如何在Scrapy中无错误地下载图片？

from scrapy import Request
from scrapy.exceptions import DropItem

class ImageDownloaderMiddleware(object):
    def process_request(self, request, spider):
        if request.meta.get('download_image', False):
            return None  # 如果请求已经标记为下载图片，则直接返回，不进行其他处理
        else:
            # 将请求标记为下载图片
            request.meta['download_image'] = True
            return request

    def process_response(self, request, response, spider):
        if response.status != 200:
            # 如果响应状态码不是200，说明下载失败，抛出DropItem异常
            raise DropItem("Image download failed")
        else:
            return response

DOWNLOADER_MIDDLEWARES = {
    'your_project_name.middlewares.ImageDownloaderMiddleware': 543,
}

import scrapy

class MyItem(scrapy.Item):
    image_urls = scrapy.Field()
    images = scrapy.Field()

from scrapy.loader import ItemLoader
from your_project_name.items import MyItem

class MySpider(scrapy.Spider):
    name = 'my_spider'
    start_urls = ['http://example.com']

    def parse(self, response):
        loader = ItemLoader(item=MyItem(), response=response)
        loader.add_xpath('image_urls', '//img/@src')
        yield loader.load_item()

ITEM_PIPELINES = {
    'scrapy.pipelines.images.ImagesPipeline': 1,
}

IMAGES_STORE = '/path/to/your/images/directory'  # 设置图片存储的目录
IMAGES_EXPIRES = 30  # 设置图片过期时间，单位为天