Add the ability to close metric and trace clients (#295)

* add the ability to close metric and trace clients

Co-authored-by: Punya Biswal <punya@google.com>

stackdriver.go

@@ -435,6 +435,16 @@ func (e *Exporter) StopMetricsExporter() {
 	e.statsExporter.stopMetricsReader()
 }
 
+// Close closes client connections.
+func (e *Exporter) Close() error {
+	tErr := e.traceExporter.close()
+	mErr := e.statsExporter.close()
+	if mErr != nil || tErr != nil {
+		return fmt.Errorf("error(s) closing trace client (%v), or metrics client (%v)", tErr, mErr)
+	}
+	return nil
+}
+
 // ExportSpan exports a SpanData to Stackdriver Trace.
 func (e *Exporter) ExportSpan(sd *trace.SpanData) {
 	if len(e.traceExporter.o.DefaultTraceAttributes) > 0 {

stats.go

@@ -149,6 +149,10 @@ func (e *statsExporter) stopMetricsReader() {
 	}
 }
 
+func (e *statsExporter) close() error {
+	return e.c.Close()
+}
+
 func (e *statsExporter) getMonitoredResource(v *view.View, tags []tag.Tag) ([]tag.Tag, *monitoredrespb.MonitoredResource) {
 	resource := e.o.Resource
 	if resource == nil {

trace.go

@@ -120,6 +120,10 @@ func (e *traceExporter) Flush() {
 	e.bundler.Flush()
 }
 
+func (e *traceExporter) close() error {
+	return e.client.Close()
+}
+
 func (e *traceExporter) pushTraceSpans(ctx context.Context, node *commonpb.Node, r *resourcepb.Resource, spans []*trace.SpanData) (int, error) {
 	ctx, span := trace.StartSpan(
 		ctx,