unittest: Add helper to run a cross-namespace HTTP server

Add helper to run a cross-namespace HTTP server.

Signed-off-by: ChengyuZhu6 <hudson@cyzhu.com>

Author: ChengyuZhu6

cmd/nerdctl/image/image_import_linux_test.go

@@ -21,7 +21,6 @@ import (
 	"bytes"
 	"errors"
 	"net/http"
-	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"strings"
@@ -72,7 +71,7 @@ func TestImageImportErrors(t *testing.T) {
 func TestImageImport(t *testing.T) {
 	testCase := nerdtest.Setup()
 
-	var urlServer *httptest.Server
+	var stopServer func()
 
 	testCase.SubTests = []*test.Case{
 		{
@@ -170,17 +169,21 @@ func TestImageImport(t *testing.T) {
 		{
 			Description: "image import from URL",
 			Cleanup: func(data test.Data, helpers test.Helpers) {
-				if urlServer != nil {
-					urlServer.Close()
+				if stopServer != nil {
+					stopServer()
+					stopServer = nil
 				}
 				helpers.Anyhow("rmi", "-f", data.Identifier())
 			},
 			Setup: func(data test.Data, helpers test.Helpers) {
-				urlServer = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 					w.Header().Set("Content-Type", "application/x-tar")
 					_, _ = w.Write(minimalRootfsTar(t).Bytes())
-				}))
-				data.Labels().Set("url", urlServer.URL)
+				})
+				url, stop, err := nerdtest.StartHTTPServer(handler)
+				assert.NilError(t, err)
+				stopServer = stop
+				data.Labels().Set("url", url)
 			},
 			Command: func(data test.Data, helpers test.Helpers) test.TestableCommand {
 				return helpers.Command("import", data.Labels().Get("url"), data.Identifier())

pkg/testutil/nerdtest/utilities_linux.go

@@ -17,6 +17,9 @@
 package nerdtest
 
 import (
+	"net"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"strconv"
 	"strings"
@@ -26,6 +29,7 @@ import (
 	"github.com/containerd/nerdctl/mod/tigron/test"
 
 	"github.com/containerd/nerdctl/v2/pkg/testutil"
+	"github.com/containerd/nerdctl/v2/pkg/testutil/nettestutil"
 )
 
 const SignalCaught = "received"
@@ -73,3 +77,27 @@ func RunSigProxyContainer(signal os.Signal, exitOnSignal bool, args []string, da
 
 	return cmd
 }
+
+// StartHTTPServer starts an HTTP server bound to 0.0.0.0 and returns a URL reachable
+// from processes that cannot access 127.0.0.1 due to namespace isolation.
+// It also returns a cleanup function that stops the server.
+func StartHTTPServer(handler http.Handler) (url string, stop func(), err error) {
+	l, err := net.Listen("tcp", "0.0.0.0:0")
+	if err != nil {
+		return "", nil, err
+	}
+	srv := &httptest.Server{Config: &http.Server{Handler: handler}}
+	srv.Listener = l
+	srv.Start()
+	hostIP, herr := nettestutil.NonLoopbackIPv4()
+	if herr != nil {
+		srv.Close()
+		return "", nil, herr
+	}
+	_, port, perr := net.SplitHostPort(l.Addr().String())
+	if perr != nil {
+		srv.Close()
+		return "", nil, perr
+	}
+	return "http://" + hostIP.String() + ":" + port, func() { srv.Close() }, nil
+}