WIP Add support for custom torrents' approval storages

* migrate torrentapproval to list storage
* add initial support for torrent file storage (watch directory with fsnotify)
* replace frontend/http/bencode package with github.com/zeebo/bencode module
* sanitize code (fix warnings)

TODO:
* parse torrent files to get hashes,
* watch directory event types

DON'T use for now

middleware/torrentapproval/container/list/list.go

@@ -0,0 +1,63 @@
+package list
+
+import (
+	"encoding/hex"
+	"fmt"
+	"github.com/chihaya/chihaya/bittorrent"
+	"github.com/chihaya/chihaya/middleware/torrentapproval/container"
+	"github.com/chihaya/chihaya/pkg/stop"
+	"sync"
+)
+
+func init() {
+	container.Register("list", Builder{})
+}
+
+type Builder struct {
+	Whitelist []string `yaml:"whitelist"`
+	Blacklist []string `yaml:"blacklist"`
+}
+
+var DUMMY struct{}
+
+func (b Builder) New() (container.Container, error) {
+	if len(b.Whitelist) > 0 && len(b.Blacklist) > 0 {
+		return nil, fmt.Errorf("using both whitelist and blacklist is invalid")
+	}
+	l := &List{
+		Hashes: sync.Map{},
+		Invert: len(b.Whitelist) == 0,
+	}
+
+	hashList := b.Whitelist
+	if l.Invert {
+		l.Invert = true
+		hashList = b.Blacklist
+	}
+
+	for _, hashString := range hashList {
+		hashinfo, err := hex.DecodeString(hashString)
+		if err != nil {
+			return nil, fmt.Errorf("whitelist : invalid hash %s", hashString)
+		}
+		if len(hashinfo) != 20 {
+			return nil, fmt.Errorf("whitelist : hash %s is not 20 byes", hashString)
+		}
+		l.Hashes.Store(bittorrent.InfoHashFromBytes(hashinfo), DUMMY)
+	}
+	return l, nil
+}
+
+type List struct {
+	Invert bool
+	Hashes sync.Map
+}
+
+func (l *List) Stop() stop.Result {
+	return stop.AlreadyStopped
+}
+
+func (l *List) Contains(hash bittorrent.InfoHash) bool {
+	_, result := l.Hashes.Load(hash)
+	return result != l.Invert
+}