Implement pkg/interval in preparation for --to-ports

go.mod

@@ -3,6 +3,7 @@ module k8s.io/ip-masq-agent
 go 1.23
 
 require (
+	github.com/google/go-cmp v0.6.0
 	k8s.io/apimachinery v0.29.1
 	k8s.io/component-base v0.29.1
 	k8s.io/klog/v2 v2.110.1
@@ -17,7 +18,6 @@ require (
 	github.com/go-logr/logr v1.3.0 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/protobuf v1.5.3 // indirect
-	github.com/google/go-cmp v0.6.0 // indirect
 	github.com/google/gofuzz v1.2.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect

pkg/interval/interval.go

@@ -0,0 +1,72 @@
+package interval
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type Interval struct {
+	First int
+	Last  int
+}
+
+func (i Interval) Size() int {
+	return max(0, i.Last-i.First+1)
+}
+
+func ParseInterval(s string) (Interval, error) {
+	var i Interval
+
+	p := strings.Split(s, "-")
+	if len(p) > 2 {
+		return i, fmt.Errorf("invalid interval %q", s)
+	}
+
+	v, err := strconv.Atoi(p[0])
+	if err != nil {
+		return i, err
+	}
+	i.First = v
+
+	if len(p) == 1 {
+		i.Last = v
+		return i, nil
+	}
+
+	v, err = strconv.Atoi(p[1])
+	if err != nil {
+		return i, err
+	}
+	i.Last = v
+
+	if i.First > i.Last {
+		return i, fmt.Errorf("first is greater than last in %q", s)
+	}
+	return i, nil
+}
+
+type Intervals []Interval
+
+func (i Intervals) Size() int {
+	var size int
+	for _, j := range i {
+		size += j.Size()
+	}
+	return size
+}
+
+func ParseIntervals(s string) (Intervals, error) {
+	var is Intervals
+
+	for _, p := range strings.Split(s, ",") {
+		i, err := ParseInterval(p)
+		if err != nil {
+			return is, err
+		}
+
+		is = append(is, i)
+	}
+
+	return is, nil
+}