otelhttp: add WithClientTrace to connect with otelhttptrace

Transport can be created with `otelhttp.NewTransport(base, otelhttp.WithClientTrace(otelhttptrace.NewClientTrace))`
for additional httptrace tracing.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

CHANGELOG.md

@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Added
+
+- Add `WithClientTrace` option to `otelhttp.Transport` (#875)
+
 ### Changed
 
 - The `Transport`, `Handler`, and HTTP client convenience wrappers in the `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp` package now use the `TracerProvider` from the parent context if one exists and none was explicitly set when configuring the instrumentation. (#873)

instrumentation/net/http/otelhttp/config.go

@@ -15,7 +15,9 @@
 package otelhttp
 
 import (
+	"context"
 	"net/http"
+	"net/http/httptrace"
 
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/metric"
@@ -39,6 +41,7 @@ type config struct {
 	WriteEvent        bool
 	Filters           []Filter
 	SpanNameFormatter func(string, *http.Request) string
+	ClientTrace       func(context.Context) *httptrace.ClientTrace
 
 	TracerProvider trace.TracerProvider
 	MeterProvider  metric.MeterProvider
@@ -174,3 +177,11 @@ func WithSpanNameFormatter(f func(operation string, r *http.Request) string) Opt
 		c.SpanNameFormatter = f
 	})
 }
+
+// WithClientTrace takes a function that returns client trace instance that will be
+// applied to the requests sent through the otelhttp Transport.
+func WithClientTrace(f func(context.Context) *httptrace.ClientTrace) Option {
+	return optionFunc(func(c *config) {
+		c.ClientTrace = f
+	})
+}

instrumentation/net/http/otelhttp/test/transport_test.go

@@ -19,6 +19,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
+	"net/http/httptrace"
 	"strings"
 	"testing"
 
@@ -166,3 +167,65 @@ func TestTransportRequestWithTraceContext(t *testing.T) {
 	assert.NotEmpty(t, spans[1].Parent().SpanID())
 	assert.Equal(t, spans[0].SpanContext().SpanID(), spans[1].Parent().SpanID())
 }
+
+func TestWithHTTPTrace(t *testing.T) {
+	spanRecorder := tracetest.NewSpanRecorder()
+	provider := sdktrace.NewTracerProvider(
+		sdktrace.WithSpanProcessor(spanRecorder),
+	)
+	content := []byte("Hello, world!")
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, err := w.Write(content)
+		require.NoError(t, err)
+	}))
+	defer ts.Close()
+
+	tracer := provider.Tracer("")
+	ctx, span := tracer.Start(context.Background(), "test_span")
+
+	r, err := http.NewRequest(http.MethodGet, ts.URL, nil)
+	require.NoError(t, err)
+
+	r = r.WithContext(ctx)
+
+	clientTracer := func(ctx context.Context) *httptrace.ClientTrace {
+		var span trace.Span
+		return &httptrace.ClientTrace{
+			GetConn: func(_ string) {
+				_, span = trace.SpanFromContext(ctx).TracerProvider().Tracer("").Start(ctx, "httptrace.GetConn")
+			},
+			GotConn: func(_ httptrace.GotConnInfo) {
+				if span != nil {
+					span.End()
+				}
+			},
+		}
+	}
+
+	tr := otelhttp.NewTransport(
+		http.DefaultTransport,
+		otelhttp.WithClientTrace(clientTracer),
+	)
+
+	c := http.Client{Transport: tr}
+	res, err := c.Do(r)
+	require.NoError(t, err)
+
+	span.End()
+
+	body, err := ioutil.ReadAll(res.Body)
+	require.NoError(t, err)
+
+	require.Equal(t, content, body)
+
+	spans := spanRecorder.Ended()
+	require.Len(t, spans, 3)
+
+	assert.Equal(t, "httptrace.GetConn", spans[0].Name())
+	assert.Equal(t, "test_span", spans[1].Name())
+	assert.Equal(t, "HTTP GET", spans[2].Name())
+	assert.NotEmpty(t, spans[1].Parent().SpanID())
+	assert.Equal(t, spans[2].SpanContext().SpanID(), spans[0].Parent().SpanID())
+	assert.Equal(t, spans[1].SpanContext().SpanID(), spans[2].Parent().SpanID())
+}

instrumentation/net/http/otelhttp/transport.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"io"
 	"net/http"
+	"net/http/httptrace"
 
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/codes"
@@ -36,6 +37,7 @@ type Transport struct {
 	spanStartOptions  []trace.SpanStartOption
 	filters           []Filter
 	spanNameFormatter func(string, *http.Request) string
+	clientTrace       func(context.Context) *httptrace.ClientTrace
 }
 
 var _ http.RoundTripper = &Transport{}
@@ -71,6 +73,7 @@ func (t *Transport) applyConfig(c *config) {
 	t.spanStartOptions = c.SpanStartOptions
 	t.filters = c.Filters
 	t.spanNameFormatter = c.SpanNameFormatter
+	t.clientTrace = c.ClientTrace
 }
 
 func defaultTransportFormatter(_ string, r *http.Request) string {
@@ -102,6 +105,10 @@ func (t *Transport) RoundTrip(r *http.Request) (*http.Response, error) {
 
 	ctx, span := tracer.Start(r.Context(), t.spanNameFormatter("", r), opts...)
 
+	if t.clientTrace != nil {
+		ctx = httptrace.WithClientTrace(ctx, t.clientTrace(ctx))
+	}
+
 	r = r.WithContext(ctx)
 	span.SetAttributes(semconv.HTTPClientAttributesFromHTTPRequest(r)...)
 	t.propagators.Inject(ctx, propagation.HeaderCarrier(r.Header))