From 1b6101b0c08d64cd1aa0c9aff04b78a921a9fc71 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@mit.edu>
Date: Mon, 23 Apr 2018 13:20:39 -0700
Subject: [PATCH] channeldb/channel: add NextLocalHtlcIndex

---
 channeldb/channel.go | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/channeldb/channel.go b/channeldb/channel.go
index b15943a2..9e13e5d3 100644
--- a/channeldb/channel.go
+++ b/channeldb/channel.go
@@ -1366,6 +1366,29 @@ func (c *OpenChannel) AdvanceCommitChainTail(fwdPkg *FwdPkg) error {
 	return nil
 }
 
+// NextLocalHtlcIndex returns the next unallocated local htlc index. To ensure
+// this always returns the next index that has been not been allocated, this
+// will first try to examine any pending commitments, before falling back to the
+// last locked-in local commitment.
+func (c *OpenChannel) NextLocalHtlcIndex() (uint64, error) {
+	// First, load the most recent commit diff that we initiated for the
+	// remote party. If no pending commit is found, this is not treated as
+	// a critical error, since we can always fall back.
+	pendingRemoteCommit, err := c.RemoteCommitChainTip()
+	if err != nil && err != ErrNoPendingCommit {
+		return 0, err
+	}
+
+	// If a pending commit was found, its local htlc index will be at least
+	// as large as the one on our local commitment.
+	if pendingRemoteCommit != nil {
+		return pendingRemoteCommit.Commitment.LocalHtlcIndex, nil
+	}
+
+	// Otherwise, fallback to using the local htlc index of our commitment.
+	return c.LocalCommitment.LocalHtlcIndex, nil
+}
+
 // LoadFwdPkgs scans the forwarding log for any packages that haven't been
 // processed, and returns their deserialized log updates in map indexed by the
 // remote commitment height at which the updates were locked in.