net/http: deep copy Request.URL also in Request.WithContext's copy

Despite the previously known behavior of Request.WithContext
shallow copying a request, usage of the request inside server.ServeHTTP
mutates the request's URL. This CL implements deep copying of the URL.

Fixes #20068

Change-Id: I86857d7259e23ac624d196401bf12dde401c42af
Reviewed-on: https://go-review.googlesource.com/41308
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/net/http/request_test.go b/src/net/http/request_test.go
index e6748375b5..1608d1c4fe 100644
--- a/src/net/http/request_test.go
+++ b/src/net/http/request_test.go
@@ -7,6 +7,7 @@ package http_test
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"encoding/base64"
 	"fmt"
 	"io"
@@ -785,6 +786,21 @@ func TestMaxBytesReaderStickyError(t *testing.T) {
 	}
 }
 
+func TestWithContextDeepCopiesURL(t *testing.T) {
+	req, err := NewRequest("POST", "https://golang.org/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	reqCopy := req.WithContext(context.Background())
+	reqCopy.URL.Scheme = "http"
+
+	firstURL, secondURL := req.URL.String(), reqCopy.URL.String()
+	if firstURL == secondURL {
+		t.Errorf("unexpected change to original request's URL")
+	}
+}
+
 // verify that NewRequest sets Request.GetBody and that it works
 func TestNewRequestGetBody(t *testing.T) {
 	tests := []struct {