknown version, or has an entry without a field it
+// needs, is an error that names the file and, where the JSON decoder
+// tells it, the line and column, or else the entry. A cache file is never
+// an error, as readCache describes.
 func Load(params Params) (*Files, error) {
 	err := checkWritable(params.Dir)
 	if err != nil {
 		return nil, fmt.Errorf("SWW_STATE_DIR cannot be written: %w", err)
 	}
 
+	err = checkWritable(params.CacheDir)
+	if err != nil {
+		return nil, fmt.Errorf("SWW_CACHE_DIR cannot be written: %w", err)
+	}
+
 	f := &Files{params: params, sums: map[string][sha256.Size]byte{}}
 
 	bansRead, bansErr := f.read(bansJSON)
 	clientsRead, clientsErr := f.read(clientsJSON)
-	lookupsRead, lookupsErr := f.read(lookupsJSON)
-	reputationRead, reputationErr := f.read(reputationJSON)
+	_, checksErr := f.read(abuseIPDBChecksSpentJSON)
 	alertsRead, alertsErr := f.read(alertsJSON)
 
-	err = errors.Join(bansErr, clientsErr, lookupsErr, reputationErr, alertsErr)
+	err = errors.Join(bansErr, clientsErr, checksErr, alertsErr)
 	if err != nil {
 		return nil, err
 	}
 
+	lookupsRead := f.readCache(lookupsJSON)
+	listsRead := f.readCache(listsJSON)
+	f.readCache(dnsblJSON)
+	f.readCache(abuseIPDBScoresJSON)
+	f.readCache(routeWatchJSON)
+
 	params.ProcessLog.Info("read the state files", "directory", params.Dir,
-		"bans", bansRead, "clients", clientsRead, "lookups", lookupsRead,
-		"lists", reputationRead, "alerts_waiting", alertsRead)
+		"cache_directory", params.CacheDir, "bans", bansRead, "clients", clientsRead,
+		"lookups", lookupsRead, "lists", listsRead, "alerts_waiting", alertsRead)
 
 	return f, nil
 }
@@ -234,38 +314,35 @@ func (f *Files) Run(ctx context.Context) {
 
 			f.logFailure(bansJSON, f.writeFile(bansJSON))
 		case <-interval.C:
-			for _, name := range []string{
-				bansJSON, clientsJSON, lookupsJSON, reputationJSON, alertsJSON,
-			} {
+			for _, name := range fileNames() {
 				f.logFailure(name, f.writeFile(name))
 			}
 		}
 	}
 }
 
-// WriteAll writes every state file, as sww stops. A file that
+// WriteAll writes every state and cache file, as sww stops. A file that
 // fails does not keep the others from being written.
 func (f *Files) WriteAll() error {
-	return errors.Join(f.writeFile(bansJSON), f.writeFile(clientsJSON),
-		f.writeFile(lookupsJSON), f.writeFile(reputationJSON), f.writeFile(alertsJSON))
-}
+	names := fileNames()
+	errs := make([]error, 0, len(names))
 
-// Watch watches Dir until ctx is done, and takes in an admin's edit of a
-// state file as soon as it is saved: what the file holds replaces what
-// sww held for it. An edit that does not parse is left for the
-// file's next write, which sets it aside, since a file can be read while
-// an editor is still writing it. If Dir cannot be watched, that is
-// logged, and an edit is taken in only before its file is written.
-func (f *Files) Watch(ctx context.Context) {
-	watcher, err := fsnotify.NewWatcher()
-	if err == nil {
-		defer func() {
-			_ = watcher.Close()
-		}()
-
-		err = watcher.Add(f.params.Dir)
+	for _, name := range names {
+		errs = append(errs, f.writeFile(name))
 	}
 
+	return errors.Join(errs...)
+}
+
+// Watch watches Dir and CacheDir until ctx is done, and takes in an
+// admin's edit of a file as soon as it is saved: what the file holds
+// replaces what sww held for it. An edit that does not parse is left for
+// the file's next write, which sets it aside, since a file can be read
+// while an editor is still writing it. A directory that cannot be watched
+// is logged, and the other is still watched. An edit in a directory not
+// watched is taken in only before its file is written.
+func (f *Files) Watch(ctx context.Context) {
+	watcher, err := fsnotify.NewWatcher()
 	if err != nil {
 		f.params.ProcessLog.Error("cannot watch the state files for edits",
 			"error", err.Error())
@@ -273,16 +350,42 @@ func (f *Files) Watch(ctx context.Context) {
 		return
 	}
 
+	defer func() {
+		_ = watcher.Close()
+	}()
+
+	var watched []string
+
+	for _, dir := range []struct{ path, failed string }{
+		{f.params.Dir, "cannot watch the state files for edits"},
+		{f.params.CacheDir, "cannot watch the cache files for edits"},
+	} {
+		err = watcher.Add(dir.path)
+		if err != nil {
+			f.params.ProcessLog.Error(dir.failed, "directory", dir.path,
+				"error", err.Error())
+
+			continue
+		}
+
+		watched = append(watched, dir.path)
+	}
+
+	if len(watched) == 0 {
+		return
+	}
+
 	f.params.ProcessLog.Info("watching the state files for edits",
-		"directory", f.params.Dir)
+		"directories", watched)
 
 	for {
 		select {
 		case <-ctx.Done():
 			return
 		case event := <-watcher.Events:
-			switch name := filepath.Base(event.Name); name {
-			case bansJSON, clientsJSON, lookupsJSON, reputationJSON, alertsJSON:
+			name := filepath.Base(event.Name)
+			if slices.Contains(fileNames(), name) &&
+				filepath.Join(f.dir(name), name) == event.Name {
 				f.fileChanged(name)
 			}
 		case err = <-watcher.Errors:
@@ -292,11 +395,14 @@ func (f *Files) Watch(ctx context.Context) {
 	}
 }
 
-// logFailure logs a write of the state file name that failed, and raises
+// logFailure logs a write of the file name that failed, and raises
 // a file_error alert for it.
 func (f *Files) logFailure(name string, err error) {
 	if err != nil {
-		const failed = "writing the state files failed"
+		failed := "writing the state files failed"
+		if isCacheFile(name) {
+			failed = "writing the cache files failed"
+		}
 
 		// Raised before it is logged, so that the alert is there once the
 		// log line is.
@@ -304,14 +410,14 @@ func (f *Files) logFailure(name string, err error) {
 			Event:  alerts.EventFileError,
 			Reason: failed,
 			Detail: map[string]any{
-				"file": filepath.Join(f.params.Dir, name), "error": err.Error(),
+				"file": filepath.Join(f.dir(name), name), "error": err.Error(),
 			},
 		})
 		f.params.ProcessLog.Error(failed, "error", err.Error())
 	}
 }
 
-// fileChanged takes in what the state file name holds, as Watch sees it
+// fileChanged takes in what the file name holds, as Watch sees it
 // change, if that is an edit made since sww last read or wrote
 // the file. A file that cannot be read or does not parse is left for its
 // next write.
@@ -327,7 +433,7 @@ func (f *Files) fileChanged(name string) {
 	_ = f.takeInEdit(name, data)
 }
 
-// takeInEdit takes in data, an edit of the state file name, as takeIn
+// takeInEdit takes in data, an edit of the file name, as takeIn
 // does, and counts and logs it. Every edit taken in while sww
 // runs, by Watch or by a write, is taken in here. An edit that does not
 // parse is neither counted nor logged, and takeIn's error returned.
@@ -341,13 +447,23 @@ func (f *Files) takeInEdit(name string, data []byte) error {
 	// log line is.
 	f.params.Metrics.StateFileEditTakenIn(name)
 	f.params.ProcessLog.Info("took in an edit of a state file",
-		"file", filepath.Join(f.params.Dir, name))
+		"file", filepath.Join(f.dir(name), name))
 
 	return nil
 }
 
-// read takes in the state file name at start, and returns how many
-// entries it holds. A missing file holds none.
+// dir returns the directory of the file name: CacheDir for a cache file,
+// and Dir for a state file.
+func (f *Files) dir(name string) string {
+	if isCacheFile(name) {
+		return f.params.CacheDir
+	}
+
+	return f.params.Dir
+}
+
+// read takes in the file name at start, and returns how many entries it
+// holds. A missing file holds none.
 func (f *Files) read(name string) (int, error) {
 	data, changed, err := f.readChanged(name)
 	if err != nil || !changed {
@@ -357,14 +473,44 @@ func (f *Files) read(name string) (int, error) {
 	return f.takeIn(name, data, false)
 }
 
-// readChanged returns what the state file name holds, and whether that
-// has changed since sww last read or wrote the file, as it has
-// for a file sww never read or wrote. A missing file has not
-// changed: it is written again at its next write.
-func (f *Files) readChanged(name string) ([]byte, bool, error) {
-	path := filepath.Join(f.params.Dir, name)
+// readCache takes in the cache file name at start, as read does. A cache
+// file that cannot be read, or does not parse, does not stop the start:
+// it is logged, and its cache starts empty and fills again. One that does
+// not parse is set aside as an edit is, and one that cannot be read is
+// written over at its next write.
+func (f *Files) readCache(name string) int {
+	data, changed, err := f.readChanged(name)
+	if err != nil || !changed {
+		f.logUnread(name, err)
 
-	data, err := os.ReadFile(path) //nolint:gosec // a state file, in SWW_STATE_DIR
+		return 0
+	}
+
+	entries, err := f.takeIn(name, data, false)
+	if err != nil {
+		f.logUnread(name, f.setAside(name, err))
+	}
+
+	return entries
+}
+
+// logUnread logs err, the reason the cache file name was not read at
+// start, unless it is nil.
+func (f *Files) logUnread(name string, err error) {
+	if err != nil {
+		f.params.ProcessLog.Warn("cannot read a cache file, so its cache starts empty",
+			"file", filepath.Join(f.dir(name), name), "error", err.Error())
+	}
+}
+
+// readChanged returns what the file name holds, and whether that has
+// changed since sww last read or wrote the file, as it has for a file
+// sww never read or wrote. A missing file has not changed: it is written
+// again at its next write.
+func (f *Files) readChanged(name string) ([]byte, bool, error) {
+	path := filepath.Join(f.dir(name), name)
+
+	data, err := os.ReadFile(path) //nolint:gosec // a file in one of the two directories
 	if errors.Is(err, fs.ErrNotExist) {
 		return nil, false, nil
 	}
@@ -376,15 +522,39 @@ func (f *Files) readChanged(name string) ([]byte, bool, error) {
 	return data, sha256.Sum256(data) != f.sums[name], nil
 }
 
-// takeIn parses data, what the state file name holds, puts it into the
+// takeIn parses data, what the file name holds, puts it into the
 // part that keeps that state, in place of what the part held, and returns
 // how many entries the file holds. edit is whether data is an admin's
 // edit taken in while sww runs, rather than the file read at the
 // start. An error names the file and, where the JSON decoder tells it,
-// the line and column, or else the entry.
+// the line and column, or else the entry. abuseipdb-checks-spent.json
+// holds no entries.
 func (f *Files) takeIn(name string, data []byte, edit bool) (int, error) {
-	path := filepath.Join(f.params.Dir, name)
+	path := filepath.Join(f.dir(name), name)
 
+	var (
+		entries int
+		err     error
+	)
+
+	if isCacheFile(name) {
+		entries, err = f.takeInCache(name, path, data)
+	} else {
+		entries, err = f.takeInState(name, path, data, edit)
+	}
+
+	if err != nil {
+		return 0, err
+	}
+
+	f.sums[name] = sha256.Sum256(data)
+
+	return entries, nil
+}
+
+// takeInState parses data, what the state file name, at path, holds, and
+// puts it in, as takeIn describes.
+func (f *Files) takeInState(name, path string, data []byte, edit bool) (int, error) {
 	var entries int
 
 	switch name {
@@ -418,6 +588,33 @@ func (f *Files) takeIn(name string, data []byte, edit bool) (int, error) {
 
 		f.params.Limiter.Load(file.Clients, f.params.Now())
 		entries = len(file.Clients)
+	case abuseIPDBChecksSpentJSON:
+		var file abuseIPDBChecksSpentFile
+
+		err := parse(path, data, &file)
+		if err != nil {
+			return 0, err
+		}
+
+		f.params.AbuseIPDB.LoadChecksSpent(reputation.ChecksSpent{
+			Day: file.Day, Spent: file.Spent,
+		})
+	case alertsJSON:
+		waiting, err := f.takeInAlerts(path, data)
+		if err != nil {
+			return 0, err
+		}
+
+		entries = waiting
+	}
+
+	return entries, nil
+}
+
+// takeInCache parses data, what the cache file name, at path, holds, and
+// puts it in, as takeIn describes.
+func (f *Files) takeInCache(name, path string, data []byte) (int, error) {
+	switch name {
 	case lookupsJSON:
 		var file lookupsFile
 
@@ -427,9 +624,10 @@ func (f *Files) takeIn(name string, data []byte, edit bool) (int, error) {
 		}
 
 		f.params.GeoJS.Load(file.Lookups)
-		entries = len(file.Lookups)
-	case reputationJSON:
-		var file reputationFile
+
+		return len(file.Lookups), nil
+	case listsJSON:
+		var file listsFile
 
 		err := parse(path, data, &file)
 		if err != nil {
@@ -441,21 +639,43 @@ func (f *Files) takeIn(name string, data []byte, edit bool) (int, error) {
 			return 0, fmt.Errorf("%s: %w", path, err)
 		}
 
-		f.params.DNSBL.Load(file.Verdicts)
-		f.params.AbuseIPDB.Load(file.AbuseIPDB)
-		entries = len(file.Lists)
-	case alertsJSON:
-		waiting, err := f.takeInAlerts(path, data)
+		return len(file.Lists), nil
+	case dnsblJSON:
+		var file dnsblFile
+
+		err := parse(path, data, &file)
 		if err != nil {
 			return 0, err
 		}
 
-		entries = waiting
+		f.params.DNSBL.Load(file.Verdicts)
+
+		return len(file.Verdicts), nil
+	case routeWatchJSON:
+		var file routeWatchFile
+
+		err := parse(path, data, &file)
+		if err != nil {
+			return 0, err
+		}
+
+		if f.params.RouteWatch != nil {
+			f.params.RouteWatch.Load(file.Answers)
+		}
+
+		return len(file.Answers), nil
+	default: // abuseipdb-scores.json
+		var file abuseIPDBScoresFile
+
+		err := parse(path, data, &file)
+		if err != nil {
+			return 0, err
+		}
+
+		f.params.AbuseIPDB.Load(file.Scores)
+
+		return len(file.Scores), nil
 	}
-
-	f.sums[name] = sha256.Sum256(data)
-
-	return entries, nil
 }
 
 // takeInAlerts parses data, what alerts.json, at path, holds, puts it
@@ -493,17 +713,22 @@ func (f *Files) takeInAlerts(path string, data []byte) (int, error) {
 	return entries, nil
 }
 
-// writeFile writes the state file name from what sww holds. An
-// edit made since sww last read or wrote the file is taken in
-// first, so that it is not overwritten, or set aside if it does not
-// parse. A file that cannot be read, or an edit that cannot be set
-// aside, is left as it is, and the write given up. Every write is counted
-// in the metrics, and one that fails or is given up as a failure.
+// writeFile writes the file name from what sww holds. An edit made since
+// sww last read or wrote the file is taken in first, so that it is not
+// overwritten, or set aside if it does not parse. A state file that
+// cannot be read, or an edit that cannot be set aside, is left as it is,
+// and the write given up. A cache file that cannot be read is written
+// over, since what it held is fetched again. Every write is counted in
+// the metrics, and one that fails or is given up as a failure.
 func (f *Files) writeFile(name string) error {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 
 	data, changed, err := f.readChanged(name)
+	if err != nil && isCacheFile(name) {
+		err = nil
+	}
+
 	if err == nil && changed {
 		err = f.takeInEdit(name, data)
 		if err != nil {
@@ -519,7 +744,7 @@ func (f *Files) writeFile(name string) error {
 	}
 
 	if err == nil {
-		err = write(f.params.Dir, name, data)
+		err = write(f.dir(name), name, data)
 	}
 
 	if err == nil {
@@ -527,7 +752,7 @@ func (f *Files) writeFile(name string) error {
 		// fails, so that its next read does not take it for an admin's
 		// edit.
 		f.sums[name] = sha256.Sum256(data)
-		err = syncDirectory(f.params.Dir)
+		err = syncDirectory(f.dir(name))
 	}
 
 	f.params.Metrics.StateFileWritten(name, len(data), err)
@@ -535,20 +760,23 @@ func (f *Files) writeFile(name string) error {
 	return err
 }
 
-// setAside renames the state file name, an edit that does not parse with
+// setAside renames the file name, an edit that does not parse with
 // parseErr, to name.bad, for the admin to mend, and logs it with where in
 // the file the error is, and raises a file_error alert for it. If the
 // rename fails, the edit is left as it is, and the error returned is
 // parseErr joined with the rename's.
 func (f *Files) setAside(name string, parseErr error) error {
-	path := filepath.Join(f.params.Dir, name)
+	path := filepath.Join(f.dir(name), name)
 
 	err := os.Rename(path, path+".bad")
 	if err != nil {
 		return errors.Join(parseErr, err)
 	}
 
-	const setAside = "set aside an edit of a state file that does not parse"
+	setAside := "set aside an edit of a state file that does not parse"
+	if isCacheFile(name) {
+		setAside = "set aside an edit of a cache file that does not parse"
+	}
 
 	// Raised before it is logged, so that the alert is there once the log
 	// line is.
@@ -563,7 +791,7 @@ func (f *Files) setAside(name string, parseErr error) error {
 	return nil
 }
 
-// encode returns the state file name as sww writes it, from a
+// encode returns the file name as sww writes it, from a
 // snapshot of the part that keeps that state.
 func (f *Files) encode(name string) ([]byte, error) {
 	switch name {
@@ -575,10 +803,24 @@ func (f *Files) encode(name string) ([]byte, error) {
 		return encodeOnePerLine("clients", f.params.Limiter.Snapshot())
 	case lookupsJSON:
 		return encodeOnePerLine("lookups", f.params.GeoJS.Snapshot())
-	case reputationJSON:
-		return encodeIndented(reputationFile{
-			Version: version, Lists: f.params.Lists.Snapshot(),
-			Verdicts: f.params.DNSBL.Snapshot(), AbuseIPDB: f.params.AbuseIPDB.Snapshot(),
+	case listsJSON:
+		return encodeIndented(listsFile{Version: version, Lists: f.params.Lists.Snapshot()})
+	case dnsblJSON:
+		return encodeOnePerLine("verdicts", f.params.DNSBL.Snapshot())
+	case abuseIPDBScoresJSON:
+		return encodeOnePerLine("scores", f.params.AbuseIPDB.Snapshot())
+	case routeWatchJSON:
+		var answers []routewatch.Answer
+		if f.params.RouteWatch != nil {
+			answers = f.params.RouteWatch.Snapshot()
+		}
+
+		return encodeOnePerLine("answers", answers)
+	case abuseIPDBChecksSpentJSON:
+		checks := f.params.AbuseIPDB.ChecksSpent()
+
+		return encodeIndented(abuseIPDBChecksSpentFile{
+			Version: version, Day: checks.Day, Spent: checks.Spent,
 		})
 	default: // alerts.json
 		held := f.params.Alerts.Snapshot()
@@ -748,14 +990,8 @@ func (f *lookupsFile) check(data []byte) error {
 // check refuses a list without its URL, which would name no list, or the
 // time it was last tried, which would have it fetched at once, and a copy
 // of it without the time it was fetched, or without its lines, which hold
-// the list. It refuses a verdict without its zone or its client, which
-// would be about no one, whether the zone lists the client, or the time
-// it was fetched, which would drop it, and so an AbuseIPDB score without
-// its client, the score, or the time it was fetched. A verdict's listed is
-// false for a client the zone does not list, and a score can be 0, which
-// the structs cannot tell from a missing one, so each is read again as
-// written.
-func (f *reputationFile) check(data []byte) error {
+// the list.
+func (f *listsFile) check([]byte) error {
 	for i, kept := range f.Lists {
 		switch {
 		case kept.URL == "":
@@ -769,6 +1005,15 @@ func (f *reputationFile) check(data []byte) error {
 		}
 	}
 
+	return nil
+}
+
+// check refuses a verdict without its zone or its client, which would be
+// about no one, whether the zone lists the client, or the time it was
+// fetched, which would drop it. A verdict's listed is false for a client
+// the zone does not list, which Verdict cannot tell from a missing one,
+// so each listed is read again as written.
+func (f *dnsblFile) check(data []byte) error {
 	var written struct {
 		Verdicts []struct {
 			Listed *bool `json:"listed"`
@@ -783,28 +1028,27 @@ func (f *reputationFile) check(data []byte) error {
 	for i, verdict := range f.Verdicts {
 		switch {
 		case verdict.Zone == "":
-			return fmt.Errorf("verdicts %w", missing(i, "zone"))
+			return missing(i, "zone")
 		case !verdict.Client.IsValid():
-			return fmt.Errorf("verdicts %w", missing(i, "client"))
+			return missing(i, "client")
 		case written.Verdicts[i].Listed == nil:
-			return fmt.Errorf("verdicts %w", missing(i, "listed"))
+			return missing(i, "listed")
 		case verdict.Fetched.IsZero():
-			return fmt.Errorf("verdicts %w", missing(i, "fetched"))
+			return missing(i, "fetched")
 		}
 	}
 
-	return checkScores(f.AbuseIPDB.Scores, data)
+	return nil
 }
 
-// checkScores refuses an AbuseIPDB score, of scores, read from data, as
-// reputationFile's check describes.
-func checkScores(scores []reputation.Score, data []byte) error {
+// check refuses an AbuseIPDB score without its client, the score, or the
+// time it was fetched. A score can be 0, which Score cannot tell from a
+// missing one, so each score is read again as written.
+func (f *abuseIPDBScoresFile) check(data []byte) error {
 	var written struct {
-		AbuseIPDB struct {
-			Scores []struct {
-				Score *int64 `json:"score"`
-			} `json:"scores"`
-		} `json:"abuseipdb"`
+		Scores []struct {
+			Score *int64 `json:"score"`
+		} `json:"scores"`
 	}
 
 	err := json.Unmarshal(data, &written)
@@ -812,20 +1056,57 @@ func checkScores(scores []reputation.Score, data []byte) error {
 		return err
 	}
 
-	for i, kept := range scores {
+	for i, kept := range f.Scores {
 		switch {
 		case !kept.Client.IsValid():
-			return fmt.Errorf("abuseipdb scores %w", missing(i, "client"))
-		case written.AbuseIPDB.Scores[i].Score == nil:
-			return fmt.Errorf("abuseipdb scores %w", missing(i, "score"))
+			return missing(i, "client")
+		case written.Scores[i].Score == nil:
+			return missing(i, "score")
 		case kept.Fetched.IsZero():
-			return fmt.Errorf("abuseipdb scores %w", missing(i, "fetched"))
+			return missing(i, "fetched")
 		}
 	}
 
 	return nil
 }
 
+// check refuses an answer without its client, which would answer for
+// nobody, its netblock, or the time routewatch gave it, which would drop
+// it. "" is the netblock of an address without a live route, which Answer
+// cannot tell from a missing one, so each netblock is read again as
+// written.
+func (f *routeWatchFile) check(data []byte) error {
+	var written struct {
+		Answers []struct {
+			Netblock *string `json:"netblock"`
+		} `json:"answers"`
+	}
+
+	err := json.Unmarshal(data, &written)
+	if err != nil {
+		return err
+	}
+
+	for i, answer := range f.Answers {
+		switch {
+		case !answer.Client.IsValid():
+			return missing(i, "client")
+		case written.Answers[i].Netblock == nil:
+			return missing(i, "netblock")
+		case answer.Answered.IsZero():
+			return missing(i, "answered")
+		}
+	}
+
+	return nil
+}
+
+// check refuses nothing, since a missing day or count means no check
+// spent.
+func (f *abuseIPDBChecksSpentFile) check([]byte) error {
+	return nil
+}
+
 // check refuses a cooldown without its event or when its alert was sent,
 // which would hold back no repeat, alerts waiting for a destination with
 // another name than webhook, slack or ntfy, most likely misspelt, an
@@ -947,22 +1228,37 @@ func (f *lookupsFile) toUTC() {
 	}
 }
 
-// toUTC converts every time of each list, verdict and AbuseIPDB score to
-// UTC.
-func (f *reputationFile) toUTC() {
+// toUTC converts both times of each list to UTC.
+func (f *listsFile) toUTC() {
 	for i := range f.Lists {
 		convertToUTC(&f.Lists[i].Tried, &f.Lists[i].Fetched)
 	}
+}
 
+// toUTC converts the time of each verdict to UTC.
+func (f *dnsblFile) toUTC() {
 	for i := range f.Verdicts {
 		convertToUTC(&f.Verdicts[i].Fetched)
 	}
+}
 
-	for i := range f.AbuseIPDB.Scores {
-		convertToUTC(&f.AbuseIPDB.Scores[i].Fetched)
+// toUTC converts the time of each AbuseIPDB score to UTC.
+func (f *abuseIPDBScoresFile) toUTC() {
+	for i := range f.Scores {
+		convertToUTC(&f.Scores[i].Fetched)
 	}
 }
 
+// toUTC converts the time of each answer to UTC.
+func (f *routeWatchFile) toUTC() {
+	for i := range f.Answers {
+		convertToUTC(&f.Answers[i].Answered)
+	}
+}
+
+// toUTC does nothing: abuseipdb-checks-spent.json holds a day, not a time.
+func (f *abuseIPDBChecksSpentFile) toUTC() {}
+
 // toUTC converts every time of each cooldown, of the hour, of each alert
 // waiting and of each anomaly counter to UTC.
 func (f *alertsFile) toUTC() {
@@ -1114,7 +1410,7 @@ func write(dir, name string, data []byte) error {
 
 // syncDirectory syncs dir to the disk, so that a rename in it lasts.
 func syncDirectory(dir string) error {
-	directory, err := os.Open(dir) //nolint:gosec // SWW_STATE_DIR itself
+	directory, err := os.Open(dir) //nolint:gosec // SWW_STATE_DIR or SWW_CACHE_DIR itself
 	if err != nil {
 		return err
 	}
@@ -1124,7 +1420,7 @@ func syncDirectory(dir string) error {
 
 // writeSynced writes data to the file at path, and syncs it to the disk.
 func writeSynced(path string, data []byte) error {
-	//nolint:gosec // a state file's temporary file, in SWW_STATE_DIR
+	//nolint:gosec // a file's temporary file, in SWW_STATE_DIR or SWW_CACHE_DIR
 	file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, fileMode)
 	if err != nil {
 		return err