1 files changed, 220 insertions, 0 deletions
diff --git a/weed/storage/volume_follow.go b/weed/storage/volume_follow.go
new file mode 100644
index 000000000..2aedd1682
--- /dev/null
+++ b/weed/storage/volume_follow.go
@@ -0,0 +1,220 @@
+package storage
+
+import (
+	"context"
+	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/operation"
+	"github.com/chrislusf/seaweedfs/weed/pb/volume_server_pb"
+	. "github.com/chrislusf/seaweedfs/weed/storage/types"
+	"google.golang.org/grpc"
+	"io"
+	"os"
+)
+
+// The volume sync with a master volume via 2 steps:
+// 1. The slave checks master side to find subscription checkpoint
+//	  to setup the replication.
+// 2. The slave receives the updates from master
+
+/*
+Assume the slave volume needs to follow the master volume.
+
+The master volume could be compacted, and could be many files ahead of
+slave volume.
+
+Step 0: // implemented in command/backup.go, to avoid dat file size overflow.
+0.1 If slave compact version is less than the master, do a local compaction, and set
+local compact version the same as the master.
+0.2 If the slave size is still bigger than the master, discard local copy and do a full copy.
+
+Step 1:
+The slave volume ask the master by the last modification time t.
+The master do a binary search in volume (use .idx as an array, and check the appendAtNs in .dat file),
+to find the first entry with appendAtNs > t.
+
+Step 2:
+The master send content bytes to the slave. The bytes are not chunked by needle.
+
+Step 3:
+The slave generate the needle map for the new bytes. (This may be optimized to incrementally
+update needle map when receiving new .dat bytes. But seems not necessary now.)
+
+*/
+
+func (v *Volume) Follow(volumeServer string, grpcDialOption grpc.DialOption) (error) {
+
+	ctx := context.Background()
+
+	startFromOffset := v.Size()
+	appendAtNs, err := v.findLastAppendAtNs()
+	if err != nil {
+		return err
+	}
+
+	err = operation.WithVolumeServerClient(volumeServer, grpcDialOption, func(client volume_server_pb.VolumeServerClient) error {
+
+		stream, err := client.VolumeFollow(ctx, &volume_server_pb.VolumeFollowRequest{
+			VolumeId: uint32(v.Id),
+			Since:    appendAtNs,
+		})
+		if err != nil {
+			return err
+		}
+
+		v.dataFile.Seek(startFromOffset, io.SeekStart)
+
+		for {
+			resp, recvErr := stream.Recv()
+			if recvErr != nil {
+				if recvErr == io.EOF {
+					break
+				} else {
+					return recvErr
+				}
+			}
+
+			_, writeErr := v.dataFile.Write(resp.FileContent)
+			if writeErr != nil {
+				return writeErr
+			}
+		}
+
+		return nil
+
+	})
+
+	if err != nil {
+		return err
+	}
+
+	// TODO add to needle map
+
+	return nil
+}
+
+func (v *Volume) findLastAppendAtNs() (uint64, error) {
+	offset, err := v.locateLastAppendEntry()
+	if err != nil {
+		return 0, err
+	}
+	if offset == 0 {
+		return 0, nil
+	}
+	return v.readAppendAtNs(offset)
+}
+
+func (v *Volume) locateLastAppendEntry() (Offset, error) {
+	indexFile, e := os.OpenFile(v.FileName()+".idx", os.O_RDONLY, 0644)
+	if e != nil {
+		return 0, fmt.Errorf("cannot read %s.idx: %v", v.FileName(), e)
+	}
+	defer indexFile.Close()
+
+	fi, err := indexFile.Stat()
+	if err != nil {
+		return 0, fmt.Errorf("file %s stat error: %v", indexFile.Name(), err)
+	}
+	fileSize := fi.Size()
+	if fileSize%NeedleEntrySize != 0 {
+		return 0, fmt.Errorf("unexpected file %s size: %d", indexFile.Name(), fileSize)
+	}
+	if fileSize == 0 {
+		return 0, nil
+	}
+
+	bytes := make([]byte, NeedleEntrySize)
+	n, e := indexFile.ReadAt(bytes, fileSize-NeedleEntrySize)
+	if n != NeedleEntrySize {
+		return 0, fmt.Errorf("file %s read error: %v", indexFile.Name(), e)
+	}
+	_, offset, _ := IdxFileEntry(bytes)
+
+	return offset, nil
+}
+
+func (v *Volume) readAppendAtNs(offset Offset) (uint64, error) {
+
+	n, bodyLength, err := ReadNeedleHeader(v.dataFile, v.SuperBlock.version, int64(offset)*NeedlePaddingSize)
+	if err != nil {
+		return 0, fmt.Errorf("ReadNeedleHeader: %v", err)
+	}
+	err = n.ReadNeedleBody(v.dataFile, v.SuperBlock.version, int64(offset)*NeedlePaddingSize, bodyLength)
+	if err != nil {
+		return 0, fmt.Errorf("ReadNeedleBody offset %d: %v", int64(offset)*NeedlePaddingSize, err)
+	}
+	return n.AppendAtNs, nil
+
+}
+
+// on server side
+func (v *Volume) BinarySearchByAppendAtNs(sinceNs uint64) (offset Offset, isLast bool, err error) {
+	indexFile, openErr := os.OpenFile(v.FileName()+".idx", os.O_RDONLY, 0644)
+	if openErr != nil {
+		err = fmt.Errorf("cannot read %s.idx: %v", v.FileName(), openErr)
+		return
+	}
+	defer indexFile.Close()
+
+	fi, statErr := indexFile.Stat()
+	if statErr != nil {
+		err = fmt.Errorf("file %s stat error: %v", indexFile.Name(), statErr)
+		return
+	}
+	fileSize := fi.Size()
+	if fileSize%NeedleEntrySize != 0 {
+		err = fmt.Errorf("unexpected file %s size: %d", indexFile.Name(), fileSize)
+		return
+	}
+
+	bytes := make([]byte, NeedleEntrySize)
+	entryCount := fileSize / NeedleEntrySize
+	l := int64(0)
+	h := entryCount
+
+	for l < h {
+
+		m := (l + h) / 2
+
+		if m == entryCount {
+			return 0, true, nil
+		}
+
+		// read the appendAtNs for entry m
+		offset, err = v.readAppendAtNsForIndexEntry(indexFile, bytes, m)
+		if err != nil {
+			return
+		}
+
+		mNs, nsReadErr := v.readAppendAtNs(offset)
+		if nsReadErr != nil {
+			err = nsReadErr
+			return
+		}
+
+		// move the boundary
+		if mNs <= sinceNs {
+			l = m + 1
+		} else {
+			h = m
+		}
+
+	}
+
+	if l == entryCount {
+		return 0, true, nil
+	}
+
+	offset, err = v.readAppendAtNsForIndexEntry(indexFile, bytes, l)
+
+	return offset, false, err
+
+}
+
+// bytes is of size NeedleEntrySize
+func (v *Volume) readAppendAtNsForIndexEntry(indexFile *os.File, bytes []byte, m int64) (Offset, error) {
+	if _, readErr := indexFile.ReadAt(bytes, m*NeedleEntrySize); readErr != nil && readErr != io.EOF {
+		return 0, readErr
+	}
+	_, offset, _ := IdxFileEntry(bytes)
+	return offset, nil
+}