Fix hostless links in notification emails (#198)

Score/peer/project notification emails are built without a request, so
public_url() relied solely on PUBLIC_BASE_URL. When that was unset or
lacked a host, it emitted hostless links like
http:///llm-zoomcamp-2026/leaderboard. Fall back to a concrete
ALLOWED_HOSTS host (or the canonical prod URL) so notification links are
always absolute, and strip whitespace from PUBLIC_BASE_URL.

Author: alexeygrigorev

course_management/datamailer/client.py

@@ -1,10 +1,13 @@
+import logging
 from dataclasses import dataclass
 from typing import Any
-from urllib.parse import urljoin
+from urllib.parse import urljoin, urlparse
 
 import requests
 from django.conf import settings
 
+logger = logging.getLogger(__name__)
+
 from .client_campaigns import DatamailerCampaignClient
 from .client_contacts import DatamailerContactClient
 from .client_recipient_lists import DatamailerRecipientListClients
@@ -94,9 +97,39 @@ def datamailer_enabled() -> bool:
 
 
 def public_url(path: str) -> str:
-    base_url = getattr(settings, "PUBLIC_BASE_URL", "")
-    if not base_url:
-        return path
-    normalized_base_url = f"{base_url.rstrip('/')}/"
+    base_url = _notification_base_url()
+    normalized_base_url = f"{base_url}/"
     normalized_path = path.lstrip("/")
     return urljoin(normalized_base_url, normalized_path)
+
+
+def _notification_base_url() -> str:
+    """Absolute base URL for links in notification emails.
+
+    Notifications are built without a request, so they can't fall back to the
+    request host the way in-app confirmation emails do. If ``PUBLIC_BASE_URL``
+    is unset or lacks a scheme/host we must still emit an absolute URL with a
+    real host — otherwise emails go out with unusable hostless links like
+    ``http:///course-slug/leaderboard``.
+    """
+    base_url = (getattr(settings, "PUBLIC_BASE_URL", "") or "").strip().rstrip("/")
+    parsed = urlparse(base_url)
+    if parsed.scheme and parsed.netloc:
+        return base_url
+
+    fallback = _fallback_base_url()
+    if base_url:
+        logger.warning(
+            "PUBLIC_BASE_URL=%r has no scheme/host; using %r for "
+            "notification links.",
+            base_url,
+            fallback,
+        )
+    return fallback
+
+
+def _fallback_base_url() -> str:
+    for host in getattr(settings, "ALLOWED_HOSTS", []):
+        if host and host != "*":
+            return f"https://{host}"
+    return "https://courses.datatalks.club"

course_management/settings.py

@@ -183,7 +183,7 @@
 VERSION = os.getenv(
     "VERSION", "local-development-build-version-not-configured"
 )
-PUBLIC_BASE_URL = os.getenv("PUBLIC_BASE_URL", "").rstrip("/")
+PUBLIC_BASE_URL = os.getenv("PUBLIC_BASE_URL", "").strip().rstrip("/")
 
 DATAMAILER_URL = os.getenv("DATAMAILER_URL", "")
 DATAMAILER_API_KEY = os.getenv("DATAMAILER_API_KEY", "")

courses/tests/test_datamailer_public_url.py

@@ -0,0 +1,41 @@
+from urllib.parse import urlparse
+
+from django.test import SimpleTestCase, override_settings
+
+from course_management.datamailer.client import public_url
+
+
+class PublicUrlTest(SimpleTestCase):
+    @override_settings(PUBLIC_BASE_URL="https://courses.datatalks.club")
+    def test_uses_public_base_url_when_configured(self):
+        self.assertEqual(
+            public_url("/llm-zoomcamp-2026/leaderboard"),
+            "https://courses.datatalks.club/llm-zoomcamp-2026/leaderboard",
+        )
+
+    @override_settings(
+        PUBLIC_BASE_URL="",
+        ALLOWED_HOSTS=["courses.datatalks.club"],
+    )
+    def test_falls_back_to_host_when_base_url_missing(self):
+        url = public_url("/llm-zoomcamp-2026/leaderboard")
+
+        # Emails must never contain a hostless link like
+        # http:///llm-zoomcamp-2026/leaderboard or a bare /path.
+        self.assertTrue(urlparse(url).netloc, f"hostless URL: {url!r}")
+        self.assertEqual(
+            url,
+            "https://courses.datatalks.club/llm-zoomcamp-2026/leaderboard",
+        )
+
+    @override_settings(
+        PUBLIC_BASE_URL="http://",
+        ALLOWED_HOSTS=["courses.datatalks.club"],
+    )
+    def test_falls_back_when_base_url_has_no_host(self):
+        url = public_url("/llm-zoomcamp-2026/leaderboard")
+
+        self.assertFalse(
+            url.startswith("http:///"), f"hostless URL: {url!r}"
+        )
+        self.assertTrue(urlparse(url).netloc, f"hostless URL: {url!r}")