Merge pull request #77 from getong/add_SO_REUSEPORT

Not sure why GitHub is not updating, but the tests are green on Travis, so merging this! 😊

https://travis-ci.org/github/PSPDFKit-labs/bypass/builds/669226501

Author: ream88

lib/bypass/instance.ex

@@ -22,7 +22,7 @@ defmodule Bypass.Instance do
 
   def init([opts]) do
     # Get a free port from the OS
-    case :ranch_tcp.listen(ip: listen_ip(), port: Keyword.get(opts, :port, 0)) do
+    case :ranch_tcp.listen(so_reuseport() ++ [ip: listen_ip(), port: Keyword.get(opts, :port, 0)]) do
       {:ok, socket} ->
         {:ok, port} = :inet.port(socket)
         :erlang.port_close(socket)
@@ -305,7 +305,7 @@ defmodule Bypass.Instance do
 
   defp do_up(port, ref) do
     plug_opts = [self()]
-    {:ok, socket} = :ranch_tcp.listen(ip: listen_ip(), port: port)
+    {:ok, socket} = :ranch_tcp.listen(so_reuseport() ++ [ip: listen_ip(), port: port])
     cowboy_opts = cowboy_opts(port, ref, socket)
     {:ok, _pid} = Plug.Cowboy.http(Bypass.Plug, plug_opts, cowboy_opts)
     socket
@@ -376,6 +376,37 @@ defmodule Bypass.Instance do
     end
   end
 
+  # Use raw socket options to set SO_REUSEPORT so we fix {:error, :eaddrinuse} - where the OS errors
+  # when we attempt to listen on the same port as before, since it's still considered in use.
+  #
+  # See https://lwn.net/Articles/542629/ for details on SO_REUSEPORT.
+  #
+  # See https://github.com/aetrion/erl-dns/blob/0c8d768/src/erldns_server_sup.erl#L81 for an
+  # Erlang library using this approach.
+  #
+  # We want to do this:
+  #
+  #     int optval = 1;
+  #     setsockopt(sfd, SOL_SOCKET, SO_REUSEPORT, &optval, sizeof(optval));
+  #
+  # Use the following C program to find the values on each OS:
+  #
+  #     #include <stdio.h>
+  #     #include <sys/socket.h>
+  #
+  #     int main() {
+  #         printf("SOL_SOCKET: %d\n", SOL_SOCKET);
+  #         printf("SO_REUSEPORT: %d\n", SO_REUSEPORT);
+  #         return 0;
+  #     }
+  defp so_reuseport() do
+    case :os.type() do
+      {:unix, :linux} -> [{:raw, 1, 15, <<1::32-native>>}]
+      {:unix, :darwin} -> [{:raw, 65535, 512, <<1::32-native>>}]
+      _ -> []
+    end
+  end
+
   # This is used to override the default behaviour of ranch_tcp
   # and limit the range of interfaces it will listen on to just
   # the configured interface. Loopback is a default interface.

test/bypass_test.exs

@@ -15,6 +15,16 @@ defmodule BypassTest do
     end
   end
 
+  test "show ISSUE #51" do
+    Enum.each(1..1000,
+      fn (_) ->
+        bypass = %Bypass{} = Bypass.open(port: 8000)
+
+        Bypass.down(bypass)
+      end
+    )
+  end
+
   test "Bypass.open can specify a port to operate on with expect" do
     1234 |> specify_port(:expect)
   end
@@ -36,7 +46,8 @@ defmodule BypassTest do
     ])
 
     assert {:ok, 200, ""} = request(port)
-    assert {:error, :eaddrinuse} == Bypass.open(port: port)
+    bypass2 = Bypass.open(port: port)
+    assert(is_map(bypass2) and bypass2.__struct__ == Bypass)
   end
 
   test "Bypass.down takes down the socket with expect" do