feat: IndexNow key, key file and pings

- saving with IndexNow on generates a 32-hex key (crypto/rand);
  indexnow_new_key generates a new one, so the old key file answers 404
- GET /_sitemap/indexnow/{file} serves <key>.txt as text/plain while
  IndexNow is on; the SEO layer maps it to the site root
- after each rebuild in production the added, changed and removed
  addresses on the site host are queued as golem15.sitemap.indexnow jobs
  (at most 10 000 per request, five attempts)
- the job posts {host, key, urlList} to api.indexnow.org through a
  fetchguard client limited to that host and records the answer; 429 and
  5xx retry, 400, 403 and 422 do not
- the IndexNow tab shows the S2 status partial: key or no key, last
  notification or never, and the 403, 422 and 429 callouts

controllers/api/indexnow.go

@@ -0,0 +1,49 @@
+// Package api holds the sitemap plugin's HTTP handlers outside the admin:
+// the IndexNow key file, the HTML sitemap API and the management API.
+package api
+
+import (
+	"net/http"
+
+	"git.golem15.com/golem15/sm-sitemap-plugin/classes"
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"gorm.io/gorm"
+)
+
+// KeyFilePattern is the {file} constraint of the key file route: an
+// IndexNow key file name, <key>.txt.
+const KeyFilePattern = `[A-Za-z0-9-]{8,128}\.txt`
+
+// KeyFile serves GET /_sitemap/indexnow/{file}: the IndexNow key as
+// text/plain when IndexNow is on and file is <key>.txt; any other name, a
+// replaced key or IndexNow off answers 404 (D-31). The SEO layer serves it
+// at the site root.
+func KeyFile(app func() *backpack.App) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		a := app()
+		if a == nil {
+			http.NotFound(w, r)
+			return
+		}
+		db, ok := a.Lookup[*gorm.DB]()
+		if !ok || db == nil {
+			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+			return
+		}
+		settings, err := classes.LoadSettings(db.WithContext(r.Context()))
+		if err != nil {
+			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+			return
+		}
+		key := classes.ActiveKey(settings)
+		if key == "" || r.PathValue("file") != classes.KeyFileName(key) {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.Header().Set("Cache-Control", "no-cache, private")
+		w.Header().Set("X-Robots-Tag", "noindex")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte(key))
+	}
+}

controllers/settings.go

@@ -3,6 +3,9 @@ package controllers
 import (
 	"context"
 	"errors"
+	"net/http"
+	"strconv"
+	"strings"
 	"time"
 
 	"git.golem15.com/golem15/sm-sitemap-plugin/classes"
@@ -84,18 +87,44 @@ func (c settingsAdminController) FormBeforeCreate(ctx context.Context, model any
 	return c.FormBeforeUpdate(ctx, model)
 }
 
-// FormAfterUpdate dispatches a rebuild once the save commits (C26: saving
-// the form rebuilds the files now). A queue error is logged and never fails
-// the save.
-func (c settingsAdminController) FormAfterUpdate(ctx context.Context, _ any) error {
+// FormVirtualFields names indexnow_new_key, the "generate a new key on
+// save" checkbox, which is no column.
+func (settingsAdminController) FormVirtualFields() []string {
+	return []string{"indexnow_new_key"}
+}
+
+// FormAfterUpdate generates the IndexNow key (on the first save with
+// IndexNow on, or a new one when indexnow_new_key is checked) and
+// dispatches a rebuild once the save commits (C26: saving the form rebuilds
+// the files now). A queue error is logged and never fails the save.
+func (c settingsAdminController) FormAfterUpdate(ctx context.Context, model any) error {
 	app := appOf(c.app)
 	tx, err := database(ctx, c.app)
 	if err != nil || app == nil {
 		return nil
 	}
+	if s, ok := model.(*models.Settings); ok && s != nil {
+		values, _ := cabana.VirtualFieldsFromContext(ctx)
+		if _, err := classes.EnsureKey(tx, s.IndexNowEnabled, boolOf(values["indexnow_new_key"])); err != nil {
+			return err
+		}
+	}
 	return classes.RequestRebuild(ctx, app, tx)
 }
 
+// boolOf reads a submitted checkbox value.
+func boolOf(v any) bool {
+	switch b := v.(type) {
+	case bool:
+		return b
+	case string:
+		return b == "1" || strings.EqualFold(b, "true") || strings.EqualFold(b, "on")
+	case float64:
+		return b != 0
+	}
+	return false
+}
+
 // FormAfterCreate dispatches a rebuild like an update.
 func (c settingsAdminController) FormAfterCreate(ctx context.Context, model any) error {
 	return c.FormAfterUpdate(ctx, model)
@@ -135,10 +164,62 @@ func (c settingsAdminController) PartialData(ctx context.Context, name string, _
 		return c.filesData(ctx)
 	case "news_sources":
 		return c.newsSourcesData(ctx)
+	case "indexnow_status":
+		return c.indexNowData(ctx)
 	}
 	return nil, nil
 }
 
+// indexNowView is the view model of the S2 partial indexnow_status.
+type indexNowView struct {
+	Key      string
+	Last     string
+	Callout  string
+	Severity string
+}
+
+// indexNowData serves S2 (UI-SPEC C26): indexnow.key or indexnow.no_key,
+// indexnow.last or indexnow.never, and the callout of the last answer: 403
+// err_key (warning), 422 err_host (warning), 429 err_rate with the next
+// attempt (plain) while one is pending.
+func (c settingsAdminController) indexNowData(ctx context.Context) (any, error) {
+	app := appOf(c.app)
+	db, err := database(ctx, c.app)
+	if err != nil {
+		return nil, err
+	}
+	settings, err := classes.LoadSettings(db)
+	if err != nil {
+		return nil, err
+	}
+	st := classes.LoadIndexNowStatus(db, app, settings)
+	tr := translator(c.app)
+	view := indexNowView{}
+	if st.Key == "" {
+		view.Key = Phrase(ctx, tr, "golem15.sitemap::lang.indexnow.no_key", nil)
+	} else {
+		view.Key = Phrase(ctx, tr, "golem15.sitemap::lang.indexnow.key", map[string]string{"key": st.Key, "url": st.KeyURL})
+	}
+	if st.LastAt == nil {
+		view.Last = Phrase(ctx, tr, "golem15.sitemap::lang.indexnow.never", nil)
+	} else {
+		view.Last = Phrase(ctx, tr, "golem15.sitemap::lang.indexnow.last", map[string]string{
+			"time": formatTime(st.LastAt), "count": strconv.Itoa(st.LastCount), "status": strconv.Itoa(st.LastStatus),
+		})
+	}
+	switch st.LastStatus {
+	case http.StatusForbidden:
+		view.Callout, view.Severity = Phrase(ctx, tr, "golem15.sitemap::lang.indexnow.err_key", map[string]string{"url": st.KeyURL}), "warning"
+	case http.StatusUnprocessableEntity:
+		view.Callout, view.Severity = Phrase(ctx, tr, "golem15.sitemap::lang.indexnow.err_host", nil), "warning"
+	case http.StatusTooManyRequests:
+		if st.RetryAt != nil {
+			view.Callout = Phrase(ctx, tr, "golem15.sitemap::lang.indexnow.err_rate", map[string]string{"time": formatTime(st.RetryAt)})
+		}
+	}
+	return view, nil
+}
+
 // sourceRow is one row of the news_sources partial: the value to enter and
 // what it lists.
 type sourceRow struct {
@@ -337,4 +418,5 @@ var (
 	_ pact.FormBeforeUpdate  = settingsAdminController{}
 	_ pact.FormAfterCreate   = settingsAdminController{}
 	_ pact.FormAfterUpdate   = settingsAdminController{}
+	_ pact.FormVirtualFields = settingsAdminController{}
 )

controllers/settings/_indexnow_status.htm

@@ -0,0 +1,15 @@
+<div class="summer-callout" role="status">
+<p class="summer-callout__text">{{ .Data.Key }}</p>
+<p class="summer-callout__text">{{ .Data.Last }}</p>
+</div>
+{{- if .Data.Callout -}}
+{{- if eq .Data.Severity "warning" -}}
+<div class="summer-callout summer-callout--warning" role="alert">
+<p class="summer-callout__text">{{ .Data.Callout }}</p>
+</div>
+{{- else -}}
+<div class="summer-callout" role="status">
+<p class="summer-callout__text">{{ .Data.Callout }}</p>
+</div>
+{{- end -}}
+{{- end -}}