Implement Socket reuse_port (=reuse_address) on Windows (#13326)

spec/std/http/server/server_spec.cr

@@ -81,7 +81,7 @@ describe HTTP::Server do
     ch.receive.end?.should be_true
   end
 
-  pending_win32 "reuses the TCP port (SO_REUSEPORT)" do
+  it "reuses the TCP port (SO_REUSEPORT)" do
     s1 = HTTP::Server.new { |ctx| }
     address = s1.bind_unused_port(reuse_port: true)
 

spec/std/socket/tcp_server_spec.cr

@@ -1,7 +1,6 @@
 {% skip_file if flag?(:wasm32) %}
 
 require "./spec_helper"
-require "../../support/win32"
 
 describe TCPServer, tags: "network" do
   describe ".new" do
@@ -52,31 +51,31 @@ describe TCPServer, tags: "network" do
       end
 
       describe "reuse_port" do
-        pending_win32 "raises when port is in use" do
+        it "raises when port is in use" do
           TCPServer.open(address, 0) do |server|
             expect_raises(Socket::BindError, "Could not bind to '#{address}:#{server.local_address.port}': ") do
               TCPServer.open(address, server.local_address.port) { }
             end
           end
         end
 
-        pending_win32 "raises when not binding with reuse_port" do
+        it "raises when not binding with reuse_port" do
           TCPServer.open(address, 0, reuse_port: true) do |server|
             expect_raises(Socket::BindError) do
               TCPServer.open(address, server.local_address.port) { }
             end
           end
         end
 
-        pending_win32 "raises when port is not ready to be reused" do
+        it "raises when port is not ready to be reused" do
           TCPServer.open(address, 0) do |server|
             expect_raises(Socket::BindError) do
               TCPServer.open(address, server.local_address.port, reuse_port: true) { }
             end
           end
         end
 
-        pending_win32 "binds to used port with reuse_port = true" do
+        it "binds to used port with reuse_port = true" do
           TCPServer.open(address, 0, reuse_port: true) do |server|
             TCPServer.open(address, server.local_address.port, reuse_port: true) { }
           end

src/crystal/system/win32/socket.cr

@@ -86,7 +86,7 @@ module Crystal::System::Socket
 
   private def initialize_handle(handle)
     value = 1_u8
-    ret = LibC.setsockopt(handle, LibC::SOL_SOCKET, LibC::SO_REUSEADDR, pointerof(value), 1)
+    ret = LibC.setsockopt(handle, LibC::SOL_SOCKET, LibC::SO_EXCLUSIVEADDRUSE, pointerof(value), 1)
     if ret == LibC::SOCKET_ERROR
       raise ::Socket::Error.from_wsa_error("setsockopt")
     end
@@ -254,11 +254,18 @@ module Crystal::System::Socket
   end
 
   private def system_reuse_port?
-    false
+    getsockopt_bool LibC::SO_REUSEADDR
   end
 
   private def system_reuse_port=(val : Bool)
-    raise NotImplementedError.new("Socket#reuse_port=")
+    if val
+      setsockopt_bool LibC::SO_EXCLUSIVEADDRUSE, false
+      setsockopt_bool LibC::SO_REUSEADDR, true
+    else
+      setsockopt_bool LibC::SO_REUSEADDR, false
+      setsockopt_bool LibC::SO_EXCLUSIVEADDRUSE, true
+    end
+    val
   end
 
   private def system_linger

src/socket.cr

@@ -339,13 +339,28 @@ class Socket < IO
       val
     end
 
-    def reuse_address? : Bool
-      getsockopt_bool LibC::SO_REUSEADDR
-    end
-
-    def reuse_address=(val : Bool)
-      setsockopt_bool LibC::SO_REUSEADDR, val
-    end
+    # SO_REUSEADDR, as used in posix, is always assumed on windows
+    # the SO_REUSEADDR flag on windows is the equivalent of SO_REUSEPORT on linux
+    # https://learn.microsoft.com/en-us/windows/win32/winsock/using-so-reuseaddr-and-so-exclusiveaddruse#application-strategies
+    {% if flag?(:win32) %}
+      # the address component of a binding can always be reused on windows
+      def reuse_address? : Bool
+        true
+      end
+
+      # there is no effect on windows
+      def reuse_address=(val : Bool)
+        val
+      end
+    {% else %}
+      def reuse_address? : Bool
+        getsockopt_bool LibC::SO_REUSEADDR
+      end
+
+      def reuse_address=(val : Bool)
+        setsockopt_bool LibC::SO_REUSEADDR, val
+      end
+    {% end %}
 
     def reuse_port? : Bool
       system_reuse_port?