Devices: fixes from review round 1

- No switching headsets (or changing the active one's user/port, or removing
  it) while installs run: they read the ssh settings step by step.
- Switching reroutes every command to the new headset at once, even if it
  never answers.
- ~/.ssh/config edits are serialized, use unique temp files, and back off if
  another program wrote the file meanwhile.
- stop() ends a handshake in progress and joins the connector.
- Pinned keys are written unhashed (HashKnownHosts=no); hashed ones are still
  found and forgotten via ssh-keygen.
- Set Up Connection changing a headset's user or port updates the registry.

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

tests/fakessh/ssh

@@ -1,7 +1,8 @@
 #!/usr/bin/env python3
 """A stand-in for OpenSSH's ssh, for tests/test_link.py: prints what `ssh -v` prints at
 each step of a connection, and plays a ControlMaster. What each HostName does comes
-from $FAKESSH_HOSTS (JSON: host -> "ok", "wrong" (a different host key) or "denied");
+from $FAKESSH_HOSTS (JSON: host -> "ok", "wrong" (a different host key), "denied" or
+"slow" (hangs after connecting);
 every call is appended to $FAKESSH_LOG as a JSON line. POSIX only."""
 import json
 import os
@@ -49,6 +50,8 @@ if what is None:
     sys.exit(255)
 say(f"debug1: Connecting to {host} [127.0.0.1] port {opts.get('port', 22)}.")
 say("debug1: Connection established.")
+if what == "slow":
+    time.sleep(30)
 say(f"debug1: Authenticating to {host}:22 as '{opts.get('user', 'tester')}'")
 say("debug1: Server host key: ssh-ed25519 SHA256:fakefakefakefakefakefakefakefakefakefakefak")
 if what == "wrong":

tests/test_devices.py

@@ -120,6 +120,13 @@ class Migration(Base):
         hosts = [a["host"] for a in self.reg.by_alias("frame")["addresses"]]
         self.assertEqual(hosts, ["192.168.1.237", "frame.tail1234.ts.net"])  # the new one first
 
+    def test_setup_changing_the_login_updates_the_headset(self):
+        self.reg.sync_from_config(seed=False)
+        (self.ssh / "config").write_text(CONFIG.replace("  User steamos\n", "  User deck\n  Port 2200\n", 1))
+        self.assertTrue(self.reg.sync_from_config(seed=False))
+        d = self.reg.by_alias("frame")
+        self.assertEqual((d["user"], d["port"]), ("deck", 2200))
+
     def test_removed_headset_stays_removed_until_setup_changes_it(self):
         self.reg.sync_from_config(seed=False)
         second = self.reg.by_alias("frame-2")
@@ -159,6 +166,21 @@ class ConfigRewrite(Base):
         if os.name != "nt":
             self.assertEqual(cfg.stat().st_mode & 0o777, 0o600)
 
+    def test_concurrent_edits_all_land(self):
+        import threading
+        def edit(alias, prefix):
+            for n in range(15):
+                fd.rewrite_block(alias, hostname=f"{prefix}.{n}")
+        threads = [threading.Thread(target=edit, args=("frame", "10.0.0")),
+                   threading.Thread(target=edit, args=("frame-2", "10.0.1"))]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+        blocks = fd.parse_blocks((self.ssh / "config").read_text())
+        self.assertEqual([b["hostname"] for b in blocks], ["10.0.0.14", "10.0.1.14"])
+        self.assertEqual([p.name for p in self.ssh.iterdir() if "frame-control." in p.name], [])  # no temp files left
+
     def test_zone_is_escaped_and_read_back(self):
         fd.rewrite_block("frame", hostname="fe80::1%en0")
         self.assertIn("HostName fe80::1%%en0", (self.ssh / "config").read_text())
@@ -193,6 +215,15 @@ class Pins(Base):
         self.assertTrue(fd.seed_pin("d3", ["frame.local"], port=2222))
         self.assertIn(f"frame-control-d3 {KEY}", fd.known_hosts().read_text())
 
+    def test_hashed_pins_are_found_and_forgotten(self):
+        fd.known_hosts().write_text(f"frame-control-d4 {KEY}\n")
+        subprocess.run(["ssh-keygen", "-H", "-f", str(fd.known_hosts())], capture_output=True, check=True)
+        self.assertNotIn("frame-control-d4", fd.known_hosts().read_text())
+        self.assertTrue(fd.pinned("d4"))
+        self.assertTrue(fd.forget_pin("d4"))
+        self.assertFalse(fd.pinned("d4"))
+        self.assertFalse(fd.known_hosts().with_name("frame-control_known_hosts.old").exists())
+
     def test_known_hosts_option_uses_the_override(self):
         self.assertEqual(fd.known_hosts_opt(), str(self.ssh / "frame-control_known_hosts"))
 

tests/test_link.py

@@ -227,6 +227,49 @@ class Connecting(unittest.TestCase):
         self.assertEqual(self.routes, [])
         self.assertTrue(all("ControlPath=none" in c for c in self.calls()))
 
+    def test_switching_to_a_headset_that_never_answers_stops_using_the_last_one(self):
+        self.device("localhost")
+        self.hosts({"localhost": "ok"})
+        self.link.connect(["start"])
+        other = self.reg.add_device("frame-other", port=self.port)
+        self.reg.add_address(other["id"], "nothing.invalid")
+        self.link.use(other["id"])
+        self.link.connect(["switch"])
+        self.assertEqual(self.link.snapshot()["phase"], "failed")
+        alias, opts = self.routes[-1]
+        self.assertEqual(alias, "frame-other")
+        self.assertIn("HostName=nothing.invalid", opts)
+        self.assertIn(f"HostKeyAlias=frame-control-{other['id']}", opts)
+
+    def test_no_switching_while_something_is_installing(self):
+        d = self.device("localhost")
+        other = self.reg.add_device("frame-other")
+        for body in ({"action": "use", "id": other["id"]}, {"action": "remove", "id": d["id"]},
+                     {"action": "update", "id": d["id"], "port": 2222}):
+            with self.assertRaises(fd.DeviceError, msg=body):
+                fl.devices_action(self.link, body, open_setup=None, busy=lambda: 1)
+        # Renaming, or changing another headset, is fine.
+        fl.devices_action(self.link, {"action": "update", "id": d["id"], "name": "Desk"}, None, busy=lambda: 1)
+        fl.devices_action(self.link, {"action": "update", "id": other["id"], "port": 2222}, None, busy=lambda: 1)
+        self.assertEqual(self.reg.get(d["id"])["name"], "Desk")
+
+    def test_stopping_mid_handshake_leaves_no_ssh_behind(self):
+        self.device("localhost")
+        self.hosts({"localhost": "slow"})
+        t = threading.Thread(target=self.link.connect, args=(["start"],), daemon=True)
+        t.start()
+        for _ in range(100):
+            if self.link.pending:
+                break
+            time.sleep(0.05)
+        proc = self.link.pending
+        self.assertIsNotNone(proc)
+        self.link.stop()
+        t.join(10)
+        self.assertFalse(t.is_alive())
+        self.assertIsNotNone(proc.poll())
+        self.assertIsNone(self.link.master)
+
     def test_devices_api_checks_everything(self):
         d = self.device("localhost")
         bad = [{"action": "address-add", "id": d["id"], "host": "-oProxyCommand=touch /tmp/x"},

ui/frame_devices.py

@@ -33,6 +33,7 @@ import os
 import re
 import secrets
 import subprocess
+import tempfile
 import threading
 import time
 from pathlib import Path
@@ -178,34 +179,63 @@ def read_config(path=None):
         return ""
 
 
-def _write_config(path, text):
-    """Swap the file in whole (same as frame_connect.write_config), keeping it private."""
-    tmp = path.with_name("config.frame-control.tmp")
-    tmp.write_text(text, encoding="utf-8")
-    if not frame_host.WINDOWS:
-        tmp.chmod(0o600)
-    for attempt in range(20):  # Windows: a running ssh.exe can hold the file for a moment
-        try:
-            os.replace(tmp, path)
-            return
-        except PermissionError:
-            time.sleep(0.25)
-    tmp.unlink()
-    raise OSError(f"{path} stayed locked by another program")
+# One edit of ~/.ssh/config at a time from this app (the connector and the page can
+# both want one); _edit_config also notices another program writing in between.
+_config_lock = threading.Lock()
+
+
+def _write_config(path, text, expected):
+    """Swap the file in whole (as frame_connect.write_config does), keeping it private.
+    Returns False, writing nothing, if the file no longer holds `expected`."""
+    fd_, tmp = tempfile.mkstemp(prefix="config.frame-control.", dir=str(path.parent))
+    tmp = Path(tmp)
+    try:
+        with os.fdopen(fd_, "w", encoding="utf-8") as fh:
+            fh.write(text)
+        if not frame_host.WINDOWS:
+            tmp.chmod(0o600)
+        for attempt in range(20):  # Windows: a running ssh.exe can hold the file for a moment
+            if read_config(path) != expected:
+                return False
+            try:
+                os.replace(tmp, path)
+                return True
+            except PermissionError:
+                time.sleep(0.25)
+        raise OSError(f"{path} stayed locked by another program")
+    finally:
+        if tmp.exists():
+            tmp.unlink()
+
+
+def _edit_config(path, change):
+    """Apply change(lines) -> new lines or None to the file, retrying if another program
+    wrote it meanwhile. -> True if the file changed."""
+    with _config_lock:
+        for _ in range(5):
+            text = read_config(path)
+            new = change(text.splitlines())
+            if new is None:
+                return False
+            if _write_config(path, "\n".join(new) + "\n", text):
+                return True
+        raise OSError(f"{path} kept changing while Frame Control tried to update it")
 
 
 def rewrite_block(alias, path=None, hostname=None, user=None, port=None):
     """Change HostName, User or Port inside ALIAS's managed block, leaving the rest of the
     file alone. -> True if the file changed. Does nothing if there's no such block."""
-    path = Path(path or ssh_config())
-    text = read_config(path)
-    lines = text.splitlines()
+    return _edit_config(Path(path or ssh_config()),
+                        lambda lines: _rewritten(lines, alias, hostname, user, port))
+
+
+def _rewritten(lines, alias, hostname, user, port):
     begin, end = begin_mark(alias), end_mark(alias)
     if begin not in lines or end not in lines:
-        return False
+        return None
     i, j = lines.index(begin), lines.index(end)
     if j < i:
-        return False
+        return None
     block = lines[i:j]
     want = {"hostname": ssh_host(hostname) if hostname else None, "user": user,
             "port": str(port) if port else None}
@@ -224,23 +254,16 @@ def rewrite_block(alias, path=None, hostname=None, user=None, port=None):
         at = next((n + 1 for n, line in enumerate(out) if line.split(None, 1)[:1] == ["HostName"]), 2)
         out.insert(at, f"  Port {want['port']}")
     new = lines[:i] + out + lines[j:]
-    if new == lines:
-        return False
-    _write_config(path, "\n".join(new) + "\n")
-    return True
+    return None if new == lines else new
 
 
 def remove_block(alias, path=None):
-    path = Path(path or ssh_config())
-    lines = read_config(path).splitlines()
-    begin, end = begin_mark(alias), end_mark(alias)
-    if begin not in lines or end not in lines:
-        return False
-    i, j = lines.index(begin), lines.index(end)
-    if j < i:
-        return False
-    _write_config(path, "\n".join(lines[:i] + lines[j + 1:]) + "\n")
-    return True
+    def change(lines):
+        begin, end = begin_mark(alias), end_mark(alias)
+        if begin not in lines or end not in lines or lines.index(end) < lines.index(begin):
+            return None
+        return lines[:lines.index(begin)] + lines[lines.index(end) + 1:]
+    return _edit_config(Path(path or ssh_config()), change)
 
 
 # ---- pinned host keys -------------------------------------------------------------
@@ -252,10 +275,26 @@ def _pin_lines(path=None):
         return []
 
 
+def _keygen(*args):
+    try:
+        return subprocess.run(["ssh-keygen", *args], capture_output=True, stdin=subprocess.DEVNULL, text=True,
+                              timeout=10)
+    except (OSError, subprocess.TimeoutExpired):
+        return None
+
+
 def pinned(device_id, path=None):
+    """Whether a key is saved for the device. The app's own entries are plain text (it
+    passes HashKnownHosts=no), but ask ssh-keygen too in case one was hashed."""
     name = host_key_alias(device_id)
-    return any(line.split(None, 1)[0].split(",").count(name) for line in _pin_lines(path)
-               if line.strip() and not line.startswith("#"))
+    target = Path(path or known_hosts())
+    if any(line.split(None, 1)[0].split(",").count(name) for line in _pin_lines(target)
+           if line.strip() and not line.startswith("#")):
+        return True
+    if not target.is_file():
+        return False
+    r = _keygen("-F", name, "-f", str(target))
+    return bool(r and r.returncode == 0 and r.stdout.strip())
 
 
 def seed_pin(device_id, hosts, port=22, sources=None, path=None):
@@ -299,10 +338,16 @@ def forget_pin(device_id, path=None):
     name = host_key_alias(device_id)
     lines = _pin_lines(target)
     kept = [line for line in lines if not (line.strip() and name in line.split(None, 1)[0].split(","))]
-    if kept != lines:
+    removed = kept != lines
+    if removed:
         target.write_text("".join(line + "\n" for line in kept), encoding="utf-8")
-        return True
-    return False
+    if target.is_file() and pinned(device_id, target):  # a hashed entry: ssh-keygen finds it
+        r = _keygen("-R", name, "-f", str(target))
+        removed = removed or bool(r and r.returncode == 0)
+        old = target.with_name(target.name + ".old")  # ssh-keygen -R leaves a backup
+        if old.exists():
+            old.unlink()
+    return removed
 
 
 # ---- address order --------------------------------------------------------------------
@@ -608,6 +653,12 @@ class Registry:
                     if seed:
                         seed_pin(d["id"], [host], b["port"])
                     changed = True
+                if d.get("config_login") != [user, b["port"]]:
+                    # Set Up Connection (or an edit) changed who to log in as, or the port.
+                    if d.get("config_login") is not None and [d["user"], d["port"]] != [user, b["port"]]:
+                        d["user"], d["port"] = user, b["port"] if 1 <= b["port"] <= 65535 else d["port"]
+                    d["config_login"] = [user, b["port"]]
+                    changed = True
                 if d["identity_files"] != b["identity_files"] and b["identity_files"]:
                     d["identity_files"] = b["identity_files"][:8]
                     changed = True

ui/frame_link.py

@@ -152,6 +152,8 @@ class Link:
         self.last_attempt = 0
         self.config_mtime = None
         self.thread = None
+        self.pending = None             # an ssh handshake still running
+        self.routed = None              # the device id every ssh command points at
 
     # ---- publishing ----
     def publish(self, **fields):
@@ -218,6 +220,9 @@ class Link:
             self.stopped = True
             self.cond.notify_all()
         self.close_master()
+        if self.thread:
+            self.thread.join(5)  # an attempt in progress notices `stopped` and ends
+        self.close_master()
 
     def alive(self):
         if self.state["phase"] != "connected":
@@ -278,7 +283,7 @@ class Link:
             return []
         return ["-o", f"HostName={frame_devices.ssh_host(host)}",
                 "-o", f"HostKeyAlias={frame_devices.host_key_alias(device['id'])}",
-                "-o", f"UserKnownHostsFile={frame_devices.known_hosts_opt()}",
+                "-o", f"UserKnownHostsFile={frame_devices.known_hosts_opt()}", "-o", "HashKnownHosts=no",
                 "-o", f"User={device['user']}", "-o", f"Port={device['port']}"]
 
     def public_device(self, d):
@@ -333,8 +338,12 @@ class Link:
             mtime = None
         if mtime != self.config_mtime:
             self.config_mtime = mtime
+            before = self.active_device()
             if self.reg.sync_from_config():
                 self.devices_changed()
+                after = self.active_device()
+                if (before.get("user"), before.get("port")) != (after.get("user"), after.get("port")):
+                    self.kick("switch")  # Set Up Connection changed the active headset's login
 
     def refresh_network(self):
         net = frame_network.current_network(self.last_fp)
@@ -348,6 +357,13 @@ class Link:
         self.last_attempt = now()
         self.close_master()
         device = self.active_device()
+        if device["id"] != self.routed:
+            # Another headset: nothing may go on reaching the last one, even if this one
+            # never answers. Its first address (and its own pinned identity) until one does.
+            first = device["addresses"][0]["host"] if device["addresses"] else None
+            self.alias, self.opts = device["alias"], self.host_opts(device, first)
+            self.apply(self.alias, self.opts)
+            self.routed = device["id"]
         with self.cond:
             self.state.update(phase="connecting", reason=why, device=self.public_device(device), via=None,
                               error=None, retry_at=None, attempt=self.state["attempt"] + 1, started=now(),
@@ -541,6 +557,9 @@ class Link:
 
     def close_master(self):
         proc, self.master = self.master, None
+        pending, self.pending = self.pending, None
+        if pending and pending.poll() is None:
+            pending.kill()
         if self.control and self.alias:
             try:
                 subprocess.run([*self.mux_base, *self.opts, "-O", "exit", self.alias], capture_output=True,
@@ -587,6 +606,7 @@ class Link:
         except OSError as e:
             self.fail("ssh", f"Couldn't run ssh: {e}", str(e))
             return "stop"
+        self.pending = proc  # so stop() can end it mid-handshake
         lines = queue.Queue()
         collecting = [True]
 
@@ -603,6 +623,9 @@ class Link:
         mismatch = False
         while True:
             left = deadline - time.monotonic()
+            if self.stopped:
+                proc.kill()
+                return "stop"
             if left <= 0:
                 proc.kill()
                 self.fail(step, self.explain(f"Timed out talking to {alias}") or "The headset took too long to answer.",
@@ -659,6 +682,10 @@ class Link:
                 self.stage("login", "done", f"Logged in as {user}")
                 step = "connected"
         collecting[0] = False  # the master keeps printing mux debug lines: drop them
+        self.pending = None
+        if self.stopped:
+            proc.kill()
+            return "stop"
         for sid in ("ssh", "identity", "login"):
             with self.cond:
                 pending = any(s["id"] == sid and s["state"] != "done" for s in self.state["stages"])
@@ -761,13 +788,19 @@ def devices_view(link):
             "kinds": frame_devices.KIND_LABEL}
 
 
-def devices_action(link, body, open_setup):
-    """POST /api/devices {"action": ..., "id": device id, ...}. -> {"message", ...devices_view}."""
+def devices_action(link, body, open_setup, busy=lambda: 0):
+    """POST /api/devices {"action": ..., "id": device id, ...}. -> {"message", ...devices_view}.
+    busy() counts installs in progress: nothing may move them to another headset."""
     reg = link.reg
     action = body.get("action")
     did = body.get("id")
     active = link.active_device()
     is_active = did == active["id"]
+    moves = action == "use" or (is_active and (action == "remove" or (
+        action == "update" and (body.get("user") is not None or body.get("port") is not None))))
+    if moves and busy():
+        raise frame_devices.DeviceError(
+            f"Wait for what's running on {active['name']} to finish (see the activity bar), then try again")
     if action == "use":
         d = reg.get(did)
         link.use(did)

ui/server.py

@@ -14,6 +14,7 @@ Env:   FRAME_ALIAS (default frame)
 """
 import argparse
 import base64
+import contextlib
 import http.client
 import json
 import os
@@ -77,20 +78,53 @@ HOST_OPTS = []
 frame_android.SSH_OPTS = SSH[1:]
 
 
+_route_lock = threading.Lock()
+
+
 def route(alias, host_opts):
     """Point every ssh, scp and rsync at `alias` with `host_opts` (frame_link calls this
     when it picks a headset and an address). The lists change in place, so code holding
     them follows; frame_titles reads frame_android.SSH_OPTS at call time."""
     global FRAME, HOST_OPTS
-    FRAME = frame_android.FRAME = alias
-    HOST_OPTS = list(host_opts)
-    MUX[:] = [*MUX_BASE, *HOST_OPTS]
-    SSH[:] = [*MUX, *SSH_TAIL]
-    frame_android.SSH_OPTS = SSH[1:]
+    with _route_lock:
+        FRAME = frame_android.FRAME = alias
+        HOST_OPTS = list(host_opts)
+        MUX[:] = [*MUX_BASE, *HOST_OPTS]
+        SSH[:] = [*MUX, *SSH_TAIL]
+        frame_android.SSH_OPTS = SSH[1:]
 
 
 LINK = None  # the connector (frame_link.Link); None on the Frame itself
 
+# Installs and other changes in progress. Switching headsets waits for them: they
+# read the ssh settings step by step, so a switch could send the rest (or a failed
+# install's clean-up) to the other headset.
+_work_lock = threading.Lock()
+_work = [0]
+
+
+@contextlib.contextmanager
+def working():
+    with _work_lock:
+        _work[0] += 1
+    try:
+        yield
+    finally:
+        with _work_lock:
+            _work[0] -= 1
+
+
+def busy_while(fn):
+    def run(*args, **kwargs):
+        with working():
+            return fn(*args, **kwargs)
+    return run
+
+
+def busy():
+    with _work_lock:
+        return _work[0]
+
 APPID = re.compile(r"^\d{1,10}$")
 FLATPAK_ID = re.compile(r"^[A-Za-z0-9][A-Za-z0-9_-]*(\.[A-Za-z0-9_-]+){2,}$")
 MAX_UPLOAD = 8 * 1024**3
@@ -181,7 +215,8 @@ def start_job(label, work):
     def run():
         fields = {}
         try:
-            result = work()
+            with working():
+                result = work()
             fields = {"message": result.get("message") or f"{label}: done", "result": result}
         except (Failure, frame_android.FrameError) as e:
             fields = {"error": unreachable(str(e)) or str(e)}
@@ -656,6 +691,7 @@ def stage_title(path, temp_dir=None, name=None):
             "token": token, "plan": frame_titles.public(plan)}
 
 
+@busy_while
 def _run_title_install(token, entry, name, exe, runtime):
     def update(**fields):  # the page reads jobs from other threads; change them under the lock
         with _titles_lock:
@@ -1090,6 +1126,7 @@ def webinstall_start(body):
     return {"job": pid}
 
 
+@busy_while
 def _webinstall_run(plan, job):
     tmp = None
     try:
@@ -1244,7 +1281,7 @@ def devices_post(body):
     if not LINK:
         raise Failure("Headsets are managed from the computer app", 400)
     try:
-        return frame_link.devices_action(LINK, body, open_setup)
+        return frame_link.devices_action(LINK, body, open_setup, busy)
     except frame_devices.DeviceError as e:
         raise Failure(str(e), 400)
 
@@ -1431,7 +1468,8 @@ class Handler(BaseHTTPRequestHandler):
         path = urlparse(self.path).path
         try:
             if path == "/api/upload":
-                self.send_json(self.upload())
+                with working():
+                    self.send_json(self.upload())
                 return
             handler = POST.get(path)
             if not handler:
@@ -1443,7 +1481,9 @@ class Handler(BaseHTTPRequestHandler):
             body = json.loads(self.rfile.read(length) or b"{}")
             if not isinstance(body, dict):
                 raise Failure("request body must be a JSON object", 400)
-            self.send_json(handler(body))
+            with (contextlib.nullcontext() if path == "/api/devices" else working()):
+                result = handler(body)
+            self.send_json(result)
         except Failure as e:
             self.send_error_json(str(e), e.status, e.apk)
         except (ValueError, TypeError) as e: