udp: Add basic logging and more comments

http/http.go

@@ -120,8 +120,7 @@ func (s *Server) connState(conn net.Conn, state http.ConnState) {
 	}
 }
 
-// Serve creates a new Server and proceeds to block while handling requests
+// Serve runs an HTTP server, blocking until the server has shut down.
-// until a graceful shutdown.
 func (s *Server) Serve() {
 	glog.V(0).Info("Starting HTTP on ", s.config.HTTPListenAddr)
 

tracker/models/models.go

@@ -39,9 +39,11 @@ var (
 
 type ClientError string
 type NotFoundError ClientError
+type ProtocolError ClientError
 
 func (e ClientError) Error() string   { return string(e) }
 func (e NotFoundError) Error() string { return string(e) }
+func (e ProtocolError) Error() string { return string(e) }
 
 type PeerList []Peer
 type PeerKey string

udp/protocol.go

@@ -7,29 +7,26 @@ package udp
 import (
 	"bytes"
 	"encoding/binary"
-	"errors"
 	"net"
 
 	"github.com/chihaya/chihaya/stats"
 	"github.com/chihaya/chihaya/tracker/models"
 )
 
+// initialConnectionID is the magic initial connection ID specified by BEP 15.
 var initialConnectionID = []byte{0, 0, 0x04, 0x17, 0x27, 0x10, 0x19, 0x80}
 
+// eventIDs maps IDs to event names.
 var eventIDs = []string{"", "completed", "started", "stopped"}
 
 var (
-	errMalformedPacket = errors.New("malformed packet")
+	errMalformedPacket = models.ProtocolError("malformed packet")
-	errMalformedIP     = errors.New("malformed IP address")
+	errMalformedIP     = models.ProtocolError("malformed IP address")
-	errMalformedEvent  = errors.New("malformed event ID")
+	errMalformedEvent  = models.ProtocolError("malformed event ID")
-	errBadConnectionID = errors.New("bad connection ID")
+	errBadConnectionID = models.ProtocolError("bad connection ID")
 )
 
-func writeHeader(response []byte, action uint32, transactionID []byte) {
+// handleTorrentError writes err to w if err is a models.ClientError.
-	binary.BigEndian.PutUint32(response, action)
-	copy(response[4:], transactionID)
-}
-
 func handleTorrentError(err error, w *Writer) {
 	if err == nil {
 		return
@@ -41,9 +38,10 @@ func handleTorrentError(err error, w *Writer) {
 	}
 }
 
-func (s *Server) handlePacket(packet []byte, addr *net.UDPAddr) (response []byte) {
+// handlePacket decodes and processes one UDP request, returning the response.
+func (s *Server) handlePacket(packet []byte, addr *net.UDPAddr) (response []byte, actionName string) {
 	if len(packet) < 16 {
-		return nil // Malformed, no client packets are less than 16 bytes.
+		return // Malformed, no client packets are less than 16 bytes.
 	}
 
 	connID := packet[0:8]
@@ -71,17 +69,16 @@ func (s *Server) handlePacket(packet []byte, addr *net.UDPAddr) (response []byte
 
 	switch action {
 	case 0:
-		// Connect request.
+		actionName = "connect"
 		if !bytes.Equal(connID, initialConnectionID) {
-			return nil // Malformed packet.
+			return // Malformed packet.
 		}
 
-		response = make([]byte, 16)
+		writer.writeHeader(0)
-		writeHeader(response, action, transactionID)
+		writer.buf.Write(generatedConnID)
-		copy(response[8:], generatedConnID)
 
 	case 1:
-		// Announce request.
+		actionName = "announce"
 		ann, err := s.newAnnounce(packet, addr.IP)
 
 		if err == nil {
@@ -91,7 +88,7 @@ func (s *Server) handlePacket(packet []byte, addr *net.UDPAddr) (response []byte
 		handleTorrentError(err, writer)
 
 	case 2:
-		// Scrape request.
+		actionName = "scrape"
 		scrape, err := s.newScrape(packet)
 
 		if err == nil {
@@ -104,6 +101,7 @@ func (s *Server) handlePacket(packet []byte, addr *net.UDPAddr) (response []byte
 	return
 }
 
+// newAnnounce decodes one announce packet, returning a models.Announce.
 func (s *Server) newAnnounce(packet []byte, ip net.IP) (*models.Announce, error) {
 	if len(packet) < 98 {
 		return nil, errMalformedPacket
@@ -151,8 +149,9 @@ func (s *Server) newAnnounce(packet []byte, ip net.IP) (*models.Announce, error)
 	}, nil
 }
 
+// newScrape decodes one announce packet, returning a models.Scrape.
 func (s *Server) newScrape(packet []byte) (*models.Scrape, error) {
-	if len(packet) < 16 {
+	if len(packet) < 36 {
 		return nil, errMalformedPacket
 	}
 

udp/udp.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by the BSD 2-Clause license,
 // which can be found in the LICENSE file.
 
-// Package udp implements a UDP BitTorrent tracker per BEP 15 and BEP 41.
+// Package udp implements a UDP BitTorrent tracker per BEP 15.
 // IPv6 is currently unsupported as there is no widely-implemented standard.
 package udp
 
@@ -55,18 +55,26 @@ func (s *Server) serve() error {
 			return err
 		}
 
+		start := time.Now()
+
 		go func() {
-			response := s.handlePacket(buffer[:n], addr)
+			response, action := s.handlePacket(buffer[:n], addr)
 			if response != nil {
 				sock.WriteToUDP(response, addr)
 			}
 			pool.GiveSlice(buffer)
+
+			if glog.V(2) {
+				duration := time.Since(start)
+				glog.Infof("[UDP - %9s] %s", duration, action)
+			}
 		}()
 	}
 
 	return nil
 }
 
+// Serve runs a UDP server, blocking until the server has shut down.
 func (s *Server) Serve() {
 	glog.V(0).Info("Starting UDP on ", s.config.UDPListenAddr)
 

udp/writer.go

@@ -12,6 +12,7 @@ import (
 	"github.com/chihaya/chihaya/tracker/models"
 )
 
+// Writer implements the tracker.Writer interface for the UDP protocol.
 type Writer struct {
 	buf *bytes.Buffer
 
@@ -19,6 +20,7 @@ type Writer struct {
 	transactionID []byte
 }
 
+// WriteError writes the failure reason as a null-terminated string.
 func (w *Writer) WriteError(err error) error {
 	w.writeHeader(3)
 	w.buf.WriteString(err.Error())
@@ -26,6 +28,7 @@ func (w *Writer) WriteError(err error) error {
 	return nil
 }
 
+// WriteAnnounce encodes an announce response according to the UDP spec.
 func (w *Writer) WriteAnnounce(res *models.AnnounceResponse) error {
 	w.writeHeader(1)
 	binary.Write(w.buf, binary.BigEndian, uint32(res.Interval/time.Second))
@@ -40,6 +43,7 @@ func (w *Writer) WriteAnnounce(res *models.AnnounceResponse) error {
 	return nil
 }
 
+// WriteAnnounce encodes a scrape response according to the UDP spec.
 func (w *Writer) WriteScrape(res *models.ScrapeResponse) error {
 	w.writeHeader(2)
 
@@ -52,6 +56,7 @@ func (w *Writer) WriteScrape(res *models.ScrapeResponse) error {
 	return nil
 }
 
+// writeHeader writes the action and transaction ID to the response.
 func (w *Writer) writeHeader(action uint32) {
 	binary.Write(w.buf, binary.BigEndian, action)
 	w.buf.Write(w.transactionID)