fix(mcpserver): honor warn_on_duplicate_resources for URI templates

Author: jack12178

src/mcp/server/mcpserver/resources/resource_manager.py

@@ -70,7 +70,11 @@ def add_template(
         meta: dict[str, Any] | None = None,
         security: ResourceSecurity = DEFAULT_RESOURCE_SECURITY,
     ) -> ResourceTemplate:
-        """Add a template from a function."""
+        """Add a template from a function.
+
+        If a template with the same URI template already exists, the existing
+        template is kept and returned, mirroring `add_resource`.
+        """
         template = ResourceTemplate.from_function(
             fn,
             uri_template=uri_template,
@@ -83,6 +87,11 @@ def add_template(
             meta=meta,
             security=security,
         )
+        existing = self._templates.get(template.uri_template)
+        if existing:
+            if self.warn_on_duplicate_resources:
+                logger.warning(f"Resource template already exists: {template.uri_template}")
+            return existing
         self._templates[template.uri_template] = template
         return template
 

tests/server/mcpserver/resources/test_resource_manager.py

@@ -71,6 +71,48 @@ def test_disable_warn_on_duplicate_resources(temp_file: Path, caplog: pytest.Log
     assert "Resource already exists" not in caplog.text
 
 
+def test_add_duplicate_template():
+    """Test adding the same template twice keeps the first one."""
+
+    def first(item_id: str) -> str:
+        return f"first:{item_id}"
+
+    def second(item_id: str) -> str:
+        return f"second:{item_id}"
+
+    manager = ResourceManager()
+    first_template = manager.add_template(first, uri_template="items://{item_id}")
+    second_template = manager.add_template(second, uri_template="items://{item_id}")
+
+    assert first_template is second_template
+    assert first_template.fn("a") == "first:a"
+    assert manager.list_templates() == [first_template]
+
+
+def test_warn_on_duplicate_templates(caplog: pytest.LogCaptureFixture):
+    """Test warning on duplicate templates."""
+
+    def handler(item_id: str) -> str:
+        return item_id
+
+    manager = ResourceManager()
+    manager.add_template(handler, uri_template="items://{item_id}")
+    manager.add_template(handler, uri_template="items://{item_id}")
+    assert "Resource template already exists" in caplog.text
+
+
+def test_disable_warn_on_duplicate_templates(caplog: pytest.LogCaptureFixture):
+    """Test disabling warning on duplicate templates."""
+
+    def handler(item_id: str) -> str:
+        return item_id
+
+    manager = ResourceManager(warn_on_duplicate_resources=False)
+    manager.add_template(handler, uri_template="items://{item_id}")
+    manager.add_template(handler, uri_template="items://{item_id}")
+    assert "Resource template already exists" not in caplog.text
+
+
 @pytest.mark.anyio
 async def test_get_resource(temp_file: Path):
     """Test getting a resource by URI."""