Remote desktop: review fixes

- Write the .rdp file through open(newline=), since Path.write_text(newline=)
  needs Python 3.10 and CI's checks job runs 3.9
- One .rdp file per address, so overlapping launches can't swap headsets
- xrdp not answering is NotListening, a 400 with its message rather than a
  500 filed as an error diagnostic
- /source-image/ lets ClientGone through instead of answering 404 mid-reply

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

tests/test_rdp.py

@@ -71,12 +71,28 @@ class OpenRdp(unittest.TestCase):
     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:
+            with self.subTest(name), platform(name), self.assertRaises(frame_host.NotListening) 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_server_says_it_as_the_persons_to_fix(self):
+        # A 400 with the message, not a 500 filed as an error diagnostic.
+        self.xrdp.close()
+        with mock.patch.multiple(server, LOCAL=False, LINK=None, HOST_OPTS=["-o", "HostName=127.0.0.1"]), \
+                self.assertRaises(server.Failure) as cm:
+            server.open_thing({"what": "rdp"})
+        self.assertEqual(cm.exception.status, 400)
+        self.assertIn("Developer Mode", str(cm.exception))
+
+    def test_one_file_per_address(self):
+        with platform("windows"):
+            a, b = frame_host.rdp_file("192.168.1.5"), frame_host.rdp_file("fe80::1%eth0")
+        self.assertNotEqual(a, b)
+        self.assertIn(b"full address:s:192.168.1.5\r\n", a.read_bytes())
+        self.assertIn(b"full address:s:fe80::1%eth0\r\n", b.read_bytes())
+
     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")

ui/frame_host.py

@@ -6,6 +6,7 @@ CLI (used by the Electron app, so terminal handling lives in one place):
   python3 ui/frame_host.py terminal -- CMD [ARG...]   # open CMD in a terminal window
 """
 import os
+import re
 import shlex
 import shutil
 import socket
@@ -33,6 +34,10 @@ class HostError(RuntimeError):
     pass
 
 
+class NotListening(HostError):
+    """The Frame answers, but a service on it doesn't: something the person can turn on."""
+
+
 def data_dir(*parts):
     """Per-user app data: ~/Library/Application Support, %APPDATA% or $XDG_DATA_HOME
     (or $FRAME_CONTROL_DATA_DIR, which the tests point at a throwaway directory)."""
@@ -286,9 +291,11 @@ def rdp_file(host):
     computer's Windows account, which xrdp turns away; the file names steamos instead."""
     if any(c in host for c in "\r\n"):
         raise HostError("That headset address can't be used for remote desktop")
-    path = cache_dir("frame.rdp")
+    # One file per address, so two launches close together can't swap headsets.
+    path = cache_dir(f"frame-{re.sub(r'[^A-Za-z0-9.-]', '_', host)}.rdp")
     path.parent.mkdir(parents=True, exist_ok=True)
-    path.write_text(f"full address:s:{host}\nusername:s:{RDP_USER}\n", encoding="utf-8", newline="\r\n")
+    with open(path, "w", encoding="utf-8", newline="\r\n") as f:  # Path.write_text(newline=) is 3.10+
+        f.write(f"full address:s:{host}\nusername:s:{RDP_USER}\n")
     return path
 
 
@@ -297,9 +304,9 @@ def open_rdp(alias, host=None):
     host = host or ssh_hostname(alias)
     # The client would open either way and then fail on its own, with nothing said here.
     if not rdp_reachable(host):
-        raise HostError(f"The Frame isn't accepting remote desktop at {host} (nothing answered on port "
-                        f"{RDP_PORT}). Turn on Developer Mode in Steam Settings > System on the headset, "
-                        "then restart it and try again.")
+        raise NotListening(f"The Frame isn't accepting remote desktop at {host} (nothing answered on port "
+                           f"{RDP_PORT}). Turn on Developer Mode in Steam Settings > System on the headset, "
+                           "then restart it and try again.")
     if MAC:
         if subprocess.run(["open", "-a", "Windows App"], capture_output=True).returncode == 0:
             return f"Opened Windows App: connect to {host} and {RDP_LOGIN}"

ui/server.py

@@ -1192,6 +1192,8 @@ def open_thing(body):
             SHOTS_DIR.mkdir(parents=True, exist_ok=True)
             frame_host.open_path(SHOTS_DIR)
             return {"message": f"Opened {SHOTS_DIR} in {frame_host.FILE_MANAGER}"}
+    except frame_host.NotListening as e:
+        raise Failure(str(e), 400)  # theirs to turn on; nothing failed here
     except frame_host.HostError as e:
         raise Failure(str(e), 500)
     raise Failure("unknown target", 400)
@@ -2338,6 +2340,8 @@ class Handler(BaseHTTPRequestHandler):
                 from apk_sources import _images
                 try:
                     self.send_bytes(*_images.image(path.rsplit("/", 1)[-1]))
+                except ClientGone:
+                    raise
                 except Exception:
                     self.send_json({"error": "Artwork unavailable"}, 404)
             elif path == "/api/sources/details":