middleware: add sanitization hook

frontend/http/frontend.go

@@ -13,6 +13,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/tylerb/graceful"
 
+	"github.com/chihaya/chihaya/bittorrent"
 	"github.com/chihaya/chihaya/frontend"
 	"github.com/chihaya/chihaya/middleware"
 )
@@ -22,6 +23,9 @@ func init() {
 	recordResponseDuration("action", nil, time.Second)
 }
 
+// ErrInvalidIP indicates an invalid IP.
+var ErrInvalidIP = bittorrent.ClientError("invalid IP")
+
 var promResponseDurationMilliseconds = prometheus.NewHistogramVec(
 	prometheus.HistogramOpts{
 		Name:    "chihaya_http_response_duration_milliseconds",
@@ -172,8 +176,19 @@ func (t *Frontend) scrapeRoute(w http.ResponseWriter, r *http.Request, _ httprou
 		return
 	}
 
-	ip := net.ParseIP(host)
-	ctx := context.WithValue(context.Background(), middleware.ScrapeIsIPv6Key, len(ip) == net.IPv6len)
+	reqIP := net.ParseIP(host)
+	af := bittorrent.IPv4
+	if reqIP.To4() != nil {
+		af = bittorrent.IPv4
+	} else if len(reqIP) == net.IPv6len { // implies reqIP.To4() == nil
+		af = bittorrent.IPv6
+	} else {
+		log.Errorln("http: invalid IP: neither v4 nor v6, RemoteAddr was", r.RemoteAddr)
+		WriteError(w, ErrInvalidIP)
+		return
+	}
+
+	ctx := context.WithValue(context.Background(), middleware.ScrapeIsIPv6Key, af == bittorrent.IPv6)
 
 	resp, err := t.logic.HandleScrape(ctx, req)
 	if err != nil {

frontend/http/parser.go

@@ -74,16 +74,11 @@ func ParseAnnounce(r *http.Request, realIPHeader string, allowIPSpoofing bool) (
 	}
 	request.Peer.Port = uint16(port)
 
-	request.Peer.IP = requestedIP(r, qp, realIPHeader, allowIPSpoofing)
-	if request.Peer.IP == nil {
+	request.Peer.IP.IP = requestedIP(r, qp, realIPHeader, allowIPSpoofing)
+	if request.Peer.IP.IP == nil {
 		return nil, bittorrent.ClientError("failed to parse peer IP address")
 	}
 
-	// Sanitize IPv4 addresses to 4 bytes.
-	if ip := request.Peer.IP.To4(); ip != nil {
-		request.Peer.IP = ip
-	}
-
 	return request, nil
 }