libcni: implement version negotiation

This implements the `cniVersions` field in the network configuration
list. It allows for CNI plugins to specify that they support multiple
versions, and the runtime may select the highest version it supports.

Signed-off-by: Casey Callendrello <c1@caseyc.net>

libcni/conf.go

@@ -23,7 +23,10 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/Masterminds/semver/v3"
+
 	"github.com/containernetworking/cni/pkg/types"
+	"github.com/containernetworking/cni/pkg/version"
 )
 
 type NotFoundError struct {
@@ -86,6 +89,47 @@ func ConfListFromBytes(bytes []byte) (*NetworkConfigList, error) {
 		}
 	}
 
+	rawVersions, ok := rawList["cniVersions"]
+	if ok {
+		// Parse the current package CNI version
+		currentVersion, err := semver.NewVersion(version.Current())
+		if err != nil {
+			panic("CNI version is invalid semver!")
+		}
+
+		rvs, ok := rawVersions.([]interface{})
+		if !ok {
+			return nil, fmt.Errorf("error parsing configuration list: invalid type for cniVersions: %T", rvs)
+		}
+		vs := make([]*semver.Version, 0, len(rvs))
+		for i, rv := range rvs {
+			v, ok := rv.(string)
+			if !ok {
+				return nil, fmt.Errorf("error parsing configuration list: invalid type for cniVersions index %d: %T", i, rv)
+			}
+			if v, err := semver.NewVersion(v); err != nil {
+				return nil, fmt.Errorf("error parsing configuration list: invalid cniVersions entry %s at index %d: %w", v, i, err)
+			} else if !v.GreaterThan(currentVersion) {
+				// Skip versions "greater" than this implementation of the spec
+				vs = append(vs, v)
+			}
+		}
+
+		// if cniVersion was already set, append it to the list for sorting.
+		if cniVersion != "" {
+			if v, err := semver.NewVersion(cniVersion); err != nil {
+				return nil, fmt.Errorf("error parsing configuration list: invalid cniVersion %s: %w", cniVersion, err)
+			} else if !v.GreaterThan(currentVersion) {
+				// ignore any versions higher than the current implemented spec version
+				vs = append(vs, v)
+			}
+		}
+		sort.Sort(semver.Collection(vs))
+		if len(vs) > 0 {
+			cniVersion = vs[len(vs)-1].String()
+		}
+	}
+
 	disableCheck := false
 	if rawDisableCheck, ok := rawList["disableCheck"]; ok {
 		disableCheck, ok = rawDisableCheck.(bool)

libcni/conf_test.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
@@ -504,6 +505,53 @@ var _ = Describe("Loading configuration from disk", func() {
 	})
 })
 
+var _ = Describe("ConfListFromBytes", func() {
+	Describe("Version selection", func() {
+		makeConfig := func(versions ...string) []byte {
+			// ugly fake json encoding, but whatever
+			vs := []string{}
+			for _, v := range versions {
+				vs = append(vs, fmt.Sprintf(`"%s"`, v))
+			}
+			return []byte(fmt.Sprintf(`{"name": "test", "cniVersions": [%s], "plugins": [{"type": "foo"}]}`, strings.Join(vs, ",")))
+		}
+		It("correctly selects the maximum version", func() {
+			conf, err := libcni.ConfListFromBytes(makeConfig("1.1.0", "0.4.0", "1.0.0"))
+			Expect(err).NotTo(HaveOccurred())
+			Expect(conf.CNIVersion).To(Equal("1.1.0"))
+		})
+
+		It("selects the highest version supported by libcni", func() {
+			conf, err := libcni.ConfListFromBytes(makeConfig("99.0.0", "1.1.0", "0.4.0", "1.0.0"))
+			Expect(err).NotTo(HaveOccurred())
+			Expect(conf.CNIVersion).To(Equal("1.1.0"))
+		})
+
+		It("fails when invalid versions are specified", func() {
+			_, err := libcni.ConfListFromBytes(makeConfig("1.1.0", "0.4.0", "1.0.f"))
+			Expect(err).To(HaveOccurred())
+		})
+
+		It("falls back to cniVersion", func() {
+			conf, err := libcni.ConfListFromBytes([]byte(`{"name": "test", "cniVersion": "1.2.3", "plugins": [{"type": "foo"}]}`))
+			Expect(err).NotTo(HaveOccurred())
+			Expect(conf.CNIVersion).To(Equal("1.2.3"))
+		})
+
+		It("merges cniVersions and cniVersion", func() {
+			conf, err := libcni.ConfListFromBytes([]byte(`{"name": "test", "cniVersion": "1.0.0", "cniVersions": ["0.1.0", "0.4.0"], "plugins": [{"type": "foo"}]}`))
+			Expect(err).NotTo(HaveOccurred())
+			Expect(conf.CNIVersion).To(Equal("1.0.0"))
+		})
+
+		It("handles an empty cniVersions array", func() {
+			conf, err := libcni.ConfListFromBytes([]byte(`{"name": "test", "cniVersions": [], "plugins": [{"type": "foo"}]}`))
+			Expect(err).NotTo(HaveOccurred())
+			Expect(conf.CNIVersion).To(Equal(""))
+		})
+	})
+})
+
 var _ = Describe("ConfListFromConf", func() {
 	var testNetConfig *libcni.NetworkConfig