lib/protocol: Use DeviceID in protocol messages, with custom marshalling

This makes the device ID a real type that can be used in the protobuf
schema. That avoids the juggling back and forth from []byte in a bunch
of places and simplifies the code.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3695

cmd/stdisco/main.go

@@ -7,7 +7,6 @@
 package main
 
 import (
-	"bytes"
 	"crypto/rand"
 	"encoding/binary"
 	"flag"
@@ -45,7 +44,7 @@ func main() {
 	flag.Parse()
 
 	if fake {
-		log.Println("My ID:", protocol.DeviceIDFromBytes(myID))
+		log.Println("My ID:", myID)
 	}
 
 	runbeacon(beacon.NewMulticast(mc), fake)
@@ -75,17 +74,17 @@ func recv(bc beacon.Interface) {
 		var ann discover.Announce
 		ann.Unmarshal(data[4:])
 
-		if bytes.Equal(ann.ID, myID) {
+		if 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.ID) + src.String()
+		key := ann.ID.String() + src.String()
 		if all || !seen[key] {
 			log.Printf("Announcement from %v\n", src)
-			log.Printf(" %v at %s\n", protocol.DeviceIDFromBytes(ann.ID), strings.Join(ann.Addresses, ", "))
+			log.Printf(" %v at %s\n", ann.ID, strings.Join(ann.Addresses, ", "))
 			seen[key] = true
 		}
 	}
@@ -106,9 +105,9 @@ func send(bc beacon.Interface) {
 }
 
 // returns a random but recognizable device ID
-func randomDeviceID() []byte {
-	var id [32]byte
+func randomDeviceID() protocol.DeviceID {
+	var id protocol.DeviceID
 	copy(id[:], randomPrefix)
 	rand.Read(id[len(randomPrefix):])
-	return id[:]
+	return id
 }