Test that data is not lost when on socket close.

tests/close_socket_test.toit

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+// Copyright (C) 2023 Toitware ApS.
+// Use of this source code is governed by a Zero-Clause BSD license that can
+// be found in the tests/LICENSE file.
+
+import expect show *
+import net
+
+// Test that written data is not lost when a socket is closed normally.
+
+main:
+  network := net.open
+  port := start_server network
+  run_client network port
+
+  port2 := start_server network
+  run_client network port2 --keep_writing
+
+run_client network port/int --keep_writing=false -> none:
+  socket := network.tcp_connect "127.0.0.1" port
+  socket.write "Hello, World!"
+  socket.no_delay = true
+  if keep_writing:
+    sleep --ms=1000
+    print
+        socket.read
+    print "Writing more"
+    socket.write "Hello, again!"
+  socket.close
+
+start_server network -> int:
+  server_socket := network.tcp_listen 0
+  port := server_socket.local_address.port
+  task::
+    while socket := server_socket.accept:
+      print "Got connection"
+      message := #[]
+      while message.size < 13:
+        data := socket.read
+        if not data: break
+        message += data
+      print "Got message size $message.size"
+      expect_equals 13 message.size
+      socket.close
+  return port