builder/docker: export the final image

builder/docker/builder.go

@@ -41,6 +41,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 		&StepPull{},
 		&StepRun{},
 		&StepProvision{},
+		&StepExport{},
 	}
 
 	// Setup the state bag and initial state for the steps

builder/docker/config.go

@@ -8,6 +8,7 @@ import (
 type Config struct {
 	common.PackerConfig `mapstructure:",squash"`
 
+	ExportPath string `mapstructure:"export_path"`
 	Image      string
 
 	tpl *packer.ConfigTemplate

builder/docker/step_export.go

@@ -0,0 +1,61 @@
+package docker
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"log"
+	"os"
+	"os/exec"
+)
+
+// StepExport exports the container to a flat tar file.
+type StepExport struct{}
+
+func (s *StepExport) Run(state multistep.StateBag) multistep.StepAction {
+	config := state.Get("config").(*Config)
+	containerId := state.Get("container_id").(string)
+	ui := state.Get("ui").(packer.Ui)
+
+	ui.Say("Exporting the container")
+
+	// Args that we're going to pass to Docker
+	args := []string{"export", containerId}
+
+	// Open the file that we're going to write to
+	f, err := os.Create(config.ExportPath)
+	if err != nil {
+		err := fmt.Errorf("Error creating output file: %s", err)
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+	defer f.Close()
+
+	// Export the thing, take stderr and point it to the file
+	var stderr bytes.Buffer
+	cmd := exec.Command("docker", args...)
+	cmd.Stdout = f
+	cmd.Stderr = &stderr
+
+	log.Printf("Starting container with args: %v", args)
+	if err := cmd.Start(); err != nil {
+		err := fmt.Errorf("Error exporting: %s", err)
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	if err := cmd.Wait(); err != nil {
+		err := fmt.Errorf("Error exporting: %s\nStderr: %s",
+			err, stderr.String())
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+
+	return multistep.ActionContinue
+}
+
+func (s *StepExport) Cleanup(state multistep.StateBag) {}