feat: exporting first byte read latency

main.go

@@ -153,6 +153,8 @@ func ReadObject(ctx context.Context, workerID int, bucketHandle *storage.BucketH
 		if err != nil {
 			return fmt.Errorf("while creating reader object: %v", err)
 		}
+		firstByteTime := time.Since(start)
+		stats.Record(ctx, firstByteReadLatency.M(float64(firstByteTime.Milliseconds())))
 
 		// Calls Reader.WriteTo implicitly.
 		_, err = io.Copy(io.Discard, rc)
@@ -234,6 +236,7 @@ func main() {
 
 	// Enable stack-driver exporter.
 	registerLatencyView()
+	registerFirstByteLatencyView()
 
 	err = enableSDExporter()
 	if err != nil {

metrics_exporter.go

@@ -15,6 +15,7 @@ import (
 var (
 	// The restaurant rating in number of stars.
 	readLatency = stats.Float64("readLatency", "Complete read latency", stats.UnitMilliseconds)
+	firstByteReadLatency = stats.Float64("firstByteReadLatency", "First byte read latency", stats.UnitMilliseconds)
 )
 
 var sdExporter *stackdriver.Exporter
@@ -32,6 +33,19 @@ func registerLatencyView() {
 		log.Fatalf("Failed to register the readLatency view: %v", err)
 	}
 }
+func registerFirstByteLatencyView() {
+	v := &view.View{
+		Name:        "princer_go_client_first_byte_read_latency",
+		Measure:     firstByteReadLatency,
+		Description: "First byte read latency for a given go-client",
+		TagKeys:     []tag.Key{tag.MustNewKey("princer_first_byte_read_latency")},
+		Aggregation: ochttp.DefaultLatencyDistribution,
+	}
+
+	if err := view.Register(v); err != nil {
+		log.Fatalf("Failed to register the readLatency view: %v", err)
+	}
+}
 
 func enableSDExporter() (err error) {
 	sdExporter, err := stackdriver.NewExporter(stackdriver.Options{