lnwallet: add new createCommitDiff method

This commit adds a new method: createCommitDiff. The method will, given
a newly constructed commitment, its signature, and HTLC signatures will
create a channeldb.CommitDiff. The CommitDiff created is to be stored
on disk, as it can be used in the case that the remote party didn’t
receive our CommitSig message and also forgot all the updates that we
queued with the update.

lnwallet/channel.go

@@ -1662,7 +1662,7 @@ type BreachRetribution struct {
 
 	// PendingHTLCs is a slice of the HTLCs which were pending at this
 	// point within the channel's history transcript.
-	PendingHTLCs []*channeldb.HTLC
+	PendingHTLCs []channeldb.HTLC
 
 	// LocalOutputSignDesc is a SignDescriptor which is capable of
 	// generating the signature necessary to sweep the output within the
@@ -2720,55 +2720,102 @@ func genRemoteHtlcSigJobs(keyRing *commitmentKeyRing,
 	return sigBatch, cancelChan, nil
 }
 
-// createCommitDiff
-func (lc *LightningChannel) createCommitDiff(commitment *commitment) (*channeldb.CommitDiff,
-	error) {
+// createCommitDiff will create a commit diff given a new pending commitment
+// for the remote party and the necessary signatures for the remote party to
+// validate this new state. This function is called right before sending the
+// new commitment to the remote party. The commit diff returned contains all
+// information necessary for retransmission.
+func (lc *LightningChannel) createCommitDiff(
+	newCommit *commitment, commitSig *btcec.Signature,
+	htlcSigs []*btcec.Signature) (*channeldb.CommitDiff, error) {
 
+	// First, we need to convert the funding outpoint into the ID that's
+	// used on the wire to identify this channel. We'll use this shortly
+	// when recording the exact CommitSig message that we'll be sending
+	// out.
 	chanID := lnwire.NewChanIDFromOutPoint(&lc.channelState.FundingOutpoint)
-	var htlcs []lnwire.Message
+
+	// We'll now run through our local update log to locate the items which
+	// were only just committed within this pending state. This will be the
+	// set of items we need to retransmit if we reconnect and find that
+	// they didn't process this new state fully.
+	var logUpdates []channeldb.LogUpdate
 	for e := lc.localUpdateLog.Front(); e != nil; e = e.Next() {
 		pd := e.Value.(*PaymentDescriptor)
 
-		// ...
-		var htlc lnwire.Message
-		if pd.addCommitHeightRemote == commitment.height {
-			switch pd.EntryType {
-			case Add:
-				continue
-			case Settle:
-				htlc = &lnwire.UpdateFufillHTLC{
-					ChanID:          chanID,
-					ID:              pd.Index,
-					PaymentPreimage: pd.RPreimage,
-				}
-			case Fail:
-				htlc = &lnwire.UpdateFailHTLC{
-					ChanID: chanID,
-					ID:     pd.Index,
-					Reason: pd.FailReason,
-				}
-			case MalformedFail:
-				htlc = &lnwire.UpdateFailMalformedHTLC{
-					ChanID:       chanID,
-					ID:           pd.Index,
-					ShaOnionBlob: pd.ShaOnionBlob,
-					FailureCode:  pd.FailCode,
-				}
+		// If this entry wasn't committed at the exact height of this
+		// remote commitment, then we'll skip it as it was already
+		// lingering in the log.
+		if pd.addCommitHeightRemote != newCommit.height &&
+			pd.removeCommitHeightRemote != newCommit.height {
+
+			continue
+		}
+
+		// Knowing that this update is a part of this new commitment,
+		// we'll create a log update and not it's index in the log so
+		// we can later restore it properly if a restart occurs.
+		logUpdate := channeldb.LogUpdate{
+			LogIndex: pd.LogIndex,
+		}
+
+		// We'll map the type of the PaymentDescriptor to one of the
+		// four messages that it corresponds to. With this set of
+		// messages obtained, we can simply read from disk and re-send
+		// them in the case of a needed channel sync.
+		switch pd.EntryType {
+		case Add:
+			htlc := &lnwire.UpdateAddHTLC{
+				ChanID:      chanID,
+				ID:          pd.HtlcIndex,
+				Amount:      pd.Amount,
+				Expiry:      pd.Timeout,
+				PaymentHash: pd.RHash,
+			}
+			copy(htlc.OnionBlob[:], pd.OnionBlob)
+			logUpdate.UpdateMsg = htlc
+
+		case Settle:
+			logUpdate.UpdateMsg = &lnwire.UpdateFufillHTLC{
+				ChanID:          chanID,
+				ID:              pd.ParentIndex,
+				PaymentPreimage: pd.RPreimage,
 			}
 
-			htlcs = append(htlcs, htlc)
+		case Fail:
+			logUpdate.UpdateMsg = &lnwire.UpdateFailHTLC{
+				ChanID: chanID,
+				ID:     pd.ParentIndex,
+				Reason: pd.FailReason,
+			}
+
+		case MalformedFail:
+			logUpdate.UpdateMsg = &lnwire.UpdateFailMalformedHTLC{
+				ChanID:       chanID,
+				ID:           pd.ParentIndex,
+				ShaOnionBlob: pd.ShaOnionBlob,
+				FailureCode:  pd.FailCode,
+			}
 		}
+
+		logUpdates = append(logUpdates, logUpdate)
 	}
 
-	delta, err := commitment.toChannelDelta(false)
-	if err != nil {
-		return nil, err
-	}
+	// With the set of log updates mapped into wire messages, we'll now
+	// convert the in-memory commit into a format suitable for writing to
+	// disk.
+	diskCommit := newCommit.toDiskCommit(false)
 
 	return &channeldb.CommitDiff{
-		PendingHeight:     commitment.height,
-		PendingCommitment: delta,
-		Updates:           htlcs,
+		Commitment: *diskCommit,
+		CommitSig: &lnwire.CommitSig{
+			ChanID: lnwire.NewChanIDFromOutPoint(
+				&lc.channelState.FundingOutpoint,
+			),
+			CommitSig: commitSig,
+			HtlcSigs:  htlcSigs,
+		},
+		LogUpdates: logUpdates,
 	}, nil
 }