Add Thrift-only real UCache test fixture

Summary:
Part of the effort to remove UCache's legacy ASCII/Caret serving path. Enable the migration away from UCache ASCII/Caret serving to be validated against a real process with no legacy listener. Keep the mode opt-in so shared protocol coverage remains unchanged, and require typed Thrift readiness so the fixture cannot report success without checking an endpoint.

The thrift-only `MCProcess` mode (`connectLegacySocket=False`) validates its inputs at construction: it requires a Thrift port and the Thrift test client, and rejects `versionPing` (which needs a legacy socket).

Reviewed By: ghostonhuang

Differential Revision: D113456755

fbshipit-source-id: 788401f2a152213500d3e021ba17336f56331633

Author: John Hugg

mcrouter/test/MCProcess.py

@@ -143,9 +143,22 @@ def __init__(
         use_ssl=False,
         versionPing=False,
         thriftPort=None,
+        connectLegacySocket=True,
     ):
+        if not connectLegacySocket:
+            if thriftPort is None:
+                raise ValueError("A Thrift port is required without a legacy socket")
+            if not McrouterGlobals.useThriftClient():
+                raise ValueError(
+                    "The Thrift test client must be enabled without a legacy socket"
+                )
+            if versionPing:
+                raise ValueError(
+                    "versionPing requires a legacy socket and is unsupported without one"
+                )
         self.fd = None
         self.versionPing = versionPing
+        self.connectLegacySocket = connectLegacySocket
         if cmd is not None and "-s" in cmd:
             if os.path.exists(addr):
                 raise Exception(f"file path {addr} already exists")
@@ -228,27 +241,28 @@ def connect(self):
 
     def ensure_connected(self):
         retry_count = 0
-        # First, try to connect
-        while True:
-            try:
-                self.connect()
-                break
-            except Exception as e:
-                retry_count += 1
-                print(
-                    # pyrefly: ignore [missing-attribute]
-                    f"Cannot connect (errno: {e.errno}). Retry {retry_count} of {self.max_retries}."
-                )
-                self.disconnect()
-                if not self.is_alive():
-                    print("Process exited unexpectedly!")
-                    self.terminate()  # This will print logs as well
+        if self.connectLegacySocket:
+            # First, try to connect
+            while True:
+                try:
+                    self.connect()
+                    break
+                except Exception as e:
+                    retry_count += 1
+                    print(
+                        # pyrefly: ignore [missing-attribute]
+                        f"Cannot connect (errno: {e.errno}). Retry {retry_count} of {self.max_retries}."
+                    )
+                    self.disconnect()
+                    if not self.is_alive():
+                        print("Process exited unexpectedly!")
+                        self.terminate()  # This will print logs as well
+                        raise
+                    # If we defined a retry count, retry until that's exceeded.
+                    if not self.max_retries or retry_count < self.max_retries:
+                        time.sleep(1)
+                        continue
                     raise
-                # If we defined a retry count, retry until that's exceeded.
-                if not self.max_retries or retry_count < self.max_retries:
-                    time.sleep(1)
-                    continue
-                raise
 
         # Then, verify Memcache is ready for traffic
         if self.versionPing:

mcrouter/tests/test_mcprocess.py

@@ -9,10 +9,22 @@
 from unittest.mock import Mock, patch
 
 from carbon.carbon_result.thrift_types import Result
-from mcrouter.test.MCProcess import MCProcess
+from mcrouter.test.MCProcess import MCProcess, McrouterGlobals
 
 
-class TestMCProcessEnsureConnected(unittest.TestCase):
+class MCProcessEnsureConnectedTest(unittest.TestCase):
+    @patch.object(McrouterGlobals, "useThriftClient", return_value=False)
+    def test_thrift_only_requires_enabled_thrift_client(self, use_thrift_client):
+        with self.assertRaisesRegex(ValueError, "Thrift test client must be enabled"):
+            MCProcess(
+                cmd=None,
+                addr=12345,
+                thriftPort=12346,
+                connectLegacySocket=False,
+            )
+
+        use_thrift_client.assert_called_once_with()
+
     def make_process(self, thrift_client=None):
         # Bypass __init__ to isolate ensure_connected: construct a bare MCProcess
         # and set only the attributes the readiness path reads. If __init__ later
@@ -23,6 +35,7 @@ def make_process(self, thrift_client=None):
         process.is_alive = Mock(return_value=True)
         process.terminate = Mock()
         process.versionPing = False
+        process.connectLegacySocket = True
         process.thrift_client = thrift_client
         process.max_retries = 4
         return process
@@ -42,6 +55,17 @@ def test_thrift_readiness_retries_until_ok(self, sleep):
         self.assertEqual(3, thrift_client.mcVersion.call_count)
         self.assertEqual(2, sleep.call_count)
 
+    def test_thrift_only_readiness_skips_legacy_connection(self):
+        thrift_client = Mock()
+        thrift_client.mcVersion.return_value = SimpleNamespace(result=Result.OK)
+        process = self.make_process(thrift_client)
+        process.connectLegacySocket = False
+
+        process.ensure_connected()
+
+        process.connect.assert_not_called()
+        thrift_client.mcVersion.assert_called_once_with()
+
     @patch("mcrouter.test.MCProcess.time.sleep")
     def test_child_exit_during_thrift_readiness_fails_promptly(self, sleep):
         error = ConnectionError("listener unavailable")