feat(agent): add Diagnostics.Writer GenServer

agent/lib/proxmox_agent/diagnostics/writer.ex

@@ -0,0 +1,95 @@
+defmodule ProxmoxAgent.Diagnostics.Writer do
+  @moduledoc """
+  Serializes diagnostic dump writes. Owns two append-only file handles
+  for commands.log and samples.log under a configured directory.
+
+  Started only when the agent's dump_dir is set. All writes are cast-based
+  to keep the caller path free of file I/O latency.
+  """
+
+  use GenServer
+  require Logger
+
+  @spec start_link(keyword()) :: GenServer.on_start()
+  def start_link(opts) do
+    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+  end
+
+  @impl true
+  def init(opts) do
+    dir = Keyword.fetch!(opts, :dir)
+
+    with {:ok, commands} <- open(Path.join(dir, "commands.log")),
+         {:ok, samples} <- open(Path.join(dir, "samples.log")) do
+      {:ok, %{dir: dir, commands: commands, samples: samples}}
+    else
+      {:error, reason} ->
+        {:stop, {:open_failed, reason}}
+    end
+  end
+
+  @impl true
+  def handle_cast({:command, cmd, args, result, duration_us}, state) do
+    write(state.commands, format_command(cmd, args, result, duration_us))
+    {:noreply, state}
+  end
+
+  def handle_cast({:sample, kind, payload}, state) do
+    write(state.samples, format_sample(kind, payload))
+    {:noreply, state}
+  end
+
+  @impl true
+  def handle_call(:flush, _from, state) do
+    {:reply, :ok, state}
+  end
+
+  @impl true
+  def terminate(_reason, state) do
+    File.close(state.commands)
+    File.close(state.samples)
+    :ok
+  end
+
+  # --- private ----------------------------------------------------------
+
+  defp open(path), do: File.open(path, [:append, :utf8])
+
+  defp write(io, data) do
+    case IO.write(io, data) do
+      :ok ->
+        :ok
+
+      {:error, reason} ->
+        Logger.warning("diagnostics writer: write failed (#{inspect(reason)})")
+        :ok
+    end
+  end
+
+  defp format_command(cmd, args, result, duration_us) do
+    header = "===== #{now_iso()} =====\n$ #{cmd} #{Enum.join(args, " ")}\n"
+
+    status =
+      case result do
+        {:ok, body} ->
+          "exit=0  duration=#{ms(duration_us)}ms  size=#{byte_size(body)}\n\n#{body}\n\n"
+
+        {:error, {:nonzero_exit, code, body}} ->
+          "exit=#{code}  duration=#{ms(duration_us)}ms  size=#{byte_size(body)}\n\n#{body}\n\n"
+
+        {:error, reason} ->
+          "error=#{inspect(reason)}  duration=#{ms(duration_us)}ms\n\n"
+      end
+
+    header <> status
+  end
+
+  defp format_sample(kind, payload) do
+    body = Jason.encode!(payload, pretty: true)
+    "===== #{now_iso()}  kind=#{kind} =====\n#{body}\n\n"
+  end
+
+  defp now_iso, do: DateTime.utc_now() |> DateTime.to_iso8601()
+
+  defp ms(us) when is_integer(us), do: div(us, 1_000)
+end