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: iterators.go
    path of file: ./repos/storj/satellite/gc/sender
    
    the code of the file until where you have to start completion: // Copyright (C) 2022 Storj Labs, Inc.
// See LICENSE for copying information.

package sender

import (
	"archive/zip"
	"bytes"
	"context"
	"io"
	"strings"
	"time"

	"github.com/zeebo/errs"

	"storj.io/common/pb"
	"storj.io/storj/satellite/internalpb"
	"storj.io/uplink"
)

// IterateZipObjectKeys checks inside the top-level of a bucket and yields the keys which look like zip files.
func 
    
func validate(fileName string, retainInfo internalpb.RetainInfo) error {
	if retainInfo.StorageNodeId.IsZero() {
		return errs.New("Storage Node ID is missing from file %s", fileName)
	}

	if fileName != retainInfo.StorageNodeId.String() {
		return errs.New("Storage Node ID %s is not equal to file name %s", retainInfo.StorageNodeId.String(), fileName)
	}

	if retainInfo.PieceCount == 0 {
		return errs.New("Retain filter count is zero for storage node %s", retainInfo.StorageNodeId.String())
	}

	if retainInfo.Filter == nil || len(retainInfo.Filter) == 0 {
		return errs.New("Retain filter is missing for storage node %s", retainInfo.StorageNodeId.String())
	}

	if len(bytes.Trim(retainInfo.Filter, "\x00")) == 0 {
		return errs.New("Retain filter is zeroes for storage node %s", retainInfo.StorageNodeId.String())
	}

	year2020 := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
	if retainInfo.CreationDate.Before(year2020) {
		return errs.New("Retain filter creation date is too long ago: %s", retainInfo.CreationDate.String())
	}

	return nil
}