first pass at remote follow UI on user page

fixes #60

app.py

@@ -35,4 +35,4 @@ cache = Cache(app)
 util.set_user_agent('Bridgy Fed (https://fed.brid.gy/)')
 
 
-import activitypub, add_webmention, pages, redirect, render, salmon, superfeedr, webfinger, webmention
+import activitypub, add_webmention, follow, pages, redirect, render, salmon, superfeedr, webfinger, webmention

follow.py

@@ -0,0 +1,76 @@
+"""Remote follow handler.
+
+https://github.com/snarfed/bridgy-fed/issues/60
+https://socialhub.activitypub.rocks/t/what-is-the-current-spec-for-remote-follow/2020
+https://www.rfc-editor.org/rfc/rfc7033
+"""
+import logging
+import urllib.parse
+
+from flask import redirect, request
+from oauth_dropins.webutil import flask_util, util
+from oauth_dropins.webutil.flask_util import error, flash
+from oauth_dropins.webutil.util import json_dumps, json_loads
+
+from app import app
+import common
+from models import User
+
+logger = logging.getLogger(__name__)
+
+SUBSCRIBE_LINK_REL = 'http://ostatus.org/schema/1.0/subscribe'
+
+
+@app.post('/follow')
+def remote_follow():
+    """Discovers and redirects to a remote follow page for a given user."""
+    logger.info(f'Got: {request.values}')
+
+    domain = request.values['domain']
+    user = User.get_by_id(domain)
+    if not user:
+        error(f'No Bridgy Fed user found for domain {domain}')
+
+    addr = request.values['address'].strip().strip('@')
+    split = addr.split('@')
+    if len(split) == 2:
+        addr_domain = split[1]
+        resource = f'acct:{addr}'
+    elif addr.startswith('http://') or addr.startswith('https://'):
+        addr_domain = util.domain_from_link(addr, minimize=False)
+        resource = addr
+    else:
+        flash('Enter your fediverse address in @user@domain.com format')
+        return redirect(f'/user/{domain}')
+
+    # look up remote user via webfinger
+    try:
+        resp = util.requests_get(
+            f'https://{addr_domain}/.well-known/webfinger?resource={resource}')
+    except BaseException as e:
+        if util.is_connection_failure(e):
+            flash(f"Couldn't connect to {addr_domain}")
+            return redirect(f'/user/{domain}')
+        raise
+
+    if not resp.ok:
+        flash(f'WebFinger on {addr_domain} returned HTTP {resp.status_code}')
+        return redirect(f'/user/{domain}')
+
+    # find remote follow link and redirect
+    try:
+        data = resp.json()
+    except ValueError as e:
+        logger.warning(f'Got {e}', exc_info=True)
+        flash(f'WebFinger on {domain} returned non-JSON')
+        return redirect(f'/user/{domain}')
+
+    logger.info(f'Got: {json_dumps(data, indent=2)}')
+    for link in data.get('links', []):
+        if link.get('rel') == SUBSCRIBE_LINK_REL:
+            template = link.get('template')
+            if template and '{uri}' in template:
+                return redirect(template.replace('{uri}', user.address()))
+
+    flash(f"Couldn't find remote follow link for {addr}")
+    return redirect(f'/user/{domain}')

templates/user.html

@@ -42,6 +42,18 @@
   &middot; <a href="/{{ domain }}">ActivityPub</a>
 </div>
 
+<div class="row">
+<form method="post" action="/follow">
+<p>
+ <label for="follow-address">Enter your fediverse address to follow:</label>
+ <input id="follow-address" name="address" type="text" required
+        placeholder="@user@domain.com" alt="fediverse address"></input>
+ <input name="domain" type="hidden" value="{{ domain }}"></input>
+ <button type="submit" class="btn btn-default">Follow</button>
+</p>
+</form>
+</div>
+
 <!-- <div class="row">Recent activity</div> -->
 
 {% include "activities.html" %}

tests/test_follow.py

@@ -0,0 +1,84 @@
+"""Unit tests for follow.py.
+"""
+from unittest.mock import patch
+
+from oauth_dropins.webutil.testutil import requests_response
+
+import common
+from models import User
+from . import testutil
+
+WEBFINGER = requests_response({
+    'subject': 'acct:foo@bar',
+    'aliases': [
+        'https://bar/foo',
+    ],
+    'links': [{
+        'rel': 'http://ostatus.org/schema/1.0/subscribe',
+        'template': 'https://bar/follow?uri={uri}'
+    }],
+})
+
+@patch('requests.get')
+class FollowTest(testutil.TestCase):
+
+    def setUp(self):
+        super().setUp()
+        User.get_or_create('me')
+
+    def test_follow_no_domain(self, mock_get):
+        got = self.client.post('/follow?address=@foo@bar')
+        self.assertEqual(400, got.status_code)
+
+    def test_follow_no_address(self, mock_get):
+        got = self.client.post('/follow?domain=baz.com')
+        self.assertEqual(400, got.status_code)
+
+    def test_follow_no_user(self, mock_get):
+        got = self.client.post('/follow?address=@foo@bar&domain=baz.com')
+        self.assertEqual(400, got.status_code)
+
+    def test_follow(self, mock_get):
+        mock_get.return_value = WEBFINGER
+        got = self.client.post('/follow?address=@foo@bar&domain=me')
+        self.assertEqual(302, got.status_code)
+        self.assertEqual('https://bar/follow?uri=@me@me',
+                         got.headers['Location'])
+
+        mock_get.assert_has_calls((
+            self.req('https://bar/.well-known/webfinger?resource=acct:foo@bar'),
+        ))
+
+    def test_follow_url(self, mock_get):
+        mock_get.return_value = WEBFINGER
+        got = self.client.post('/follow?address=https://bar/foo&domain=me')
+        self.assertEqual(302, got.status_code)
+        self.assertEqual('https://bar/follow?uri=@me@me', got.headers['Location'])
+
+        mock_get.assert_has_calls((
+            self.req('https://bar/.well-known/webfinger?resource=https://bar/foo'),
+        ))
+
+    def test_follow_no_webfinger_subscribe_link(self, mock_get):
+        mock_get.return_value = requests_response({
+            'subject': 'acct:foo@bar',
+            'links': [{'rel': 'other', 'template': 'meh'}],
+        })
+
+        got = self.client.post('/follow?address=https://bar/foo&domain=me')
+        self.assertEqual(302, got.status_code)
+        self.assertEqual('/user/me', got.headers['Location'])
+
+    def test_follow_no_webfinger_subscribe_link(self, mock_get):
+        mock_get.return_value = requests_response(status_code=500)
+
+        got = self.client.post('/follow?address=https://bar/foo&domain=me')
+        self.assertEqual(302, got.status_code)
+        self.assertEqual('/user/me', got.headers['Location'])
+
+    def test_follow_no_webfinger_subscribe_link(self, mock_get):
+        mock_get.return_value = requests_response('<html>not json</html>')
+
+        got = self.client.post('/follow?address=https://bar/foo&domain=me')
+        self.assertEqual(302, got.status_code)
+        self.assertEqual('/user/me', got.headers['Location'])