htlcswitch: add heldHtlcSet

Isolation of the set logic so that it will be easier to add watchdog functionality later.

htlcswitch/held_htlc_set.go

@@ -0,0 +1,75 @@
+package htlcswitch
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/channeldb"
+)
+
+// heldHtlcSet keeps track of outstanding intercepted forwards. It exposes
+// several methods to manipulate the underlying map structure in a consistent
+// way.
+type heldHtlcSet struct {
+	set map[channeldb.CircuitKey]InterceptedForward
+}
+
+func newHeldHtlcSet() *heldHtlcSet {
+	return &heldHtlcSet{
+		set: make(map[channeldb.CircuitKey]InterceptedForward),
+	}
+}
+
+// forEach iterates over all held forwards and calls the given callback for each
+// of them.
+func (h *heldHtlcSet) forEach(cb func(InterceptedForward)) {
+	for _, fwd := range h.set {
+		cb(fwd)
+	}
+}
+
+// popAll calls the callback for each forward and removes them from the set.
+func (h *heldHtlcSet) popAll(cb func(InterceptedForward)) {
+	for _, fwd := range h.set {
+		cb(fwd)
+	}
+
+	h.set = make(map[channeldb.CircuitKey]InterceptedForward)
+}
+
+// pop returns the specified forward and removes it from the set.
+func (h *heldHtlcSet) pop(key channeldb.CircuitKey) (InterceptedForward, error) {
+	intercepted, ok := h.set[key]
+	if !ok {
+		return nil, fmt.Errorf("fwd %v not found", key)
+	}
+
+	delete(h.set, key)
+
+	return intercepted, nil
+}
+
+// exists tests whether the specified forward is part of the set.
+func (h *heldHtlcSet) exists(key channeldb.CircuitKey) bool {
+	_, ok := h.set[key]
+
+	return ok
+}
+
+// push adds the specified forward to the set. An error is returned if the
+// forward exists already.
+func (h *heldHtlcSet) push(key channeldb.CircuitKey,
+	fwd InterceptedForward) error {
+
+	if fwd == nil {
+		return errors.New("nil fwd pushed")
+	}
+
+	if h.exists(key) {
+		return errors.New("htlc already exists in set")
+	}
+
+	h.set[key] = fwd
+
+	return nil
+}