.

t/neo/storage/fs1/filestorage.go

@@ -131,6 +131,7 @@ func errf(e xerr, subj, format string, a ...interface{}) error {
 }
 
 // decodeErr is syntactic shortcut for errf("decode", ...)
+// TODO in many places "decode" -> "selfcheck"
 func decodeErr(e xerr, format string, a ...interface{}) error {
 	return errf(e, "decode", format, a...)
 }
@@ -345,6 +346,17 @@ func (txnh *TxnHeader) LoadNext(r io.ReaderAt, flags TxnLoadFlags) error {
 }
 
 
+// Len returns whole data record length
+func (dh *DataHeader) Len() int64 {
+	dataLen := dh.DataLen
+	if dataLen == 0 {
+		// XXX -> .DataLen() ?
+		dataLen = 8 // back-pointer | oid removal
+	}
+
+	return DataHeaderSize + dataLen
+}
+
 
 // load reads and decodes data record header
 // pos: points to data header start
@@ -496,6 +508,52 @@ func (dh *DataHeader) LoadBack(r io.ReaderAt /* *os.File */) error {
 	return err
 }
 
+// LoadNext reads and decodes data header for next data record in the same transaction
+// prerequisite: dh .Pos .DataLen are initialized
+// when there is no more data records: io.EOF is returned
+//
+// XXX NOTE(self): iteration starts with {Pos: txnh.Pos, DataLen: -DataHeaderSize}
+func (dh *DataHeader) LoadNext(r io.ReaderAt /* *os.File */, txnh *TxnHeader) error {
+	err := dh.loadNext(r, txnh)
+	if err != nil && err != io.EOF {
+		err = txnh.err("iterating", err)
+	}
+	return err
+}
+
+func (dh *DataHeader) loadNext(r io.ReaderAt /* *os.File */, txnh *TxnHeader) error {
+	// position of txn tail - right after last data record byte
+	txnTailPos := txnh.Pos + txnh.Len - 8
+
+	// NOTE we know nextPos does not overlap txnTailPos - it was checked by
+	// previous LoadNext()
+	nextPos := dh.Pos + dh.Len()
+	if nextPos == txnTailPos {
+		return io.EOF
+	}
+
+	if nextPos + DataHeaderSize > txnTailPos {
+		return &ErrDataRecord{nextPos, "decode", fmt.Errorf("data record header overlaps txn boundary")}	// XXX
+	}
+
+	err := dh.Load(r, nextPos)
+	if err != nil {
+		return err
+	}
+
+	if dh.Tid != txnh.Tid {
+		return decodeErr(dh, "tid != txn.Tid")	// XXX
+	}
+	if dh.TxnPos != txnh.Pos {
+		return decodeErr(dh, "txnPos != txn.Pos")	// XXX
+	}
+	if dh.Pos + dh.Len() > txnTailPos {
+		return decodeErr(dh, "data record overlaps txn boundary")	// XXX
+	}
+
+	return nil
+}
+
 
 func Open(path string) (*FileStorage, error) {
 	f, err := os.Open(path)	// XXX opens in O_RDONLY

t/neo/storage/fs1/filestorage_test.go

@@ -105,8 +105,6 @@ func TestLoad(t *testing.T) {
 		checkLoad(t, fs, xid, expect)
 	}
 
-	return
-
 	// check iterating	XXX move to separate test ?
 	// tids we will use for tid{Min,Max}
 	tidv := []zodb.Tid{zodb.Tid(0)}