plugins: support Close() for Tracer plugins as well

Most of the tracers available need to properly close to send
the remaining traces before the process exit.

plugin/daemon.go

@@ -7,8 +7,7 @@ import (
 // PluginDaemon is an interface for daemon plugins. These plugins will be run on
 // the daemon and will be given access to an implementation of the CoreAPI.
 type PluginDaemon interface {
-	Plugin
+	Closer
 
 	Start(coreiface.CoreAPI) error
-	Close() error
 }

plugin/loader/loader.go

@@ -266,7 +266,7 @@ func (loader *PluginLoader) Close() error {
 	started := loader.started
 	loader.started = nil
 	for _, pl := range started {
-		if pl, ok := pl.(plugin.PluginDaemon); ok {
+		if pl, ok := pl.(plugin.Closer); ok {
 			err := pl.Close()
 			if err != nil {
 				errs = append(errs, fmt.Sprintf(

plugin/plugin.go

@@ -9,7 +9,7 @@ type Environment struct {
 	Config interface{}
 }
 
-// Plugin is base interface for all kinds of go-ipfs plugins
+// Plugin is the base interface for all kinds of go-ipfs plugins
 // It will be included in interfaces of different Plugins
 type Plugin interface {
 	// Name should return unique name of the plugin
@@ -23,3 +23,11 @@ type Plugin interface {
 	// (possibly uninitialized) IPFS repo and the plugin's config.
 	Init(env *Environment) error
 }
+
+// Closer plugin support closing when go-ipfs is terminating
+type Closer interface {
+	Plugin
+
+	// Close is called once when the Plugin is being unloaded
+	Close() error
+}

plugin/tracer.go

@@ -6,6 +6,7 @@ import (
 
 // PluginTracer is an interface that can be implemented to add a tracer
 type PluginTracer interface {
-	Plugin
+	Closer
+
 	InitTracer() (opentracing.Tracer, error)
 }