feat(worker): Implemented docker executor, close #55

if docker is enabled in configure file and `docker_image` is set on mirror config, the command would

be executed via `docker run ...`

worker/docker.go

@@ -0,0 +1,98 @@
+package worker
+
+import (
+	"fmt"
+	"os"
+)
+
+type dockerHook struct {
+	emptyHook
+	provider mirrorProvider
+	image    string
+	volumes  []string
+	options  []string
+}
+
+func newDockerHook(p mirrorProvider, gCfg dockerConfig, mCfg mirrorConfig) *dockerHook {
+	volumes := []string{}
+	volumes = append(volumes, gCfg.Volumes...)
+	volumes = append(volumes, mCfg.DockerVolumes...)
+
+	options := []string{}
+	options = append(options, gCfg.Options...)
+	options = append(options, mCfg.DockerOptions...)
+
+	return &dockerHook{
+		provider: p,
+		image:    mCfg.DockerImage,
+		volumes:  volumes,
+		options:  options,
+	}
+}
+
+func (d *dockerHook) preExec() error {
+	p := d.provider
+	logFile := p.LogFile()
+	workingDir := p.WorkingDir()
+
+	if _, err := os.Stat(workingDir); os.IsNotExist(err) {
+		logger.Debugf("Making dir %s", workingDir)
+		if err = os.MkdirAll(workingDir, 0755); err != nil {
+			return fmt.Errorf("Error making dir %s: %s", workingDir, err.Error())
+		}
+	}
+
+	logFileNew := "/log_latest"
+	workingDirNew := "/data"
+
+	// Override workingDir
+	ctx := p.EnterContext()
+	ctx.Set(_WorkingDirKey, workingDirNew)
+	ctx.Set(_LogFileKey+":docker", logFileNew)
+	ctx.Set(
+		"volumes", []string{
+			fmt.Sprintf("%s:%s", logFile, logFileNew),
+			fmt.Sprintf("%s:%s", workingDir, workingDirNew),
+		},
+	)
+	return nil
+}
+
+func (d *dockerHook) postExec() error {
+	// sh.Command(
+	// 	"docker", "rm", "-f", d.Name(),
+	// ).Run()
+	d.provider.ExitContext()
+	return nil
+}
+
+// Volumes returns the configured volumes and
+// runtime-needed volumes, including mirror dirs
+// and log files
+func (d *dockerHook) Volumes() []string {
+	vols := make([]string, len(d.volumes))
+	copy(vols, d.volumes)
+
+	p := d.provider
+	ctx := p.Context()
+	if ivs, ok := ctx.Get("volumes"); ok {
+		vs := ivs.([]string)
+		vols = append(vols, vs...)
+	}
+	return vols
+}
+
+func (d *dockerHook) LogFile() string {
+	p := d.provider
+	ctx := p.Context()
+	if iv, ok := ctx.Get(_LogFileKey + ":docker"); ok {
+		v := iv.(string)
+		return v
+	}
+	return p.LogFile()
+}
+
+func (d *dockerHook) Name() string {
+	p := d.provider
+	return "tunasync-job-" + p.Name()
+}