fix(client): close the socket when the browser dies before the close handshake

lib/ferrum/client.rb

@@ -299,6 +299,7 @@ def close
       @pendings.clear
       @thread.kill unless @thread.join(1)
       @subscriber.close
+      @ws.force_close
     end
 
     #

lib/ferrum/client/web_socket.rb

@@ -141,6 +141,24 @@ def close
         @driver_mutex.synchronize { @driver.close }
       end
 
+      #
+      # Closes the underlying socket whether or not the close handshake ever
+      # completed.
+      #
+      # {#close} only sends a close frame; the socket itself is closed by
+      # {#on_close}, which runs when the browser answers with a close frame of
+      # its own. A browser that is already dead never answers, so without this
+      # the socket stays open until GC finalizes it -- long enough to exhaust
+      # the process's file descriptors when browsers are restarted in a loop.
+      #
+      # @return [void]
+      #
+      def force_close
+        @sock.close unless @sock.closed?
+      rescue IOError, SystemCallError
+        # nop
+      end
+
       private
 
       def start

sig/ferrum/client/web_socket.rbs

@@ -30,6 +30,8 @@ module Ferrum
 
       def close: () -> void
 
+      def force_close: () -> void
+
       private
 
       def start: () -> void

spec/client_spec.rb

@@ -38,6 +38,16 @@ def messages
       expect(Ferrum::Utils::ElapsedTime.elapsed_time(start)).to be < 1
     end
 
+    it "closes the socket when the browser dies before answering the close frame" do
+      remote.create_page
+      socket = remote.client.instance_variable_get(:@ws).instance_variable_get(:@sock)
+      Process.kill("KILL", -remote.process.pid)
+
+      remote.quit
+
+      expect(socket).to be_closed
+    end
+
     it "reports an unexpected reader error instead of raising in the main thread" do
       page = remote.create_page
       driver = remote.client.instance_variable_get(:@ws).instance_variable_get(:@driver)