TUN-4063: Cleanup dependencies between packages.

- Move packages the provide generic functionality (such as config) from `cmd` subtree to top level.
- Remove all dependencies on `cmd` subtree from top level packages.
- Consolidate all code dealing with token generation and transfer to a single cohesive package.

config/manager.go

@@ -0,0 +1,112 @@
+package config
+
+import (
+	"io"
+	"os"
+
+	"github.com/cloudflare/cloudflared/watcher"
+
+	"github.com/pkg/errors"
+	"github.com/rs/zerolog"
+	"gopkg.in/yaml.v2"
+)
+
+// Notifier sends out config updates
+type Notifier interface {
+	ConfigDidUpdate(Root)
+}
+
+// Manager is the base functions of the config manager
+type Manager interface {
+	Start(Notifier) error
+	Shutdown()
+}
+
+// FileManager watches the yaml config for changes
+// sends updates to the service to reconfigure to match the updated config
+type FileManager struct {
+	watcher    watcher.Notifier
+	notifier   Notifier
+	configPath string
+	log        *zerolog.Logger
+	ReadConfig func(string, *zerolog.Logger) (Root, error)
+}
+
+// NewFileManager creates a config manager
+func NewFileManager(watcher watcher.Notifier, configPath string, log *zerolog.Logger) (*FileManager, error) {
+	m := &FileManager{
+		watcher:    watcher,
+		configPath: configPath,
+		log:        log,
+		ReadConfig: readConfigFromPath,
+	}
+	err := watcher.Add(configPath)
+	return m, err
+}
+
+// Start starts the runloop to watch for config changes
+func (m *FileManager) Start(notifier Notifier) error {
+	m.notifier = notifier
+
+	// update the notifier with a fresh config on start
+	config, err := m.GetConfig()
+	if err != nil {
+		return err
+	}
+	notifier.ConfigDidUpdate(config)
+
+	m.watcher.Start(m)
+	return nil
+}
+
+// GetConfig reads the yaml file from the disk
+func (m *FileManager) GetConfig() (Root, error) {
+	return m.ReadConfig(m.configPath, m.log)
+}
+
+// Shutdown stops the watcher
+func (m *FileManager) Shutdown() {
+	m.watcher.Shutdown()
+}
+
+func readConfigFromPath(configPath string, log *zerolog.Logger) (Root, error) {
+	if configPath == "" {
+		return Root{}, errors.New("unable to find config file")
+	}
+
+	file, err := os.Open(configPath)
+	if err != nil {
+		return Root{}, err
+	}
+	defer file.Close()
+
+	var config Root
+	if err := yaml.NewDecoder(file).Decode(&config); err != nil {
+		if err == io.EOF {
+			log.Error().Msgf("Configuration file %s was empty", configPath)
+			return Root{}, nil
+		}
+		return Root{}, errors.Wrap(err, "error parsing YAML in config file at "+configPath)
+	}
+
+	return config, nil
+}
+
+// File change notifications from the watcher
+
+// WatcherItemDidChange triggers when the yaml config is updated
+// sends the updated config to the service to reload its state
+func (m *FileManager) WatcherItemDidChange(filepath string) {
+	config, err := m.GetConfig()
+	if err != nil {
+		m.log.Err(err).Msg("Failed to read new config")
+		return
+	}
+	m.log.Info().Msg("Config file has been updated")
+	m.notifier.ConfigDidUpdate(config)
+}
+
+// WatcherDidError notifies of errors with the file watcher
+func (m *FileManager) WatcherDidError(err error) {
+	m.log.Err(err).Msg("Config watcher encountered an error")
+}