Allow creating sockets from raw file descriptors

src/socket.cr

@@ -79,7 +79,8 @@ class Socket < IO
     end
   end
 
-  protected def initialize(@fd : Int32, @family, @type, @protocol = Protocol::IP, blocking = false)
+  # Creates a Socket from an existing socket file descriptor.
+  def initialize(@fd : Int32, @family, @type, @protocol = Protocol::IP, blocking = false)
     @closed = false
     init_close_on_exec(@fd)
 

src/socket/tcp_server.cr

@@ -48,6 +48,11 @@ class TCPServer < TCPSocket
     end
   end
 
+  # Creates a TCPServer from an already configured raw file descriptor
+  def initialize(*, fd : Int32, family : Family = Family::INET)
+    super(fd: fd, family: family)
+  end
+
   # Creates a new TCP server, listening on all local interfaces (`::`).
   def self.new(port : Int, backlog = SOMAXCONN, reuse_port = false)
     new("::", port, backlog, reuse_port: reuse_port)
@@ -100,7 +105,7 @@ class TCPServer < TCPSocket
   # ```
   def accept?
     if client_fd = accept_impl
-      sock = TCPSocket.new(client_fd, family, type, protocol)
+      sock = TCPSocket.new(fd: client_fd, family: family, type: type, protocol: protocol)
       sock.sync = sync?
       sock
     end

src/socket/tcp_socket.cr

@@ -42,6 +42,11 @@ class TCPSocket < IPSocket
     super fd, family, type, protocol
   end
 
+  # Creates a TCPSocket from an already configured raw file descriptor
+  def initialize(*, fd : Int32, family : Family = Family::INET)
+    super fd, family, Type::STREAM, Protocol::TCP
+  end
+
   # Opens a TCP socket to a remote TCP server, yields it to the block, then
   # eventually closes the socket when the block returns.
   #

src/socket/unix_server.cr

@@ -45,6 +45,11 @@ class UNIXServer < UNIXSocket
     end
   end
 
+  # Creates a UNIXServer from an already configured raw file descriptor
+  def initialize(*, fd : Int32, type : Type = Type::STREAM, @path : String? = nil)
+    super(fd: fd, type: type, path: @path)
+  end
+
   # Creates a new UNIX server and yields it to the block. Eventually closes the
   # server socket when the block returns.
   #
@@ -64,7 +69,7 @@ class UNIXServer < UNIXSocket
   # this method.
   def accept? : UNIXSocket?
     if client_fd = accept_impl
-      sock = UNIXSocket.new(client_fd, type, @path)
+      sock = UNIXSocket.new(fd: client_fd, type: type, path: @path)
       sock.sync = sync?
       sock
     end

src/socket/unix_socket.cr

@@ -28,7 +28,8 @@ class UNIXSocket < Socket
     super family, type, Protocol::IP
   end
 
-  protected def initialize(fd : Int32, type : Type, @path : String? = nil)
+  # Creates a UNIXSocket from an already configured raw file descriptor
+  def initialize(*, fd : Int32, type : Type = Type::STREAM, @path : String? = nil)
     super fd, Family::UNIX, type, Protocol::IP
   end
 
@@ -71,7 +72,7 @@ class UNIXSocket < Socket
       raise Errno.new("socketpair:")
     end
 
-    {UNIXSocket.new(fds[0], type), UNIXSocket.new(fds[1], type)}
+    {UNIXSocket.new(fd: fds[0], type: type), UNIXSocket.new(fd: fds[1], type: type)}
   end
 
   # Creates a pair of unamed UNIX sockets (see `pair`) and yields them to the