Fix download issues

pkg/chunk/manager.go

@@ -1,8 +1,8 @@
 package chunk
 
 import (
+	"crypto/sha256"
 	"encoding/binary"
-	"encoding/hex"
 	"fmt"
 	"os"
 
@@ -144,7 +144,12 @@ func (m *Manager) GetChunk(object *torrent.File, offset, size int64) ([]byte, er
 }
 
 func buildRequestID(object *torrent.File, offset int64) (id RequestID) {
-	hex.Decode(id[:], []byte(object.Link))
+	fileID := object.Link
+	if fileID == "" {
+		fileID = object.Path
+	}
+	hash := sha256.Sum256([]byte(fileID))
+	copy(id[:16], hash[:16])
 	binary.BigEndian.PutUint64(id[16:], uint64(offset))
 	return
 }