+ err := mnt.BlockRead(ctx, li.hash, streamer)
+ if err != nil {
+ if streamer.WroteAt() != 0 {
+ // BlockRead encountered an error
+ // after writing some data, so it's
+ // too late to try another
+ // volume. Flush streamer before
+ // calling Wrote() to ensure our
+ // return value accurately reflects
+ // the number of bytes written to
+ // opts.WriteTo.
+ streamer.Close()
+ return streamer.Wrote(), err
+ }
+ if !os.IsNotExist(err) {
+ errToCaller = err
+ }
+ continue
+ }
+ if li.size == 0 {
+ // hashCheckingWriter isn't in use because we
+ // don't know the expected size. All we can do
+ // is check after writing all the data, and
+ // trust the caller is doing a HEAD request so
+ // it's not too late to set an error code in
+ // the response header.
+ err = streamer.Close()
+ if hash := fmt.Sprintf("%x", hashcheck.Sum(nil)); hash != li.hash && err == nil {
+ err = errChecksum
+ }
+ if rw, ok := opts.WriteTo.(http.ResponseWriter); ok {
+ // We didn't set the content-length header
+ // above because we didn't know the block size
+ // until now.
+ rw.Header().Set("Content-Length", fmt.Sprintf("%d", streamer.WroteAt()))
+ }
+ return streamer.WroteAt(), err
+ } else if streamer.WroteAt() != li.size {