make DefaultClient immutable

Author: KonstantinosTsitoumis

instrumentation/net/http/otelhttp/client.go

@@ -9,20 +9,27 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
+	"sync"
 )
 
-// DefaultClient is the default Client and is used by Get, Head, Post and PostForm.
-// Please be careful of initialization order - for example, if you change
-// the global propagator, the DefaultClient might still be using the old one.
-var DefaultClient = &http.Client{Transport: NewTransport(http.DefaultTransport)}
+var (
+	defaultClient *http.Client
+	clientOnce    = &sync.Once{}
+)
+
+// GetDefaultClient provides the default Client and is used by Get, Head, Post and PostForm.
+func GetDefaultClient() *http.Client {
+	clientOnce.Do(func() { defaultClient = &http.Client{Transport: NewTransport(http.DefaultTransport)} })
+	return defaultClient
+}
 
 // Get is a convenient replacement for http.Get that adds a span around the request.
 func Get(ctx context.Context, targetURL string) (resp *http.Response, err error) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, targetURL, http.NoBody)
 	if err != nil {
 		return nil, err
 	}
-	return DefaultClient.Do(req)
+	return GetDefaultClient().Do(req)
 }
 
 // Head is a convenient replacement for http.Head that adds a span around the request.
@@ -31,7 +38,7 @@ func Head(ctx context.Context, targetURL string) (resp *http.Response, err error
 	if err != nil {
 		return nil, err
 	}
-	return DefaultClient.Do(req)
+	return GetDefaultClient().Do(req)
 }
 
 // Post is a convenient replacement for http.Post that adds a span around the request.
@@ -41,7 +48,7 @@ func Post(ctx context.Context, targetURL, contentType string, body io.Reader) (r
 		return nil, err
 	}
 	req.Header.Set("Content-Type", contentType)
-	return DefaultClient.Do(req)
+	return GetDefaultClient().Do(req)
 }
 
 // PostForm is a convenient replacement for http.PostForm that adds a span around the request.

instrumentation/net/http/otelhttp/client_test.go

@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package otelhttp_test
+package otelhttp
 
 import (
 	"net/http"
@@ -14,21 +14,19 @@ import (
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/otel/sdk/trace"
 	"go.opentelemetry.io/otel/sdk/trace/tracetest"
-
-	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 )
 
 func TestConvenienceWrappers(t *testing.T) {
 	sr := tracetest.NewSpanRecorder()
 	provider := trace.NewTracerProvider(trace.WithSpanProcessor(sr))
-	orig := otelhttp.DefaultClient
-	otelhttp.DefaultClient = &http.Client{
-		Transport: otelhttp.NewTransport(
+	orig := GetDefaultClient()
+	defaultClient = &http.Client{
+		Transport: NewTransport(
 			http.DefaultTransport,
-			otelhttp.WithTracerProvider(provider),
+			WithTracerProvider(provider),
 		),
 	}
-	defer func() { otelhttp.DefaultClient = orig }()
+	defer func() { defaultClient = orig }()
 
 	content := []byte("Hello, world!")
 
@@ -40,27 +38,27 @@ func TestConvenienceWrappers(t *testing.T) {
 	defer ts.Close()
 
 	ctx := t.Context()
-	res, err := otelhttp.Get(ctx, ts.URL)
+	res, err := Get(ctx, ts.URL)
 	if err != nil {
 		t.Fatal(err)
 	}
 	res.Body.Close()
 
-	res, err = otelhttp.Head(ctx, ts.URL)
+	res, err = Head(ctx, ts.URL)
 	if err != nil {
 		t.Fatal(err)
 	}
 	res.Body.Close()
 
-	res, err = otelhttp.Post(ctx, ts.URL, "text/plain", strings.NewReader("test"))
+	res, err = Post(ctx, ts.URL, "text/plain", strings.NewReader("test"))
 	if err != nil {
 		t.Fatal(err)
 	}
 	res.Body.Close()
 
 	form := make(url.Values)
 	form.Set("foo", "bar")
-	res, err = otelhttp.PostForm(ctx, ts.URL, form)
+	res, err = PostForm(ctx, ts.URL, form)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -90,7 +88,7 @@ func TestClientWithTraceContext(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	res, err := otelhttp.Get(ctx, ts.URL)
+	res, err := Get(ctx, ts.URL)
 	if err != nil {
 		t.Fatal(err)
 	}