add Write method to config source

config/source/cli/cli.go

@@ -78,6 +78,11 @@ func (c *cliSource) Watch() (source.Watcher, error) {
 	return source.NewNoopWatcher()
 }
 
+// Write is unsupported
+func (c *cliSource) Write(cs *source.ChangeSet) error {
+	return nil
+}
+
 func (c *cliSource) String() string {
 	return "cli"
 }

config/source/env/env.go

@@ -105,6 +105,10 @@ func (e *env) Watch() (source.Watcher, error) {
 	return newWatcher()
 }
 
+func (e *env) Write(cs *source.ChangeSet) error {
+	return nil
+}
+
 func (e *env) String() string {
 	return "env"
 }

config/source/etcd/etcd.go

@@ -76,6 +76,10 @@ func (c *etcd) Watch() (source.Watcher, error) {
 	return newWatcher(c.prefix, c.stripPrefix, c.client.Watcher, cs, c.opts)
 }
 
+func (c *etcd) Write(cs *source.ChangeSet) error {
+	return nil
+}
+
 func NewSource(opts ...source.Option) source.Source {
 	options := source.NewOptions(opts...)
 

config/source/file/file.go

@@ -54,6 +54,10 @@ func (f *file) Watch() (source.Watcher, error) {
 	return newWatcher(f)
 }
 
+func (f *file) Write(cs *source.ChangeSet) error {
+	return nil
+}
+
 func NewSource(opts ...source.Option) source.Source {
 	options := source.NewOptions(opts...)
 	path := DefaultPath

config/source/flag/flag.go

@@ -77,6 +77,10 @@ func (fs *flagsrc) Watch() (source.Watcher, error) {
 	return source.NewNoopWatcher()
 }
 
+func (fs *flagsrc) Write(cs *source.ChangeSet) error {
+	return nil
+}
+
 func (fs *flagsrc) String() string {
 	return "flag"
 }

config/source/memory/memory.go

@@ -41,6 +41,10 @@ func (s *memory) Watch() (source.Watcher, error) {
 	return w, nil
 }
 
+func (m *memory) Write(cs *source.ChangeSet) error {
+	return nil
+}
+
 // Update allows manual updates of the config data.
 func (s *memory) Update(c *source.ChangeSet) {
 	// don't process nil

config/source/source.go

@@ -15,6 +15,7 @@ var (
 type Source interface {
 	Read() (*ChangeSet, error)
 	Watch() (Watcher, error)
+	Write(*ChangeSet) error
 	String() string
 }