Check that public key exists when creating machine

Fixes #4

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

commands.go

@@ -180,6 +180,14 @@ func (cli *DockerCli) CmdCreate(args ...string) error {
 		return nil
 	}
 
+	keyExists, err := drivers.PublicKeyExists()
+	if err != nil {
+		return err
+	}
+	if !keyExists {
+		log.Fatalf("Identity auth public key does not exist at %s. Please run the docker client without any options to create it.", drivers.PublicKeyPath())
+	}
+
 	name := cmd.Arg(0)
 
 	store := NewStore()

drivers/utils.go

@@ -6,8 +6,12 @@ import (
 	"path/filepath"
 )
 
+func PublicKeyPath() string {
+	return filepath.Join(os.Getenv("HOME"), ".docker/public-key.json")
+}
+
 func AddPublicKeyToAuthorizedHosts(d Driver, authorizedKeysPath string) error {
-	f, err := os.Open(filepath.Join(os.Getenv("HOME"), ".docker/public-key.json"))
+	f, err := os.Open(PublicKeyPath())
 	if err != nil {
 		return err
 	}
@@ -21,3 +25,13 @@ func AddPublicKeyToAuthorizedHosts(d Driver, authorizedKeysPath string) error {
 	cmd.Stdin = f
 	return cmd.Run()
 }
+
+func PublicKeyExists() (bool, error) {
+	_, err := os.Stat(PublicKeyPath())
+	if err == nil {
+		return true, nil
+	} else if os.IsNotExist(err) {
+		return false, nil
+	}
+	return false, err
+}