builder/docker: Add type assertion check when reading config from state bag

builder/docker/step_commit.go

@@ -14,11 +14,17 @@ type StepCommit struct {
 }
 
 func (s *StepCommit) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
+	ui := state.Get("ui").(packer.Ui)
+	config, ok := state.Get("config").(*Config)
+	if !ok {
+		err := fmt.Errorf("error encountered obtaining docker config")
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
 	driver := state.Get("driver").(Driver)
 	containerId := state.Get("container_id").(string)
-	config := state.Get("config").(*Config)
-	ui := state.Get("ui").(packer.Ui)
-
 	if config.WindowsContainer {
 		// docker can't commit a running Windows container
 		err := driver.StopContainer(containerId)

builder/docker/step_connect_docker.go

@@ -12,7 +12,13 @@ import (
 type StepConnectDocker struct{}
 
 func (s *StepConnectDocker) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
-	config := state.Get("config").(*Config)
+	config, ok := state.Get("config").(*Config)
+	if !ok {
+		err := fmt.Errorf("error encountered obtaining docker config")
+		state.Put("error", err)
+		return multistep.ActionHalt
+	}
+
 	containerId := state.Get("container_id").(string)
 	driver := state.Get("driver").(Driver)
 	tempDir := state.Get("temp_dir").(string)

builder/docker/step_export.go

@@ -14,11 +14,14 @@ import (
 type StepExport struct{}
 
 func (s *StepExport) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
-	config := state.Get("config").(*Config)
-
-	driver := state.Get("driver").(Driver)
-	containerId := state.Get("container_id").(string)
 	ui := state.Get("ui").(packer.Ui)
+	config, ok := state.Get("config").(*Config)
+	if !ok {
+		err := fmt.Errorf("error encountered obtaining docker config")
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
 
 	// We should catch this in validation, but guard anyway
 	if config.ExportPath == "" {
@@ -44,6 +47,9 @@ func (s *StepExport) Run(ctx context.Context, state multistep.StateBag) multiste
 		return multistep.ActionHalt
 	}
 
+	driver := state.Get("driver").(Driver)
+	containerId := state.Get("container_id").(string)
+
 	ui.Say("Exporting the container")
 	if err := driver.Export(containerId, f); err != nil {
 		f.Close()

builder/docker/step_pull.go

@@ -12,9 +12,14 @@ import (
 type StepPull struct{}
 
 func (s *StepPull) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
-	config := state.Get("config").(*Config)
-	driver := state.Get("driver").(Driver)
 	ui := state.Get("ui").(packer.Ui)
+	config, ok := state.Get("config").(*Config)
+	if !ok {
+		err := fmt.Errorf("error encountered obtaining docker config")
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
 
 	if !config.Pull {
 		log.Println("Pull disabled, won't docker pull")
@@ -38,6 +43,7 @@ func (s *StepPull) Run(ctx context.Context, state multistep.StateBag) multistep.
 		config.LoginPassword = password
 	}
 
+	driver := state.Get("driver").(Driver)
 	if config.Login || config.EcrLogin {
 		ui.Message("Logging in...")
 		err := driver.Login(

builder/docker/step_run.go

@@ -13,10 +13,14 @@ type StepRun struct {
 }
 
 func (s *StepRun) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
-	config := state.Get("config").(*Config)
-	driver := state.Get("driver").(Driver)
-	tempDir := state.Get("temp_dir").(string)
 	ui := state.Get("ui").(packer.Ui)
+	config, ok := state.Get("config").(*Config)
+	if !ok {
+		err := fmt.Errorf("error encountered obtaining docker config")
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
 
 	runConfig := ContainerConfig{
 		Image:      config.Image,
@@ -28,8 +32,11 @@ func (s *StepRun) Run(ctx context.Context, state multistep.StateBag) multistep.S
 	for host, container := range config.Volumes {
 		runConfig.Volumes[host] = container
 	}
+
+	tempDir := state.Get("temp_dir").(string)
 	runConfig.Volumes[tempDir] = config.ContainerDir
 
+	driver := state.Get("driver").(Driver)
 	ui.Say("Starting docker container...")
 	containerId, err := driver.StartContainer(&runConfig)
 	if err != nil {