pkg/ns: introduce error types indicate NS verification

ns/ns.go

@@ -81,11 +81,23 @@ const (
 	PROCFS_MAGIC = 0x9fa0
 )
 
-func IsNS(nspath string) (isNS bool, msg string, err error) {
+type NSPathNotExistErr struct{ msg string }
+
+func (e NSPathNotExistErr) Error() string { return e.msg }
+
+type NSPathNotNSErr struct{ msg string }
+
+func (e NSPathNotNSErr) Error() string { return e.msg }
+
+func IsNSorErr(nspath string) error {
 	stat := syscall.Statfs_t{}
-	if err = syscall.Statfs(nspath, &stat); err != nil {
+	if err := syscall.Statfs(nspath, &stat); err != nil {
-		err = fmt.Errorf("failed to Statfs %s: %v", nspath, err)
+		if os.IsNotExist(err) {
-		return
+			err = NSPathNotExistErr{msg: fmt.Sprintf("failed to Statfs %q: %v", nspath, err)}
+		} else {
+			err = fmt.Errorf("failed to Statfs %q: %v", nspath, err)
+		}
+		return err
 	}
 
 	switch stat.Type {
@@ -95,33 +107,29 @@ func IsNS(nspath string) (isNS bool, msg string, err error) {
 		validPathContent := "ns/"
 		validName := strings.Contains(nspath, validPathContent)
 		if !validName {
-			msg = fmt.Sprintf("path doesn't contain %q", validPathContent)
+			return NSPathNotNSErr{msg: fmt.Sprintf("path %q doesn't contain %q", nspath, validPathContent)}
-			return
 		}
-		isNS = true
+
+		return nil
 	case NSFS_MAGIC:
 		// Kernel >= 3.19
 
-		isNS = true
+		return nil
 	default:
-		msg = fmt.Sprintf("unknown FS magic: %x", stat.Type)
+		return NSPathNotNSErr{msg: fmt.Sprintf("unknown FS magic on %q: %x", nspath, stat.Type)}
 	}
-	return
 }
 
 // Returns an object representing the namespace referred to by @path
 func GetNS(nspath string) (NetNS, error) {
-	isNS, msg, err := IsNS(nspath)
+	err := IsNSorErr(nspath)
 	if err != nil {
 		return nil, err
 	}
-	if !isNS {
-		return nil, fmt.Errorf("no network namespace detected on %s: %s", nspath, msg)
-	}
 
 	fd, err := os.Open(nspath)
 	if err != nil {
-		return nil, fmt.Errorf("Failed to open %v: %v", nspath, err)
+		return nil, err
 	}
 
 	return &netNS{file: fd}, nil

ns/ns_test.go

@@ -181,8 +181,8 @@ var _ = Describe("Linux namespace operations", func() {
 
 				_, err = ns.GetNS(nspath)
 				Expect(err).To(HaveOccurred())
-				errString := fmt.Sprintf("%v", err)
+				Expect(err).To(BeAssignableToTypeOf(ns.NSPathNotNSErr{}))
-				Expect(errString).To(HavePrefix("no network namespace detected on %s", nspath))
+				Expect(err).NotTo(BeAssignableToTypeOf(ns.NSPathNotExistErr{}))
 			})
 		})
 
@@ -214,13 +214,11 @@ var _ = Describe("Linux namespace operations", func() {
 		})
 	})
 
-	Describe("IsNS", func() {
+	Describe("IsNSorErr", func() {
 		It("should detect a namespace", func() {
 			createdNetNS, err := ns.NewNS()
-			isNSFS, msg, err := ns.IsNS(createdNetNS.Path())
+			err = ns.IsNSorErr(createdNetNS.Path())
 			Expect(err).NotTo(HaveOccurred())
-			Expect(msg).To(Equal(""))
-			Expect(isNSFS).To(Equal(true))
 		})
 
 		It("should refuse other paths", func() {
@@ -231,9 +229,17 @@ var _ = Describe("Linux namespace operations", func() {
 			nspath := tempFile.Name()
 			defer os.Remove(nspath)
 
-			isNSFS, _, err := ns.IsNS(nspath)
+			err = ns.IsNSorErr(nspath)
-			Expect(err).NotTo(HaveOccurred())
+			Expect(err).To(HaveOccurred())
-			Expect(isNSFS).To(Equal(false))
+			Expect(err).To(BeAssignableToTypeOf(ns.NSPathNotNSErr{}))
+			Expect(err).NotTo(BeAssignableToTypeOf(ns.NSPathNotExistErr{}))
+		})
+
+		It("should error on non-existing paths", func() {
+			err := ns.IsNSorErr("/tmp/IDoNotExist")
+			Expect(err).To(HaveOccurred())
+			Expect(err).To(BeAssignableToTypeOf(ns.NSPathNotExistErr{}))
+			Expect(err).NotTo(BeAssignableToTypeOf(ns.NSPathNotNSErr{}))
 		})
 	})
 })