pkg/version: add VersionsFrom function

So plugins can easily declare support for "from version 0.3 and
beyond".

Signed-off-by: Casey Callendrello <[email protected]>

Author: squeed

Diff for: pkg/version/version.go

@@ -19,7 +19,7 @@ import (
 	"fmt"
 
 	"github.com/containernetworking/cni/pkg/types"
-	"github.com/containernetworking/cni/pkg/types/100"
+	types100 "github.com/containernetworking/cni/pkg/types/100"
 	"github.com/containernetworking/cni/pkg/types/create"
 )
 
@@ -38,6 +38,22 @@ func Current() string {
 var Legacy = PluginSupports("0.1.0", "0.2.0")
 var All = PluginSupports("0.1.0", "0.2.0", "0.3.0", "0.3.1", "0.4.0", "1.0.0")
 
+// VersionsFrom returns a list of versions starting from min, inclusive
+func VersionsStartingFrom(min string) PluginInfo {
+	out := []string{}
+	// cheat, just assume ordered
+	ok := false
+	for _, v := range All.SupportedVersions() {
+		if !ok && v == min {
+			ok = true
+		}
+		if ok {
+			out = append(out, v)
+		}
+	}
+	return PluginSupports(out...)
+}
+
 // Finds a Result object matching the requested version (if any) and asks
 // that object to parse the plugin result, returning an error if parsing failed.
 func NewResult(version string, resultBytes []byte) (types.Result, error) {

Diff for: pkg/version/version_test.go

@@ -28,6 +28,11 @@ import (
 )
 
 var _ = Describe("Version operations", func() {
+	It("computes a list of versions correctly", func() {
+		actual := version.VersionsStartingFrom("0.3.1")
+		Expect(actual.SupportedVersions()).To(Equal([]string{"0.3.1", "0.4.0", "1.0.0"}))
+	})
+
 	Context("when a prevResult is available", func() {
 		It("parses the prevResult", func() {
 			rawBytes := []byte(`{