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 granary import as2, microformats2
import mf2util
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 Follower, MagicKey
from httpsig.requests_auth import HTTPSignatureAuth

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
    """
    logging.info('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
    acct = 'acct:%s@%s' % (user_domain, user_domain)
    key = MagicKey.get_or_create(user_domain)
    auth = HTTPSignatureAuth(secret=key.private_pem(), key_id=acct,
                             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),
    }
    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):
    """Serves /[DOMAIN], fetches its mf2, converts to AS Actor, and serves it."""
    tld = domain.split('.')[-1]
    if tld in common.TLD_BLOCKLIST:
        error('', status=404)

    mf2 = util.fetch_mf2(f'http://{domain}/', gateway=True, headers=common.HEADERS)

    hcard = mf2util.representative_hcard(mf2, mf2['url'])
    logging.info(f'Representative h-card: {json_dumps(hcard, indent=2)}')
    if not hcard:
        error(f"Couldn't find a representative h-card (http://microformats.org/wiki/representative-hcard-parsing) on {mf2['url']}")

    key = MagicKey.get_or_create(domain)
    obj = common.postprocess_as2(
        as2.from_as1(microformats2.json_to_object(hcard)), key=key)
    obj.update({
        'preferredUsername': domain,
        'inbox': f'{request.host_url}{domain}/inbox',
        'outbox': f'{request.host_url}{domain}/outbox',
        'following': f'{request.host_url}{domain}/following',
        'followers': f'{request.host_url}{domain}/followers',
    })
    logging.info(f'Returning: {json_dumps(obj, indent=2)}')

    return (obj, {
        'Content-Type': common.CONTENT_TYPE_AS2,
        'Access-Control-Allow-Origin': '*',
    })


@app.post(f'/<regex("{common.DOMAIN_RE}"):domain>/inbox')
def inbox(domain):
    """Accepts POSTs to /[DOMAIN]/inbox and converts to outbound webmentions."""
    body = request.get_data(as_text=True)
    logging.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)

    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 == 'Create':
        type = obj.get('type')
    elif 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':
        id = obj.get('id')

        # !!! temporarily disabled actually deleting Followers below because
        # mastodon.social sends Deletes for every Bridgy Fed account, all at
        # basically the same time, and we have many Follower objects, so we
        # have to do this table scan for each one, so the requests take a
        # long time and end up spawning extra App Engine instances that we
        # get billed for. and the Delete requests are almost never for
        # followers we have. TODO: revisit this and do it right.

        # if isinstance(id, str):
        #     # assume this is an actor
        #     # https://github.com/snarfed/bridgy-fed/issues/63
        #     for key in Follower.query().iter(keys_only=True):
        #         if key.id().split(' ')[-1] == id:
        #             key.delete()
        return ''

    # fetch actor if necessary so we have name, profile photo, etc
    for elem in obj, activity:
        actor = elem.get('actor')
        if actor and isinstance(actor, str):
            elem['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)
    common.send_webmentions(as1, proxy=True, protocol='activitypub',
                            source_as2=json_dumps(activity_unwrapped))

    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
    """
    logging.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)
    Follower.get_or_create(user_domain, 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):
    """Replies to an AP Follow request with an Accept request.

    Args:
      undo_unwrapped: dict, AP Undo activity with redirect URLs unwrapped
    """
    logging.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)
    follower_obj = Follower.get_by_id(Follower._id(user_domain, follower))
    if follower_obj:
        logging.info(f'Marking {follower_obj.key} as inactive')
        follower_obj.status = 'inactive'
        follower_obj.put()
    else:
        logging.warning(f'No Follower found for {user_domain} {follower}')

    # TODO send webmention with 410 of u-follow