add needle reading in chunks

weed/storage/needle/needle_read_page.go

@@ -0,0 +1,77 @@
+package needle
+
+import (
+	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/storage/backend"
+	. "github.com/chrislusf/seaweedfs/weed/storage/types"
+	"github.com/chrislusf/seaweedfs/weed/util"
+	"io"
+)
+
+// ReadNeedleData uses a needle without n.Data to read the content
+// volumeOffset: the offset within the volume
+// needleOffset: the offset within the needle Data
+func (n *Needle) ReadNeedleData(r backend.BackendStorageFile, volumeOffset int64, data []byte, needleOffset int64) (count int, err error) {
+
+	sizeToRead := min(int64(len(data)), int64(n.DataSize)-needleOffset)
+	if sizeToRead <= 0 {
+		return 0, io.EOF
+	}
+	startOffset := volumeOffset + NeedleHeaderSize + DataSizeSize + needleOffset
+
+	count, err = r.ReadAt(data[:sizeToRead], startOffset)
+	if err != nil {
+		fileSize, _, _ := r.GetStat()
+		glog.Errorf("%s read %d %d size %d at offset %d fileSize %d: %v", r.Name(), n.Id, needleOffset, sizeToRead, volumeOffset, fileSize, err)
+	}
+	return
+
+}
+
+// ReadNeedleMeta fills all metadata except the n.Data
+func (n *Needle) ReadNeedleMeta(r backend.BackendStorageFile, offset int64, size Size, version Version) (checksumValue uint32, err error) {
+
+	bytes := make([]byte, NeedleHeaderSize+DataSizeSize)
+
+	count, err := r.ReadAt(bytes, offset)
+	if count != NeedleHeaderSize+DataSizeSize || err != nil {
+		return 0, err
+	}
+	n.ParseNeedleHeader(bytes)
+	n.DataSize = util.BytesToUint32(bytes[NeedleHeaderSize : NeedleHeaderSize+DataSizeSize])
+
+	startOffset := offset + NeedleHeaderSize + DataSizeSize + int64(n.DataSize)
+	dataSize := GetActualSize(size, version)
+	stopOffset := offset + dataSize
+	metaSize := stopOffset - startOffset
+	fmt.Printf("offset %d dataSize %d\n", offset, dataSize)
+	fmt.Printf("read needle meta [%d,%d) size %d\n", startOffset, stopOffset, metaSize)
+	metaSlice := make([]byte, int(metaSize))
+
+	count, err = r.ReadAt(metaSlice, startOffset)
+	if err != nil && int64(count) == metaSize {
+		err = nil
+	}
+	if err != nil {
+		return 0, err
+	}
+
+	var index int
+	index, err = n.readNeedleDataVersion2NonData(metaSlice)
+
+	checksumValue = util.BytesToUint32(metaSlice[index : index+NeedleChecksumSize])
+	if version == Version3 {
+		n.AppendAtNs = util.BytesToUint64(metaSlice[index+NeedleChecksumSize : index+NeedleChecksumSize+TimestampSize])
+	}
+
+	return checksumValue, err
+
+}
+
+func min(x, y int64) int64 {
+	if x < y {
+		return x
+	}
+	return y
+}