WithNetNS restores original namespace when callback errors

- adds test coverage of WithNetNS in BDD-style

ns/ns.go

@@ -82,11 +82,11 @@ func WithNetNS(ns *os.File, lockThread bool, f func(*os.File) error) error {
 	if err = SetNS(ns, syscall.CLONE_NEWNET); err != nil {
 		return fmt.Errorf("Error switching to ns %v: %v", ns.Name(), err)
 	}
+	defer SetNS(thisNS, syscall.CLONE_NEWNET) // switch back
 
 	if err = f(thisNS); err != nil {
 		return err
 	}
 
-	// switch back
-	return SetNS(thisNS, syscall.CLONE_NEWNET)
+	return nil
 }

ns/ns_suite_test.go

@@ -0,0 +1,20 @@
+package ns_test
+
+import (
+	"math/rand"
+	"runtime"
+
+	. "github.com/onsi/ginkgo"
+	"github.com/onsi/ginkgo/config"
+	. "github.com/onsi/gomega"
+
+	"testing"
+)
+
+func TestNs(t *testing.T) {
+	rand.Seed(config.GinkgoConfig.RandomSeed)
+	runtime.LockOSThread()
+
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "pkg/ns Suite")
+}

ns/ns_test.go

@@ -0,0 +1,153 @@
+package ns_test
+
+import (
+	"errors"
+	"fmt"
+	"math/rand"
+	"os"
+	"os/exec"
+	"path/filepath"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/appc/cni/pkg/ns"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+func getInode(path string) (uint64, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return 0, err
+	}
+	defer file.Close()
+	return getInodeF(file)
+}
+
+func getInodeF(file *os.File) (uint64, error) {
+	stat := &unix.Stat_t{}
+	err := unix.Fstat(int(file.Fd()), stat)
+	return stat.Ino, err
+}
+
+const CurrentNetNS = "/proc/self/ns/net"
+
+var _ = Describe("Linux namespace operations", func() {
+	Describe("WithNetNS", func() {
+		var (
+			originalNetNS *os.File
+
+			targetNetNSName string
+			targetNetNSPath string
+			targetNetNS     *os.File
+		)
+
+		BeforeEach(func() {
+			var err error
+			originalNetNS, err = os.Open(CurrentNetNS)
+			Expect(err).NotTo(HaveOccurred())
+
+			targetNetNSName = fmt.Sprintf("test-netns-%d", rand.Int())
+
+			err = exec.Command("ip", "netns", "add", targetNetNSName).Run()
+			Expect(err).NotTo(HaveOccurred())
+
+			targetNetNSPath = filepath.Join("/var/run/netns/", targetNetNSName)
+			targetNetNS, err = os.Open(targetNetNSPath)
+			Expect(err).NotTo(HaveOccurred())
+		})
+
+		AfterEach(func() {
+			Expect(targetNetNS.Close()).To(Succeed())
+
+			err := exec.Command("ip", "netns", "del", targetNetNSName).Run()
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(originalNetNS.Close()).To(Succeed())
+		})
+
+		It("executes the callback within the target network namespace", func() {
+			expectedInode, err := getInode(targetNetNSPath)
+			Expect(err).NotTo(HaveOccurred())
+
+			var actualInode uint64
+			var innerErr error
+			err = ns.WithNetNS(targetNetNS, false, func(*os.File) error {
+				actualInode, innerErr = getInode(CurrentNetNS)
+				return nil
+			})
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(innerErr).NotTo(HaveOccurred())
+			Expect(actualInode).To(Equal(expectedInode))
+		})
+
+		It("provides the original namespace as the argument to the callback", func() {
+			hostNSInode, err := getInode(CurrentNetNS)
+			Expect(err).NotTo(HaveOccurred())
+
+			var inputNSInode uint64
+			var innerErr error
+			err = ns.WithNetNS(targetNetNS, false, func(inputNS *os.File) error {
+				inputNSInode, err = getInodeF(inputNS)
+				return nil
+			})
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(innerErr).NotTo(HaveOccurred())
+			Expect(inputNSInode).To(Equal(hostNSInode))
+		})
+
+		It("restores the calling thread to the original network namespace", func() {
+			preTestInode, err := getInode(CurrentNetNS)
+			Expect(err).NotTo(HaveOccurred())
+
+			err = ns.WithNetNS(targetNetNS, false, func(*os.File) error {
+				return nil
+			})
+			Expect(err).NotTo(HaveOccurred())
+
+			postTestInode, err := getInode(CurrentNetNS)
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(postTestInode).To(Equal(preTestInode))
+		})
+
+		Context("when the callback returns an error", func() {
+			It("restores the calling thread to the original namespace before returning", func() {
+				preTestInode, err := getInode(CurrentNetNS)
+				Expect(err).NotTo(HaveOccurred())
+
+				_ = ns.WithNetNS(targetNetNS, false, func(*os.File) error {
+					return errors.New("potato")
+				})
+
+				postTestInode, err := getInode(CurrentNetNS)
+				Expect(err).NotTo(HaveOccurred())
+
+				Expect(postTestInode).To(Equal(preTestInode))
+			})
+
+			It("returns the error from the callback", func() {
+				err := ns.WithNetNS(targetNetNS, false, func(*os.File) error {
+					return errors.New("potato")
+				})
+				Expect(err).To(MatchError("potato"))
+			})
+		})
+
+		Describe("validating inode mapping to namespaces", func() {
+			It("checks that different namespaces have different inodes", func() {
+				hostNSInode, err := getInode(CurrentNetNS)
+				Expect(err).NotTo(HaveOccurred())
+
+				testNsInode, err := getInode(targetNetNSPath)
+				Expect(err).NotTo(HaveOccurred())
+
+				Expect(hostNSInode).NotTo(Equal(0))
+				Expect(testNsInode).NotTo(Equal(0))
+				Expect(testNsInode).NotTo(Equal(hostNSInode))
+			})
+		})
+	})
+})