Verifying the --swarm-discovery flag

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

commands/create.go

@@ -3,6 +3,7 @@ package commands
 import (
 	"fmt"
 	"path/filepath"
+	"regexp"
 
 	"github.com/docker/machine/log"
 
@@ -35,6 +36,10 @@ func cmdCreate(c *cli.Context) {
 		log.Fatal("You must specify a machine name")
 	}
 
+	if err := validateSwarmDiscovery(c.String("swarm-discovery")); err != nil {
+		log.Fatalf("Error parsing swarm discovery: %s", err)
+	}
+
 	certInfo := getCertPathInfo(c)
 
 	if err := setupCertificates(
@@ -118,3 +123,20 @@ func trimDriverFlags(driver string, cmds []cli.Command) ([]cli.Command, error) {
 
 	return filteredCmds, nil
 }
+
+func validateSwarmDiscovery(discovery string) error {
+	if discovery == "" {
+		return nil
+	}
+
+	matched, err := regexp.MatchString(`[^:]*://.*`, discovery)
+	if err != nil {
+		return err
+	}
+
+	if matched {
+		return nil
+	}
+
+	return fmt.Errorf("Swarm Discovery URL was in the wrong format: %s", discovery)
+}

commands/create_test.go

@@ -1 +1,22 @@
 package commands
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestValidateSwarmDiscoveryErrorsGivenInvalidURL(t *testing.T) {
+	err := validateSwarmDiscovery("foo")
+	assert.Error(t, err)
+}
+
+func TestValidateSwarmDiscoveryAcceptsEmptyString(t *testing.T) {
+	err := validateSwarmDiscovery("")
+	assert.NoError(t, err)
+}
+
+func TestValidateSwarmDiscoveryAcceptsValidFormat(t *testing.T) {
+	err := validateSwarmDiscovery("token://deadbeefcafe")
+	assert.NoError(t, err)
+}