如何在PWA共享目标中脱机处理图像? [英] How to handle images offline in a PWA share target?

问题描述

我可以将我的Progressive Web App注册为 ):

I can register my Progressive Web App as a share target for images (supported from Chrome Android 76):

"share_target": {
    "action": "/share-target",
    "method": "POST",
    "enctype": "multipart/form-data",
    "params": {
      "files": [
        {
          "name": "myImage",
          "accept": ["image/jpeg", "image/png"]
        }
      ]
    }
  }

然后我可以拦截尝试在服务工作者中与应用共享图像的尝试:

I can then intercept attempts to share images to the app in a service worker:

self.addEventListener('fetch', e => {
  if (e.request.method === 'POST' && e.request.url.endsWith('/share-target')) {
    // todo
  }
})

如何在离线PWA中显示共享图像?

How would I display the shared image in my offline PWA?

推荐答案

这里有一些不同的步骤.

There are a few different steps to take here.

我在 https://web-share-offline.glitch.me/上汇总了一个工作示例.，其来源为 https://glitch.com/edit/#！/web-share-offline

这是先决条件，我通过生成将使用工作箱.

This is a prerequisite, and I accomplished it by generating a service worker that would precache my HTML, JS, and CSS using Workbox.

加载首页时运行的JS使用Cache Storage API读取已缓存的图像URL的列表，以在与每个URL对应的页面上创建< img> 元素一个.

The JS that runs when the home page is loaded uses the Cache Storage API to read a list of image URLs that have been cached, to creates <img> elements on the page corresponding to each one.

我也为此使用了Workbox，但这涉及更多.重点是:

I also used Workbox for this, but it's a bit more involved. The salient points are:

• 确保您拦截了针对配置的共享目标URL的 POST 请求.
• 由您决定要读取共享图像的正文，然后使用Cache Storage API将它们写入本地缓存中.
• 将共享图像保存到缓存后，最好使用POST ="noreferrer"> HTTP 303 重定向响应，以便浏览器将显示Web应用程序的实际主页.

• Make sure that you intercept POST requests for the configured share target URL.
• It's up to you to read in the body of the shared images and to write them to your local cache using the Cache Storage API.
• After you save the shared image to cache, it's a good idea to respond to the POST with a HTTP 303 redirected response, so that the browser will display the actual home page for your web app.

这是我用来处理此问题的Workbox配置代码:

Here's the Workbox configuration code that I used to handle this:

const shareTargetHandler = async ({event}) => {
  const formData = await event.request.formData();
  const cache = await caches.open('images');

  await cache.put(
      // TODO: Come up with a more meaningful cache key.
      `/images/${Date.now()}`,
      // TODO: Get more meaningful metadata and use it
      // to construct the response.
      new Response(formData.get('image'))
  );

  // After the POST succeeds, redirect to the main page.
  return Response.redirect('/', 303);
};

module.exports = {
  // ... other Workbox config ...
  runtimeCaching: [{
    // Create a 'fake' route to handle the incoming POST.
    urlPattern: '/share-target',
    method: 'POST',
    handler: shareTargetHandler,
  }, {
    // Create a route to serve the cached images.
    urlPattern: new RegExp('/images/\\d+'),
    handler: 'CacheOnly',
    options: {
      cacheName: 'images',
    },
  }],
};

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