filer.backup: backup small files if the file is saved in filer (saveToFilerLimit > 0)

fix https://github.com/seaweedfs/seaweedfs/issues/3468

weed/replication/sink/azuresink/azure_sink.go

@@ -119,6 +119,10 @@ func (g *AzureSink) CreateEntry(key string, entry *filer_pb.Entry, signatures []
 		return writeErr
 	}
 
+	if len(entry.Content) > 0 {
+		return writeFunc(entry.Content)
+	}
+
 	if err := repl_util.CopyFromChunkViews(chunkViews, g.filerSource, writeFunc); err != nil {
 		return err
 	}

weed/replication/sink/b2sink/b2_sink.go

@@ -101,13 +101,16 @@ func (g *B2Sink) CreateEntry(key string, entry *filer_pb.Entry, signatures []int
 
 	targetObject := bucket.Object(key)
 	writer := targetObject.NewWriter(context.Background())
+	defer writer.Close()
 
 	writeFunc := func(data []byte) error {
 		_, writeErr := writer.Write(data)
 		return writeErr
 	}
 
-	defer writer.Close()
+	if len(entry.Content) > 0 {
+		return writeFunc(entry.Content)
+	}
 
 	if err := repl_util.CopyFromChunkViews(chunkViews, g.filerSource, writeFunc); err != nil {
 		return err

weed/replication/sink/gcssink/gcs_sink.go

@@ -107,6 +107,10 @@ func (g *GcsSink) CreateEntry(key string, entry *filer_pb.Entry, signatures []in
 		return writeErr
 	}
 
+	if len(entry.Content) > 0 {
+		return writeFunc(entry.Content)
+	}
+
 	if err := repl_util.CopyFromChunkViews(chunkViews, g.filerSource, writeFunc); err != nil {
 		return err
 	}

weed/replication/sink/localsink/local_sink.go

@@ -101,6 +101,10 @@ func (localsink *LocalSink) CreateEntry(key string, entry *filer_pb.Entry, signa
 		return writeErr
 	}
 
+	if len(entry.Content) > 0 {
+		return writeFunc(entry.Content)
+	}
+
 	if err := repl_util.CopyFromChunkViews(chunkViews, localsink.filerSource, writeFunc); err != nil {
 		return err
 	}

weed/replication/sink/s3sink/s3_sink.go

@@ -1,6 +1,7 @@
 package S3Sink
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"strings"
@@ -121,6 +122,7 @@ func (s3sink *S3Sink) CreateEntry(key string, entry *filer_pb.Entry, signatures
 	}
 
 	totalSize := filer.FileSize(entry)
+
 	chunkViews := filer.ViewFromChunks(s3sink.filerSource.LookupFileId, entry.Chunks, 0, int64(totalSize))
 
 	parts := make([]*s3.CompletedPart, len(chunkViews))
@@ -141,6 +143,17 @@ func (s3sink *S3Sink) CreateEntry(key string, entry *filer_pb.Entry, signatures
 	}
 	wg.Wait()
 
+	// for small files
+	if len(entry.Content) > 0 {
+		parts = make([]*s3.CompletedPart, 1)
+		if part, uploadErr := s3sink.doUploadPart(key, uploadId, 1, bytes.NewReader(entry.Content)); uploadErr != nil {
+			err = uploadErr
+			glog.Errorf("uploadPart: %v", uploadErr)
+		} else {
+			parts[0] = part
+		}
+	}
+
 	if err != nil {
 		s3sink.abortMultipartUpload(key, uploadId)
 		return fmt.Errorf("uploadPart: %v", err)

weed/replication/sink/s3sink/s3_write.go

@@ -116,6 +116,11 @@ func (s3sink *S3Sink) uploadPart(key, uploadId string, partId int, chunk *filer.
 		return nil, fmt.Errorf("[%s] uploadPart %s %d read: %v", s3sink.bucket, key, partId, err)
 	}
 
+	return s3sink.doUploadPart(key, uploadId, partId, readSeeker)
+}
+
+func (s3sink *S3Sink) doUploadPart(key, uploadId string, partId int, readSeeker io.ReadSeeker) (*s3.CompletedPart, error) {
+
 	input := &s3.UploadPartInput{
 		Body:       readSeeker,
 		Bucket:     aws.String(s3sink.bucket),