rate_limit: Show html page when rate limited at /new/ endpoint.

Previously this showed a json error, but this is an endpoint that human
users use in the browser, so a proper HTML page is more appropriate.

templates/zerver/rate_limit_exceeded.html

@@ -0,0 +1,23 @@
+{% extends "zerver/portico.html" %}
+
+{% block portico_content %}
+
+<div class="error_page">
+    <div class="container">
+        <div class="row-fluid">
+            <img src="/static/images/500art.svg" alt=""/>
+            <div class="errorbox">
+                <div class="errorcontent">
+                    <h1 class="lead">{{ _("Rate limit exceeded.") }}</h1>
+                    <p>
+                        {% trans %}You have exceeded the limit for how
+                        often a user can perform this action.{% endtrans %}
+                        {% trans %}You can try again in {{retry_after}} seconds.{% endtrans %}
+                    </p>
+                </div>
+            </div>
+        </div>
+    </div>
+</div>
+
+{% endblock %}

zerver/tests/test_external.py

@@ -1,5 +1,5 @@
 import time
-from typing import Callable
+from typing import Callable, Optional
 from unittest import mock, skipUnless
 
 import DNS
@@ -134,19 +134,29 @@ class RateLimitTests(ZulipTestCase):
         newlimit = int(result["X-RateLimit-Remaining"])
         self.assertEqual(limit, newlimit + 1)
 
-    def do_test_hit_ratelimits(self, request_func: Callable[[], HttpResponse]) -> HttpResponse:
+    def do_test_hit_ratelimits(
+        self,
+        request_func: Callable[[], HttpResponse],
+        assert_func: Optional[Callable[[HttpResponse], None]] = None,
+    ) -> HttpResponse:
+        def default_assert_func(result: HttpResponse) -> None:
+            self.assertEqual(result.status_code, 429)
+            json = result.json()
+            self.assertEqual(json.get("result"), "error")
+            self.assertIn("API usage exceeded rate limit", json.get("msg"))
+            self.assertEqual(json.get("retry-after"), 0.5)
+            self.assertTrue("Retry-After" in result)
+            self.assertEqual(result["Retry-After"], "0.5")
+
+        if assert_func is None:
+            assert_func = default_assert_func
+
         start_time = time.time()
         for i in range(6):
             with mock.patch("time.time", return_value=(start_time + i * 0.1)):
                 result = request_func()
 
-        self.assertEqual(result.status_code, 429)
-        json = result.json()
-        self.assertEqual(json.get("result"), "error")
-        self.assertIn("API usage exceeded rate limit", json.get("msg"))
-        self.assertEqual(json.get("retry-after"), 0.5)
-        self.assertTrue("Retry-After" in result)
-        self.assertEqual(result["Retry-After"], "0.5")
+        assert_func(result)
 
         # We simulate waiting a second here, rather than force-clearing our history,
         # to make sure the rate-limiting code automatically forgives a user
@@ -173,12 +183,17 @@ class RateLimitTests(ZulipTestCase):
             remove_ratelimit_rule(1, 5, domain="api_by_ip")
 
     def test_create_realm_rate_limiting(self) -> None:
+        def assert_func(result: HttpResponse) -> None:
+            self.assertEqual(result.status_code, 429)
+            self.assert_in_response("Rate limit exceeded.", result)
+
         with self.settings(OPEN_REALM_CREATION=True):
             add_ratelimit_rule(1, 5, domain="create_realm_by_ip")
             try:
                 RateLimitedIPAddr("127.0.0.1").clear_history()
                 self.do_test_hit_ratelimits(
-                    lambda: self.client_post("/new/", {"email": "new@zulip.com"})
+                    lambda: self.client_post("/new/", {"email": "new@zulip.com"}),
+                    assert_func=assert_func,
                 )
             finally:
                 remove_ratelimit_rule(1, 5, domain="create_realm_by_ip")

zerver/views/registration.py

@@ -45,6 +45,7 @@ from zerver.lib.actions import (
     lookup_default_stream_groups,
 )
 from zerver.lib.email_validation import email_allowed_for_realm, validate_email_not_already_in_realm
+from zerver.lib.exceptions import RateLimited
 from zerver.lib.onboarding import send_initial_realm_messages, setup_realm_internal_bots
 from zerver.lib.pysa import mark_sanitized
 from zerver.lib.send_email import EmailNotDeliveredException, FromAddress, send_email
@@ -590,7 +591,16 @@ def create_realm(request: HttpRequest, creation_key: Optional[str] = None) -> Ht
     if request.method == "POST":
         form = RealmCreationForm(request.POST)
         if form.is_valid():
-            rate_limit_request_by_ip(request, domain="create_realm_by_ip")
+            try:
+                rate_limit_request_by_ip(request, domain="create_realm_by_ip")
+            except RateLimited as e:
+                assert e.secs_to_freedom is not None
+                return render(
+                    request,
+                    "zerver/rate_limit_exceeded.html",
+                    context={"retry_after": int(e.secs_to_freedom)},
+                    status=429,
+                )
 
             email = form.cleaned_data["email"]
             activation_url = prepare_activation_url(email, request, realm_creation=True)