feat: add response size metrics

Signed-off-by: Ilham Syahid S <[email protected]>

metrics/response_size.go

@@ -0,0 +1,36 @@
+package metrics
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/riandyrn/otelchi"
+	otelmetric "go.opentelemetry.io/otel/metric"
+)
+
+// [NewResponseSizeBytes] creates a new instance of [responseSizeBytes].
+func NewResponseSizeBytes() otelchi.MetricsRecorder {
+	return &responseSizeBytes{}
+}
+
+// [responseSizeBytes] is a metrics recorder for recording response size in bytes.
+type responseSizeBytes struct {
+	responseSizeBytes otelmetric.Int64Histogram
+}
+
+func (r *responseSizeBytes) RegisterMetric(ctx context.Context, cfg otelchi.RegisterMetricConfig) {
+	httpResponseSizeBytes, err := cfg.Meter.Int64Histogram("response_size_bytes")
+	if err != nil {
+		panic(fmt.Sprintf("unable to create response_size_bytes histogram: %v", err))
+	}
+	r.responseSizeBytes = httpResponseSizeBytes
+}
+
+func (r *responseSizeBytes) StartMetric(ctx context.Context, opts otelchi.MetricOpts) {}
+
+func (r *responseSizeBytes) EndMetric(ctx context.Context, opts otelchi.MetricOpts) {
+	r.responseSizeBytes.Record(ctx,
+		int64(opts.ResponseData.WrittenBytes),
+		opts.Measurement,
+	)
+}