[POC] Secure channel abstraction

tensorflow_federated/python/core/impl/executors/BUILD

@@ -422,6 +422,7 @@ py_library(
     srcs = ["federating_executor.py"],
     srcs_version = "PY3",
     deps = [
+        ":channel_base",
         ":executor_base",
         ":executor_utils",
         ":executor_value_base",
@@ -439,6 +440,12 @@ py_library(
     ],
 )
 
+py_library(
+    name = "channel_base",
+    srcs = ["channel_base.py"],
+    srcs_version = "PY3",
+)
+
 py_test(
     name = "federating_executor_test",
     size = "small",

tensorflow_federated/python/core/impl/executors/channel_base.py

@@ -0,0 +1,35 @@
+import abc
+from dataclasses import dataclass
+from typing import Tuple, Dict
+
+from tensorflow_federated.python.common_libs import py_typecheck
+from tensorflow_federated.python.core.impl.compiler import placement_literals
+
+PlacementPair = Tuple[placement_literals.PlacementLiteral,
+                      placement_literals.PlacementLiteral]
+
+
+class Channel(metaclass=abc.ABCMeta):
+
+  @abc.abstractmethod
+  async def send(self, value, sender=None, receiver=None):
+    pass
+
+  @abc.abstractmethod
+  async def receive(self, value, sender=None, receiver=None):
+    pass
+
+  @abc.abstractmethod
+  async def setup(self):
+    pass
+
+
+@dataclass
+class ChannelGrid:
+  channel_dict: Dict[PlacementPair, Channel]
+
+  def __getitem__(self, placements: PlacementPair):
+    py_typecheck.check_type(placements, tuple)
+    py_typecheck.check_len(placements, 2)
+    sorted_placements = sorted(placements, key=lambda p: p.uri)
+    return self.channel_dict.get(tuple(sorted_placements))