bulb: `on` waits up to 30 s for the gateway

The bulb stayed off after a resume while the LED strip came back.
hypridle's after_sleep_cmd runs `udt-bulb on` the moment the resume
finishes, and the wired link only came up 4 s later (16:52:22 resume,
16:52:26 eth0 carrier in the log). A request sent before that fails at
once, and udt-bulb gave up after one try; the strip survived because a
failed cached address makes it listen for its broadcast for up to 20 s.

`on` now polls the first bulb every 2 s until the gateway answers, for
up to 30 s, which also covers the same race at login. `off` still makes
a single attempt, since it runs as the session ends and cannot wait.

The cause is read from timing, not observed: nothing logs what the
after_sleep_cmd did. The next resume confirms it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/bin/udt-bulb b/bin/udt-bulb
index b2eddf5..eee17bc 100755
--- a/bin/udt-bulb
+++ b/bin/udt-bulb
@@ -30,6 +30,7 @@ import secrets
 import shutil
 import subprocess
 import sys
+import time
 from pathlib import Path
 
 CONFIG = Path.home() / ".config/udt/tradfri.json"
@@ -65,6 +66,22 @@ def coap(method, url, ident, key, payload=None):
     return out.strip()
 
 
+def wait_for_gateway(url, auth, seconds, now=time.monotonic, nap=time.sleep):
+    """True once a get on url answers, False if it has not by `seconds`.
+
+    For `on`, which runs straight after a resume and at login: the wired link
+    came up 4 s after the resume finished, and a request sent before that
+    fails at once, with nothing to try again. `off` never waits, since it runs
+    as the session ends.
+    """
+    end = now() + seconds
+    while coap("get", url, *auth) is None:
+        if now() >= end:
+            return False
+        nap(2)
+    return True
+
+
 def light_states(colour):
     """3311 states for #rrggbb, sent in order."""
     h, s, _ = colorsys.rgb_to_hsv(*(int(colour[i:i + 2], 16) / 255 for i in (1, 3, 5)))
@@ -102,6 +119,20 @@ def selftest():
     # A pastel keeps its hue and loses its paleness to the floor.
     colour = light_states("#8080ff")[0]
     assert (colour["5707"], colour["5708"]) == (round(HUE_MAX * 2 / 3), HUE_MAX)
+
+    # The wait for the gateway retries until it answers, and gives up at the
+    # deadline. coap and the clock are swapped for fakes.
+    global coap
+    real, answers, naps = coap, [None, None, "{}"], []
+    coap = lambda *a: answers.pop(0)
+    clock = iter(range(100))
+    try:
+        assert wait_for_gateway("u", ("i", "k"), 30, lambda: next(clock), naps.append)
+        assert len(naps) == 2, naps
+        coap = lambda *a: None
+        assert not wait_for_gateway("u", ("i", "k"), 3, lambda: next(clock), naps.append)
+    finally:
+        coap = real
     print("ok")
 
 
@@ -132,6 +163,10 @@ def main():
     else:
         return
     auth = cfg["identity"], cfg["key"]
+    first = f"coaps://{cfg['host']}:5684/{DEVICES}/{cfg['bulbs'][0]}"
+    if args == ["on"] and not wait_for_gateway(first, auth, 30):
+        print("udt-bulb: the gateway did not answer for 30 s", file=sys.stderr)
+        return
     for dev in cfg["bulbs"]:
         url = f"coaps://{cfg['host']}:5684/{DEVICES}/{dev}"
         if not args: