Implement a check to see if an ISO URL is valid (#3287)

* Implement a check to see if an ISO URL is valid

* Use strings.TrimPrefix instead of []rune casting for 'file://' prefix removal

* Handle file permissions error with a user-friendly message

cmd/minikube/cmd/config/config.go

@@ -90,7 +90,7 @@ var settings = []Setting{
 	{
 		name:        "iso-url",
 		set:         SetString,
-		validations: []setFn{IsValidURL},
+		validations: []setFn{IsValidURL, IsURLExists},
 	},
 	{
 		name: config.WantUpdateNotification,

cmd/minikube/cmd/config/validations.go

@@ -18,15 +18,15 @@ package config
 
 import (
 	"fmt"
+	"github.com/docker/go-units"
+	"github.com/pkg/errors"
+	"k8s.io/minikube/pkg/minikube/assets"
+	"k8s.io/minikube/pkg/minikube/constants"
 	"net"
 	"net/url"
 	"os"
 	"strconv"
-
-	units "github.com/docker/go-units"
-	"github.com/pkg/errors"
-	"k8s.io/minikube/pkg/minikube/assets"
-	"k8s.io/minikube/pkg/minikube/constants"
+	"strings"
 )
 
 func IsValidDriver(string, driver string) error {
@@ -59,6 +59,39 @@ func IsValidURL(name string, location string) error {
 	return nil
 }
 
+func IsURLExists(name string, location string) error {
+	parsed, err := url.Parse(location)
+	if err != nil {
+		return fmt.Errorf("%s is not a valid URL", location)
+	}
+
+	// we can only validate if local files exist, not other urls
+	if parsed.Scheme != "file" {
+		return nil
+	}
+
+	// chop off "file://" from the location, giving us the real system path
+	sysPath := strings.TrimPrefix(location, "file://")
+	stat, err := os.Stat(sysPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return fmt.Errorf("%s does not exist", location)
+		}
+
+		if os.IsPermission(err) {
+			return fmt.Errorf("%s could not be opened (permission error: %s)", location, err.Error())
+		}
+
+		return err
+	}
+
+	if stat.IsDir() {
+		return fmt.Errorf("%s is a directory", location)
+	}
+
+	return nil
+}
+
 func IsPositive(name string, val string) error {
 	i, err := strconv.Atoi(val)
 	if err != nil {

cmd/minikube/cmd/config/validations_test.go

@@ -16,7 +16,10 @@ limitations under the License.
 
 package config
 
-import "testing"
+import (
+	"os"
+	"testing"
+)
 
 type validationTest struct {
 	value     string
@@ -94,3 +97,25 @@ func TestValidCIDR(t *testing.T) {
 
 	runValidations(t, tests, "cidr", IsValidCIDR)
 }
+
+func TestIsURLExists(t *testing.T) {
+
+	self, err := os.Executable()
+	if err != nil {
+		t.Error(err)
+	}
+
+	tests := []validationTest{
+		{
+			value:     "file://" + self,
+			shouldErr: false,
+		},
+
+		{
+			value:     "file://" + self + "/subpath-of-file",
+			shouldErr: true,
+		},
+	}
+
+	runValidations(t, tests, "url", IsURLExists)
+}