add cmd/dump - a dumper

Walk needed to be added to NeedleMap and CompactMap, to be able to add WalkKeys and WalkValues to volume. This is needed for iterating through all the stored needles in a volume - this was dump's purpose.

weed-fs/src/pkg/storage/needle_read_write.go

@@ -2,10 +2,10 @@ package storage
 
 import (
 	"errors"
+	"fmt"
 	"io"
 	"os"
 	"pkg/util"
-	"fmt"
 )
 
 func (n *Needle) Append(w io.Writer, version Version) uint32 {
@@ -62,7 +62,8 @@ func (n *Needle) Append(w io.Writer, version Version) uint32 {
 	return n.Size
 }
 func (n *Needle) Read(r io.Reader, size uint32, version Version) (int, error) {
-	if version == Version1 {
+	switch version {
+	case Version1:
 		bytes := make([]byte, NeedleHeaderSize+size+NeedleChecksumSize)
 		ret, e := r.Read(bytes)
 		n.readNeedleHeader(bytes)
@@ -72,7 +73,7 @@ func (n *Needle) Read(r io.Reader, size uint32, version Version) (int, error) {
 			return 0, errors.New("CRC error! Data On Disk Corrupted!")
 		}
 		return ret, e
-	} else if version == Version2 {
+	case Version2:
 		if size == 0 {
 			return 0, nil
 		}
@@ -95,7 +96,7 @@ func (n *Needle) Read(r io.Reader, size uint32, version Version) (int, error) {
 		}
 		return ret, e
 	}
-	return 0, errors.New("Unsupported Version!")
+	return 0, fmt.Errorf("Unsupported Version! (%d)", version)
 }
 func (n *Needle) readNeedleHeader(bytes []byte) {
 	n.Cookie = util.BytesToUint32(bytes[0:4])