Merge pull request #326 from TheBlueMatt/2019-03-temp-failure-use-cases

Update docs for TemporaryFailure to note other use-cases

diff --combined src/ln/channelmonitor.rs
index ac03b7bb8c1c6983f8b7caf0272ab75dc77ca5ee,a06d530a9a68e39e759fdb609c21c282088eff21..25f41d882964d0e6d0af4ac89f36f9d0bcb1ddf8
--- 1/src/ln/channelmonitor.rs
--- 2/src/ln/channelmonitor.rs
+++ b/src/ln/channelmonitor.rs
@@@ -48,8 -48,8 +48,8 @@@ use std::{hash,cmp, mem}
  /// An error enum representing a failure to persist a channel monitor update.
  #[derive(Clone)]
  pub enum ChannelMonitorUpdateErr {
-       /// Used to indicate a temporary failure (eg connection to a watchtower failed, but is expected
-       /// to succeed at some point in the future).
+       /// Used to indicate a temporary failure (eg connection to a watchtower or remote backup of
+       /// our state failed, but is expected to succeed at some point in the future).
        ///
        /// Such a failure will "freeze" a channel, preventing us from revoking old states or
        /// submitting new commitment transactions to the remote party.
@@@ -71,6 -71,10 +71,10 @@@
        /// Note that even if updates made after TemporaryFailure succeed you must still call
        /// test_restore_channel_monitor to ensure you have the latest monitor and re-enable normal
        /// channel operation.
+       ///
+       /// For deployments where a copy of ChannelMonitors and other local state are backed up in a
+       /// remote location (with local copies persisted immediately), it is anticipated that all
+       /// updates will return TemporaryFailure until the remote copies could be updated.
        TemporaryFailure,
        /// Used to indicate no further channel monitor updates will be allowed (eg we've moved on to a
        /// different watchtower and cannot update with all watchtowers that were previously informed
@@@ -1873,9 -1877,8 +1877,9 @@@ impl ChannelMonitor 
                        macro_rules! log_claim {
                                ($tx_info: expr, $local_tx: expr, $htlc: expr, $source_avail: expr) => {
                                        // We found the output in question, but aren't failing it backwards
 -                                      // as we have no corresponding source. This implies either it is an
 -                                      // inbound HTLC or an outbound HTLC on a revoked transaction.
 +                                      // as we have no corresponding source and no valid remote commitment txid
 +                                      // to try a weak source binding with same-hash, same-value still-valid offered HTLC.
 +                                      // This implies either it is an inbound HTLC or an outbound HTLC on a revoked transaction.
                                        let outbound_htlc = $local_tx == $htlc.offered;
                                        if ($local_tx && revocation_sig_claim) ||
                                                        (outbound_htlc && !$source_avail && (accepted_preimage_claim || offered_preimage_claim)) {
@@@ -1892,22 -1895,6 +1896,22 @@@
                                }
                        }
  
 +                      macro_rules! check_htlc_valid_remote {
 +                              ($remote_txid: expr, $htlc_output: expr) => {
 +                                      if let &Some(txid) = $remote_txid {
 +                                              for &(ref pending_htlc, ref pending_source) in self.remote_claimable_outpoints.get(&txid).unwrap() {
 +                                                      if pending_htlc.payment_hash == $htlc_output.payment_hash && pending_htlc.amount_msat == $htlc_output.amount_msat {
 +                                                              if let &Some(ref source) = pending_source {
 +                                                                      log_claim!("revoked remote commitment tx", false, pending_htlc, true);
 +                                                                      payment_data = Some(((**source).clone(), $htlc_output.payment_hash));
 +                                                                      break;
 +                                                              }
 +                                                      }
 +                                              }
 +                                      }
 +                              }
 +                      }
 +
                        macro_rules! scan_commitment {
                                ($htlcs: expr, $tx_info: expr, $local_tx: expr) => {
                                        for (ref htlc_output, source_option) in $htlcs {
@@@ -1920,17 -1907,7 +1924,17 @@@
                                                                // has timed out, or we screwed up. In any case, we should now
                                                                // resolve the source HTLC with the original sender.
                                                                payment_data = Some(((*source).clone(), htlc_output.payment_hash));
 -                                                      } else {
 +                                                      } else if !$local_tx {
 +                                                              if let Storage::Local { ref current_remote_commitment_txid, .. } = self.key_storage {
 +                                                                      check_htlc_valid_remote!(current_remote_commitment_txid, htlc_output);
 +                                                              }
 +                                                              if payment_data.is_none() {
 +                                                                      if let Storage::Local { ref prev_remote_commitment_txid, .. } = self.key_storage {
 +                                                                              check_htlc_valid_remote!(prev_remote_commitment_txid, htlc_output);
 +                                                                      }
 +                                                              }
 +                                                      }
 +                                                      if payment_data.is_none() {
                                                                log_claim!($tx_info, $local_tx, htlc_output, false);
                                                                continue 'outer_loop;
                                                        }