filer.sync: show active chunk transfers when sync progress stalls

When the sync watermark is not advancing, print each in-progress chunk
transfer with its file path, bytes received so far, and current status
(downloading, uploading, or waiting with backoff duration). This helps
diagnose which files are blocking progress during replication.

Closes #8542

weed/replication/sink/filersink/fetch_write.go

@@ -241,6 +241,14 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 		return "", fmt.Errorf("upload data: %w", err)
 	}
 
+	transferStatus := &ChunkTransferStatus{
+		ChunkFileId: sourceChunk.GetFileIdString(),
+		Path:        path,
+		Status:      "downloading",
+	}
+	fs.activeTransfers.Store(sourceChunk.GetFileIdString(), transferStatus)
+	defer fs.activeTransfers.Delete(sourceChunk.GetFileIdString())
+
 	eofBackoff := time.Duration(0)
 	var partialData []byte
 	var savedFilename string
@@ -282,6 +290,9 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 			fullData = data
 		}
 
+		transferStatus.BytesReceived = int64(len(fullData))
+		transferStatus.Status = "uploading"
+
 		currentFileId, uploadResult, uploadErr, _ := uploader.UploadWithRetry(
 			fs,
 			&filer_pb.AssignVolumeRequest{
@@ -326,9 +337,12 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 		}
 		if isEofError(retryErr) {
 			eofBackoff = nextEofBackoff(eofBackoff)
+			transferStatus.BytesReceived = int64(len(partialData))
+			transferStatus.Status = fmt.Sprintf("waiting %v", eofBackoff)
 			glog.V(0).Infof("source connection interrupted while replicating %s for %s (%d bytes received so far), backing off %v: %v",
 				sourceChunk.GetFileIdString(), path, len(partialData), eofBackoff, retryErr)
 			time.Sleep(eofBackoff)
+			transferStatus.Status = "downloading"
 		} else {
 			glog.V(0).Infof("replicate %s for %s: %v", sourceChunk.GetFileIdString(), path, retryErr)
 		}