middleware : add torrent approval package

this makes it possible to specify a torrent whitelist/blacklist in the
configuration file based on their hexadecimal hash.

Fixes #375

Signed-off-by: Pierre-Alain TORET <pierre-alain.toret@protonmail.com>

middleware/torrentapproval/torrentapproval.go

@@ -0,0 +1,109 @@
+// Package torrentapproval implements a Hook that fails an Announce based on a
+// whitelist or blacklist of torrent hash.
+package torrentapproval
+
+import (
+	"context"
+	"encoding/hex"
+	"fmt"
+
+	"gopkg.in/yaml.v2"
+
+	"github.com/chihaya/chihaya/bittorrent"
+	"github.com/chihaya/chihaya/middleware"
+)
+
+// Name is the name by which this middleware is registered with Chihaya.
+const Name = "torrent approval"
+
+func init() {
+	middleware.RegisterDriver(Name, driver{})
+}
+
+var _ middleware.Driver = driver{}
+
+type driver struct{}
+
+func (d driver) NewHook(optionBytes []byte) (middleware.Hook, error) {
+	var cfg Config
+	err := yaml.Unmarshal(optionBytes, &cfg)
+	if err != nil {
+		return nil, fmt.Errorf("invalid options for middleware %s: %s", Name, err)
+	}
+
+	return NewHook(cfg)
+}
+
+// ErrTorrentUnapproved is the error returned when a torrent hash is invalid.
+var ErrTorrentUnapproved = bittorrent.ClientError("unapproved torrent")
+
+// Config represents all the values required by this middleware to validate
+// torrents based on their hash value.
+type Config struct {
+	Whitelist []string `yaml:"whitelist"`
+	Blacklist []string `yaml:"blacklist"`
+}
+
+type hook struct {
+	approved   map[bittorrent.InfoHash]struct{}
+	unapproved map[bittorrent.InfoHash]struct{}
+}
+
+// NewHook returns an instance of the torrent approval middleware.
+func NewHook(cfg Config) (middleware.Hook, error) {
+	h := &hook{
+		approved:   make(map[bittorrent.InfoHash]struct{}),
+		unapproved: make(map[bittorrent.InfoHash]struct{}),
+	}
+
+	if len(cfg.Whitelist) > 0 && len(cfg.Blacklist) > 0 {
+		return nil, fmt.Errorf("using both whitelist and blacklist is invalid")
+	}
+
+	for _, hashString := range cfg.Whitelist {
+		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)
+		}
+		h.approved[bittorrent.InfoHashFromBytes(hashinfo)] = struct{}{}
+	}
+
+	for _, hashString := range cfg.Blacklist {
+		hashinfo, err := hex.DecodeString(hashString)
+		if err != nil {
+			return nil, fmt.Errorf("blacklist : invalid hash %s", hashString)
+		}
+		if len(hashinfo) != 20 {
+			return nil, fmt.Errorf("blacklist : hash %s is not 20 byes", hashString)
+		}
+		h.unapproved[bittorrent.InfoHashFromBytes(hashinfo)] = struct{}{}
+	}
+
+	return h, nil
+}
+
+func (h *hook) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest, resp *bittorrent.AnnounceResponse) (context.Context, error) {
+	infohash := req.InfoHash
+
+	if len(h.approved) > 0 {
+		if _, found := h.approved[infohash]; !found {
+			return ctx, ErrTorrentUnapproved
+		}
+	}
+
+	if len(h.unapproved) > 0 {
+		if _, found := h.unapproved[infohash]; found {
+			return ctx, ErrTorrentUnapproved
+		}
+	}
+
+	return ctx, nil
+}
+
+func (h *hook) HandleScrape(ctx context.Context, req *bittorrent.ScrapeRequest, resp *bittorrent.ScrapeResponse) (context.Context, error) {
+	// Scrapes don't require any protection.
+	return ctx, nil
+}