Make `Channel`'s block connection API more electrum-friendly

Electrum clients primarily operate in a world where they query (and
subscribe to notifications for) transactions by script_pubkeys.
They may never learn very much about the actual blockchain and
orient their events around individual transactions, not the
blockchain.

This makes our ChannelManager interface somewhat more amenable to
such a client by splitting `block_connected` into
`transactions_confirmed` and `update_best_block`. The first handles
checking the funding transaction and storing its height/confirmation
block, whereas the second handles funding_locked and reorg logic.

Sadly, this interface is somewhat easy to misuse - notifying the
channel of the funding transaction being reorganized out of the
chain is complicated when the only notification received is that
a new block is connected at a given height. This will be addressed
in a future commit.

diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index 66f1a9e7e31f8c222728e26df1686d4b73015d3c..1279f310d4bfdbcfd134a9b53c95674fa0dd21bf 100644 (file)
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -3502,34 +3502,7 @@ impl<Signer: Sign> Channel<Signer> {
                self.network_sync == UpdateStatus::DisabledMarked
        }
 
-       /// When we receive a new block, we (a) check whether the block contains the funding
-       /// transaction (which would start us counting blocks until we send the funding_signed), and
-       /// (b) check the height of the block against outbound holding cell HTLCs in case we need to
-       /// give up on them prematurely and time them out. Everything else (e.g. commitment
-       /// transaction broadcasts, channel closure detection, HTLC transaction broadcasting, etc) is
-       /// handled by the ChannelMonitor.
-       ///
-       /// If we return Err, the channel may have been closed, at which point the standard
-       /// requirements apply - no calls may be made except those explicitly stated to be allowed
-       /// post-shutdown.
-       /// Only returns an ErrorAction of DisconnectPeer, if Err.
-       ///
-       /// May return some HTLCs (and their payment_hash) which have timed out and should be failed
-       /// back.
-       pub fn block_connected(&mut self, header: &BlockHeader, txdata: &TransactionData, height: u32) -> Result<(Option<msgs::FundingLocked>, Vec<(HTLCSource, PaymentHash)>), msgs::ErrorMessage> {
-               let mut timed_out_htlcs = Vec::new();
-               self.holding_cell_htlc_updates.retain(|htlc_update| {
-                       match htlc_update {
-                               &HTLCUpdateAwaitingACK::AddHTLC { ref payment_hash, ref source, ref cltv_expiry, .. } => {
-                                       if *cltv_expiry <= height + HTLC_FAIL_BACK_BUFFER {
-                                               timed_out_htlcs.push((source.clone(), payment_hash.clone()));
-                                               false
-                                       } else { true }
-                               },
-                               _ => true
-                       }
-               });
-
+       pub fn transactions_confirmed(&mut self, block_hash: &BlockHash, height: u32, txdata: &TransactionData) -> Result<(), msgs::ErrorMessage> {
                let non_shutdown_state = self.channel_state & (!MULTI_STATE_FLAGS);
                if non_shutdown_state & !(ChannelState::TheirFundingLocked as u32) == ChannelState::FundingSent as u32 {
                        for &(index_in_block, tx) in txdata.iter() {
@@ -3565,7 +3538,7 @@ impl<Signer: Sign> Channel<Signer> {
                                                        }
                                                }
                                                self.funding_tx_confirmation_height = height as u64;
-                                               self.funding_tx_confirmed_in = Some(header.block_hash());
+                                               self.funding_tx_confirmed_in = Some(*block_hash);
                                                self.short_channel_id = match scid_from_parts(height as u64, index_in_block as u64, txo_idx as u64) {
                                                        Ok(scid) => Some(scid),
                                                        Err(_) => panic!("Block was bogus - either height was > 16 million, had > 16 million transactions, or had > 65k outputs"),
@@ -3574,11 +3547,52 @@ impl<Signer: Sign> Channel<Signer> {
                                }
                        }
                }
+               Ok(())
+       }
 
+       /// When a new block is connected, we check the height of the block against outbound holding
+       /// cell HTLCs in case we need to give up on them prematurely and time them out. Everything
+       /// else (e.g. commitment transaction broadcasts, HTLC transaction broadcasting, etc) is
+       /// handled by the ChannelMonitor.
+       ///
+       /// If we return Err, the channel may have been closed, at which point the standard
+       /// requirements apply - no calls may be made except those explicitly stated to be allowed
+       /// post-shutdown.
+       ///
+       /// May return some HTLCs (and their payment_hash) which have timed out and should be failed
+       /// back.
+       pub fn update_best_block(&mut self, height: u32, highest_header_time: u32) -> Result<(Option<msgs::FundingLocked>, Vec<(HTLCSource, PaymentHash)>), msgs::ErrorMessage> {
+               let mut timed_out_htlcs = Vec::new();
+               let unforwarded_htlc_cltv_limit = height + HTLC_FAIL_BACK_BUFFER;
+               self.holding_cell_htlc_updates.retain(|htlc_update| {
+                       match htlc_update {
+                               &HTLCUpdateAwaitingACK::AddHTLC { ref payment_hash, ref source, ref cltv_expiry, .. } => {
+                                       if *cltv_expiry <= unforwarded_htlc_cltv_limit {
+                                               timed_out_htlcs.push((source.clone(), payment_hash.clone()));
+                                               false
+                                       } else { true }
+                               },
+                               _ => true
+                       }
+               });
 
-               self.update_time_counter = cmp::max(self.update_time_counter, header.time);
+               self.update_time_counter = cmp::max(self.update_time_counter, highest_header_time);
                if self.funding_tx_confirmation_height > 0 {
                        let funding_tx_confirmations = height as i64 - self.funding_tx_confirmation_height as i64 + 1;
+                       if funding_tx_confirmations <= 0 {
+                               self.funding_tx_confirmation_height = 0;
+                       }
+
+                       let non_shutdown_state = self.channel_state & (!MULTI_STATE_FLAGS);
+                       if (non_shutdown_state >= ChannelState::ChannelFunded as u32 ||
+                          (non_shutdown_state & ChannelState::OurFundingLocked as u32) == ChannelState::OurFundingLocked as u32) &&
+                           funding_tx_confirmations < self.minimum_depth as i64 / 2 {
+                               return Err(msgs::ErrorMessage {
+                                       channel_id: self.channel_id(),
+                                       data: format!("Funding transaction was un-confirmed. Locked at {} confs, now have {} confs.", self.minimum_depth, funding_tx_confirmations),
+                               });
+                       }
+
                        if funding_tx_confirmations == self.minimum_depth as i64 {
                                let need_commitment_update = if non_shutdown_state == ChannelState::FundingSent as u32 {
                                        self.channel_state |= ChannelState::OurFundingLocked as u32;
@@ -3617,25 +3631,35 @@ impl<Signer: Sign> Channel<Signer> {
                                }
                        }
                }
+
                Ok((None, timed_out_htlcs))
        }
 
+       /// When we receive a new block, we (a) check whether the block contains the funding
+       /// transaction (which would start us counting blocks until we send the funding_signed), and
+       /// (b) check the height of the block against outbound holding cell HTLCs in case we need to
+       /// give up on them prematurely and time them out. Everything else (e.g. commitment
+       /// transaction broadcasts, channel closure detection, HTLC transaction broadcasting, etc) is
+       /// handled by the ChannelMonitor.
+       ///
+       /// If we return Err, the channel may have been closed, at which point the standard
+       /// requirements apply - no calls may be made except those explicitly stated to be allowed
+       /// post-shutdown.
+       /// Only returns an ErrorAction of DisconnectPeer, if Err.
+       ///
+       /// May return some HTLCs (and their payment_hash) which have timed out and should be failed
+       /// back.
+       pub fn block_connected(&mut self, header: &BlockHeader, txdata: &TransactionData, height: u32) -> Result<(Option<msgs::FundingLocked>, Vec<(HTLCSource, PaymentHash)>), msgs::ErrorMessage> {
+               self.transactions_confirmed(&header.block_hash(), height, txdata)?;
+               self.update_best_block(height, header.time)
+       }
+
        /// Called by channelmanager based on chain blocks being disconnected.
        /// Returns true if we need to close the channel now due to funding transaction
        /// unconfirmation/reorg.
-       pub fn block_disconnected(&mut self, header: &BlockHeader, height: u32) -> bool {
-               if self.funding_tx_confirmation_height > 0 {
-                       let funding_tx_confirmations = height as i64 - self.funding_tx_confirmation_height as i64 + 1;
-                       if funding_tx_confirmations <= 0 {
-                               self.funding_tx_confirmation_height = 0;
-                       }
-
-                       let non_shutdown_state = self.channel_state & (!MULTI_STATE_FLAGS);
-                       if (non_shutdown_state >= ChannelState::ChannelFunded as u32 ||
-                          (non_shutdown_state & ChannelState::OurFundingLocked as u32) == ChannelState::OurFundingLocked as u32) &&
-                           funding_tx_confirmations < self.minimum_depth as i64 / 2 {
-                               return true;
-                       }
+       pub fn block_disconnected(&mut self, header: &BlockHeader, new_height: u32) -> bool {
+               if self.update_best_block(new_height, header.time).is_err() {
+                       return true;
                }
                false
        }