tests: fix test_grpc_custommsg_notification flake#9154
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Changelog-Added: askrene: askrene-remove-channel-update, a new RPC to remove channel_update entries from layers. Signed-off-by: Lagrang3 <lagrang3@protonmail.com>
The test was missing the same synchronization barrier that test_grpc_connect_notification already has: after calling SubscribeCustomMsg() on the Python side the gRPC server-side subscribe_custom_msg() handler runs asynchronously, so the broadcast::Receiver is not yet registered when the event fires. Waiting for 'plugin-cln-grpc: received settings ACK' (emitted by the h2 HTTP/2 layer on receipt of the client's SETTINGS_ACK frame) ensures the full connection handshake has completed and the subscription is live before we trigger the custommsg.
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Problem
test_grpc_custommsg_notificationwas flaky (example failure: https://github.com/ElementsProject/lightning/actions/runs/26100805227/job/76753937004).Root Cause
After
SubscribeCustomMsg()returns on the Python side, the gRPC server-side handler (subscribe_custom_msgincln-grpc/src/server.rs) runs asynchronously in the Rust async runtime. It creates abroadcast::Receiverby callingself.events.subscribe(), which only receives events published after registration. Ifsendcustommsgfires before the handler has registered the receiver, the notification is broadcast with no listeners and is permanently lost.Fix
test_grpc_connect_notificationalready has this exact fix (and a FIXME comment explaining it): wait for'plugin-cln-grpc: received settings ACK'in the node log before triggering the event. This string is emitted by the h2 HTTP/2 library (used internally by tonic) when the server receives the client'sSETTINGS_ACKframe — guaranteeing the full connection handshake is complete and the subscription receiver is live.Apply the same synchronization barrier to
test_grpc_custommsg_notification.