Merge pull request jruby#9326 from kares/fix-npe-openfile_channel-10.0

[fix] NullPointerException from closed IO

Author: kares

core/src/main/java/org/jruby/util/io/OpenFile.java

@@ -2578,37 +2578,39 @@ public ChannelFD fd() {
     }
 
     public Channel channel() {
-        assert(fd != null);
+        // MRI equivalent: rb_io_check_closed(fptr) + fptr->fd access in io.c
+        // when an IO was closed from another thread MRI raises IOError("closed stream") via io_fd_check_closed (io.c)
+        checkClosed();
         return fd.ch;
     }
 
     public ReadableByteChannel readChannel() {
-        assert(fd != null);
+        checkClosed();
         return fd.chRead;
     }
 
     public WritableByteChannel writeChannel() {
-        assert(fd != null);
+        checkClosed();
         return fd.chWrite;
     }
 
     public SeekableByteChannel seekChannel() {
-        assert(fd != null);
+        checkClosed();
         return fd.chSeek;
     }
 
     public SelectableChannel selectChannel() {
-        assert(fd != null);
+        checkClosed();
         return fd.chSelect;
     }
 
     public FileChannel fileChannel() {
-        assert(fd != null);
+        checkClosed();
         return fd.chFile;
     }
 
     public SocketChannel socketChannel() {
-        assert(fd != null);
+        checkClosed();
         return fd.chSock;
     }
 

test/jruby/test_io.rb

@@ -651,4 +651,35 @@ def out_stream.read(*n)
     assert_equal before, after, "no wrappers should have been registered"
   end
 
+  # https://github.com/jruby/jruby/issues/9324
+  def test_accept_on_closed_server_raises_ioerror
+    require 'socket'
+
+    # Concurrent threads create timing pressure needed to hit the race between one accept returning and the next start.
+    500.times do
+      tcp = TCPServer.new("127.0.0.1", 0)
+      port = tcp.connect_address.ip_port
+
+      thread = Thread.new do
+        Thread.current.abort_on_exception = false
+        Thread.current.report_on_exception = false
+        loop do
+          c = tcp.accept
+          c.close
+        end
+      rescue IOError, Errno::EBADF, Errno::EINVAL, Errno::ECONNABORTED, Errno::ENOTSOCK, Errno::ECONNRESET
+        # expected on shutdown — before the fix, NullPointerException/AssertionError escapes here
+      end
+
+      10.times { Thread.new { begin; TCPSocket.new("127.0.0.1", port).close; rescue; end } }
+      Thread.pass
+      tcp.close rescue nil
+
+      thread.join(2)
+      thread.kill if thread.alive?
+    end
+    # If we reach here, no AssertionError killed the process
+    assert true
+  end
+
 end