Backport: Support for Resource and ResourceTemplate metadata (#1928)

Co-authored-by: Jacem Elwaar <jacem@mcpappsbuilders.com>

tests/server/fastmcp/resources/test_function_resources.py

@@ -155,3 +155,38 @@ class TestFunctionResource:
         assert resource.mime_type == "text/plain"
         assert resource.name == "test"
         assert resource.uri == AnyUrl("function://test")
+
+
+class TestFunctionResourceMetadata:
+    def test_from_function_with_metadata(self):
+        # from_function() accepts meta dict and stores it on the resource for static resources
+
+        def get_data() -> str:  # pragma: no cover
+            return "test data"
+
+        metadata = {"cache_ttl": 300, "tags": ["data", "readonly"]}
+
+        resource = FunctionResource.from_function(
+            fn=get_data,
+            uri="resource://data",
+            meta=metadata,
+        )
+
+        assert resource.meta is not None
+        assert resource.meta == metadata
+        assert resource.meta["cache_ttl"] == 300
+        assert "data" in resource.meta["tags"]
+        assert "readonly" in resource.meta["tags"]
+
+    def test_from_function_without_metadata(self):
+        # meta parameter is optional and defaults to None for backward compatibility
+
+        def get_data() -> str:  # pragma: no cover
+            return "test data"
+
+        resource = FunctionResource.from_function(
+            fn=get_data,
+            uri="resource://data",
+        )
+
+        assert resource.meta is None

tests/server/fastmcp/resources/test_resource_manager.py

@@ -134,3 +134,43 @@ class TestResourceManager:
         resources = manager.list_resources()
         assert len(resources) == 2
         assert resources == [resource1, resource2]
+
+
+class TestResourceManagerMetadata:
+    """Test ResourceManager Metadata"""
+
+    def test_add_template_with_metadata(self):
+        """Test that ResourceManager.add_template() accepts and passes meta parameter."""
+
+        manager = ResourceManager()
+
+        def get_item(id: str) -> str:  # pragma: no cover
+            return f"Item {id}"
+
+        metadata = {"source": "database", "cached": True}
+
+        template = manager.add_template(
+            fn=get_item,
+            uri_template="resource://items/{id}",
+            meta=metadata,
+        )
+
+        assert template.meta is not None
+        assert template.meta == metadata
+        assert template.meta["source"] == "database"
+        assert template.meta["cached"] is True
+
+    def test_add_template_without_metadata(self):
+        """Test that ResourceManager.add_template() works without meta parameter."""
+
+        manager = ResourceManager()
+
+        def get_item(id: str) -> str:  # pragma: no cover
+            return f"Item {id}"
+
+        template = manager.add_template(
+            fn=get_item,
+            uri_template="resource://items/{id}",
+        )
+
+        assert template.meta is None

tests/server/fastmcp/resources/test_resource_template.py

@@ -258,3 +258,50 @@ class TestResourceTemplateAnnotations:
         # Verify the resource works correctly
         content = await resource.read()
         assert content == "Item 123"
+
+
+class TestResourceTemplateMetadata:
+    """Test ResourceTemplate meta handling."""
+
+    def test_template_from_function_with_metadata(self):
+        """Test that ResourceTemplate.from_function() accepts and stores meta parameter."""
+
+        def get_user(user_id: str) -> str:  # pragma: no cover
+            return f"User {user_id}"
+
+        metadata = {"requires_auth": True, "rate_limit": 100}
+
+        template = ResourceTemplate.from_function(
+            fn=get_user,
+            uri_template="resource://users/{user_id}",
+            meta=metadata,
+        )
+
+        assert template.meta is not None
+        assert template.meta == metadata
+        assert template.meta["requires_auth"] is True
+        assert template.meta["rate_limit"] == 100
+
+    @pytest.mark.anyio
+    async def test_template_created_resources_inherit_metadata(self):
+        """Test that resources created from templates inherit meta from template."""
+
+        def get_item(item_id: str) -> str:
+            return f"Item {item_id}"
+
+        metadata = {"category": "inventory", "cacheable": True}
+
+        template = ResourceTemplate.from_function(
+            fn=get_item,
+            uri_template="resource://items/{item_id}",
+            meta=metadata,
+        )
+
+        # Create a resource from the template
+        resource = await template.create_resource("resource://items/123", {"item_id": "123"})
+
+        # The resource should inherit the template's metadata
+        assert resource.meta is not None
+        assert resource.meta == metadata
+        assert resource.meta["category"] == "inventory"
+        assert resource.meta["cacheable"] is True

tests/server/fastmcp/resources/test_resources.py

@@ -193,3 +193,41 @@ class TestAnnotationsValidation:
         # Invalid roles should raise validation error
         with pytest.raises(Exception):  # Pydantic validation error
             Annotations(audience=["invalid_role"])  # type: ignore
+
+
+class TestResourceMetadata:
+    """Test metadata field on base Resource class."""
+
+    def test_resource_with_metadata(self):
+        """Test that Resource base class accepts meta parameter."""
+
+        def dummy_func() -> str:  # pragma: no cover
+            return "data"
+
+        metadata = {"version": "1.0", "category": "test"}
+
+        resource = FunctionResource(
+            uri=AnyUrl("resource://test"),
+            name="test",
+            fn=dummy_func,
+            meta=metadata,
+        )
+
+        assert resource.meta is not None
+        assert resource.meta == metadata
+        assert resource.meta["version"] == "1.0"
+        assert resource.meta["category"] == "test"
+
+    def test_resource_without_metadata(self):
+        """Test that meta field defaults to None."""
+
+        def dummy_func() -> str:  # pragma: no cover
+            return "data"
+
+        resource = FunctionResource(
+            uri=AnyUrl("resource://test"),
+            name="test",
+            fn=dummy_func,
+        )
+
+        assert resource.meta is None

tests/server/fastmcp/test_server.py

@@ -953,6 +953,74 @@ class TestServerResourceTemplates:
             assert result.contents[0].text == "csv for bob"
 
 
+class TestServerResourceMetadata:
+    """Test FastMCP @resource decorator meta parameter for list operations.
+
+    Meta flows: @resource decorator -> resource/template storage -> list_resources/list_resource_templates.
+    Note: read_resource does NOT pass meta to protocol response (lowlevel/server.py only extracts content/mime_type).
+    """
+
+    @pytest.mark.anyio
+    async def test_resource_decorator_with_metadata(self):
+        """Test that @resource decorator accepts and passes meta parameter."""
+        # Tests static resource flow: decorator -> FunctionResource -> list_resources (server.py:544,635,361)
+        mcp = FastMCP()
+
+        metadata = {"ui": {"component": "file-viewer"}, "priority": "high"}
+
+        @mcp.resource("resource://config", meta=metadata)
+        def get_config() -> str:  # pragma: no cover
+            return '{"debug": false}'
+
+        resources = await mcp.list_resources()
+        assert len(resources) == 1
+        assert resources[0].meta is not None
+        assert resources[0].meta == metadata
+        assert resources[0].meta["ui"]["component"] == "file-viewer"
+        assert resources[0].meta["priority"] == "high"
+
+    @pytest.mark.anyio
+    async def test_resource_template_decorator_with_metadata(self):
+        """Test that @resource decorator passes meta to templates."""
+        # Tests template resource flow: decorator -> add_template() -> list_resource_templates (server.py:544,622,377)
+        mcp = FastMCP()
+
+        metadata = {"api_version": "v2", "deprecated": False}
+
+        @mcp.resource("resource://{city}/weather", meta=metadata)
+        def get_weather(city: str) -> str:  # pragma: no cover
+            return f"Weather for {city}"
+
+        templates = await mcp.list_resource_templates()
+        assert len(templates) == 1
+        assert templates[0].meta is not None
+        assert templates[0].meta == metadata
+        assert templates[0].meta["api_version"] == "v2"
+
+    @pytest.mark.anyio
+    async def test_read_resource_returns_meta(self):
+        """Test that read_resource includes meta in response."""
+        # Tests end-to-end: Resource.meta -> ReadResourceContents.meta -> protocol _meta (lowlevel/server.py:341,371)
+        mcp = FastMCP()
+
+        metadata = {"version": "1.0", "category": "config"}
+
+        @mcp.resource("resource://data", meta=metadata)
+        def get_data() -> str:
+            return "test data"
+
+        async with client_session(mcp._mcp_server) as client:
+            result = await client.read_resource(AnyUrl("resource://data"))
+
+            # Verify content and metadata in protocol response
+            assert isinstance(result.contents[0], TextResourceContents)
+            assert result.contents[0].text == "test data"
+            assert result.contents[0].meta is not None
+            assert result.contents[0].meta == metadata
+            assert result.contents[0].meta["version"] == "1.0"
+            assert result.contents[0].meta["category"] == "config"
+
+
 class TestContextInjection:
     """Test context injection in tools, resources, and prompts."""
 

tests/server/lowlevel/test_helper_types.py

@@ -0,0 +1,60 @@
+"""Test helper_types.py meta field.
+
+These tests verify the changes made to helper_types.py:11 where we added:
+    meta: dict[str, Any] | None = field(default=None)
+
+ReadResourceContents is the return type for resource read handlers. It's used internally
+by the low-level server to package resource content before sending it over the MCP protocol.
+"""
+
+from mcp.server.lowlevel.helper_types import ReadResourceContents
+
+
+class TestReadResourceContentsMetadata:
+    """Test ReadResourceContents meta field.
+
+    ReadResourceContents is an internal helper type used by the low-level MCP server.
+    When a resource is read, the server creates a ReadResourceContents instance that
+    contains the content, mime type, and now metadata. The low-level server then
+    extracts the meta field and includes it in the protocol response as _meta.
+    """
+
+    def test_read_resource_contents_with_metadata(self):
+        """Test that ReadResourceContents accepts meta parameter."""
+        # Bridge between Resource.meta and MCP protocol _meta field (helper_types.py:11)
+        metadata = {"version": "1.0", "cached": True}
+
+        contents = ReadResourceContents(
+            content="test content",
+            mime_type="text/plain",
+            meta=metadata,
+        )
+
+        assert contents.meta is not None
+        assert contents.meta == metadata
+        assert contents.meta["version"] == "1.0"
+        assert contents.meta["cached"] is True
+
+    def test_read_resource_contents_without_metadata(self):
+        """Test that ReadResourceContents meta defaults to None."""
+        # Ensures backward compatibility - meta defaults to None, _meta omitted from protocol (helper_types.py:11)
+        contents = ReadResourceContents(
+            content="test content",
+            mime_type="text/plain",
+        )
+
+        assert contents.meta is None
+
+    def test_read_resource_contents_with_bytes(self):
+        """Test that ReadResourceContents works with bytes content and meta."""
+        # Verifies meta works with both str and bytes content (binary resources like images, PDFs)
+        metadata = {"encoding": "utf-8"}
+
+        contents = ReadResourceContents(
+            content=b"binary content",
+            mime_type="application/octet-stream",
+            meta=metadata,
+        )
+
+        assert contents.content == b"binary content"
+        assert contents.meta == metadata