.

t/neo/storage/fs1/filestorage.go

@@ -32,7 +32,7 @@ type FileStorage struct {
 	file	*os.File
 	index	*fsIndex	// oid -> data record position in transaction which last changed oid
 	topPos	int64		// position pointing just past last committed transaction
-				// (= size(f) when no commit is in progress)
+				// (= size(.file) when no commit is in progress)
 
 	// min/max tids committed
 	tidMin, tidMax	zodb.Tid
@@ -51,15 +51,16 @@ type TxnHeader struct {
 	// transaction metadata tself
 	zodb.TxnInfo
 
-	// underlying memory for header loading and for user/desc/extension
+	// underlying memory for header loading and for user/desc/extension strings
 	workMem	[]byte
 }
 
 // DataHeader represents header of a data record
 type DataHeader struct {
-	Pos		int64	// position of data record
+	Pos		int64	// position of data record start
 	Oid             zodb.Oid
 	Tid             zodb.Tid
+	// XXX -> .PosPrevRev  .PosTxn  .LenData
 	PrevRevPos	int64	// position of this oid's previous-revision data record	XXX naming
 	TxnPos          int64	// position of transaction record this data record belongs to
 	//_		uint16	// 2-bytes with zero values. (Was version length.)
@@ -71,13 +72,12 @@ type DataHeader struct {
 	// XXX include word0 ?
 }
 
-// on-disk sizes
 const (
-	Magic		= "FS21"
-
-	TxnHeaderFixSize	= 8+8+1+2+2+2		// on-disk size without user/desc/ext strings
-	txnXHeaderFixSize	= 8 + TxnHeaderFixSize	// with trail LenPrev from previous record
+	Magic = "FS21"	// every FileStorage file starts with this
 
+	// on-disk sizes
+	TxnHeaderFixSize	= 8+8+1+2+2+2		// without user/desc/ext strings
+	txnXHeaderFixSize	= 8 + TxnHeaderFixSize	// ^^^ with trail LenPrev from previous record
 	DataHeaderSize		= 8+8+8+8+2+8
 
 	// txn/data pos that are < vvv are for sure invalid
@@ -86,7 +86,6 @@ const (
 )
 
 // ErrTxnRecord is returned on transaction record read / decode errors
-// XXX merge with ErrDataRecord -> ErrRecord{pos, "transaction|data", "read", err} ?
 type ErrTxnRecord struct {
 	Pos	int64	// position of transaction record
 	Subj	string	// about what .Err is
@@ -97,6 +96,20 @@ func (e *ErrTxnRecord) Error() string {
 	return fmt.Sprintf("transaction record @%v: %v: %v", e.Pos, e.Subj, e.Err)
 }
 
+// err creates ErrTxnRecord for transaction located at txnh.Pos
+func (txnh *TxnHeader) err(subj string, err error) *ErrTxnRecord {
+	return &ErrTxnRecord{txnh.Pos, subj, err}
+}
+
+// errf is syntatic shortcut for err and fmt.Errorf
+func (txnh *TxnHeader) errf(subj, format string, a ...interface{}) *ErrTxnRecord {
+	return txnh.err(subj, fmt.Errorf(format, a...))
+}
+
+func (txnh *TxnHeader) decodeErr(format string, a ...interface{}) *ErrTxnRecord {
+	return txnh.errf("decode", format, a...)
+}
+
 // ErrDataRecord is returned on data record read / decode errors
 type ErrDataRecord struct {
 	Pos	int64	// position of data record
@@ -108,11 +121,17 @@ func (e *ErrDataRecord) Error() string {
 	return fmt.Sprintf("data record @%v: %v: %v", e.Pos, e.Subj, e.Err)
 }
 
+// err creates ErrDataRecord for data record located at dh.Pos
+// XXX add link to containing txn? (check whether we can do it on data access) ?
+func (dh *DataHeader) err(subj string, err error) *ErrDataRecord {
+	return &ErrDataRecord{dh.Pos, subj, err}
+}
+
+// TODO errf, decodeErr
+
 // // XXX -> zodb?
 // var ErrVersionNonZero = errors.New("non-zero version")
 
-var bugPosition = errors.New("software bug: invalid position")
-
 // noEOF returns err, but changes io.EOF -> io.ErrUnexpectedEOF
 func noEOF(err error) error {
 	if err == io.EOF {
@@ -129,6 +148,10 @@ const (
 	LoadNoStrings			= 0x01 // do not load user/desc/ext strings
 )
 
+// it is software bug to pass invalid position to Load*()
+// this error will be paniced
+var bugPositionInvalid = errors.New("software bug: invalid position")
+
 // Load reads and decodes transaction record header
 // pos: points to transaction start
 // no requirements are made to previous txnh state
@@ -139,16 +162,13 @@ func (txnh *TxnHeader) Load(r io.ReaderAt /* *os.File */, pos int64, flags TxnLo
 	}
 	work := txnh.workMem[:txnXHeaderFixSize]
 
+	// XXX recheck rules about error exit
 	txnh.Pos = pos
-	txnh.Len = 0		// XXX recheck rules about error exit
+	txnh.Len = 0
 	txnh.LenPrev = 0
 
 	if pos < txnValidFrom {
-		panic(&ErrTxnRecord{pos, "read", bugPosition})
-	}
-
-	decodeErr := func(format string, a ...interface{}) *ErrTxnRecord {
-		return &ErrTxnRecord{pos, "decode", fmt.Errorf(format, a...)}
+		panic(txnh.err("read", bugPositionInvalid))
 	}
 
 	var n int
@@ -161,7 +181,7 @@ func (txnh *TxnHeader) Load(r io.ReaderAt /* *os.File */, pos int64, flags TxnLo
 		if n >= 0 {
 			lenPrev := 8 + int64(binary.BigEndian.Uint64(work[8-8:]))
 			if lenPrev < TxnHeaderFixSize {
-				return decodeErr("invalid txn prev record length: %v", lenPrev)
+				return txnh.decodeErr("invalid txn prev record length: %v", lenPrev)
 			}
 			txnh.LenPrev = lenPrev
 		}
@@ -178,23 +198,23 @@ func (txnh *TxnHeader) Load(r io.ReaderAt /* *os.File */, pos int64, flags TxnLo
 
 		// EOF after txn header is not good - because at least
 		// redundand lenght should be also there
-		return &ErrTxnRecord{pos, "read", noEOF(err)}
+		return txnh.err("read", noEOF(err))
 	}
 
 	txnh.Tid = zodb.Tid(binary.BigEndian.Uint64(work[8+0:]))
 	if !txnh.Tid.Valid() {
-		return decodeErr("invalid tid: %v", txnh.Tid)
+		return txnh.decodeErr("invalid tid: %v", txnh.Tid)
 	}
 
 	tlen := 8 + int64(binary.BigEndian.Uint64(work[8+8:]))
 	if tlen < TxnHeaderFixSize {
-		return decodeErr("invalid txn record length: %v", tlen)
+		return txnh.decodeErr("invalid txn record length: %v", tlen)
 	}
 	txnh.Len = tlen
 
 	txnh.Status = zodb.TxnStatus(work[8+16])
 	if !txnh.Status.Valid() {
-		return decodeErr("invalid status: %v", txnh.Status)
+		return txnh.decodeErr("invalid status: %v", txnh.Status)
 	}
 
 
@@ -210,13 +230,11 @@ func (txnh *TxnHeader) Load(r io.ReaderAt /* *os.File */, pos int64, flags TxnLo
 		txnh.workMem = txnh.workMem[:lstr]
 	}
 
-	work = txnh.workMem[:lstr]
-
 	// NOTE we encode each x string length into cap(x)
 	//      and set len(x) = 0 to indicate x is not loaded yet
-	txnh.User	 = work[0:0:luser]
-	txnh.Description = work[luser:luser:ldesc]
-	txnh.Extension	 = work[luser+ldesc:luser+ldesc:lext]
+	txnh.User	 = txnh.workMem[0:0:luser]
+	txnh.Description = txnh.workMem[luser:luser:ldesc]
+	txnh.Extension	 = txnh.workMem[luser+ldesc:luser+ldesc:lext]
 
 	if flags & LoadNoStrings == 0 {
 		err = txnh.loadStrings(r)
@@ -232,7 +250,7 @@ func (txnh *TxnHeader) loadStrings(r io.ReaderAt /* *os.File */) error {
 	// we rely on Load leaving len(workMem) = sum of all strings length ...
 	_, err := r.ReadAt(txnh.workMem, txnh.Pos + TxnHeaderFixSize)
 	if err != nil {
-		return &ErrTxnRecord{txnh.Pos, "read strings", noEOF(err)}
+		return txnh.err("read strings", noEOF(err))
 	}
 
 	// ... and presetting x to point to appropriate places in .workMem .
@@ -247,17 +265,35 @@ func (txnh *TxnHeader) loadStrings(r io.ReaderAt /* *os.File */) error {
 // LoadPrev reads and decodes previous transaction record header
 // txnh should be already initialized by previous call to load()
 func (txnh *TxnHeader) LoadPrev(r io.ReaderAt, flags TxnLoadFlags) error {
-	if txnh.LenPrev == 0 {
+	lenPrev := txnh.LenPrev
+	if lenPrev == 0 {
 		return io.EOF
 	}
 
-	return txnh.Load(r, txnh.Pos - txnh.LenPrev, flags)
+	err := txnh.Load(r, txnh.Pos - lenPrev, flags)
+	if err != nil {
+		return err
+	}
+
+	if txnh.Len != lenPrev {
+		return txnh.decodeErr("redundant lengths mismatch: %v, %v", txnh.Len, lenPrev)
+	}
+
+	return nil
 }
 
 // LoadNext reads and decodes next transaction record header
 // txnh should be already initialized by previous call to load()
 func (txnh *TxnHeader) LoadNext(r io.ReaderAt, flags TxnLoadFlags) error {
-	return txnh.Load(r, txnh.Pos + txnh.Len, flags)
+	lenCur := txnh.Len
+
+	err := txnh.Load(r, txnh.Pos + txnh.Len, flags)
+	// TODO XXX
+	if txnh.LenPrev != lenCur {
+	}
+	if err != nil {
+		return err
+	}
 }
 
 
@@ -265,7 +301,7 @@ func (txnh *TxnHeader) LoadNext(r io.ReaderAt, flags TxnLoadFlags) error {
 // decode reads and decodes data record header
 func (dh *DataHeader) load(r io.ReaderAt /* *os.File */, pos int64, tmpBuf *[DataHeaderSize]byte) error {
 	if pos < dataValidFrom {
-		panic(&ErrDataRecord{pos, "read", bugPosition})
+		panic(&ErrDataRecord{pos, "read", bugPositionInvalid})
 	}
 
 	dh.Pos = pos