Add --if-not-exists flag to receive-wal

This flag prevents `receive-wal` from exiting with an error when
a slot with the same name already exists. This is the same behavior
as calling `pg_receivewal` with the same flag.

References: #1049.

Author: crazybolillo

barman/cli.py

@@ -1683,6 +1683,11 @@ def archive_wal(args):
             help="create the replication slot, if it does not exist",
             action="store_true",
         ),
+        argument(
+            "--if-not-exists",
+            help="Do not error out when --create-slot is specified and a slot with the specified name already exists.",
+            action="store_true",
+        ),
         argument(
             "--drop-slot",
             help="drop the replication slot, if it exists",
@@ -1714,7 +1719,7 @@ def receive_wal(args):
         server.kill("receive-wal")
     elif args.create_slot:
         with closing(server):
-            server.create_physical_repslot()
+            server.create_physical_repslot(ignore_duplicate=args.if_not_exists)
     elif args.drop_slot:
         with closing(server):
             server.drop_repslot()

barman/server.py

@@ -2809,7 +2809,7 @@ def archive_wal(self, verbose=True):
                 "on server %s. Skipping to the next server" % self.config.name
             )
 
-    def create_physical_repslot(self):
+    def create_physical_repslot(self, ignore_duplicate=False):
         """
         Create a physical replication slot using the streaming connection
         """
@@ -2852,7 +2852,11 @@ def create_physical_repslot(self):
             self.streaming.create_physical_repslot(self.config.slot_name)
             output.info("Replication slot '%s' created", self.config.slot_name)
         except PostgresDuplicateReplicationSlot:
-            output.error("Replication slot '%s' already exists", self.config.slot_name)
+            args = "Replication slot '%s' already exists", self.config.slot_name
+            if ignore_duplicate:
+                output.info(*args)
+            else:
+                output.error(*args)
         except PostgresReplicationSlotsFull:
             output.error(
                 "All replication slots for server '%s' are in use\n"

tests/test_server.py

@@ -1953,6 +1953,14 @@ def test_create_physical_repslot(self, capsys):
         out, err = capsys.readouterr()
         assert "Replication slot 'test_repslot' already exists" in err
 
+        # If the replication slot was already created but duplicates are ignored
+        # check that no error is reported
+        create_physical_repslot.side_effect = PostgresDuplicateReplicationSlot
+        server.create_physical_repslot(ignore_duplicate=True)
+        create_physical_repslot.assert_called_with("test_repslot")
+        out, err = capsys.readouterr()
+        assert not err
+
         # Test the method failure if the replication slots
         # on the server are all taken
         create_physical_repslot.side_effect = PostgresReplicationSlotsFull