feat(seo): add sitemap generator

pkg/revalidate/revalidate.go

@@ -0,0 +1,78 @@
+// Package revalidate pings the frontend's on-demand cache revalidation
+// endpoint so sitemap-relevant changes (new signups, content re-seeds) surface
+// within seconds instead of waiting out the frontend's daily ISR window.
+package revalidate
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/url"
+	"time"
+
+	"go.uber.org/zap"
+)
+
+// Client posts to <frontend>/api/revalidate. Safe to use when nil or when the
+// frontend URL / secret are unset — Trigger becomes a no-op (so dev / misconfig
+// never breaks the calling flow).
+type Client struct {
+	base   string
+	secret string
+	logger *zap.Logger
+}
+
+func New(frontendURL, secret string, logger *zap.Logger) *Client {
+	return &Client{
+		base:   trimRightSlash(frontendURL),
+		secret: secret,
+		logger: logger,
+	}
+}
+
+// Trigger fires a fire-and-forget POST to revalidate the given cache tag.
+// Never blocks the caller and never errors out of band — use from request
+// handlers (e.g. signup) on a long-lived server.
+func (c *Client) Trigger(tag string) {
+	if c == nil || c.base == "" || c.secret == "" {
+		return
+	}
+	go func() {
+		if err := c.TriggerSync(tag); err != nil && c.logger != nil {
+			c.logger.Warn("revalidate ping failed", zap.String("tag", tag), zap.Error(err))
+		}
+	}()
+}
+
+// TriggerSync POSTs synchronously and returns any error. Use from short-lived
+// CLIs (e.g. the indexer) that would exit before a background goroutine ran.
+// No-op (nil) when the client / URL / secret is unset.
+func (c *Client) TriggerSync(tag string) error {
+	if c == nil || c.base == "" || c.secret == "" {
+		return nil
+	}
+	endpoint := fmt.Sprintf("%s/api/revalidate?tag=%s&secret=%s",
+		c.base, url.QueryEscape(tag), url.QueryEscape(c.secret))
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, nil)
+	if err != nil {
+		return err
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode >= 300 {
+		return fmt.Errorf("revalidate returned %d", resp.StatusCode)
+	}
+	return nil
+}
+
+func trimRightSlash(s string) string {
+	for len(s) > 0 && s[len(s)-1] == '/' {
+		s = s[:len(s)-1]
+	}
+	return s
+}