Update

vendor/tailscale.com/appc/ippool.go

@@ -0,0 +1,61 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package appc
+
+import (
+	"errors"
+	"net/netip"
+
+	"go4.org/netipx"
+)
+
+// errPoolExhausted is returned when there are no more addresses to iterate over.
+var errPoolExhausted = errors.New("ip pool exhausted")
+
+// ippool allows for iteration over all the addresses within a netipx.IPSet.
+// netipx.IPSet has a Ranges call that returns the "minimum and sorted set of IP ranges that covers [the set]".
+// netipx.IPRange is "an inclusive range of IP addresses from the same address family.". So we can iterate over
+// all the addresses in the set by keeping a track of the last address we returned, calling Next on the last address
+// to get the new one, and if we run off the edge of the current range, starting on the next one.
+type ippool struct {
+	// ranges defines the addresses in the pool
+	ranges []netipx.IPRange
+	// last is internal tracking of which the last address provided was.
+	last netip.Addr
+	// rangeIdx is internal tracking of which netipx.IPRange from the IPSet we are currently on.
+	rangeIdx int
+}
+
+func newIPPool(ipset *netipx.IPSet) *ippool {
+	if ipset == nil {
+		return &ippool{}
+	}
+	return &ippool{ranges: ipset.Ranges()}
+}
+
+// next returns the next address from the set, or errPoolExhausted if we have
+// iterated over the whole set.
+func (ipp *ippool) next() (netip.Addr, error) {
+	if ipp.rangeIdx >= len(ipp.ranges) {
+		// ipset is empty or we have iterated off the end
+		return netip.Addr{}, errPoolExhausted
+	}
+	if !ipp.last.IsValid() {
+		// not initialized yet
+		ipp.last = ipp.ranges[0].From()
+		return ipp.last, nil
+	}
+	currRange := ipp.ranges[ipp.rangeIdx]
+	if ipp.last == currRange.To() {
+		// then we need to move to the next range
+		ipp.rangeIdx++
+		if ipp.rangeIdx >= len(ipp.ranges) {
+			return netip.Addr{}, errPoolExhausted
+		}
+		ipp.last = ipp.ranges[ipp.rangeIdx].From()
+		return ipp.last, nil
+	}
+	ipp.last = ipp.last.Next()
+	return ipp.last, nil
+}