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/conf.go

@@ -39,7 +39,73 @@ func ConfFromFile(filename string) (*NetworkConfig, error) {
 	return ConfFromBytes(bytes)
 }
 
-func ConfFiles(dir string) ([]string, error) {
+func ConfListFromBytes(bytes []byte) (*NetworkConfigList, error) {
+	rawList := make(map[string]interface{})
+	if err := json.Unmarshal(bytes, &rawList); err != nil {
+		return nil, fmt.Errorf("error parsing configuration list: %s", err)
+	}
+
+	rawName, ok := rawList["name"]
+	if !ok {
+		return nil, fmt.Errorf("error parsing configuration list: no name")
+	}
+	name, ok := rawName.(string)
+	if !ok {
+		return nil, fmt.Errorf("error parsing configuration list: invalid name type %T", rawName)
+	}
+
+	var cniVersion string
+	rawVersion, ok := rawList["cniVersion"]
+	if ok {
+		cniVersion, ok = rawVersion.(string)
+		if !ok {
+			return nil, fmt.Errorf("error parsing configuration list: invalid cniVersion type %T", rawVersion)
+		}
+	}
+
+	list := &NetworkConfigList{
+		Name:       name,
+		CNIVersion: cniVersion,
+		Bytes:      bytes,
+	}
+
+	var plugins []interface{}
+	plug, ok := rawList["plugins"]
+	if !ok {
+		return nil, fmt.Errorf("error parsing configuration list: no 'plugins' key")
+	}
+	plugins, ok = plug.([]interface{})
+	if !ok {
+		return nil, fmt.Errorf("error parsing configuration list: invalid 'plugins' type %T", plug)
+	}
+	if len(plugins) == 0 {
+		return nil, fmt.Errorf("error parsing configuration list: no plugins in list")
+	}
+
+	for i, conf := range plugins {
+		newBytes, err := json.Marshal(conf)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to marshal plugin config %d: %v", i, err)
+		}
+		netConf, err := ConfFromBytes(newBytes)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to parse plugin config %d: %v", i, err)
+		}
+		list.Plugins = append(list.Plugins, netConf)
+	}
+
+	return list, nil
+}
+
+func ConfListFromFile(filename string) (*NetworkConfigList, error) {
+	bytes, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, fmt.Errorf("error reading %s: %s", filename, err)
+	}
+	return ConfListFromBytes(bytes)
+}
+
+func ConfFiles(dir string, extensions []string) ([]string, error) {
 	// In part, adapted from rkt/networking/podenv.go#listFiles
 	files, err := ioutil.ReadDir(dir)
 	switch {
@@ -56,15 +122,17 @@ func ConfFiles(dir string) ([]string, error) {
 			continue
 		}
 		fileExt := filepath.Ext(f.Name())
-		if fileExt == ".conf" || fileExt == ".json" {
-			confFiles = append(confFiles, filepath.Join(dir, f.Name()))
+		for _, ext := range extensions {
+			if fileExt == ext {
+				confFiles = append(confFiles, filepath.Join(dir, f.Name()))
+			}
 		}
 	}
 	return confFiles, nil
 }
 
 func LoadConf(dir, name string) (*NetworkConfig, error) {
-	files, err := ConfFiles(dir)
+	files, err := ConfFiles(dir, []string{".conf", ".json"})
 	switch {
 	case err != nil:
 		return nil, err
@@ -85,6 +153,28 @@ func LoadConf(dir, name string) (*NetworkConfig, error) {
 	return nil, fmt.Errorf(`no net configuration with name "%s" in %s`, name, dir)
 }
 
+func LoadConfList(dir, name string) (*NetworkConfigList, error) {
+	files, err := ConfFiles(dir, []string{".conflist"})
+	switch {
+	case err != nil:
+		return nil, err
+	case len(files) == 0:
+		return nil, fmt.Errorf("no net configuration lists found")
+	}
+	sort.Strings(files)
+
+	for _, confFile := range files {
+		conf, err := ConfListFromFile(confFile)
+		if err != nil {
+			return nil, err
+		}
+		if conf.Name == name {
+			return conf, nil
+		}
+	}
+	return nil, fmt.Errorf(`no net configuration list with name "%s" in %s`, name, dir)
+}
+
 func InjectConf(original *NetworkConfig, key string, newValue interface{}) (*NetworkConfig, error) {
 	config := make(map[string]interface{})
 	err := json.Unmarshal(original.Bytes, &config)