From 832b4408a596dca81a88ee21619a8378baa42cd8 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 9 Nov 2013 21:26:05 -0800
Subject: [PATCH] builder/docker: verify docker is available on path

---
 builder/docker/builder.go       | 9 ++++++---
 builder/docker/driver.go        | 3 +++
 builder/docker/driver_docker.go | 8 ++++++++
 builder/docker/driver_mock.go   | 7 +++++++
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/builder/docker/builder.go b/builder/docker/builder.go
index 824f1697f..0cf9d6aa9 100644
--- a/builder/docker/builder.go
+++ b/builder/docker/builder.go
@@ -25,6 +25,11 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 }
 
 func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packer.Artifact, error) {
+	driver := &DockerDriver{Ui: ui}
+	if err := driver.Verify(); err != nil {
+		return nil, err
+	}
+
 	steps := []multistep.Step{
 		&StepTempDir{},
 		&StepPull{},
@@ -40,9 +45,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 	state.Put("ui", ui)
 
 	// Setup the driver that will talk to Docker
-	state.Put("driver", &DockerDriver{
-		Ui: ui,
-	})
+	state.Put("driver", driver)
 
 	// Run!
 	if b.config.PackerDebug {
diff --git a/builder/docker/driver.go b/builder/docker/driver.go
index 04f4e3fd5..c19a8823b 100644
--- a/builder/docker/driver.go
+++ b/builder/docker/driver.go
@@ -20,6 +20,9 @@ type Driver interface {
 
 	// StopContainer forcibly stops a container.
 	StopContainer(id string) error
+
+	// Verify verifies that the driver can run
+	Verify() error
 }
 
 // ContainerConfig is the configuration used to start a container.
diff --git a/builder/docker/driver_docker.go b/builder/docker/driver_docker.go
index 932d46101..91e367acc 100644
--- a/builder/docker/driver_docker.go
+++ b/builder/docker/driver_docker.go
@@ -82,3 +82,11 @@ func (d *DockerDriver) StartContainer(config *ContainerConfig) (string, error) {
 func (d *DockerDriver) StopContainer(id string) error {
 	return exec.Command("docker", "kill", id).Run()
 }
+
+func (d *DockerDriver) Verify() error {
+	if _, err := exec.LookPath("docker"); err != nil {
+		return err
+	}
+
+	return nil
+}
diff --git a/builder/docker/driver_mock.go b/builder/docker/driver_mock.go
index 9cf2fb31b..be28d680d 100644
--- a/builder/docker/driver_mock.go
+++ b/builder/docker/driver_mock.go
@@ -12,6 +12,7 @@ type MockDriver struct {
 	StartID      string
 	StartError   error
 	StopError    error
+	VerifyError  error
 
 	ExportCalled bool
 	ExportID     string
@@ -21,6 +22,7 @@ type MockDriver struct {
 	StartConfig  *ContainerConfig
 	StopCalled   bool
 	StopID       string
+	VerifyCalled bool
 }
 
 func (d *MockDriver) Export(id string, dst io.Writer) error {
@@ -54,3 +56,8 @@ func (d *MockDriver) StopContainer(id string) error {
 	d.StopID = id
 	return d.StopError
 }
+
+func (d *MockDriver) Verify() error {
+	d.VerifyCalled = true
+	return d.VerifyError
+}