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/protocol/bep_extensions.go

@@ -0,0 +1,96 @@
+// Copyright (C) 2014 The Protocol Authors.
+
+//go:generate go run ../../script/protofmt.go bep.proto
+//go:generate protoc --proto_path=../../../../../:../../../../gogo/protobuf/protobuf:. --gogofast_out=. bep.proto
+
+package protocol
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"fmt"
+)
+
+var (
+	sha256OfEmptyBlock = sha256.Sum256(make([]byte, BlockSize))
+	HelloMessageMagic  = uint32(0x2EA7D90B)
+)
+
+func (m Hello) Magic() uint32 {
+	return HelloMessageMagic
+}
+
+func (f FileInfo) String() string {
+	return fmt.Sprintf("File{Name:%q, Permissions:0%o, Modified:%d, Version:%v, Length:%d, Deleted:%v, Invalid:%v, NoPermissions:%v, Blocks:%v}",
+		f.Name, f.Permissions, f.Modified, f.Version, f.Size, f.Deleted, f.Invalid, f.NoPermissions, f.Blocks)
+}
+
+func (f FileInfo) IsDeleted() bool {
+	return f.Deleted
+}
+
+func (f FileInfo) IsInvalid() bool {
+	return f.Invalid
+}
+
+func (f FileInfo) IsDirectory() bool {
+	return f.Type == FileInfoTypeDirectory
+}
+
+func (f FileInfo) IsSymlink() bool {
+	switch f.Type {
+	case FileInfoTypeSymlinkDirectory, FileInfoTypeSymlinkFile, FileInfoTypeSymlinkUnknown:
+		return true
+	default:
+		return false
+	}
+}
+
+func (f FileInfo) HasPermissionBits() bool {
+	return !f.NoPermissions
+}
+
+func (f FileInfo) FileSize() int64 {
+	if f.IsDirectory() || f.IsDeleted() {
+		return 128
+	}
+	return f.Size
+}
+
+func (f FileInfo) FileName() string {
+	return f.Name
+}
+
+// WinsConflict returns true if "f" is the one to choose when it is in
+// conflict with "other".
+func (f FileInfo) WinsConflict(other FileInfo) bool {
+	// If a modification is in conflict with a delete, we pick the
+	// modification.
+	if !f.IsDeleted() && other.IsDeleted() {
+		return true
+	}
+	if f.IsDeleted() && !other.IsDeleted() {
+		return false
+	}
+
+	// The one with the newer modification time wins.
+	if f.Modified > other.Modified {
+		return true
+	}
+	if f.Modified < other.Modified {
+		return false
+	}
+
+	// The modification times were equal. Use the device ID in the version
+	// vector as tie breaker.
+	return f.Version.Compare(other.Version) == ConcurrentGreater
+}
+
+func (b BlockInfo) String() string {
+	return fmt.Sprintf("Block{%d/%d/%x}", b.Offset, b.Size, b.Hash)
+}
+
+// IsEmpty returns true if the block is a full block of zeroes.
+func (b BlockInfo) IsEmpty() bool {
+	return b.Size == BlockSize && bytes.Equal(b.Hash, sha256OfEmptyBlock[:])
+}