lib/protocol, lib/discover, lib/db: Use protocol buffer serialization (fixes #3080)

This changes the BEP protocol to use protocol buffer serialization
instead of XDR, and therefore also the database format. The local
discovery protocol is also updated to be protocol buffer format.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3276
LGTM: AudriusButkevicius

cmd/stdisco/main.go

@@ -9,6 +9,7 @@ package main
 import (
 	"bytes"
 	"crypto/rand"
+	"encoding/binary"
 	"flag"
 	"log"
 	"strings"
@@ -66,24 +67,25 @@ func recv(bc beacon.Interface) {
 	seen := make(map[string]bool)
 	for {
 		data, src := bc.Recv()
-		var ann discover.Announce
-		ann.UnmarshalXDR(data)
+		if m := binary.BigEndian.Uint32(data); m != discover.Magic {
+			log.Printf("Incorrect magic %x in announcement from %v", m, src)
+			continue
+		}
 
-		if bytes.Equal(ann.This.ID, myID) {
+		var ann discover.Announce
+		ann.Unmarshal(data[4:])
+
+		if bytes.Equal(ann.ID, myID) {
 			// This is one of our own fake packets, don't print it.
 			continue
 		}
 
 		// Print announcement details for the first packet from a given
 		// device ID and source address, or if -all was given.
-		key := string(ann.This.ID) + src.String()
+		key := string(ann.ID) + src.String()
 		if all || !seen[key] {
 			log.Printf("Announcement from %v\n", src)
-			log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(ann.This.ID), strings.Join(addrStrs(ann.This), ", "))
-
-			for _, dev := range ann.Extra {
-				log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(dev.ID), strings.Join(addrStrs(dev), ", "))
-			}
+			log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(ann.ID), strings.Join(ann.Addresses, ", "))
 			seen[key] = true
 		}
 	}
@@ -92,15 +94,10 @@ func recv(bc beacon.Interface) {
 // sends fake discovery announcements once every second
 func send(bc beacon.Interface) {
 	ann := discover.Announce{
-		Magic: discover.AnnouncementMagic,
-		This: discover.Device{
-			ID: myID,
-			Addresses: []discover.Address{
-				{URL: "tcp://fake.example.com:12345"},
-			},
-		},
+		ID:        myID,
+		Addresses: []string{"tcp://fake.example.com:12345"},
 	}
-	bs, _ := ann.MarshalXDR()
+	bs, _ := ann.Marshal()
 
 	for {
 		bc.Send(bs)
@@ -108,15 +105,6 @@ func send(bc beacon.Interface) {
 	}
 }
 
-// returns the list of address URLs
-func addrStrs(dev discover.Device) []string {
-	ss := make([]string, len(dev.Addresses))
-	for i, addr := range dev.Addresses {
-		ss[i] = addr.URL
-	}
-	return ss
-}
-
 // returns a random but recognizable device ID
 func randomDeviceID() []byte {
 	var id [32]byte