WIP daemon:

Implement
* pruning on source side
* local job
* test subcommand for doing a dry-run of a prune policy

* use a non-blocking callback from autosnap to trigger the depending
jobs -> avoids races, looks saner in the debug log

cmd/config.go

@@ -3,6 +3,8 @@ package cmd
 import (
 	"io"
 
+	"fmt"
+	"github.com/pkg/errors"
 	"github.com/zrepl/zrepl/zfs"
 )
 
@@ -11,6 +13,14 @@ type Config struct {
 	Jobs   map[string]Job
 }
 
+func (c *Config) LookupJob(name string) (j Job, err error) {
+	j, ok := conf.Jobs[name]
+	if !ok {
+		return nil, errors.Errorf("job '%s' is not defined", name)
+	}
+	return j, nil
+}
+
 type Global struct {
 	Serve struct {
 		Stdinserver struct {
@@ -47,3 +57,40 @@ type SSHStdinServerConnectDescr struct {
 type PrunePolicy interface {
 	Prune(fs *zfs.DatasetPath, versions []zfs.FilesystemVersion) (keep, remove []zfs.FilesystemVersion, err error)
 }
+
+type PruningJob interface {
+	Pruner(side PrunePolicySide, dryRun bool) (Pruner, error)
+}
+
+// A type for constants describing different prune policies of a PruningJob
+// This is mostly a special-case for LocalJob, which is the only job that has two prune policies
+// instead of one.
+// It implements github.com/spf13/pflag.Value to be used as CLI flag for the test subcommand
+type PrunePolicySide string
+
+const (
+	PrunePolicySideDefault PrunePolicySide = ""
+	PrunePolicySideLeft    PrunePolicySide = "left"
+	PrunePolicySideRight   PrunePolicySide = "right"
+)
+
+func (s *PrunePolicySide) String() string {
+	return string(*s)
+}
+
+func (s *PrunePolicySide) Set(news string) error {
+	p := PrunePolicySide(news)
+	switch p {
+	case PrunePolicySideRight:
+		fallthrough
+	case PrunePolicySideLeft:
+		*s = p
+	default:
+		return errors.Errorf("must be either %s or %s", PrunePolicySideLeft, PrunePolicySideRight)
+	}
+	return nil
+}
+
+func (s *PrunePolicySide) Type() string {
+	return fmt.Sprintf("%s | %s", PrunePolicySideLeft, PrunePolicySideRight)
+}