f - add duplicate funding txid protection

Author: ViktorTigerstrom

lightning/src/ln/channelmanager.rs

@@ -4539,8 +4539,18 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 			},
 			hash_map::Entry::Vacant(e) => {
 				let mut id_to_peer = self.id_to_peer.lock().unwrap();
-				if id_to_peer.insert(funding_msg.channel_id, *counterparty_node_id).is_some() {
-					panic!("id_to_peer map already contained funding txid, which shouldn't be possible");
+				match id_to_peer.entry(chan.channel_id()) {
+					hash_map::Entry::Occupied(_) => {
+						return Err(MsgHandleErrInternal::send_err_msg_no_close(
+							"Funding txid already exists with for another peer (or likely the
+							same peer using a different id). The counterparty must have sent a
+							txid in the FundingCreated msgs for a tx with a different
+							script_pubkey than the one agreed upon".to_owned(),
+							funding_msg.channel_id))
+					},
+					hash_map::Entry::Vacant(i_e) => {
+						i_e.insert(chan.get_counterparty_node_id());
+					}
 				}
 				channel_state.pending_msg_events.push(events::MessageSendEvent::SendFundingSigned {
 					node_id: counterparty_node_id.clone(),