Allow users to retrieve posts from remote communities

app/activitypub/util.py

@@ -2326,10 +2326,10 @@ def can_delete(user_ap_id, post):
     return can_edit(user_ap_id, post)
 
 
-def resolve_remote_post(uri: str, community_id: int, announce_actor=None) -> Union[str, None]:
+def resolve_remote_post(uri: str, community_id: int, announce_actor=None) -> Union[Post, None]:
     post = Post.query.filter_by(ap_id=uri).first()
     if post:
-        return post.id
+        return post
 
     community = Community.query.get(community_id)
     site = Site.query.get(1)
@@ -2350,7 +2350,7 @@ def resolve_remote_post(uri: str, community_id: int, announce_actor=None) -> Uni
         # check again that it doesn't already exist (can happen with different but equivilent URLs)
         post = Post.query.filter_by(ap_id=post_data['id']).first()
         if post:
-            return post.id
+            return post
         if 'attributedTo' in post_data:
             if isinstance(post_data['attributedTo'], str):
                 actor = post_data['attributedTo']
@@ -2366,6 +2366,46 @@ def resolve_remote_post(uri: str, community_id: int, announce_actor=None) -> Uni
         if uri_domain != actor_domain:
             return None
 
+        if not announce_actor:
+            # make sure that the post actually belongs in the community a user says it does
+            remote_community = None
+            if post_data['type'] == 'Page':                                          # lemmy
+                remote_community = post_data['audience'] if 'audience' in post_data else None
+                if remote_community and remote_community.lower() != community.ap_profile_id:
+                    return None
+            elif post_data['type'] == 'Video':                                       # peertube
+                if 'attributedTo' in post_data and isinstance(post_data['attributedTo'], list):
+                    for a in post_data['attributedTo']:
+                        if a['type'] == 'Group':
+                            remote_community = a['id']
+                            break
+                if remote_community and remote_community.lower() != community.ap_profile_id:
+                    return None
+            else:                                                                   # mastodon, etc
+                if 'inReplyTo' not in post_data or post_data['inReplyTo'] != None:
+                    return None
+                community_found = False
+                if not community_found and 'to' in post_data and isinstance(post_data['to'], str):
+                    remote_community = post_data['to']
+                    if remote_community.lower() == community.ap_profile_id:
+                        community_found = True
+                if not community_found and 'cc' in post_data and isinstance(post_data['cc'], str):
+                    remote_community = post_data['cc']
+                    if remote_community.lower() == community.ap_profile_id:
+                        community_found = True
+                if not community_found and 'to' in post_data and isinstance(post_data['to'], list):
+                    for t in post_data['to']:
+                        if t.lower() == community.ap_profile_id:
+                            community_found = True
+                            break
+                if not community_found and 'cc' in post_data and isinstance(post_data['cc'], list):
+                    for c in post_data['cc']:
+                        if c.lower() == community.ap_profile_id:
+                            community_found = True
+                            break
+                if not community_found:
+                    return None
+
         activity_log = ActivityPubLog(direction='in', activity_id=post_data['id'], activity_type='Resolve Post', result='failure')
         if site.log_activitypub_json:
             activity_log.activity_json = json.dumps(post_data)
@@ -2378,6 +2418,10 @@ def resolve_remote_post(uri: str, community_id: int, announce_actor=None) -> Uni
             }
             post = create_post(activity_log, community, request_json, user)
             if post:
-                return post.id
+                if 'published' in post_data:
+                    post.posted_at=post_data['published']
+                    post.last_active=post_data['published']
+                    db.session.commit()
+                return post
 
     return None

app/community/forms.py

@@ -262,3 +262,8 @@ class ReportCommunityForm(FlaskForm):
 
 class DeleteCommunityForm(FlaskForm):
     submit = SubmitField(_l('Delete community'))
+
+
+class RetrieveRemotePost(FlaskForm):
+    address = StringField(_l('Full URL'), render_kw={'placeholder': 'e.g. https://lemmy.world/post/123', 'autofocus': True}, validators=[DataRequired()])
+    submit = SubmitField(_l('Retrieve'))

app/community/routes.py

@@ -10,12 +10,12 @@ from sqlalchemy import or_, desc, text
 
 from app import db, constants, cache
 from app.activitypub.signature import RsaKeys, post_request, default_context
-from app.activitypub.util import notify_about_post, make_image_sizes
+from app.activitypub.util import notify_about_post, make_image_sizes, resolve_remote_post
 from app.chat.util import send_message
 from app.community.forms import SearchRemoteCommunity, CreateDiscussionForm, CreateImageForm, CreateLinkForm, \
     ReportCommunityForm, \
     DeleteCommunityForm, AddCommunityForm, EditCommunityForm, AddModeratorForm, BanUserCommunityForm, \
-    EscalateReportForm, ResolveReportForm, CreateVideoForm, CreatePollForm
+    EscalateReportForm, ResolveReportForm, CreateVideoForm, CreatePollForm, RetrieveRemotePost
 from app.community.util import search_for_community, actor_to_community, \
     opengraph_parse, url_to_thumbnail_file, save_post, save_icon_file, save_banner_file, send_to_remote_instance, \
     delete_post_from_community, delete_post_reply_from_community, community_in_list
@@ -129,6 +129,24 @@ def add_remote():
                            joined_communities=joined_communities(current_user.get_id()))
 
 
+@bp.route('/retrieve_remote_post/<int:community_id>', methods=['GET', 'POST'])
+@login_required
+def retrieve_remote_post(community_id: int):
+    if current_user.banned:
+        return show_ban_message()
+    form = RetrieveRemotePost()
+    new_post = None
+    community = Community.query.get_or_404(community_id)
+    if form.validate_on_submit():
+        address = form.address.data.strip()
+        new_post =  resolve_remote_post(address, community_id)
+        if new_post is None:
+            flash(_('Post not found.'), 'warning')
+
+    return render_template('community/retrieve_remote_post.html',
+                           title=_('Retrieve Remote Post'), form=form, new_post=new_post, community=community)
+
+
 # @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):
 

app/templates/community/community.html

@@ -151,6 +151,9 @@
                     <p>
                        <a href="{{ community.profile_id() }}">View community on original server</a>
                     </p>
+                    <p>
+                       <a href="/community/retrieve_remote_post/{{ community.id }}">Retrieve a post from the original server</a>
+                    </p>
                 {% endif %}
                 {% if community.local_only %}
                 <p>{{ _('Only people on %(instance_name)s can post or reply in this community.', instance_name=current_app.config['SERVER_NAME']) }}</p>

app/templates/community/retrieve_remote_post.html

@@ -0,0 +1,37 @@
+{% if theme() and file_exists('app/templates/themes/' + theme() + '/base.html') %}
+    {% extends 'themes/' + theme() + '/base.html' %}
+{% else %}
+    {% extends "base.html" %}
+{% endif %} %}
+{% from 'bootstrap/form.html' import render_form %}
+
+{% block app_content %}
+        <div class="row">
+            <div class="col mx-auto">
+                <div class="card mt-5">
+                    <div class="card-body p-6">
+                        <div class="card-title">{{ _('Retrieve Remote Post') }}</div>
+                        <p>Enter the full URL of the post submitted to {{ community.ap_id }}</p>
+                        <p>Note: URL needs to match the one from the post author's instance (which may be different than the community's instance)</p>
+                        {{ render_form(form) }}
+                    </div>
+                </div>
+            </div>
+        </div>
+        {% if new_post %}
+            <div class="row">
+                <div class="col mx-auto">
+                    <div class="card mt-5">
+                        <div class="card-body p-6">
+                            <div class="card-title">{{ _('Found a post:') }}</div>
+                            <div class="card-body">
+                                <p>
+                                    <a href="/post/{{ new_post.id }}">{{ new_post.title }}</a>
+                                </p>
+                            </div>
+                        </div>
+                    </div>
+                </div>
+            </div>
+        {% endif %}
+{% endblock %}