Fix Back-Forward-Cache Lighthouse error by adding proper Cache-Control headers

app.py

@@ -1,4 +1,4 @@
-from flask import Flask, render_template, request, redirect, url_for, session, abort, jsonify, g
+from flask import Flask, render_template, request, redirect, url_for, session, abort, jsonify, g, make_response
 from flask_babel import Babel, gettext, ngettext, get_locale
 from datetime import datetime, timedelta
 import numpy as np
@@ -20,7 +20,23 @@ app.config['BABEL_TRANSLATION_DIRECTORIES'] = 'translations'
 babel = Babel()
 
 # Version der App
-APP_VERSION = "1.4.10"
+APP_VERSION = "1.4.11"
+
+def add_cache_headers(response):
+    """Fügt Cache-Control-Header hinzu, die den Back-Forward-Cache ermöglichen"""
+    # Cache-Control für statische Inhalte und API-Endpunkte
+    if request.path.startswith('/static/') or request.path.startswith('/api/'):
+        response.headers['Cache-Control'] = 'public, max-age=3600, s-maxage=3600'
+    else:
+        # Für HTML-Seiten: kurze Cache-Zeit, aber Back-Forward-Cache erlauben
+        response.headers['Cache-Control'] = 'public, max-age=60, s-maxage=300'
+    
+    # Wichtig: Keine Vary-Header für User-Agent oder andere dynamische Werte
+    # Dies verhindert den Back-Forward-Cache
+    if 'Vary' in response.headers:
+        del response.headers['Vary']
+    
+    return response
 
 # HTML-Template wird jetzt aus templates/index.html geladen
 
@@ -229,9 +245,10 @@ def index():
                             plusminus_result = f"Datum {d.strftime('%d.%m.%Y')} {'plus' if anzahl_int>=0 else 'minus'} {abs(anzahl_int)} Monate: {result.strftime('%d.%m.%Y')}"
             except Exception:
                 plusminus_result = gettext('Ungültige Eingabe')
-    return render_template('index.html', tage=tage, werktage=werktage, wochentag=wochentag, plusminus_result=plusminus_result, kw_berechnen=kw_berechnen, kw_datum=kw_datum, active_idx=active_idx
+    response = make_response(render_template('index.html', tage=tage, werktage=werktage, wochentag=wochentag, plusminus_result=plusminus_result, kw_berechnen=kw_berechnen, kw_datum=kw_datum, active_idx=active_idx
         , feiertage_anzahl=feiertage_anzahl, wochenendtage_anzahl=wochenendtage_anzahl, app_version=APP_VERSION, get_locale=get_locale
-    )
+    ))
+    return add_cache_headers(response)
 
 
 def parse_log_stats(log_path):
@@ -304,11 +321,14 @@ def stats():
                 session['stats_auth'] = True
                 return redirect(url_for('stats'))
             else:
-                return render_template('stats_login.html', error='Falsches Passwort!')
-        return render_template('stats_login.html', error=None)
+                        response = make_response(render_template('stats_login.html', error='Falsches Passwort!'))
+        return add_cache_headers(response)
+    response = make_response(render_template('stats_login.html', error=None))
+    return add_cache_headers(response)
     log_path = os.path.join('log', 'pageviews.log')
     pageviews, func_counts, func_counts_hourly, impressions_per_day, impressions_per_hour, api_counts, api_counts_hourly = parse_log_stats(log_path)
-    return render_template('stats_dashboard.html', pageviews=pageviews, func_counts=func_counts, func_counts_hourly=func_counts_hourly, impressions_per_day=impressions_per_day, impressions_per_hour=impressions_per_hour, api_counts=api_counts, api_counts_hourly=api_counts_hourly)
+    response = make_response(render_template('stats_dashboard.html', pageviews=pageviews, func_counts=func_counts, func_counts_hourly=func_counts_hourly, impressions_per_day=impressions_per_day, impressions_per_hour=impressions_per_hour, api_counts=api_counts, api_counts_hourly=api_counts_hourly))
+    return add_cache_headers(response)
 
 # --- REST API ---
 def log_api_usage(api_name):
@@ -342,7 +362,8 @@ def api_tage_werktage():
             tage = int(np.busday_count(d1.date(), (d2 + timedelta(days=1)).date(), holidays=holidays))
         else:
             tage = abs((d2 - d1).days)
-        return jsonify({'result': tage})
+        response = jsonify({'result': tage})
+        return add_cache_headers(response)
     except Exception as e:
         return jsonify({'error': 'Ungültige Eingabe', 'details': str(e)}), 400
 
@@ -355,7 +376,8 @@ def api_wochentag():
         d = datetime.strptime(datum, '%Y-%m-%d')
         wochentage = get_wochentage()
         wochentag = wochentage[d.weekday()]
-        return jsonify({'result': wochentag})
+        response = jsonify({'result': wochentag})
+        return add_cache_headers(response)
     except Exception as e:
         return jsonify({'error': 'Ungültige Eingabe', 'details': str(e)}), 400
 
@@ -372,7 +394,8 @@ def api_kw_berechnen():
             kw_berechnen = f"Week {kw} ({d.year})"
         else:
             kw_berechnen = f"KW {kw} ({d.year})"
-        return jsonify({'result': kw_berechnen, 'kw': kw, 'jahr': d.year})
+        response = jsonify({'result': kw_berechnen, 'kw': kw, 'jahr': d.year})
+        return add_cache_headers(response)
     except Exception as e:
         return jsonify({'error': 'Ungültige Eingabe', 'details': str(e)}), 400
 
@@ -392,7 +415,8 @@ def api_kw_datum():
             kw_datum = f"{start.strftime('%m/%d/%Y')} to {end.strftime('%m/%d/%Y')}"
         else:
             kw_datum = f"{start.strftime('%d.%m.%Y')} bis {end.strftime('%d.%m.%Y')}"
-        return jsonify({'result': kw_datum, 'start': start.strftime('%Y-%m-%d'), 'end': end.strftime('%Y-%m-%d')})
+        response = jsonify({'result': kw_datum, 'start': start.strftime('%Y-%m-%d'), 'end': end.strftime('%Y-%m-%d')})
+        return add_cache_headers(response)
     except Exception as e:
         return jsonify({'error': 'Ungültige Eingabe', 'details': str(e)}), 400
 
@@ -415,22 +439,26 @@ def api_plusminus():
             if is_werktage:
                 result = np.busday_offset(d.date(), anzahl_int, roll='forward')
                 result_dt = datetime.strptime(str(result), '%Y-%m-%d')
-                return jsonify({'result': result_dt.strftime('%Y-%m-%d')})
+                response = jsonify({'result': result_dt.strftime('%Y-%m-%d')})
+                return add_cache_headers(response)
             else:
                 result = d + timedelta(days=anzahl_int)
-                return jsonify({'result': result.strftime('%Y-%m-%d')})
+                response = jsonify({'result': result.strftime('%Y-%m-%d')})
+                return add_cache_headers(response)
         elif einheit == 'wochen':
             if is_werktage:
                 return jsonify({'error': 'Nicht unterstützt: Werktage + Wochen.'}), 400
             else:
                 result = d + timedelta(weeks=anzahl_int)
-                return jsonify({'result': result.strftime('%Y-%m-%d')})
+                response = jsonify({'result': result.strftime('%Y-%m-%d')})
+                return add_cache_headers(response)
         elif einheit == 'monate':
             if is_werktage:
                 return jsonify({'error': 'Nicht unterstützt: Werktage + Monate.'}), 400
             else:
                 result = d + relativedelta(months=anzahl_int)
-                return jsonify({'result': result.strftime('%Y-%m-%d')})
+                response = jsonify({'result': result.strftime('%Y-%m-%d')})
+                return add_cache_headers(response)
         else:
             return jsonify({'error': 'Ungültige Einheit'}), 400
     except Exception as e:
@@ -440,12 +468,13 @@ def api_plusminus():
 def api_stats():
     log_path = os.path.join('log', 'pageviews.log')
     pageviews, func_counts, func_counts_hourly, impressions_per_day, impressions_per_hour, api_counts, api_counts_hourly = parse_log_stats(log_path)
-    return jsonify({
+    response = jsonify({
         "pageviews": pageviews,
         "func_counts": func_counts,
         "impressions_per_day": impressions_per_day,
         "api_counts": api_counts
     })
+    return add_cache_headers(response)
 
 @app.route('/api/monitor', methods=['GET'])
 def api_monitor():
@@ -457,17 +486,19 @@ def api_monitor():
                 if 'PAGEVIEW' in line:
                     pageviews += 1
     uptime = int(time.time() - app_start_time)
-    return jsonify({
+    response = jsonify({
         "status": "ok",
         "message": "App running",
         "time": datetime.now().isoformat(),
         "uptime_seconds": uptime,
         "pageviews_last_7_days": pageviews
     })
+    return add_cache_headers(response)
 
 @app.route('/api-docs')
 def api_docs():
-    return render_template('swagger.html')
+    response = make_response(render_template('swagger.html'))
+    return add_cache_headers(response)
 
 
 if __name__ == '__main__':