api,libcni: add network config list-based plugin chaining

Using a new ".configlist" file format that allows specifying
a list of CNI network configurations to run, add new libcni
helper functions to call each plugin in the list, injecting
the overall name, CNI version, and previous plugin's Result
structure into the configuration of the next plugin.

libcni/api.go

@@ -34,7 +34,17 @@ type NetworkConfig struct {
 	Bytes   []byte
 }
 
+type NetworkConfigList struct {
+	Name       string
+	CNIVersion string
+	Plugins    []*NetworkConfig
+	Bytes      []byte
+}
+
 type CNI interface {
+	AddNetworkList(net *NetworkConfigList, rt *RuntimeConf) (*types.Result, error)
+	DelNetworkList(net *NetworkConfigList, rt *RuntimeConf) error
+
 	AddNetwork(net *NetworkConfig, rt *RuntimeConf) (*types.Result, error)
 	DelNetwork(net *NetworkConfig, rt *RuntimeConf) error
 }
@@ -46,6 +56,76 @@ type CNIConfig struct {
 // CNIConfig implements the CNI interface
 var _ CNI = &CNIConfig{}
 
+func buildOneConfig(list *NetworkConfigList, orig *NetworkConfig, prevResult *types.Result) (*NetworkConfig, error) {
+	var err error
+
+	// Ensure every config uses the same name and version
+	orig, err = InjectConf(orig, "name", list.Name)
+	if err != nil {
+		return nil, err
+	}
+	orig, err = InjectConf(orig, "cniVersion", list.CNIVersion)
+	if err != nil {
+		return nil, err
+	}
+
+	// Add previous plugin result
+	if prevResult != nil {
+		orig, err = InjectConf(orig, "prevResult", prevResult)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return orig, nil
+}
+
+// AddNetworkList executes a sequence of plugins with the ADD command
+func (c *CNIConfig) AddNetworkList(list *NetworkConfigList, rt *RuntimeConf) (*types.Result, error) {
+	var prevResult *types.Result
+	for _, net := range list.Plugins {
+		pluginPath, err := invoke.FindInPath(net.Network.Type, c.Path)
+		if err != nil {
+			return nil, err
+		}
+
+		newConf, err := buildOneConfig(list, net, prevResult)
+		if err != nil {
+			return nil, err
+		}
+
+		prevResult, err = invoke.ExecPluginWithResult(pluginPath, newConf.Bytes, c.args("ADD", rt))
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return prevResult, nil
+}
+
+// DelNetworkList executes a sequence of plugins with the DEL command
+func (c *CNIConfig) DelNetworkList(list *NetworkConfigList, rt *RuntimeConf) error {
+	for i := len(list.Plugins) - 1; i >= 0; i-- {
+		net := list.Plugins[i]
+
+		pluginPath, err := invoke.FindInPath(net.Network.Type, c.Path)
+		if err != nil {
+			return err
+		}
+
+		newConf, err := buildOneConfig(list, net, nil)
+		if err != nil {
+			return err
+		}
+
+		if err := invoke.ExecPluginWithoutResult(pluginPath, newConf.Bytes, c.args("DEL", rt)); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // AddNetwork executes the plugin with the ADD command
 func (c *CNIConfig) AddNetwork(net *NetworkConfig, rt *RuntimeConf) (*types.Result, error) {
 	pluginPath, err := invoke.FindInPath(net.Network.Type, c.Path)