bittorrent: add initial request sanitizer

bittorrent/bittorrent.go

@@ -81,6 +81,9 @@ type AnnounceRequest struct {
 	Event           Event
 	InfoHash        InfoHash
 	Compact         bool
+	EventProvided   bool
+	NumWantProvided bool
+	IPProvided      bool
 	NumWant         uint32
 	Left            uint64
 	Downloaded      uint64

bittorrent/request_sanitizer.go

@@ -0,0 +1,61 @@
+package bittorrent
+
+import (
+	"net"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// ErrInvalidIP indicates an invalid IP for an Announce.
+var ErrInvalidIP = ClientError("invalid IP")
+
+// RequestSanitizer is used to replace unreasonable values in requests parsed
+// from a frontend into sane values.
+type RequestSanitizer struct {
+	MaxNumWant          uint32 `yaml:"max_numwant"`
+	DefaultNumWant      uint32 `yaml:"default_numwant"`
+	MaxScrapeInfoHashes uint32 `yaml:"max_scrape_infohashes"`
+}
+
+// SanitizeAnnounce enforces a max and default NumWant and coerces the peer's
+// IP address into the proper format.
+func (rs *RequestSanitizer) SanitizeAnnounce(r *AnnounceRequest) error {
+	if !r.NumWantProvided {
+		r.NumWant = rs.DefaultNumWant
+	} else if r.NumWant > rs.MaxNumWant {
+		r.NumWant = rs.MaxNumWant
+	}
+
+	if ip := r.Peer.IP.To4(); ip != nil {
+		r.Peer.IP.IP = ip
+		r.Peer.IP.AddressFamily = IPv4
+	} else if len(r.Peer.IP.IP) == net.IPv6len { // implies r.Peer.IP.To4() == nil
+		r.Peer.IP.AddressFamily = IPv6
+	} else {
+		return ErrInvalidIP
+	}
+
+	log.Debug("sanitized announce", rs, r)
+	return nil
+}
+
+// SanitizeScrape enforces a max number of infohashes for a single scrape
+// request.
+func (rs *RequestSanitizer) SanitizeScrape(r *ScrapeRequest) error {
+	if len(r.InfoHashes) > int(rs.MaxScrapeInfoHashes) {
+		r.InfoHashes = r.InfoHashes[:rs.MaxScrapeInfoHashes]
+	}
+
+	log.Debug("sanitized scrape", rs, r)
+	return nil
+}
+
+// LogFields renders the request sanitizer's configuration as a set of loggable
+// fields.
+func (rs *RequestSanitizer) LogFields() log.Fields {
+	return log.Fields{
+		"maxNumWant":          rs.MaxNumWant,
+		"defaultNumWant":      rs.DefaultNumWant,
+		"maxScrapeInfohashes": rs.MaxScrapeInfoHashes,
+	}
+}