Add a client extension API (#3034)

tests/shared/test_extension.py

@@ -0,0 +1,56 @@
+"""The extension-identifier grammar in `mcp.shared.extension`, shared by server and client."""
+
+from typing import Any
+
+import pytest
+
+import mcp.server.extension
+import mcp.shared.extension
+from mcp.shared.extension import validate_extension_identifier
+
+
+def test_server_extension_module_reexports_shared_validator() -> None:
+    """SDK-defined: `mcp.server.extension` re-exports the shared validator as the same function object."""
+    assert mcp.server.extension.validate_extension_identifier is mcp.shared.extension.validate_extension_identifier
+
+
+@pytest.mark.parametrize(
+    "identifier",
+    [
+        "io.modelcontextprotocol/ui",
+        "com.example/my_ext",
+        "com.x-y.z2/n.a-b_c",
+        "example/x",
+        "a/b",
+        "com.example/9start",
+    ],
+)
+def test_grammar_conformant_extension_identifiers_are_accepted(identifier: str) -> None:
+    """Spec `_meta` key grammar: conformant `vendor-prefix/name` identifiers are accepted."""
+    validate_extension_identifier(identifier, owner="T")
+
+
+@pytest.mark.parametrize(
+    "identifier",
+    [
+        "noprefix",
+        "-foo/bar",
+        ".leading/x",
+        "a..b/x",
+        "foo-/x",
+        "9foo/x",
+        "foo/-bar",
+        "foo/bar-",
+        "foo/",
+        "/bar",
+        "foo/ba r",
+        "io.modelcontextprotocol/ui\n",
+        "",
+        None,
+        42,
+    ],
+)
+def test_malformed_extension_identifiers_are_rejected(identifier: Any) -> None:
+    """Spec `_meta` key grammar: malformed prefixes, malformed names, and non-strings are rejected."""
+    with pytest.raises(TypeError):
+        validate_extension_identifier(identifier, owner="T")