1 files changed, 73 insertions, 0 deletions
diff --git a/internal/net/session_close_test.go b/internal/net/session_close_test.go
new file mode 100644
index 0000000..7cb54b6
--- /dev/null
+++ b/internal/net/session_close_test.go
@@ -0,0 +1,73 @@
+package net
+
+// Close/broadcast race regression: a broadcast racing Session.Close() used
+// to send on the outbound channel while Close closed the same channel — a
+// genuine data race (closechan vs chansend) that the old panic-recover only
+// hid. Closing is now signaled through a separate channel that is only ever
+// closed, never sent to.
+
+import (
+	stdnet "net"
+	"sync"
+	"testing"
+	"time"
+)
+
+// newTestSocketPair returns a synchronous, unbuffered connection pair: a
+// write blocks until the peer reads, which is exactly the stall condition
+// the echo test has to reproduce.
+func newTestSocketPair() (stdnet.Conn, stdnet.Conn) { return stdnet.Pipe() }
+
+func testTimeout() <-chan time.Time { return time.After(200 * time.Millisecond) }
+
+func TestConcurrentWriteCloseIsRaceFree(t *testing.T) {
+	for i := 0; i < 50; i++ {
+		sess := &Session{Conn: &testConn{}}
+		sess.StartWriter()
+		var wg sync.WaitGroup
+		wg.Add(2)
+		start := make(chan struct{})
+		go func() {
+			defer wg.Done()
+			<-start
+			for j := 0; j < 100; j++ {
+				sess.WriteLine("broadcast")
+			}
+		}()
+		go func() {
+			defer wg.Done()
+			<-start
+			sess.Close()
+		}()
+		close(start)
+		wg.Wait()
+		<-sess.writeDone
+	}
+}
+
+// Echo negotiation regression: login flips telnet echo on the game owner's
+// goroutine. Writing the negotiation inline made that write a direct socket
+// I/O, so a client that never read (full receive window, stalled socket)
+// blocked the entire game loop behind one connection. Queued sessions must
+// route the negotiation through the outbound writer instead.
+func TestSetEchoQueuedDoesNotBlockCaller(t *testing.T) {
+	local, peer := newTestSocketPair()
+	defer local.Close()
+	defer peer.Close()
+	sess := &Session{Conn: newTCPConn(local)}
+	sess.StartWriter()
+	defer sess.Close()
+
+	done := make(chan struct{})
+	go func() {
+		sess.SetEcho(false) // what the login path calls for password entry
+		close(done)
+	}()
+	select {
+	case <-done:
+	case <-testTimeout():
+		peer.Close() // unblock the writer so the test can exit
+		<-done
+		t.Fatal("SetEcho blocked the caller instead of queueing the negotiation")
+	}
+}