Randomize `user_channel_id` for inbound channels

Previously, all inbound channels defaulted to a `user_channel_id` of 0,
which didn't allow for them being discerned on that basis. Here, we
simply randomize the identifier to fix this and enable the use of
`user_channel_id` as a true identifier for channels (assuming an equally
reasonable value is chosen for outbound channels and given upon
`create_channel()`).

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index 465256d21ea99bfa136062c8272c4dc34f65316b..30aad9f0b59d56b527a7ec26d968bfb02e4557e5 100644 (file)
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -1719,10 +1719,9 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
        ///
        /// `user_channel_id` will be provided back as in
        /// [`Event::FundingGenerationReady::user_channel_id`] to allow tracking of which events
-       /// correspond with which `create_channel` call. Note that the `user_channel_id` defaults to 0
-       /// for inbound channels, so you may wish to avoid using 0 for `user_channel_id` here.
-       /// `user_channel_id` has no meaning inside of LDK, it is simply copied to events and otherwise
-       /// ignored.
+       /// correspond with which `create_channel` call. Note that the `user_channel_id` defaults to a
+       /// randomized value for inbound channels. `user_channel_id` has no meaning inside of LDK, it
+       /// is simply copied to events and otherwise ignored.
        ///
        /// Raises [`APIError::APIMisuseError`] when `channel_value_satoshis` > 2**24 or `push_msat` is
        /// greater than `channel_value_satoshis * 1k` or `channel_value_satoshis < 1000`.
@@ -4604,9 +4603,13 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
                        return Err(MsgHandleErrInternal::send_err_msg_no_close("No inbound channels accepted".to_owned(), msg.temporary_channel_id.clone()));
                }
 
+               let mut random_bytes = [0u8; 8];
+               random_bytes.copy_from_slice(&self.keys_manager.get_secure_random_bytes()[..8]);
+               let user_channel_id = u64::from_be_bytes(random_bytes);
+
                let outbound_scid_alias = self.create_and_insert_outbound_scid_alias();
                let mut channel = match Channel::new_from_req(&self.fee_estimator, &self.keys_manager,
-                       counterparty_node_id.clone(), &their_features, msg, 0, &self.default_configuration,
+                       counterparty_node_id.clone(), &their_features, msg, user_channel_id, &self.default_configuration,
                        self.best_block.read().unwrap().height(), &self.logger, outbound_scid_alias)
                {
                        Err(e) => {