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

lib/model/sharedpullerstate.go

@@ -12,7 +12,6 @@ import (
 	"path/filepath"
 	"time"
 
-	"github.com/syncthing/syncthing/lib/db"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sync"
 )
@@ -150,7 +149,7 @@ func (s *sharedPullerState) tempFile() (io.WriterAt, error) {
 	if s.sparse && !s.file.IsSymlink() {
 		// Truncate sets the size of the file. This creates a sparse file or a
 		// space reservation, depending on the underlying filesystem.
-		if err := fd.Truncate(s.file.Size()); err != nil {
+		if err := fd.Truncate(s.file.Size); err != nil {
 			s.failLocked("dst truncate", err)
 			return nil, err
 		}
@@ -293,8 +292,8 @@ func (s *sharedPullerState) Progress() *pullerProgress {
 		CopiedFromElsewhere: s.copyTotal - s.copyNeeded - s.copyOrigin,
 		Pulled:              s.pullTotal - s.pullNeeded,
 		Pulling:             s.pullNeeded,
-		BytesTotal:          db.BlocksToSize(total),
-		BytesDone:           db.BlocksToSize(done),
+		BytesTotal:          blocksToSize(total),
+		BytesDone:           blocksToSize(done),
 	}
 }
 
@@ -321,3 +320,10 @@ func (s *sharedPullerState) Available() []int32 {
 	s.mut.RUnlock()
 	return blocks
 }
+
+func blocksToSize(num int) int64 {
+	if num < 2 {
+		return protocol.BlockSize / 2
+	}
+	return int64(num-1)*protocol.BlockSize + protocol.BlockSize/2
+}