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/state/state.go

@@ -222,7 +222,7 @@ func (f *Files) Watch(ctx context.Context) {
 		case event := <-watcher.Events:
 			switch name := filepath.Base(event.Name); name {
 			case bansJSON, clientsJSON, lookupsJSON:
-				f.takeInEdit(name)
+				f.fileChanged(name)
 			}
 		case err = <-watcher.Errors:
 			f.params.ProcessLog.Warn("watching the state files failed",
@@ -239,10 +239,11 @@ func (f *Files) logFailure(err error) {
 	}
 }
 
-// takeInEdit takes in an edit of the state file name and logs it, if the
-// file has changed since smallwebwaf last read or wrote it and parses. A
-// file that cannot be read or does not parse is left for its next write.
-func (f *Files) takeInEdit(name string) {
+// fileChanged takes in what the state file name holds, as Watch sees it
+// change, if that is an edit made since smallwebwaf last read or wrote
+// the file. A file that cannot be read or does not parse is left for its
+// next write.
+func (f *Files) fileChanged(name string) {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 
@@ -251,9 +252,17 @@ func (f *Files) takeInEdit(name string) {
 		return
 	}
 
-	_, err = f.takeIn(name, data)
+	_ = f.takeInEdit(name, data)
+}
+
+// takeInEdit takes in data, an edit of the state file name, as takeIn
+// does, and counts and logs it. Every edit taken in while smallwebwaf
+// 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.
+func (f *Files) takeInEdit(name string, data []byte) error {
+	_, err := f.takeIn(name, data)
 	if err != nil {
-		return
+		return err
 	}
 
 	// Counted before it is logged, so that the count is there once the
@@ -261,6 +270,8 @@ func (f *Files) takeInEdit(name string) {
 	f.params.Metrics.StateFileEditTakenIn(name)
 	f.params.ProcessLog.Info("took in an edit of a state file",
 		"file", filepath.Join(f.params.Dir, name))
+
+	return nil
 }
 
 // read takes in the state file name at start, and returns how many
@@ -357,10 +368,8 @@ func (f *Files) writeFile(name string) error {
 
 	data, changed, err := f.readChanged(name)
 	if err == nil && changed {
-		_, err = f.takeIn(name, data)
-		if err == nil {
-			f.params.Metrics.StateFileEditTakenIn(name)
-		} else {
+		err = f.takeInEdit(name, data)
+		if err != nil {
 			err = f.setAside(name, err)
 		}
 	}

internal/state/state_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"io/fs"
 	"log/slog"
+	"maps"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -774,6 +775,53 @@ func TestEditsTakenInAreCountedInTheMetrics(t *testing.T) {
 		`smallwebwaf_state_file_edits_taken_in_total{file="bans.json"}`, 2)
 }
 
+func TestEditTakenInByAWriteIsLoggedAsWatchLogsIt(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	params := newParams(dir)
+	lines := logInto(&params)
+	files := load(t, params)
+
+	// An edit taken in by Watch, which is then stopped.
+	ctx, stop := context.WithCancel(t.Context())
+	stopped := make(chan struct{})
+
+	go func() {
+		files.Watch(ctx)
+		close(stopped)
+	}()
+
+	lines.waitFor(t, watching)
+	edit(t, dir, bansJSON, `{"version": 1, "bans": []}`)
+	byWatch := lines.waitFor(t, tookIn)
+
+	stop()
+	<-stopped
+
+	// An edit taken in by the write of its file. Nothing logs after the
+	// write, so the log is closed, and a write that does not log the edit
+	// fails the test at once instead of waiting for the line.
+	edit(t, dir, bansJSON, permanentBansJSON)
+
+	err := files.WriteAll()
+	if err != nil {
+		t.Fatalf("write: %v", err)
+	}
+
+	close(lines)
+
+	byWrite := lines.waitFor(t, tookIn)
+
+	// The two lines differ only in their time.
+	delete(byWatch, "time")
+	delete(byWrite, "time")
+
+	if !maps.Equal(byWrite, byWatch) {
+		t.Errorf("the write logged %v, where Watch logged %v", byWrite, byWatch)
+	}
+}
+
 func TestEditsSetAsideAreCountedInTheMetrics(t *testing.T) {
 	t.Parallel()
 
@@ -957,8 +1005,9 @@ func (l processLog) Write(line []byte) (int, error) {
 }
 
 // waitFor returns the next line of the process log whose message is msg,
-// passing over the lines before it. It waits as long as that takes, so
-// that a slow test process cannot fail the test.
+// passing over the lines before it, or nil if the log is closed first. It
+// waits as long as that takes, so that a slow test process cannot fail
+// the test.
 func (l processLog) waitFor(t *testing.T, msg string) map[string]any {
 	t.Helper()
 
@@ -975,7 +1024,7 @@ func (l processLog) waitFor(t *testing.T, msg string) map[string]any {
 		}
 	}
 
-	return nil // never reached: nothing closes the log
+	return nil
 }
 
 // wantTakenIn waits for the next edit taken in, and checks that it is of