cas: move push_message into CASRemote

Part of #802

buildstream/_artifactcache.py

@@ -733,7 +733,7 @@ class ArtifactCache():
                                 "servers are configured as push remotes.")
 
         for remote in push_remotes:
-            message_digest = self.cas.push_message(remote, message)
+            message_digest = remote.push_message(message)
 
         return message_digest
 

buildstream/_cas/cascache.py

@@ -331,29 +331,6 @@ class CASCache():
 
         self._send_directory(remote, directory.ref)
 
-    # push_message():
-    #
-    # Push the given protobuf message to a remote.
-    #
-    # Args:
-    #     remote (CASRemote): The remote to push to
-    #     message (Message): A protobuf message to push.
-    #
-    # Raises:
-    #     (CASError): if there was an error
-    #
-    def push_message(self, remote, message):
-
-        message_buffer = message.SerializeToString()
-        message_digest = utils._message_digest(message_buffer)
-
-        remote.init()
-
-        with io.BytesIO(message_buffer) as b:
-            remote._send_blob(message_digest, b)
-
-        return message_digest
-
     # objpath():
     #
     # Return the path of an object based on its digest.

buildstream/_cas/casremote.py

@@ -229,6 +229,28 @@ class CASRemote():
 
         return True
 
+    # push_message():
+    #
+    # Push the given protobuf message to a remote.
+    #
+    # Args:
+    #     message (Message): A protobuf message to push.
+    #
+    # Raises:
+    #     (CASError): if there was an error
+    #
+    def push_message(self, message):
+
+        message_buffer = message.SerializeToString()
+        message_digest = utils._message_digest(message_buffer)
+
+        remote.init()
+
+        with io.BytesIO(message_buffer) as b:
+            remote._send_blob(message_digest, b)
+
+        return message_digest
+
     ################################################
     #             Local Private Methods            #
     ################################################

buildstream/sandbox/_sandboxremote.py

@@ -310,12 +310,12 @@ class SandboxRemote(Sandbox):
 
             # Push command and action
             try:
-                cascache.push_message(casremote, command_proto)
+                casremote.push_message(command_proto)
             except grpc.RpcError as e:
                 raise SandboxError("Failed to push command to remote: {}".format(e))
 
             try:
-                cascache.push_message(casremote, action)
+                casremote.push_message(action)
             except grpc.RpcError as e:
                 raise SandboxError("Failed to push action to remote: {}".format(e))