libcni: add specific type for CHECK not supported

Previously, we returned an arbitrary string error if the given CNI
version didn't support CHECK. This is not useful for downstream
consumption and matching.

So, declare an error variable so that users can use `errors.Is()`
instead of matching on a string.

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

Author: squeed

libcni/api.go

@@ -38,6 +38,8 @@ import (
 
 var (
 	CacheDir = "/var/lib/cni"
+	// slightly awkward wording to preserve anyone matching on error strings
+	ErrorCheckNotSupp = fmt.Errorf("does not support the CHECK command")
 )
 
 const (
@@ -453,7 +455,7 @@ func (c *CNIConfig) CheckNetworkList(ctx context.Context, list *NetworkConfigLis
 	if gtet, err := version.GreaterThanOrEqualTo(list.CNIVersion, "0.4.0"); err != nil {
 		return err
 	} else if !gtet {
-		return fmt.Errorf("configuration version %q does not support the CHECK command", list.CNIVersion)
+		return fmt.Errorf("configuration version %q %w", list.CNIVersion, ErrorCheckNotSupp)
 	}
 
 	if list.DisableCheck {
@@ -547,7 +549,7 @@ func (c *CNIConfig) CheckNetwork(ctx context.Context, net *NetworkConfig, rt *Ru
 	if gtet, err := version.GreaterThanOrEqualTo(net.Network.CNIVersion, "0.4.0"); err != nil {
 		return err
 	} else if !gtet {
-		return fmt.Errorf("configuration version %q does not support the CHECK command", net.Network.CNIVersion)
+		return fmt.Errorf("configuration version %q %w", net.Network.CNIVersion, ErrorCheckNotSupp)
 	}
 
 	cachedResult, err := c.getCachedResult(net.Network.Name, net.Network.CNIVersion, rt)

libcni/api_test.go

@@ -1280,6 +1280,7 @@ var _ = Describe("Invoking plugins", func() {
 						Expect(err).NotTo(HaveOccurred())
 						err = cniConfig.CheckNetworkList(ctx, netConfigList, runtimeConfig)
 						Expect(err).To(MatchError("configuration version \"0.3.1\" does not support the CHECK command"))
+						Expect(errors.Is(err, libcni.ErrorCheckNotSupp)).To(BeTrue())
 					})
 				})
 			})