1 files changed, 146 insertions, 0 deletions
diff --git a/weed/filer2/reader_at.go b/weed/filer2/reader_at.go
new file mode 100644
index 000000000..b9913d2ca
--- /dev/null
+++ b/weed/filer2/reader_at.go
@@ -0,0 +1,146 @@
+package filer2
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"sync"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
+	"github.com/chrislusf/seaweedfs/weed/pb/pb_cache"
+	"github.com/chrislusf/seaweedfs/weed/util"
+	"github.com/chrislusf/seaweedfs/weed/wdclient"
+)
+
+type ChunkReadAt struct {
+	masterClient *wdclient.MasterClient
+	chunkViews   []*ChunkView
+	buffer       []byte
+	bufferOffset int64
+	lookupFileId func(fileId string) (targetUrl string, err error)
+	readerLock   sync.Mutex
+
+	chunkCache *pb_cache.ChunkCache
+}
+
+// var _ = io.ReaderAt(&ChunkReadAt{})
+
+func NewChunkReaderAtFromClient(filerClient filer_pb.FilerClient, chunkViews []*ChunkView, chunkCache *pb_cache.ChunkCache) *ChunkReadAt {
+
+	return &ChunkReadAt{
+		chunkViews: chunkViews,
+		lookupFileId: func(fileId string) (targetUrl string, err error) {
+			err = filerClient.WithFilerClient(func(client filer_pb.SeaweedFilerClient) error {
+				vid := VolumeId(fileId)
+				resp, err := client.LookupVolume(context.Background(), &filer_pb.LookupVolumeRequest{
+					VolumeIds: []string{vid},
+				})
+				if err != nil {
+					return err
+				}
+
+				locations := resp.LocationsMap[vid]
+				if locations == nil || len(locations.Locations) == 0 {
+					glog.V(0).Infof("failed to locate %s", fileId)
+					return fmt.Errorf("failed to locate %s", fileId)
+				}
+
+				volumeServerAddress := filerClient.AdjustedUrl(locations.Locations[0].Url)
+
+				targetUrl = fmt.Sprintf("http://%s/%s", volumeServerAddress, fileId)
+
+				return nil
+			})
+			return
+		},
+		bufferOffset: -1,
+		chunkCache:   chunkCache,
+	}
+}
+
+func (c *ChunkReadAt) ReadAt(p []byte, offset int64) (n int, err error) {
+
+	c.readerLock.Lock()
+	defer c.readerLock.Unlock()
+
+	for n < len(p) && err == nil {
+		readCount, readErr := c.doReadAt(p[n:], offset+int64(n))
+		n += readCount
+		err = readErr
+		if readCount == 0 {
+			return n, nil
+		}
+	}
+	return
+}
+
+func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
+
+	var found bool
+	for _, chunk := range c.chunkViews {
+		if chunk.LogicOffset <= offset && offset < chunk.LogicOffset+int64(chunk.Size) {
+			found = true
+			if c.bufferOffset != chunk.LogicOffset {
+				c.buffer, err = c.fetchChunkData(chunk)
+				c.bufferOffset = chunk.LogicOffset
+			}
+			break
+		}
+	}
+	if !found {
+		return 0, io.EOF
+	}
+
+	n = copy(p, c.buffer[offset-c.bufferOffset:])
+
+	// fmt.Printf("> doReadAt [%d,%d), buffer:[%d,%d)\n", offset, offset+int64(n), c.bufferOffset, c.bufferOffset+int64(len(c.buffer)))
+
+	return
+
+}
+
+func (c *ChunkReadAt) fetchChunkData(chunkView *ChunkView) (data []byte, err error) {
+
+	// fmt.Printf("fetching %s [%d,%d)\n", chunkView.FileId, chunkView.LogicOffset, chunkView.LogicOffset+int64(chunkView.Size))
+
+	chunkData := c.chunkCache.GetChunk(chunkView.FileId)
+	if chunkData != nil {
+		glog.V(3).Infof("cache hit %s [%d,%d)", chunkView.FileId, chunkView.LogicOffset, chunkView.LogicOffset+int64(chunkView.Size))
+	} else {
+		chunkData, err = c.doFetchFullChunkData(chunkView.FileId, chunkView.CipherKey, chunkView.IsGzipped)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	if int64(len(chunkData)) < chunkView.Offset+int64(chunkView.Size) {
+		return nil, fmt.Errorf("unexpected larger chunkView [%d,%d) than chunk %d", chunkView.Offset, chunkView.Offset+int64(chunkView.Size), len(chunkData))
+	}
+
+	data = chunkData[chunkView.Offset : chunkView.Offset+int64(chunkView.Size)]
+
+	c.chunkCache.SetChunk(chunkView.FileId, chunkData)
+
+	return data, nil
+}
+
+func (c *ChunkReadAt) doFetchFullChunkData(fileId string, cipherKey []byte, isGzipped bool) ([]byte, error) {
+
+	urlString, err := c.lookupFileId(fileId)
+	if err != nil {
+		glog.V(1).Infof("operation LookupFileId %s failed, err: %v", fileId, err)
+		return nil, err
+	}
+	var buffer bytes.Buffer
+	err = util.ReadUrlAsStream(urlString, cipherKey, isGzipped, true, 0, 0, func(data []byte) {
+		buffer.Write(data)
+	})
+	if err != nil {
+		glog.V(1).Infof("read %s failed, err: %v", fileId, err)
+		return nil, err
+	}
+
+	return buffer.Bytes(), nil
+}