bridgy-fed/activitypub.py

"""Handles requests for ActivityPub endpoints: actors, inbox, etc.
"""
from base64 import b64encode
import datetime
from hashlib import sha256
import logging
import re

from flask import request
from google.cloud import ndb
from google.cloud.ndb import OR
from granary import as2
from oauth_dropins.webutil import flask_util, util
from oauth_dropins.webutil.flask_util import error
from oauth_dropins.webutil.util import json_dumps, json_loads

from app import app, cache
import common
from common import redirect_unwrap, redirect_wrap
from models import Activity, Follower, User
from httpsig.requests_auth import HTTPSignatureAuth

logger = logging.getLogger(__name__)

CACHE_TIME = datetime.timedelta(seconds=15)

SUPPORTED_TYPES = (
    'Accept',
    'Announce',
    'Article',
    'Audio',
    'Create',
    'Delete',
    'Follow',
    'Image',
    'Like',
    'Note',
    'Undo',
    'Video',
)


def send(activity, inbox_url, user_domain):
    """Sends an ActivityPub request to an inbox.

    Args:
      activity: dict, AS2 activity
      inbox_url: string
      user_domain: string, domain of the bridgy fed user sending the request

    Returns:
      requests.Response
    """
    logger.info(f'Sending AP request from {user_domain}: {json_dumps(activity, indent=2)}')

    # prepare HTTP Signature (required by Mastodon)
    # https://w3c.github.io/activitypub/#authorization
    # https://tools.ietf.org/html/draft-cavage-http-signatures-07
    # https://github.com/tootsuite/mastodon/issues/4906#issuecomment-328844846
    key_id = request.host_url + user_domain
    user = User.get_or_create(user_domain)
    auth = HTTPSignatureAuth(secret=user.private_pem(), key_id=key_id,
                             algorithm='rsa-sha256', sign_header='signature',
                             headers=('Date', 'Digest', 'Host'))

    # deliver to inbox
    body = json_dumps(activity).encode()
    headers = {
        'Content-Type': common.CONTENT_TYPE_AS2,
        # required for HTTP Signature
        # https://tools.ietf.org/html/draft-cavage-http-signatures-07#section-2.1.3
        'Date': datetime.datetime.utcnow().strftime('%a, %d %b %Y %H:%M:%S GMT'),
        # required by Mastodon
        # https://github.com/tootsuite/mastodon/pull/14556#issuecomment-674077648
        'Digest': 'SHA-256=' + b64encode(sha256(body).digest()).decode(),
        'Host': util.domain_from_link(inbox_url, minimize=False),
    }
    return common.requests_post(inbox_url, data=body, auth=auth,
                                headers=headers)


@app.get(f'/<regex("{common.DOMAIN_RE}"):domain>')
@flask_util.cached(cache, CACHE_TIME)
def actor(domain):
    """Fetches a domain's h-card and converts to AS2 actor."""
    actor = common.actor(domain)
    return (actor, {
        'Content-Type': common.CONTENT_TYPE_AS2,
        'Access-Control-Allow-Origin': '*',
    })


@app.post(f'/inbox')
@app.post(f'/<regex("{common.DOMAIN_RE}"):domain>/inbox')
def inbox(domain=None):
    """Handles ActivityPub inbox delivery."""
    body = request.get_data(as_text=True)
    logger.info(f'Got: {body}')

    # parse and validate AS2 activity
    try:
        activity = request.json
        assert activity
    except (TypeError, ValueError, AssertionError):
        error("Couldn't parse body as JSON", exc_info=True)

    logger.info(f'Got: {json_dumps(activity, indent=2)}')

    obj = activity.get('object') or {}
    if isinstance(obj, str):
        obj = {'id': obj}

    type = activity.get('type')
    if type == 'Accept':  # eg in response to a Follow
        return ''  # noop
    if type not in SUPPORTED_TYPES:
        error('Sorry, %s activities are not supported yet.' % type,
                     status=501)

    # TODO: verify signature if there is one

    if type == 'Undo' and obj.get('type') == 'Follow':
        # skip actor fetch below; we don't need it to undo a follow
        undo_follow(redirect_unwrap(activity))
        return ''
    elif type == 'Delete':
        # we currently only actually delete followers for Deletes that are sent
        # to the shared inbox, not individual users' inboxes, to help scaling
        # background: https://github.com/snarfed/bridgy-fed/issues/284
        if domain:
            logger.info('Skipping Delete sent to individual user inbox')
            return 'OK'

        id = obj.get('id') if isinstance(obj, dict) else obj
        if not isinstance(id, str):
            error("Couldn't find id of object to delete")
            # assume this is an actor
            # https://github.com/snarfed/bridgy-fed/issues/63
        logger.info(f'Deactivating Followers with src or dest = {id}')
        followers = Follower.query(OR(Follower.src == id,
                                      Follower.dest == id)
                                   ).fetch()
        for f in followers:
            f.status = 'inactive'
        ndb.put_multi(followers)
        return 'OK'

    # fetch actor if necessary so we have name, profile photo, etc
    actor = activity.get('actor')
    if actor and isinstance(actor, str):
        actor = activity['actor'] = common.get_as2(actor).json()

    activity_unwrapped = redirect_unwrap(activity)
    if type == 'Follow':
        return accept_follow(activity, activity_unwrapped)

    # send webmentions to each target
    as1 = as2.to_as1(activity)
    source_as2 = json_dumps(activity_unwrapped)
    sent = common.send_webmentions(as1, proxy=True, protocol='activitypub',
                                   source_as2=source_as2)

    if not sent and type in ('Create', 'Announce'):
        # check that this activity is public. only do this check for Creates,
        # not Like, Follow, or other activity types, since Mastodon doesn't
        # currently mark those as explicitly public.
        if not as2.is_public(activity_unwrapped):
            logging.info('Dropping non-public activity')
            return ''

        # normal post, deliver to BF followers
        source = activity.get('url') or activity.get('id')
        domains = []
        if actor:
            actor_id = actor.get('id')
            if actor_id:
                logging.info(f'Finding followers of {actor_id}')
                domains = [f.src for f in
                           Follower.query(Follower.dest == actor_id,
                                          projection=[Follower.src]).fetch()]
        key = Activity(source=source, target='Public', direction='in',
                       protocol='activitypub', domain=domains, status='complete',
                       source_as2=source_as2).put()
        logging.info(f'Wrote Activity {key} with {len(domains)} follower domains')

    return ''


def accept_follow(follow, follow_unwrapped):
    """Replies to an AP Follow request with an Accept request.

    Args:
      follow: dict, AP Follow activity
      follow_unwrapped: dict, same, except with redirect URLs unwrapped
    """
    logger.info('Replying to Follow with Accept')

    followee = follow.get('object')
    followee_unwrapped = follow_unwrapped.get('object')
    follower = follow.get('actor')
    if not followee or not followee_unwrapped or not follower:
        error('Follow activity requires object and actor. Got: %s' % follow)

    inbox = follower.get('inbox')
    follower_id = follower.get('id')
    if not inbox or not follower_id:
        error('Follow actor requires id and inbox. Got: %s', follower)

    # store Follower
    user_domain = util.domain_from_link(followee_unwrapped, minimize=False)
    Follower.get_or_create(dest=user_domain, src=follower_id,
                           last_follow=json_dumps(follow))

    # send AP Accept
    accept = {
        '@context': 'https://www.w3.org/ns/activitystreams',
        'id': util.tag_uri(request.host, 'accept/%s/%s' % (
            (user_domain, follow.get('id')))),
        'type': 'Accept',
        'actor': followee,
        'object': {
            'type': 'Follow',
            'actor': follower_id,
            'object': followee,
        }
    }
    resp = send(accept, inbox, user_domain)

    # send webmention
    common.send_webmentions(as2.to_as1(follow), proxy=True, protocol='activitypub',
                            source_as2=json_dumps(follow_unwrapped))

    return resp.text, resp.status_code


@ndb.transactional()
def undo_follow(undo_unwrapped):
    """Handles an AP Undo Follow request by deactivating the Follower entity.

    Args:
      undo_unwrapped: dict, AP Undo activity with redirect URLs unwrapped
    """
    logger.info('Undoing Follow')

    follow = undo_unwrapped.get('object', {})
    follower = follow.get('actor')
    followee = follow.get('object')
    if not follower or not followee:
        error('Undo of Follow requires object with actor and object. Got: %s' % follow)

    # deactivate Follower
    user_domain = util.domain_from_link(followee, minimize=False)
    follower_obj = Follower.get_by_id(Follower._id(dest=user_domain, src=follower))
    if follower_obj:
        logger.info(f'Marking {follower_obj.key} as inactive')
        follower_obj.status = 'inactive'
        follower_obj.put()
    else:
        logger.warning(f'No Follower found for {user_domain} {follower}')

    # TODO send webmention with 410 of u-follow