feat: NServ example

A simple NNTP server that serves content from a directory.

config/config.exs

@@ -1,5 +1,8 @@
 use Mix.Config
 
+config :logger, :console,
+  format: "$time $metadata[$level] $levelpad$message\n"
+
 if Mix.env == :dev do
   config :mix_test_watch,
     clear: true

examples/nserv.exs

@@ -0,0 +1,131 @@
+# Usage: mix run examples/nserv.exs -d <data-dir> [optional switches]
+#   -d <data-dir>   - directory whose files will be served
+# Optional switches:
+#   -b <address>    - ip address to bind to (default is 0.0.0.0)
+#   -p <port>       - port number for the first instance (default is 6791)
+#
+# Hit Ctrl+C twice to stop it.
+
+require Logger
+
+defmodule NServ do
+  @moduledoc """
+  A simple NNTP server that serves content from a directory.
+
+  Clients can request articles that are parts of a file using a specific format
+  for message-id. See `c:handle_ARTICLE/2` for that format.
+  """
+  @behaviour GenNNTP
+
+  @regex ~r/<([\w\/.-]+)\?(\d+)=(\d+):(\d+)>/
+
+  @defaults [port: 6791]
+
+  def child_spec(arg) do
+    %{
+      id: __MODULE__,
+      start: {__MODULE__, :start, arg}
+    }
+  end
+
+  def start(datadir, options \\ []) do
+    options = Keyword.merge(@defaults, options)
+    Logger.info("Listening on port #{options[:port]}")
+    GenNNTP.start(__MODULE__, datadir, options)
+  end
+
+  # Callbacks
+
+  @impl true
+  def init(datadir) do
+    Logger.info("[S] Incoming connection")
+    {:ok, datadir}
+  end
+
+  @doc """
+  Returns an article based on its `message_id`.
+
+  In NServ `message_id` has a special format which includes information about
+  file and portion of the file to be returned:
+
+  `ARTICLE <file-path-relative-to-datapath?xxx=yyy:zzz>`
+
+  where:
+
+  - `xxx` - part number (integer)
+  - `yyy` - offset from which to read the files (integer)
+  - `zzz` - size of file block to return (integer)
+  """
+  @impl true
+  def handle_ARTICLE(message_id, datadir) when is_binary(message_id) do
+    Logger.info("[S] Received: ARTICLE #{message_id}")
+    [_, file_path, xxx, yyy, zzz] = Regex.run(@regex, message_id)
+    Logger.info("[S] Serving: #{message_id}")
+    filename = Path.basename(file_path)
+
+    Logger.info("[S] Sending segment #{filename} (#{xxx}=#{yyy}:#{zzz})")
+
+    body = datadir
+    |> Path.join(file_path)
+    |> Path.absname
+    |> File.stream!([], String.to_integer(zzz))
+    |> Enum.at(String.to_integer(xxx))
+
+    IO.inspect(body)
+
+    article = %{
+      id: message_id,
+      headers: %{
+        "Message-ID" => message_id,
+        "Subject" => filename
+      },
+      body: body
+    }
+
+    {:ok, {0, article}, datadir}
+  end
+
+  @impl true
+  def handle_CAPABILITIES(datadir) do
+    {:ok, ["READER"], datadir}
+  end
+
+  @impl true
+  def handle_HELP(datadir) do
+    {:ok, "Self-serve", datadir}
+  end
+
+end
+
+defmodule App do
+  @moduledoc """
+  Your application entry-point.
+  For actual applications, start/1 should be start/2.
+  """
+
+  def start({data_dir, options}) do
+    import Supervisor.Spec
+
+    children = [
+      {NServ, [data_dir, options]},
+    ]
+
+    Supervisor.start_link(children, strategy: :one_for_one)
+  end
+end
+
+# Start the app and wait forever
+Logger.info("NServ 1.0 (Test NNTP server)")
+Logger.info("Press Ctrl+C to quit")
+
+{options, _argv, _invalid} = System.argv()
+|> OptionParser.parse(
+  aliases: [d: :data_dir, b: :address, p: :port],
+  strict: [data_dir: :string, address: :string, port: :integer]
+)
+
+if options[:data_dir] do
+  App.start(Keyword.pop(options, :data_dir))
+
+  Process.sleep(:infinity)
+end