federating replies and lots of caching

app/activitypub/routes.py

@@ -13,7 +13,7 @@ from app.models import User, Community, CommunityJoinRequest, CommunityMember, C
     PostReply, Instance, PostVote, PostReplyVote, File, AllowedInstances, BannedInstances
 from app.activitypub.util import public_key, users_total, active_half_year, active_month, local_posts, local_comments, \
     post_to_activity, find_actor_or_create, default_context, instance_blocked, find_reply_parent, find_liked_object, \
-    lemmy_site_data, instance_weight
+    lemmy_site_data, instance_weight, cache_key_by_ap_header, is_activitypub_request
 from app.utils import gibberish, get_setting, is_image_url, allowlist_html, html_to_markdown, render_template, \
     domain_from_url, markdown_to_html, community_membership, ap_datetime
 import werkzeug.exceptions
@@ -69,6 +69,7 @@ def webfinger():
 
 
 @bp.route('/.well-known/nodeinfo')
+@cache.cached(timeout=600)
 def nodeinfo():
     nodeinfo_data = {"links": [{"rel": "http://nodeinfo.diaspora.software/ns/schema/2.0",
                                 "href": f"https://{current_app.config['SERVER_NAME']}/nodeinfo/2.0"}]}
@@ -77,6 +78,7 @@ def nodeinfo():
 
 @bp.route('/nodeinfo/2.0')
 @bp.route('/nodeinfo/2.0.json')
+@cache.cached(timeout=600)
 def nodeinfo2():
 
     nodeinfo_data = {
@@ -103,11 +105,13 @@ def nodeinfo2():
 
 
 @bp.route('/api/v3/site')
+@cache.cached(timeout=600)
 def lemmy_site():
     return jsonify(lemmy_site_data())
 
 
 @bp.route('/api/v3/federated_instances')
+@cache.cached(timeout=600)
 def lemmy_federated_instances():
     instances = Instance.query.all()
     linked = []
@@ -133,11 +137,8 @@ def lemmy_federated_instances():
     })
 
 
-def is_activitypub_request():
-    return 'application/ld+json' in request.headers.get('Accept', '') or 'application/activity+json' in request.headers.get('Accept', '')
-
-
 @bp.route('/u/<actor>', methods=['GET'])
+@cache.cached(timeout=10, make_cache_key=cache_key_by_ap_header)
 def user_profile(actor):
     """ Requests to this endpoint can be for a JSON representation of the user, or a HTML rendering of their profile.
     The two types of requests are differentiated by the header """
@@ -290,7 +291,8 @@ def shared_inbox():
                             community = find_actor_or_create(community_ap_id)
                             user = find_actor_or_create(user_ap_id)
                             if user and community:
-                                user.last_seen = datetime.utcnow()
+                                user.last_seen = community.last_active = datetime.utcnow()
+
                                 object_type = request_json['object']['type']
                                 new_content_types = ['Page', 'Article', 'Link', 'Note']
                                 if object_type in new_content_types:  # create a new post
@@ -399,7 +401,7 @@ def shared_inbox():
                                 community = find_actor_or_create(community_ap_id)
                                 user = find_actor_or_create(user_ap_id)
                                 if user and community:
-                                    user.last_seen = datetime.utcnow()
+                                    user.last_seen = community.last_active = datetime.utcnow()
                                     object_type = request_json['object']['object']['type']
                                     new_content_types = ['Page', 'Article', 'Link', 'Note']
                                     if object_type in new_content_types:      # create a new post
@@ -853,6 +855,13 @@ def shared_inbox():
                                     activity_log.result = 'success'
                                 else:
                                     activity_log.exception_message = 'Could not find user or content for vote'
+                        # Flush the caches of any major object that was created. To be sure.
+                        if 'user' in vars() and user is not None:
+                            user.flush_cache()
+                        #if 'community' in vars() and community is not None:
+                        #    community.flush_cache()
+                        if 'post' in vars() and post is not None:
+                            post.flush_cache()
                     else:
                         activity_log.exception_message = 'Instance banned'
             else:
@@ -889,6 +898,7 @@ def community_outbox(actor):
 
 
 @bp.route('/c/<actor>/moderators', methods=['GET'])
+@cache.cached(timeout=10, make_cache_key=cache_key_by_ap_header)
 def community_moderators(actor):
     actor = actor.strip()
     community = Community.query.filter_by(name=actor, banned=False, ap_id=None).first()
@@ -935,6 +945,7 @@ def inbox(actor):
 
 
 @bp.route('/comment/<int:comment_id>', methods=['GET'])
+@cache.cached(timeout=10, make_cache_key=cache_key_by_ap_header)
 def comment_ap(comment_id):
     if is_activitypub_request():
         reply = PostReply.query.get_or_404(comment_id)
@@ -974,6 +985,7 @@ def comment_ap(comment_id):
 
 
 @bp.route('/post/<int:post_id>', methods=['GET', 'POST'])
+@cache.cached(timeout=10, make_cache_key=cache_key_by_ap_header)
 def post_ap(post_id):
     if request.method == 'GET' and is_activitypub_request():
         post = Post.query.get_or_404(post_id)

app/activitypub/util.py

@@ -2,7 +2,7 @@ import json
 import os
 from datetime import datetime
 from typing import Union, Tuple
-from flask import current_app
+from flask import current_app, request
 from sqlalchemy import text
 from app import db, cache
 from app.models import User, Post, Community, BannedInstances, File, PostReply, AllowedInstances, Instance
@@ -405,6 +405,15 @@ def instance_weight(domain):
     return 1.0
 
 
+def is_activitypub_request():
+    return 'application/ld+json' in request.headers.get('Accept', '') or 'application/activity+json' in request.headers.get('Accept', '')
+
+
+# differentiate between cached JSON and cached HTML by appending is_activitypub_request() to the cache key
+def cache_key_by_ap_header(**kwargs):
+    return request.path + "_" + str(is_activitypub_request())
+
+
 def lemmy_site_data():
     data = {
       "site_view": {

app/community/routes.py

@@ -16,7 +16,8 @@ from app.models import User, Community, CommunityMember, CommunityJoinRequest, C
     File, PostVote
 from app.community import bp
 from app.utils import get_setting, render_template, allowlist_html, markdown_to_html, validation_required, \
-    shorten_string, markdown_to_text, domain_from_url, validate_image, gibberish, community_membership, ap_datetime
+    shorten_string, markdown_to_text, domain_from_url, validate_image, gibberish, community_membership, ap_datetime, \
+    request_etag_matches, return_304
 import os
 from PIL import Image, ImageOps
 from datetime import datetime
@@ -87,6 +88,12 @@ def add_remote():
 
 # @bp.route('/c/<actor>', methods=['GET']) - defined in activitypub/routes.py, which calls this function for user requests. A bit weird.
 def show_community(community: Community):
+
+    # If nothing has changed since their last visit, return HTTP 304
+    current_etag = f"{community.id}_{hash(community.last_active)}"
+    if request_etag_matches(current_etag):
+        return return_304(current_etag)
+
     mods = community.moderators()
 
     is_moderator = current_user.is_authenticated and any(mod.user_id == current_user.id for mod in mods)
@@ -110,7 +117,7 @@ def show_community(community: Community):
     return render_template('community/community.html', community=community, title=community.title,
                            is_moderator=is_moderator, is_owner=is_owner, mods=mod_list, posts=posts, description=description,
                            og_image=og_image, POST_TYPE_IMAGE=POST_TYPE_IMAGE, POST_TYPE_LINK=POST_TYPE_LINK, SUBSCRIPTION_PENDING=SUBSCRIPTION_PENDING,
-                           SUBSCRIPTION_MEMBER=SUBSCRIPTION_MEMBER)
+                           SUBSCRIPTION_MEMBER=SUBSCRIPTION_MEMBER, etag=f"{community.id}_{hash(community.last_active)}")
 
 
 @bp.route('/<actor>/subscribe', methods=['GET'])

app/models.py

@@ -355,8 +355,6 @@ class User(UserMixin, db.Model):
     def profile_id(self):
         return self.ap_profile_id if self.ap_profile_id else f"https://{current_app.config['SERVER_NAME']}/u/{self.user_name}"
 
-
-
     def created_recently(self):
         return self.created and self.created > datetime.utcnow() - timedelta(days=7)
 
@@ -369,6 +367,10 @@ class User(UserMixin, db.Model):
             return
         return User.query.get(id)
 
+    def flush_cache(self):
+        cache.delete('/u/' + self.user_name + '_False')
+        cache.delete('/u/' + self.user_name + '_True')
+
     def purge_content(self):
         files = File.query.join(Post).filter(Post.user_id == self.id).all()
         for file in files:
@@ -446,6 +448,7 @@ class Post(db.Model):
     image = db.relationship(File, lazy='joined', foreign_keys=[image_id], cascade="all, delete")
     domain = db.relationship('Domain', lazy='joined', foreign_keys=[domain_id])
     author = db.relationship('User', lazy='joined', overlaps='posts', foreign_keys=[user_id])
+    replies = db.relationship('PostReply', lazy='dynamic', backref='post')
 
     def is_local(self):
         return self.ap_id is None or self.ap_id.startswith('https://' + current_app.config['SERVER_NAME'])
@@ -472,6 +475,10 @@ class Post(db.Model):
     def profile_id(self):
         return f"https://{current_app.config['SERVER_NAME']}/post/{self.id}"
 
+    def flush_cache(self):
+        cache.delete(f'/post/{self.id}_False')
+        cache.delete(f'/post/{self.id}_True')
+
 
 class PostReply(db.Model):
     query_class = FullTextSearchQuery
@@ -515,7 +522,10 @@ class PostReply(db.Model):
         return cls.query.filter_by(ap_id=ap_id).first()
 
     def profile_id(self):
-        return f"https://{current_app.config['SERVER_NAME']}/comment/{self.id}"
+        if self.ap_id:
+            return self.ap_id
+        else:
+            return f"https://{current_app.config['SERVER_NAME']}/comment/{self.id}"
 
     # the ap_id of the parent object, whether it's another PostReply or a Post
     def in_reply_to(self):

app/post/routes.py

@@ -1,12 +1,13 @@
 from datetime import datetime
 
-from flask import redirect, url_for, flash, request, make_response, session, Markup, current_app, abort
+from flask import redirect, url_for, flash, current_app, abort
 from flask_login import login_user, logout_user, current_user, login_required
 from flask_babel import _
 from sqlalchemy import or_, desc
 
 from app import db, constants
 from app.activitypub.signature import HttpSignature
+from app.activitypub.util import default_context
 from app.community.util import save_post
 from app.post.forms import NewReplyForm
 from app.community.forms import CreatePostForm
@@ -16,11 +17,18 @@ from app.models import Post, PostReply, \
     PostReplyVote, PostVote, Notification
 from app.post import bp
 from app.utils import get_setting, render_template, allowlist_html, markdown_to_html, validation_required, \
-    shorten_string, markdown_to_text, domain_from_url, validate_image, gibberish, ap_datetime
+    shorten_string, markdown_to_text, domain_from_url, validate_image, gibberish, ap_datetime, return_304, \
+    request_etag_matches
 
 
 def show_post(post_id: int):
     post = Post.query.get_or_404(post_id)
+
+    # If nothing has changed since their last visit, return HTTP 304
+    current_etag = f"{post.id}_{hash(post.last_active)}"
+    if request_etag_matches(current_etag):
+        return return_304(current_etag)
+
     mods = post.community.moderators()
     is_moderator = current_user.is_authenticated and any(mod.user_id == current_user.id for mod in mods)
 
@@ -33,11 +41,12 @@ def show_post(post_id: int):
                           notify_author=form.notify_author.data)
         if post.notify_author and current_user.id != post.user_id:    # todo: check if replier is blocked
             notification = Notification(title=_('Reply: ') + shorten_string(form.body.data), user_id=post.user_id,
-                                        author_id=current_user.id, url=url_for('post.show_post', post_id=post.id))
+                                        author_id=current_user.id, url=url_for('activitypub.post_ap', post_id=post.id))
             db.session.add(notification)
         post.last_active = post.community.last_active = datetime.utcnow()
         post.reply_count += 1
         post.community.post_reply_count += 1
+
         db.session.add(reply)
         db.session.commit()
         reply.ap_id = reply.profile_id()
@@ -47,7 +56,9 @@ def show_post(post_id: int):
         db.session.commit()
         form.body.data = ''
         flash('Your comment has been added.')
-        # todo: flush cache
+
+        post.flush_cache()
+
         # federation
         if not post.community.is_local():    # this is a remote community, send it to the instance that hosts it
             reply_json = {
@@ -100,7 +111,7 @@ def show_post(post_id: int):
         else:                       # local community - send it to followers on remote instances
             ...
 
-        return redirect(url_for('post.show_post',
+        return redirect(url_for('activitypub.post_ap',
                                 post_id=post_id))  # redirect to current page to avoid refresh resubmitting the form
     else:
         replies = post_replies(post.id, 'top')
@@ -112,7 +123,8 @@ def show_post(post_id: int):
     return render_template('post/post.html', title=post.title, post=post, is_moderator=is_moderator,
                            canonical=post.ap_id, form=form, replies=replies, THREAD_CUTOFF_DEPTH=constants.THREAD_CUTOFF_DEPTH,
                            description=description, og_image=og_image, POST_TYPE_IMAGE=constants.POST_TYPE_IMAGE,
-                           POST_TYPE_LINK=constants.POST_TYPE_LINK, POST_TYPE_ARTICLE=constants.POST_TYPE_ARTICLE)
+                           POST_TYPE_LINK=constants.POST_TYPE_LINK, POST_TYPE_ARTICLE=constants.POST_TYPE_ARTICLE,
+                           etag=f"{post.id}_{hash(post.last_active)}")
 
 
 @bp.route('/post/<int:post_id>/<vote_direction>', methods=['GET', 'POST'])
@@ -163,6 +175,7 @@ def post_vote(post_id: int, vote_direction):
         db.session.add(vote)
     current_user.last_seen = datetime.utcnow()
     db.session.commit()
+    post.flush_cache()
     return render_template('post/_post_voting_buttons.html', post=post,
                            upvoted_class=upvoted_class,
                            downvoted_class=downvoted_class)
@@ -214,6 +227,7 @@ def comment_vote(comment_id, vote_direction):
         db.session.add(vote)
     current_user.last_seen = datetime.utcnow()
     db.session.commit()
+    comment.post.flush_cache()
     return render_template('post/_voting_buttons.html', comment=comment,
                            upvoted_class=upvoted_class,
                            downvoted_class=downvoted_class)
@@ -249,7 +263,7 @@ def add_reply(post_id: int, comment_id: int):
         db.session.add(reply)
         if in_reply_to.notify_author and current_user.id != in_reply_to.user_id and in_reply_to.author.ap_id is None:    # todo: check if replier is blocked
             notification = Notification(title=_('Reply: ') + shorten_string(form.body.data), user_id=in_reply_to.user_id,
-                                        author_id=current_user.id, url=url_for('post.show_post', post_id=post.id))
+                                        author_id=current_user.id, url=url_for('activitypub.post_ap', post_id=post.id))
             db.session.add(notification)
         db.session.commit()
         reply.ap_id = reply.profile_id()
@@ -262,7 +276,8 @@ def add_reply(post_id: int, comment_id: int):
         db.session.commit()
         form.body.data = ''
         flash('Your comment has been added.')
-        # todo: flush cache
+
+        post.flush_cache()
 
         # federation
         if not post.community.is_local():    # this is a remote community, send it to the instance that hosts it
@@ -271,13 +286,16 @@ def add_reply(post_id: int, comment_id: int):
                 'id': reply.profile_id(),
                 'attributedTo': current_user.profile_id(),
                 'to': [
-                    'https://www.w3.org/ns/activitystreams#Public'
+                    'https://www.w3.org/ns/activitystreams#Public',
+                    in_reply_to.author.profile_id()
                 ],
                 'cc': [
                     post.community.profile_id(),
+                    current_user.followers_url()
                 ],
                 'content': reply.body_html,
                 'inReplyTo': in_reply_to.profile_id(),
+                'url': reply.profile_id(),
                 'mediaType': 'text/html',
                 'source': {
                     'content': reply.body,
@@ -285,31 +303,28 @@ def add_reply(post_id: int, comment_id: int):
                 },
                 'published': ap_datetime(datetime.utcnow()),
                 'distinguished': False,
-                'audience': post.community.profile_id()
+                'audience': post.community.profile_id(),
+                'contentMap': {
+                    'en': reply.body_html
+                }
             }
             create_json = {
+                '@context': default_context(),
                 'type': 'Create',
                 'actor': current_user.profile_id(),
                 'audience': post.community.profile_id(),
                 'to': [
-                    'https://www.w3.org/ns/activitystreams#Public'
+                    'https://www.w3.org/ns/activitystreams#Public',
+                    in_reply_to.author.profile_id()
                 ],
                 'cc': [
-                    post.community.ap_profile_id
+                    post.community.profile_id(),
+                    current_user.followers_url()
                 ],
                 'object': reply_json,
                 'id': f"https://{current_app.config['SERVER_NAME']}/activities/create/{gibberish(15)}"
             }
             if in_reply_to.notify_author and in_reply_to.author.ap_id is not None:
-                create_json['cc'].append(in_reply_to.author.ap_profile_id)
-                create_json['tag'] = [
-                    {
-                        'href': in_reply_to.author.ap_profile_id,
-                        'name': '@' + in_reply_to.author.ap_id,
-                        'type': 'Mention'
-                    }
-                ]
-                reply_json['cc'].append(in_reply_to.author.ap_profile_id)
                 reply_json['tag'] = [
                     {
                         'href': in_reply_to.author.ap_profile_id,
@@ -327,12 +342,12 @@ def add_reply(post_id: int, comment_id: int):
                     current_app.logger.error('Response code for reply attempt was ' +
                                              str(message.status_code) + ' ' + message.text)
             except Exception as ex:
-                flash('Failed to send request to subscribe: ' + str(ex), 'error')
+                flash('Failed to send reply: ' + str(ex), 'error')
-                current_app.logger.error("Exception while trying to subscribe" + str(ex))
+                current_app.logger.error("Exception while trying to send reply" + str(ex))
         else:                       # local community - send it to followers on remote instances
             ...
         if reply.depth <= constants.THREAD_CUTOFF_DEPTH:
-            return redirect(url_for('post.show_post', post_id=post_id, _anchor=f'comment_{reply.parent_id}'))
+            return redirect(url_for('activitypub.post_ap', post_id=post_id, _anchor=f'comment_{reply.parent_id}'))
         else:
             return redirect(url_for('post.continue_discussion', post_id=post_id, comment_id=reply.parent_id))
     else:
@@ -365,8 +380,9 @@ def post_edit(post_id: int):
             post.community.last_active = datetime.utcnow()
             post.edited_at = datetime.utcnow()
             db.session.commit()
+            post.flush_cache()
             flash(_('Your changes have been saved.'), 'success')
-            return redirect(url_for('post.show_post', post_id=post.id))
+            return redirect(url_for('activitypub.post_ap', post_id=post.id))
         else:
             if post.type == constants.POST_TYPE_ARTICLE:
                 form.type.data = 'discussion'
@@ -392,6 +408,7 @@ def post_delete(post_id: int):
     community = post.community
     if post.user_id == current_user.id or community.is_moderator():
         post.delete_dependencies()
+        post.flush_cache()
         db.session.delete(post)
         db.session.commit()
         flash('Post deleted.')

app/templates/post/_post_teaser.html

@@ -4,7 +4,7 @@
             <div class="row main_row">
                 <div class="col">
                     <h3>
-                        <a href="{{ url_for('post.show_post', post_id=post.id) }}">{{ post.title }}</a>
+                        <a href="{{ url_for('activitypub.post_ap', post_id=post.id) }}">{{ post.title }}</a>
                         {% if post.type == POST_TYPE_IMAGE %}<span class="fe fe-image"> </span>{% endif %}
                         {% if post.type == POST_TYPE_LINK and post.domain_id %}
                             {% if post.url and 'youtube.com' in post.url %}
@@ -19,7 +19,7 @@
                     <span class="small">{{ render_username(post.author) }} · {{ moment(post.posted_at).fromNow() }}</span>
                 {% if post.image_id %}
                     <div class="thumbnail">
-                        <a href="{{ url_for('post.show_post', post_id=post.id) }}"><img src="{{ post.image.thumbnail_url() }}" alt="{{ post.image.alt_text }}"
+                        <a href="{{ url_for('activitypub.post_ap', post_id=post.id) }}"><img src="{{ post.image.thumbnail_url() }}" alt="{{ post.image.alt_text }}"
                                                                                              height="50" /></a>
                     </div>
                 {% endif %}
@@ -28,8 +28,8 @@
             </div>
             <div class="row utilities_row">
                 <div class="col-6">
-                    <a href="{{ url_for('post.show_post', post_id=post.id, _anchor='replies') }}"><span class="fe fe-reply"></span></a>
+                    <a href="{{ url_for('activitypub.post_ap', post_id=post.id, _anchor='replies') }}"><span class="fe fe-reply"></span></a>
-                    <a href="{{ url_for('post.show_post', post_id=post.id, _anchor='replies') }}">{{ post.reply_count }}</a>
+                    <a href="{{ url_for('activitypub.post_ap', post_id=post.id, _anchor='replies') }}">{{ post.reply_count }}</a>
                 </div>
                 <div class="col-2"><a href="{{ url_for('post.post_options', post_id=post.id) }}"><span class="fe fe-options" title="Options"> </span></a></div>
             </div>

app/templates/post/continue_discussion.html

@@ -5,7 +5,7 @@
 <div class="row">
     <div class="col-12 col-md-8 position-relative main_pane">
         {% include 'post/_post_full.html' %}
-        <p><a href="{{ url_for('post.show_post', post_id=post.id, _anchor='replies') }}">Back to main discussion</a></p>
+        <p><a href="{{ url_for('activitypub.post_ap', post_id=post.id, _anchor='replies') }}">Back to main discussion</a></p>
         <div class="row post_replies">
             <div class="col">
                 {% macro render_comment(comment) %}

app/templates/user/notifications.html

@@ -93,7 +93,7 @@
                 <div class="card-body">
                         <ul>
                             {% for post in upvoted %}
-                                <li><a href="{{ url_for('post.show_post', post_id=post.id) }}">{{ post.title }}</a></li>
+                                <li><a href="{{ url_for('activitypub.post_ap', post_id=post.id) }}">{{ post.title }}</a></li>
                             {% endfor %}
                         </ul>
 

app/templates/user/show_profile.html

@@ -143,7 +143,7 @@
 
                         <ul>
                             {% for post in upvoted %}
-                                <li><a href="{{ url_for('post.show_post', post_id=post.id) }}">{{ post.title }}</a></li>
+                                <li><a href="{{ url_for('activitypub.post_ap', post_id=post.id) }}">{{ post.title }}</a></li>
                             {% endfor %}
                         </ul>
 

app/user/routes.py

@@ -4,7 +4,7 @@ from flask import redirect, url_for, flash, request, make_response, session, Mar
 from flask_login import login_user, logout_user, current_user, login_required
 from flask_babel import _
 
-from app import db
+from app import db, cache
 from app.models import Post, Community, CommunityMember, User, PostReply, PostVote, Notification
 from app.user import bp
 from app.user.forms import ProfileForm, SettingsForm
@@ -47,9 +47,11 @@ def edit_profile(actor):
         if form.password_field.data.strip() != '':
             current_user.set_password(form.password_field.data)
         current_user.about = form.about.data
+        current_user.flush_cache()
         db.session.commit()
 
         flash(_('Your changes have been saved.'), 'success')
+
         return redirect(url_for('user.edit_profile', actor=actor))
     elif request.method == 'GET':
         form.email.data = current_user.email

app/utils.py

@@ -11,7 +11,7 @@ from bs4 import BeautifulSoup
 import requests
 import os
 import imghdr
-from flask import current_app, json, redirect, url_for, request
+from flask import current_app, json, redirect, url_for, request, make_response, Response
 from flask_login import current_user
 from sqlalchemy import text
 
@@ -20,12 +20,33 @@ from app.models import Settings, Domain, Instance, BannedInstances, User, Commun
 
 
 # Flask's render_template function, with support for themes added
-def render_template(template_name: str, **context) -> str:
+def render_template(template_name: str, **context) -> Response:
     theme = get_setting('theme', '')
     if theme != '':
-        return flask.render_template(f'themes/{theme}/{template_name}', **context)
+        content = flask.render_template(f'themes/{theme}/{template_name}', **context)
     else:
-        return flask.render_template(template_name, **context)
+        content = flask.render_template(template_name, **context)
+
+    # Browser caching using ETags and Cache-Control
+    resp = make_response(content)
+    if 'etag' in context:
+        resp.headers.add_header('ETag', context['etag'])
+    resp.headers.add_header('Cache-Control', 'no-cache, max-age=600, must-revalidate')
+    return resp
+
+
+def request_etag_matches(etag):
+    if 'If-None-Match' in request.headers:
+        old_etag = request.headers['If-None-Match']
+        return old_etag == etag
+    return False
+
+
+def return_304(etag):
+    resp = make_response('', 304)
+    resp.headers.add_header('ETag', request.headers['If-None-Match'])
+    resp.headers.add_header('Cache-Control', 'no-cache, max-age=600, must-revalidate')
+    return resp
 
 
 # Jinja: when a file was modified. Useful for cache-busting