Do not rely directly on the ranch

lib/bypass/instance.ex

@@ -25,7 +25,10 @@ defmodule Bypass.Instance do
 
   def init([opts]) do
     # Get a free port from the OS
-    case :ranch_tcp.listen(so_reuseport() ++ [ip: listen_ip(), port: Keyword.get(opts, :port, 0)]) do
+    case :gen_tcp.listen(
+           Keyword.get(opts, :port, 0),
+           so_reuseport() ++ [ip: listen_ip()] ++ default_socket_opts()
+         ) do
       {:ok, socket} ->
         {:ok, port} = :inet.port(socket)
         :erlang.port_close(socket)
@@ -340,7 +343,10 @@ defmodule Bypass.Instance do
 
   defp do_up(port, ref) do
     plug_opts = [bypass_instance: self()]
-    {:ok, socket} = :ranch_tcp.listen(so_reuseport() ++ [ip: listen_ip(), port: port])
+
+    {:ok, socket} =
+      :gen_tcp.listen(port, so_reuseport() ++ [ip: listen_ip()] ++ default_socket_opts())
+
     cowboy_opts = cowboy_opts(port, ref, socket)
     {:ok, _pid} = Plug.Cowboy.http(Bypass.Plug, plug_opts, cowboy_opts)
     socket
@@ -442,34 +448,40 @@ defmodule Bypass.Instance do
     [ref: ref, port: port, transport_options: [num_acceptors: 5, socket: socket]]
   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, 65_535, 512, <<1::32-native>>}]
-      _ -> []
+  if System.otp_release() >= "26" do
+    defp so_reuseport() do
+      [reuseport: true]
+    end
+  else
+    # 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, 65_535, 512, <<1::32-native>>}]
+        _ -> []
+      end
     end
   end
 
@@ -494,4 +506,17 @@ defmodule Bypass.Instance do
         end
     end
   end
+
+  defp default_socket_opts do
+    # ref: https://github.com/ninenines/ranch/blob/a8f31f3/src/ranch_tcp.erl#L104-L110
+    [
+      {:backlog, 1024},
+      {:nodelay, true},
+      {:send_timeout, 30_000},
+      {:send_timeout_close, true},
+      :binary,
+      {:active, false},
+      {:packet, :raw}
+    ]
+  end
 end

mix.exs

@@ -31,7 +31,6 @@ defmodule Bypass.Mixfile do
     [
       {:plug_cowboy, "~> 2.0"},
       {:plug, "~> 1.7"},
-      {:ranch, "~> 1.7"},
       {:ex_doc, "> 0.0.0", only: :dev},
       {:espec, "~> 1.6", only: [:dev, :test]},
       {:mint, "~> 1.1", only: :test},