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

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

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