Support returning the current and next boot slots

lib/nerves_runtime/fwup_ops.ex

@@ -104,6 +104,29 @@ defmodule Nerves.Runtime.FwupOps do
     end
   end
 
+  @doc """
+  Return boot status
+
+  This invokes the "status" task in the `ops.fw` to report the current
+  firmware slot and what slot will be tried on the next reboot. The `ops.fw`
+  is expected to print the slot name or two slot names separated by "->".
+  """
+  @spec status(options()) ::
+          {:ok, %{current: String.t(), next: String.t()}} | {:error, reason :: any}
+  def status(opts \\ []) do
+    with {:ok, raw_result} <- run_fwup("status", opts),
+         {:ok, result} <- deframe(raw_result, []) do
+      Enum.find_value(result, {:error, "Invalid status"}, &find_status/1)
+    end
+  end
+
+  defp find_status({:warning, <<slot::1-bytes>>}), do: {:ok, %{current: slot, next: slot}}
+
+  defp find_status({:warning, <<current::1-bytes, "->", next::1-bytes>>}),
+    do: {:ok, %{current: current, next: next}}
+
+  defp find_status(_status), do: nil
+
   defp run_fwup(task, opts) do
     devpath = Keyword.get(opts, :devpath, "/dev/rootdisk0")
     cmd_opts = [env: Keyword.get(opts, :env, %{})]

test/nerves_runtime/fwup_ops_test.exs

@@ -50,6 +50,20 @@ defmodule NervesRuntime.FwupOpsTest do
     assert {:error, "prevent-revert error"} = FwupOps.prevent_revert(@fwup_fail_options)
   end
 
+  defp status_ops(status) do
+    Keyword.put(@fwup_options, :env, %{"STATUS" => status})
+  end
+
+  test "status" do
+    # ops.conf lets you set the status via $STATUS
+    assert {:ok, %{current: "a", next: "b"}} = FwupOps.status(status_ops("a->b"))
+    assert {:ok, %{current: "b", next: "a"}} = FwupOps.status(status_ops("b->a"))
+    assert {:ok, %{current: "c", next: "c"}} = FwupOps.status(status_ops("c"))
+    assert {:error, "Invalid status"} = FwupOps.status(status_ops("xyz"))
+
+    assert {:error, "status error"} = FwupOps.status(@fwup_fail_options)
+  end
+
   test "missing ops.fw" do
     Application.put_env(:nerves_runtime, :revert_fw_path, "/does/not/exist/missing_ops.fw")