ctl shutdown: infer hostnames from node names

inet_db is not a very reliable source as it doesn't take
node name CLI arguments and ERL_INETRC file settings.
That can lead to false positives in environments where
inet_db returns the same value (e.g. `localhost`) for
every cluster member.

Per discussion with @gerhard.

Closes #327.
References #309.

3 files changed, 50 insertions, 39 deletions

diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/core/node_name.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/core/node_name.ex
index ec200161e5..df5d0e97b2 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/core/node_name.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/core/node_name.ex
@@ -34,6 +34,40 @@ defmodule RabbitMQ.CLI.Core.NodeName do
   def hostname, do: :inet_db.gethostname() |> List.to_string()
 
   @doc """
+  Get hostname part of current node name
+  """
+  def hostname_from_node do
+    [_, hostname] = split_node(Node.self())
+    hostname
+  end
+
+  @doc """
+  Get hostname part of given node name
+  """
+  def hostname_from_node(name) do
+    [_, hostname] = split_node(name)
+    hostname
+  end
+
+  def split_node(name) when is_atom(name) do
+    split_node(to_string(name))
+  end
+
+  def split_node(name) do
+    case String.split(name, "@", parts: 2) do
+      ["", host] ->
+        default_name = to_string(Config.get_option(:node))
+        [default_name, host]
+
+      [_head, _host] = rslt ->
+        rslt
+
+      [head] ->
+        [head, ""]
+    end
+  end
+
+  @doc """
   Get local domain. If unavailable, makes a good guess. We're using
   :inet_db here because that's what Erlang/OTP uses when it creates a node
   name:
@@ -43,6 +77,10 @@ defmodule RabbitMQ.CLI.Core.NodeName do
     domain(1)
   end
 
+  #
+  # Implementation
+  #
+
   defp domain(attempt) do
     case {attempt, :inet_db.res_option(:domain), :os.type()} do
       {1, [], _} ->
@@ -162,24 +200,6 @@ defmodule RabbitMQ.CLI.Core.NodeName do
     Regex.match?(rx, head)
   end
 
-  defp split_node(name) when is_atom(name) do
-    split_node(to_string(name))
-  end
-
-  defp split_node(name) do
-    case String.split(name, "@", parts: 2) do
-      ["", host] ->
-        default_name = to_string(Config.get_option(:node))
-        [default_name, host]
-
-      [_head, _host] = rslt ->
-        rslt
-
-      [head] ->
-        [head, ""]
-    end
-  end
-
   defp do_load_resolv do
     # It could be we haven't read domain name from resolv file yet
     :ok = :inet_config.do_load_resolv(:os.type(), :longnames)
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/shutdown_command.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/shutdown_command.ex
index 051bc89e4d..74a9b53333 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/shutdown_command.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/shutdown_command.ex
@@ -15,7 +15,7 @@
 
 defmodule RabbitMQ.CLI.Ctl.Commands.ShutdownCommand do
   @behaviour RabbitMQ.CLI.CommandBehaviour
-  alias RabbitMQ.CLI.Core.OsPid
+  alias RabbitMQ.CLI.Core.{OsPid, NodeName}
 
   def switches() do
     [timeout: :integer,
@@ -32,18 +32,17 @@ defmodule RabbitMQ.CLI.Ctl.Commands.ShutdownCommand do
     :ok
   end
 
-  def validate([], %{node: node_name, wait: true, timeout: timeout}) do
-    hostname = :inet_db.gethostname()
-    case :rabbit_misc.rpc_call(node_name, :inet_db, :gethostname, [], timeout) do
-      {:badrpc, _} = err -> {:error, err}
-      remote_hostname    ->
-        case hostname == remote_hostname do
-          true  -> :ok;
-          false ->
-            msg = "\nThis command can only --wait for shutdown of local nodes but node #{node_name} is remote (local hostname: #{hostname}, remote: #{remote_hostname}).\n" <>
-                  "Pass --no-wait to shut node #{node_name} down without waiting.\n"
-            {:validation_failure, {:unsupported_target, msg}}
-        end
+  def validate([], %{node: node_name, wait: true}) do
+    local_hostname = NodeName.hostname_from_node(Node.self())
+    remote_hostname = NodeName.hostname_from_node(node_name)
+    case local_hostname == remote_hostname do
+      true  -> :ok;
+      false ->
+        msg = "\nThis command can only --wait for shutdown of local nodes " <>
+              "but node #{node_name} seems to be remote " <>
+              "(local hostname: #{local_hostname}, remote: #{remote_hostname}).\n" <>
+              "Pass --no-wait to shut node #{node_name} down without waiting.\n"
+        {:validation_failure, {:unsupported_target, msg}}
     end
   end
   use RabbitMQ.CLI.Core.AcceptsNoPositionalArguments
diff --git a/deps/rabbitmq_cli/test/ctl/shutdown_command_test.exs b/deps/rabbitmq_cli/test/ctl/shutdown_command_test.exs
index b427c967dd..c4f658687b 100644
--- a/deps/rabbitmq_cli/test/ctl/shutdown_command_test.exs
+++ b/deps/rabbitmq_cli/test/ctl/shutdown_command_test.exs
@@ -42,14 +42,6 @@ defmodule ShutdownCommandTest do
     assert @command.validate([], Map.merge(%{wait: false}, context[:opts])) == :ok
   end
 
-  # this command performs rpc calls in validate/2
-  test "validate: request to a non-existent node returns nodedown" do
-    target = :jake@thedog
-
-    opts = %{node: target, wait: true, timeout: 10}
-    assert match?({:error, {:badrpc, _}}, @command.validate([], opts))
-  end
-
   test "run: request to a non-existent node returns nodedown" do
     target = :jake@thedog