Remote desktop from Windows: sign in as steamos, and say when xrdp isn't there

A Windows user reported "RDP not working". Frame Control ran `mstsc /v:HOST`,
which offers the Windows account; the Frame's xrdp (TLS, no NLA) only accepts
steamos with the Developer Mode password. The app also said "Opened Remote
Desktop" without checking that anything answered on port 3389.

- open_rdp checks port 3389 first and explains how to turn xrdp on
- On Windows, launch mstsc with a .rdp file naming user steamos (CRLF)
- Every platform's message says to sign in as steamos with the Developer Mode password
- The server no longer logs a page closing mid-reply (WinError 10053 on
  Windows) as a 500 with an error diagnostic

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/test_rdp.py

@@ -0,0 +1,130 @@
+"""Remote desktop to the Frame (frame_host.open_rdp) on each computer, with the client
+launch stubbed and a real socket standing in for the Frame's xrdp. Also the server
+staying quiet when the page goes away mid-reply, which on Windows is
+ConnectionAbortedError (WinError 10053).
+
+Run: python3 -m unittest discover -s tests
+"""
+import sandbox  # noqa: F401  (first: keeps tests off real data and services)
+import email.message
+import io
+import socket
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+from unittest import mock
+
+ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(ROOT / "ui"))
+
+import frame_host  # noqa: E402
+import server  # noqa: E402
+
+
+def platform(name):
+    """Patches frame_host to behave as on `name` ("mac", "windows" or "linux")."""
+    return mock.patch.multiple(frame_host, MAC=name == "mac", WINDOWS=name == "windows",
+                               LINUX=name == "linux")
+
+
+class OpenRdp(unittest.TestCase):
+    def setUp(self):
+        self.xrdp = socket.socket()
+        self.xrdp.bind(("127.0.0.1", 0))
+        self.xrdp.listen(4)
+        self.addCleanup(self.xrdp.close)
+        port = mock.patch.object(frame_host, "RDP_PORT", self.xrdp.getsockname()[1])
+        port.start()
+        self.addCleanup(port.stop)
+        self.spawned = []
+        spawn = mock.patch.object(frame_host, "_spawn", self.spawned.append)
+        spawn.start()
+        self.addCleanup(spawn.stop)
+        cache = tempfile.TemporaryDirectory()
+        self.addCleanup(cache.cleanup)
+        self.cache = Path(cache.name)
+        where = mock.patch.object(frame_host, "cache_dir", lambda *p: self.cache.joinpath(*p))
+        where.start()
+        self.addCleanup(where.stop)
+
+    def test_windows_signs_in_as_steamos(self):
+        # The report: mstsc /v:HOST alone offers the Windows account, which xrdp rejects.
+        with platform("windows"):
+            message = frame_host.open_rdp("frame", "127.0.0.1")
+        self.assertEqual(len(self.spawned), 1)
+        argv = self.spawned[0]
+        self.assertEqual(argv[0], "mstsc.exe")
+        self.assertNotIn("/v:127.0.0.1", argv)
+        rdp = Path(argv[1])
+        self.assertEqual(rdp.suffix, ".rdp")
+        data = rdp.read_bytes()  # CRLF lines, as mstsc writes them, however this OS ends lines
+        self.assertNotIn(b"\r\r", data)
+        lines = data.decode("utf-8").split("\r\n")
+        self.assertIn("full address:s:127.0.0.1", lines)
+        self.assertIn("username:s:steamos", lines)
+        self.assertIn("steamos", message)
+        self.assertIn("Developer Mode password", message)
+
+    def test_nothing_listening_says_why_and_opens_nothing(self):
+        self.xrdp.close()
+        for name in ("windows", "mac", "linux"):
+            with self.subTest(name), platform(name), self.assertRaises(frame_host.HostError) as cm:
+                frame_host.open_rdp("frame", "127.0.0.1")
+            self.assertIn("Developer Mode", str(cm.exception))
+            self.assertIn(f"port {frame_host.RDP_PORT}", str(cm.exception))
+        self.assertEqual(self.spawned, [])
+
+    def test_address_cant_add_lines_to_the_file(self):
+        with platform("windows"), self.assertRaises(frame_host.HostError):
+            frame_host.rdp_file("frame\r\nusername:s:root")
+        self.assertEqual(list(self.cache.iterdir()), [])
+
+    def test_linux_clients_get_the_user(self):
+        with platform("linux"), mock.patch.object(frame_host, "which",
+                                                  lambda n, *e: "/usr/bin/xfreerdp" if n == "xfreerdp" else None):
+            message = frame_host.open_rdp("frame", "127.0.0.1")
+        self.assertEqual(self.spawned, [["xfreerdp", "/v:127.0.0.1", "/u:steamos", "/dynamic-resolution"]])
+        self.assertIn("steamos", message)
+
+
+class PageGoneAway(unittest.TestCase):
+    """The report's server log: the page closed while index.html was being sent, and the
+    server logged it as a 500, tried to answer anyway, and filed an error diagnostic."""
+
+    def handler(self, path="/"):
+        h = server.Handler.__new__(server.Handler)
+        h.command, h.path, h.request_version = "GET", path, "HTTP/1.1"
+        h.requestline, h.client_address = f"GET {path} HTTP/1.1", ("127.0.0.1", 1)
+        h.headers = email.message.Message()
+        h.headers["Host"] = "127.0.0.1:1"
+        h.wfile = mock.Mock(write=mock.Mock(side_effect=ConnectionAbortedError(10053, "aborted")))
+        h.close_connection = True
+        return h
+
+    def test_not_a_server_error(self):
+        h = self.handler()
+        with mock.patch.object(server.frame_telemetry, "diagnostic") as diagnostic, \
+                mock.patch.object(sys, "stderr", io.StringIO()), self.assertRaises(server.ClientGone):
+            h.do_GET()
+        diagnostic.assert_not_called()
+        self.assertEqual(h.wfile.write.call_count, 1)  # no second, 500 reply
+
+    def test_server_logs_nothing(self):
+        srv = server.LoopbackServer.__new__(server.LoopbackServer)
+        err = io.StringIO()
+        with mock.patch.object(sys, "stderr", err):
+            try:
+                raise server.ClientGone()
+            except server.ClientGone:
+                srv.handle_error(None, ("127.0.0.1", 1))
+            self.assertEqual(err.getvalue(), "")
+            try:
+                raise RuntimeError("real")
+            except RuntimeError:
+                srv.handle_error(None, ("127.0.0.1", 1))
+        self.assertIn("RuntimeError: real", err.getvalue())
+
+
+if __name__ == "__main__":
+    unittest.main()