run server using unix domain socket (#16)

try to reduce the security risk as it is pointed out #14

Author: slashmili

.travis.yml

@@ -2,7 +2,7 @@ language: elixir
 elixir:
   - 1.4.2
 otp_release:
-  - 18.0
+  - 19.0
 sudo: false
 install: mix local.hex --force
 script:

README.md

@@ -37,22 +37,24 @@ Example for a completion request:
 COMP { "def", [ context: Elixir, imports: [Enum], aliases: [{MyList, List}] ] }
 ```
 
-## Read/Write through network socket
+## Read/Write through unix domain socket
 ```
 $ cd elixir_project
 $ elixir path/to/alchemist-server/run.exs --env=dev --listen
-ok|localhost:55580
+ok|localhost:/tmp/alchemist-server-1500797742260403000.sock
 ```
 In this mode, when a client connects to the port, it
 responds by sending information back to the opened connection
 
 Example for a completion request:
 
 ```
-$ nc localhost 55580
+$ nc -U /tmp/alchemist-server-1500797742260403000.sock
 COMP { "def", [ context: Elixir, imports: [Enum], aliases: [{MyList, List}] ] }
 ```
 
+Unix domain socket is introduced since OTP 19.
+
 # API
 
 ## Completion

lib/server/socket.exs

@@ -9,19 +9,22 @@ defmodule Alchemist.Server.Socket do
 
     env = Keyword.get(opts, :env)
     port = Keyword.get(opts, :port, 0)
+    socket_file = opts
+                  |> Keyword.get( :socket_file, socket_file())
+                  |> String.to_charlist
 
     children = [
       supervisor(Task.Supervisor, [[name: Alchemist.Server.Socket.TaskSupervisor]]),
-      worker(Task, [__MODULE__, :accept, [env, port]])
+      worker(Task, [__MODULE__, :accept, [env, port, socket_file]])
     ]
 
     opts = [strategy: :one_for_one, name: Alchemist.Server.Socket.Supervisor]
     Supervisor.start_link(children, opts)
   end
 
-  def accept(env, port) do
+  def accept(env, port, socket_file) do
     {:ok, socket} = :gen_tcp.listen(port,
-                    [:binary, packet: :line, active: false, reuseaddr: true])
+                    [:binary, packet: :line, active: false, reuseaddr: true, ifaddr: {:local, socket_file}])
     {:ok, port} = :inet.port(socket)
     IO.puts "ok|localhost:#{port}"
     loop_acceptor(socket, env)
@@ -58,4 +61,9 @@ defmodule Alchemist.Server.Socket do
   defp write_line(line, socket) do
     :gen_tcp.send(socket, line)
   end
+
+  defp socket_file do
+    sock_id = :erlang.system_time()
+    "/tmp/alchemist-server-#{sock_id}.sock"
+  end
 end

test/server/socket_test.exs

@@ -7,13 +7,12 @@ defmodule Alchemist.Server.SocketTest do
   alias Alchemist.Server.Socket, as: ServerSocket
 
   setup do
-    ServerSocket.start([env: "dev", port: 55293])
-    :ok
-  end
-
-  setup do
+    sock_id = :erlang.system_time()
+    {:ok, server_pid} = ServerSocket.start([env: "dev", socket_file: "/tmp/alchemist-server-#{sock_id}.sock"])
+    Process.sleep(100)
+    socket_file = String.to_charlist("/tmp/alchemist-server-#{sock_id}.sock")
     opts = [:binary, packet: :line, active: false]
-    {:ok, socket} = :gen_tcp.connect('localhost', 55293, opts)
+    {:ok, socket} = :gen_tcp.connect({:local, socket_file}, 0, opts)
     {:ok, socket: socket}
   end