X neo/storage: Also provide NextSerial in AnswerObject

Do this by ways of directly using FileStorage and temporarily extending
it with load function which returns both serial and next_serial on load.

We currently need next_serial to be there in AnswerObject for neo/py
client cache - as its code currently depends on next_serial (= next_tid)
for its computations.

This however can be reworked and next_serial not used there at all.
See also 5886aad3 (X zodb: Clarify Load interface)
.

go/neo/server/cluster_test.go

@@ -469,7 +469,7 @@ func TestMasterStorage(t *testing.T) {
 	tc.Expect(conntx("s:3", "c:2", 3, &neo.AnswerObject{
 		Oid:		xid1.Oid,
 		Serial:		serial1,
-		NextSerial:	0,		// XXX
+		NextSerial:	neo.INVALID_TID,
 		Compression:	false,
 		Data:		buf1,
 		DataSerial:	0,		// XXX
@@ -478,6 +478,41 @@ func TestMasterStorage(t *testing.T) {
 
 	xwait(wg)
 
+	// verify NextSerial is properly returned in AnswerObject via trace-loading prev. revision of obj1
+	// (XXX we currently need NextSerial for neo/py client cache)
+	wg = &errgroup.Group{}
+	xid1prev := zodb.Xid{Oid: 1, At: serial1 - 1}
+	buf1prev, serial1prev, err := zstor.Load(bg, xid1prev)
+	exc.Raiseif(err)
+	gox(wg, func() {
+		buf, serial, err := C.Load(bg, xid1prev)
+		exc.Raiseif(err)
+
+		if !(bytes.Equal(buf.Data, buf1prev.Data) && serial==serial1prev) {
+			exc.Raisef("C.Load(%v) ->\ndata:\n%s\nserial:\n%s\n", xid1prev,
+				pretty.Compare(buf1prev.Data, buf.Data), pretty.Compare(serial1prev, serial))
+		}
+	})
+
+	// ... -> GetObject(xid1prev)
+	tc.Expect(conntx("c:2", "s:3", 5, &neo.GetObject{
+		Oid:	xid1prev.Oid,
+		Tid:	serial1,
+		Serial: neo.INVALID_TID,
+	}))
+	tc.Expect(conntx("s:3", "c:2", 5, &neo.AnswerObject{
+		Oid:		xid1prev.Oid,
+		Serial:		serial1prev,
+		NextSerial:	serial1,
+		Compression:	false,
+		Data:		buf1prev,
+		DataSerial:	0,		// XXX
+		Checksum:	sha1.Sum(buf1prev.Data),
+	}))
+
+	xwait(wg)
+
+
 	// C loads every other {<,=}serial:oid - established link is reused
 	ziter := zstor.Iterate(0, zodb.TidMax)
 

go/neo/server/storage.go

@@ -33,6 +33,7 @@ import (
 	"lab.nexedi.com/kirr/neo/go/neo"
 	"lab.nexedi.com/kirr/neo/go/neo/internal/common"
 	"lab.nexedi.com/kirr/neo/go/zodb"
+	"lab.nexedi.com/kirr/neo/go/zodb/storage/fs1"
 	"lab.nexedi.com/kirr/neo/go/xcommon/log"
 	"lab.nexedi.com/kirr/neo/go/xcommon/task"
 	"lab.nexedi.com/kirr/neo/go/xcommon/xcontext"
@@ -58,7 +59,15 @@ type Storage struct {
 	//	    1 inbox/	(commit queues)
 	//	    2 ? (data.fs)
 	//	    3 packed/	(deltified objects)
-	zstor zodb.IStorageDriver // underlying ZODB storage	XXX -> directly work with fs1 & friends
+	//
+	// XXX we currently depend on extra functionality FS provides over
+	// plain zodb.IStorage (e.g. loading with nextSerial) and even if
+	// nextSerial will be gone in the future, we will probably depend on
+	// particular layout more and more -> directly work with fs1 & friends.
+	//
+	// TODO -> abstract into backend interfaces so various backands are
+	// possible (e.g. +SQL)
+	zstor *fs1.FileStorage // underlying ZODB storage
 
 	//nodeCome chan nodeCome	// node connected
 }
@@ -67,7 +76,7 @@ type Storage struct {
 //
 // The storage uses zstor as underlying backend for storing data.
 // Use Run to actually start running the node.
-func NewStorage(clusterName, masterAddr, serveAddr string, net xnet.Networker, zstor zodb.IStorageDriver) *Storage {
+func NewStorage(clusterName, masterAddr, serveAddr string, net xnet.Networker, zstor *fs1.FileStorage) *Storage {
 	stor := &Storage{
 		node:  neo.NewNodeApp(net, neo.STORAGE, clusterName, masterAddr, serveAddr),
 		zstor: zstor,
@@ -548,7 +557,8 @@ func (stor *Storage) serveClient1(ctx context.Context, req neo.Msg) (resp neo.Ms
 			xid.At = common.Before2At(req.Tid)
 		}
 
-		buf, serial, err := stor.zstor.Load(ctx, xid)
+		// FIXME kill nextSerial support after neo/py cache does not depend on next_serial
+		buf, serial, nextSerial, err := stor.zstor.Load_XXXWithNextSerialXXX(ctx, xid)
 		if err != nil {
 			// translate err to NEO protocol error codes
 			e := err.(*zodb.OpError)	// XXX move this to ErrEncode?
@@ -566,10 +576,15 @@ func (stor *Storage) serveClient1(ctx context.Context, req neo.Msg) (resp neo.Ms
 		        }
 		}
 
+		// no next serial -> None
+		if nextSerial == zodb.TidMax {
+			nextSerial = neo.INVALID_TID
+		}
 
 		return &neo.AnswerObject{
-			Oid:	xid.Oid,
-			Serial: serial,
+			Oid:	    xid.Oid,
+			Serial:     serial,
+			NextSerial: nextSerial,
 
 			Compression:	false,
 			Data:		buf,

go/zodb/storage/fs1/filestorage.go

@@ -126,21 +126,34 @@ func (dh *DataHeader) Free() {
 	dhPool.Put(dh)
 }
 
+
 func (fs *FileStorage) Load(_ context.Context, xid zodb.Xid) (buf *mem.Buf, serial zodb.Tid, err error) {
 	// FIXME zodb.TidMax is only 7fff... tid from outside can be ffff...
 	// -> TODO reject tid out of range
-	buf, serial, err = fs.load(xid)
+
+	// FIXME kill Load_XXXWithNextSerial after neo/py cache does not depend on next_serial
+	buf, serial, _, err = fs.Load_XXXWithNextSerialXXX(nil, xid)
+	return buf, serial, err
+}
+
+// XXX temporary function - will go away:
+//
+// FIXME kill Load_XXXWithNextSerialXXX after neo/py cache does not depend on next_serial
+func (fs *FileStorage) Load_XXXWithNextSerialXXX(_ context.Context, xid zodb.Xid) (buf *mem.Buf, serial, nextSerial zodb.Tid, err error) {
+	buf, serial, nextSerial, err = fs.load(xid)
 	if err != nil {
 		err = &zodb.OpError{URL: fs.URL(), Op: "load", Args: xid, Err: err}
 	}
-	return buf, serial, err
+	return buf, serial, nextSerial, err
 }
 
-func (fs *FileStorage) load(xid zodb.Xid) (buf *mem.Buf, serial zodb.Tid, err error) {
+
+// FIXME kill nextSerial support after neo/py cache does not depend on next_serial
+func (fs *FileStorage) load(xid zodb.Xid) (buf *mem.Buf, serial, nextSerial zodb.Tid, err error) {
 	// lookup in index position of oid data record within latest transaction which changed this oid
 	dataPos, ok := fs.index.Get(xid.Oid)
 	if !ok {
-		return nil, 0, &zodb.NoObjectError{Oid: xid.Oid}
+		return nil, 0, 0, &zodb.NoObjectError{Oid: xid.Oid}
 	}
 
 	// XXX go compiler cannot deduce dh should be on stack here
@@ -150,14 +163,17 @@ func (fs *FileStorage) load(xid zodb.Xid) (buf *mem.Buf, serial zodb.Tid, err er
 	dh.Tid = zodb.TidMax
 	dh.PrevRevPos = dataPos
 	//defer dh.Free()
-	buf, serial, err = fs._load(dh, xid)
+	buf, serial, nextSerial, err = fs._load(dh, xid)
 	dh.Free()
-	return buf, serial, err
+	return buf, serial, nextSerial, err
 }
 
-func (fs *FileStorage) _load(dh *DataHeader, xid zodb.Xid) (*mem.Buf, zodb.Tid, error) {
+// FIXME kill nextSerial support after neo/py cache does not depend on next_serial
+func (fs *FileStorage) _load(dh *DataHeader, xid zodb.Xid) (*mem.Buf, zodb.Tid, zodb.Tid, error) {
 	// search backwards for when we first have data record with tid satisfying xid.At
+	var nextSerial zodb.Tid
 	for {
+		nextSerial = dh.Tid
 		err := dh.LoadPrevRev(fs.file)
 		if err != nil {
 			if err == io.EOF {
@@ -165,7 +181,7 @@ func (fs *FileStorage) _load(dh *DataHeader, xid zodb.Xid) (*mem.Buf, zodb.Tid,
 				err = &zodb.NoDataError{Oid: xid.Oid, DeletedAt: 0}
 			}
 
-			return nil, 0, err
+			return nil, 0, 0, err
 		}
 
 		if dh.Tid <= xid.At {
@@ -179,14 +195,14 @@ func (fs *FileStorage) _load(dh *DataHeader, xid zodb.Xid) (*mem.Buf, zodb.Tid,
 
 	buf, err := dh.LoadData(fs.file)
 	if err != nil {
-		return nil, 0, err
+		return nil, 0, 0, err
 	}
 	if buf.Data == nil {
 		// object was deleted
-		return nil, 0, &zodb.NoDataError{Oid: xid.Oid, DeletedAt: serial}
+		return nil, 0, 0, &zodb.NoDataError{Oid: xid.Oid, DeletedAt: serial}
 	}
 
-	return buf, serial, nil
+	return buf, serial, nextSerial, nil
 }
 
 // --- ZODB-level iteration ---