lnwallet: move commitChain to its own file.

lnwallet/commitment_chain.go

@@ -0,0 +1,58 @@
+package lnwallet
+
+import "container/list"
+
+// commitmentChain represents a chain of unrevoked commitments. The tail of the
+// chain is the latest fully signed, yet unrevoked commitment. Two chains are
+// tracked, one for the local node, and another for the remote node. New
+// commitments we create locally extend the remote node's chain, and vice
+// versa. Commitment chains are allowed to grow to a bounded length, after
+// which the tail needs to be "dropped" before new commitments can be received.
+// The tail is "dropped" when the owner of the chain sends a revocation for the
+// previous tail.
+type commitmentChain struct {
+	// commitments is a linked list of commitments to new states. New
+	// commitments are added to the end of the chain with increase height.
+	// Once a commitment transaction is revoked, the tail is incremented,
+	// freeing up the revocation window for new commitments.
+	commitments *list.List
+}
+
+// newCommitmentChain creates a new commitment chain.
+func newCommitmentChain() *commitmentChain {
+	return &commitmentChain{
+		commitments: list.New(),
+	}
+}
+
+// addCommitment extends the commitment chain by a single commitment. This
+// added commitment represents a state update proposed by either party. Once
+// the commitment prior to this commitment is revoked, the commitment becomes
+// the new defacto state within the channel.
+func (s *commitmentChain) addCommitment(c *commitment) {
+	s.commitments.PushBack(c)
+}
+
+// advanceTail reduces the length of the commitment chain by one. The tail of
+// the chain should be advanced once a revocation for the lowest unrevoked
+// commitment in the chain is received.
+func (s *commitmentChain) advanceTail() {
+	s.commitments.Remove(s.commitments.Front())
+}
+
+// tip returns the latest commitment added to the chain.
+func (s *commitmentChain) tip() *commitment {
+	return s.commitments.Back().Value.(*commitment)
+}
+
+// tail returns the lowest unrevoked commitment transaction in the chain.
+func (s *commitmentChain) tail() *commitment {
+	return s.commitments.Front().Value.(*commitment)
+}
+
+// hasUnackedCommitment returns true if the commitment chain has more than one
+// entry. The tail of the commitment chain has been ACKed by revoking all prior
+// commitments, but any subsequent commitments have not yet been ACKed.
+func (s *commitmentChain) hasUnackedCommitment() bool {
+	return s.commitments.Front() != s.commitments.Back()
+}