Address virtual host style addressing bugs for short subdomains provided in endpoint_url

.changes/next-release/bugfix-EndpointProvider-38157.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "EndpointProvider",
+  "description": "Fixed bug in virtual addressing for S3 Buckets `#2938 <https://github.com/boto/botocore/issues/2938>`__"
+}

botocore/endpoint_provider.py

@@ -398,13 +398,9 @@ def aws_is_virtual_hostable_s3_bucket(self, value, allow_subdomains):
         ):
             return False
 
-        if allow_subdomains is True:
-            return all(
-                self.aws_is_virtual_hostable_s3_bucket(label, False)
-                for label in value.split(".")
-            )
-
-        return self.is_valid_host_label(value, allow_subdomains=False)
+        return self.is_valid_host_label(
+            value, allow_subdomains=allow_subdomains
+        )
 
 
 # maintains backwards compatibility as `Library` was misspelled

tests/functional/test_s3.py

@@ -3487,6 +3487,24 @@ def _addressing_for_presigned_url_test_cases():
         signature_version="s3",
         expected_url="https://s3.us-west-1.amazonaws.com/foo.bar.biz/key",
     )
+    # Bucket names that contain dots and subcomponents that are less than
+    # 3 characters should still use virtual host style addressing if
+    # configured by the customer and they provide their own ``endpoint_url``
+    # that is insecure. https://github.com/boto/botocore/issues/2938
+    yield dict(
+        bucket="foo.b.biz",
+        key="key",
+        s3_config={"addressing_style": "virtual"},
+        customer_provided_endpoint="http://s3.us-west-2.amazonaws.com",
+        expected_url="http://foo.b.biz.s3.us-west-2.amazonaws.com/key",
+    )
+    yield dict(
+        bucket="foo.b.biz",
+        key="key",
+        s3_config={"addressing_style": "virtual"},
+        customer_provided_endpoint="https://s3.us-west-2.amazonaws.com",
+        expected_url="https://s3.us-west-2.amazonaws.com/foo.b.biz/key",
+    )
 
 
 @pytest.mark.parametrize(

tests/unit/test_endpoint_provider.py

@@ -491,3 +491,23 @@ def test_endpoint_reevaluates_result(endpoint_provider, monkeypatch):
     for region in regions:
         endpoint_provider.resolve_endpoint(Region=region)
     assert mock_evaluate.call_count == 2
+
+
+@pytest.mark.parametrize(
+    "bucket, expected_value",
+    [
+        ("mybucket", True),
+        ("ab", False),
+        ("a.b", True),
+        ("my.great.bucket.aws.com", True),
+        ("mY.GREAT.bucket.aws.com", False),
+        ("192.168.1.1", False),
+    ],
+)
+def test_aws_is_virtual_hostable_s3_bucket_allow_subdomains(
+    rule_lib, bucket, expected_value
+):
+    assert (
+        rule_lib.aws_is_virtual_hostable_s3_bucket(bucket, True)
+        == expected_value
+    )