fix: do not read everything into memory on metrics collection when re…

…quest/response body provided as stream

otelfiber/fiber.go

@@ -2,6 +2,8 @@ package otelfiber
 
 import (
 	"context"
+	"github.com/valyala/fasthttp"
+	"io"
 	"net/http"
 	"time"
 
@@ -31,6 +33,27 @@ const (
 	UnitMilliseconds  = "ms"
 )
 
+var _ io.Reader = (*bodyStreamSizeReader)(nil)
+
+type bodyStreamSizeReader struct {
+	impl       io.Reader
+	histogram  metric.Int64Histogram
+	measureOpt metric.MeasurementOption
+	ctx        context.Context
+	read       int64
+}
+
+func (b *bodyStreamSizeReader) Read(p []byte) (n int, err error) {
+	n, err = b.impl.Read(p)
+	b.read += int64(n)
+	if err == io.EOF {
+		b.histogram.Record(b.ctx, b.read, b.measureOpt)
+		b.read = 0
+	}
+
+	return n, err
+}
+
 // Middleware returns fiber handler which will trace incoming requests.
 func Middleware(opts ...Option) fiber.Handler {
 	cfg := config{}
@@ -134,16 +157,46 @@ func Middleware(opts ...Option) fiber.Handler {
 		)
 
 		var (
-			requestSize  int64 = -1
-			responseSize int64 = -1
+			requestSize  int64
+			responseSize int64
 		)
 
 		if !request.IsBodyStream() {
 			requestSize = int64(len(request.Body()))
+		} else {
+			// NOTICE: we have to create response copy because underlying steam closed before change
+			copyReq := &fasthttp.Request{}
+			request.CopyTo(copyReq)
+			copyReq.SetBodyStream(&bodyStreamSizeReader{
+				impl:      response.BodyStream(),
+				histogram: httpServerRequestSize,
+				measureOpt: metric.WithAttributes(append(
+					responseMetricAttrs,
+					responseAttrs...)...),
+				ctx:  context.WithoutCancel(savedCtx),
+				read: 0,
+			}, -1)
+
+			request = copyReq
 		}
 
 		if !response.IsBodyStream() {
 			responseSize = int64(len(response.Body()))
+		} else {
+			// NOTICE: we have to create response copy because underlying steam closed before change
+			copyResp := &fasthttp.Response{}
+			response.CopyTo(copyResp)
+			copyResp.SetBodyStream(&bodyStreamSizeReader{
+				impl:      response.BodyStream(),
+				histogram: httpServerResponseSize,
+				measureOpt: metric.WithAttributes(append(
+					responseMetricAttrs,
+					responseAttrs...)...),
+				ctx:  context.WithoutCancel(savedCtx),
+				read: 0,
+			}, -1)
+
+			response = copyResp
 		}
 
 		defer func() {
@@ -153,8 +206,13 @@ func Middleware(opts ...Option) fiber.Handler {
 
 			httpServerActiveRequests.Add(savedCtx, -1, metric.WithAttributes(requestMetricsAttrs...))
 			httpServerDuration.Record(savedCtx, float64(time.Since(start).Microseconds())/1000, metric.WithAttributes(responseMetricAttrs...))
-			httpServerRequestSize.Record(savedCtx, requestSize, metric.WithAttributes(responseMetricAttrs...))
-			httpServerResponseSize.Record(savedCtx, responseSize, metric.WithAttributes(responseMetricAttrs...))
+			if !request.IsBodyStream() {
+				httpServerRequestSize.Record(savedCtx, requestSize, metric.WithAttributes(responseMetricAttrs...))
+			}
+
+			if !response.IsBodyStream() {
+				httpServerResponseSize.Record(savedCtx, responseSize, metric.WithAttributes(responseMetricAttrs...))
+			}
 
 			c.SetUserContext(savedCtx)
 			cancel()

otelfiber/otelfiber_test/fiber_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -446,3 +447,79 @@ func TestCustomAttributes(t *testing.T) {
 	assert.Contains(t, attr, attribute.String("http.route", "/user/:id"))
 	assert.Contains(t, attr, attribute.String("http.query_params", "foo=bar"))
 }
+
+type fakeFile interface {
+	io.Reader
+}
+
+var _ fakeFile = (*fakeFileImpl)(nil)
+
+type fakeFileImpl struct {
+	done bool
+	pos  int
+}
+
+const fakeFileLen = 4096 * 2
+
+func (f *fakeFileImpl) Read(p []byte) (n int, err error) {
+	if f.done {
+		f.done = false
+		f.pos = 0
+		return 0, io.EOF
+	}
+
+	toRead := len(p)
+	if toRead > fakeFileLen-f.pos {
+		toRead = fakeFileLen - f.pos
+	}
+
+	for ix := 0; ix < toRead; ix++ {
+		p[ix] = byte(ix)
+		f.pos++
+	}
+
+	f.done = fakeFileLen-f.pos == 0
+	return toRead, nil
+}
+
+func TestStreamedResponseBody(t *testing.T) {
+	reader := metric.NewManualReader()
+	meterProvider := metric.NewMeterProvider(metric.WithReader(reader))
+	sr := new(tracetest.SpanRecorder)
+	tracerProvider := sdktrace.NewTracerProvider(sdktrace.WithSpanProcessor(sr))
+
+	app := fiber.New()
+	app.Use(
+		otelfiber.Middleware(
+			otelfiber.WithMeterProvider(meterProvider),
+			otelfiber.WithTracerProvider(tracerProvider),
+		),
+	)
+
+	app.Post("/streams", func(ctx *fiber.Ctx) error {
+		return ctx.SendStream(&fakeFileImpl{})
+	})
+
+	request := httptest.NewRequest(http.MethodPost, "/streams", nil)
+	resp, err := app.Test(request, 3000)
+
+	// do and verify the request
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+
+	spans := sr.Ended()
+	require.Len(t, spans, 1)
+
+	metrics := metricdata.ResourceMetrics{}
+	err = reader.Collect(context.Background(), &metrics)
+	assert.NoError(t, err)
+
+	assert.Len(t, metrics.ScopeMetrics, 1)
+	scopeMetrics := metrics.ScopeMetrics[0].Metrics
+	for _, m := range scopeMetrics {
+		if m.Name == otelfiber.MetricNameHttpServerResponseSize {
+			histogram := m.Data.(metricdata.Histogram[int64])
+			assert.Len(t, histogram.DataPoints, 1)
+			assert.Equal(t, histogram.DataPoints[0].Sum, int64(fakeFileLen))
+		}
+	}
+}