You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sync_from_server_file.go
    path of file: ./repos/client/go/kbfs/libdokan
    
    the code of the file until where you have to start completion: // Copyright 2016 Keybase Inc. All rights reserved.
// Use of this source code is governed by a BSD
// license that can be found in the LICENSE file.

package libdokan

import (
	"github.com/keybase/client/go/kbfs/data"
	"github.com/keybase/client/go/kbfs/dokan"
	"github.com/keybase/client/go/kbfs/libkbfs"
	"golang.org/x/net/context"
)

// SyncFromServerFile represents a write-only file when any write of
// at least one byte triggers a sync of the folder from the server.
// A sync:
//
//   - Waits for any outs
    
func (f *SyncFromServerFile) WriteFile(ctx context.Context, fi *dokan.FileInfo, bs []byte, offset int64) (n int, err error) {
	f.folder.fs.logEnter(ctx, "SyncFromServerFile Write")
	defer func() { f.folder.reportErr(ctx, libkbfs.WriteMode, err) }()
	if len(bs) == 0 {
		return 0, nil
	}
	folderBranch := f.folder.getFolderBranch()
	if folderBranch == (data.FolderBranch{}) {
		// Nothing to do.
		return len(bs), nil
	}
	err = f.folder.fs.config.KBFSOps().SyncFromServer(
		ctx, folderBranch, nil)
	if err != nil {
		return 0, err
	}
	f.folder.fs.NotificationGroupWait()
	return len(bs), nil
}