Add helper to get only the hostname out of MEDIA_URL (#14723)

settings.MEDIA_URL (passed in here as media_url) is a custom route on our CDN
that points to a cloud bucket, which we use for uploaded media from the CMS.

Specifically, due to infra constraints, it has to point to a _sub-path_ in the bucket,
not the top/root of it. It also needs to be distinct from the CDN route that points to our
collected static assets (which are at https://<CDN_HOSTNAME>/media/ - that is STATIC_URL)
With all this in mind, MEDIA_URL, when set, points to https://<CDN_HOSTNAME>/media/cms/
When django-storages computes the URL for a object in that CMS bucket, it wants
just the hostname of the bucket, not the full CDN/proxy path to the subdir in the bucket,
because it opinionatedly concatenates it with GS_LOCATION (which is needed to ensure
the files are uploaded to the sub-path mentioned above).

TLDR: We just need the root of the CDN, from MEDIA_URL.

bedrock/base/tests/test_settings.py

@@ -7,6 +7,10 @@
 from django.conf import settings
 from django.test import override_settings
 
+import pytest
+
+from bedrock.settings.base import _get_media_cdn_hostname_for_storage_backend
+
 
 @override_settings(DEV=False, PROD_LANGUAGES=("de", "fr", "nb-NO", "ja", "ja-JP-mac", "en-US", "en-GB"))
 def test_lang_groups():
@@ -15,3 +19,17 @@ def test_lang_groups():
         "ja": ["ja-JP-mac", "ja"],
         "en": ["en-US", "en-GB"],
     }
+
+
+@pytest.mark.parametrize(
+    "media_url, expected_hostname",
+    (
+        ("https://www-dev.allizom.org/media/cms/", "https://www-dev.allizom.org"),
+        ("https://www-dev.allizom.org/some/future/assets/path/", "https://www-dev.allizom.org"),
+        ("https://www.allizom.org/media/cms/", "https://www.allizom.org"),
+        ("https://www.mozilla.org/media/cms/", "https://www.mozilla.org"),
+        ("/custom-media/", "/custom-media/"),  # this one is the default, used in local dev
+    ),
+)
+def test_get_media_cdn_hostname(media_url, expected_hostname):
+    assert _get_media_cdn_hostname_for_storage_backend(media_url) == expected_hostname

bedrock/settings/base.py

@@ -13,6 +13,7 @@
 import sys
 from os.path import abspath
 from pathlib import Path
+from urllib.parse import urlparse
 
 from django.conf.locale import LANG_INFO  # we patch this in bedrock.base.apps.BaseAppConfig  # noqa: F401
 from django.utils.functional import lazy
@@ -601,8 +602,35 @@ def language_url_map_with_fallbacks():
     "cache_control": "max-age=2592000, public, immutable"  # 2592000 == 30 days / 1 month
 }
 
+
+def _get_media_cdn_hostname_for_storage_backend(media_url):
+    # settings.MEDIA_URL (passed in here as media_url) is a custom route on our CDN
+    # that points to a cloud bucket, which we use for uploaded media from the CMS.
+    #
+    # Specifically, due to infra constraints, it has to point to a _sub-path_ in the bucket,
+    # not the top/root of it. It also needs to be distinct from the CDN route that points to our
+    # collected static assets (which are at https://<CDN_HOSTNAME>/media/ - that is STATIC_URL)
+    #
+    # With all this in mind, MEDIA_URL, when set, points to https://<CDN_HOSTNAME>/media/cms/
+    #
+    # When django-storages computes the URL for a object in that CMS bucket, it wants
+    # just the hostname of the bucket, not the full CDN/proxy path to the subdir in the bucket,
+    # because it opinionatedly concatenates it with GS_LOCATION (defined below, which ensures
+    # the files are uploaded to the sub-path mentioned above).
+    #
+    # TLDR: We just need the root of the CDN, from MEDIA_URL.
+
+    if media_url.startswith("http"):
+        media_url_parsed = urlparse(media_url)
+        media_cdn_hostname = f"{media_url_parsed.scheme}://{media_url_parsed.hostname}"
+    else:
+        media_cdn_hostname = media_url
+
+    return media_cdn_hostname
+
+
 if GS_BUCKET_NAME and GS_PROJECT_ID:
-    GS_CUSTOM_ENDPOINT = MEDIA_URL.rstrip("/")  # hostname that proxies the storage bucket
+    GS_CUSTOM_ENDPOINT = _get_media_cdn_hostname_for_storage_backend(MEDIA_URL)  # hostname that proxies the storage bucket
     GS_FILE_OVERWRITE = False
     GS_LOCATION = "media/cms"  # path within the bucket to upload to